1.
POWER RANGERNOTES MARINE BIOLOGY
1
Marine environment and their divisions
The ocean currently covers 71% of the earth’s surface. Around two thirds of earth’s land area is found in the Northern
Hemisphere .
 The marine ecosystem is the largest aquatic system of the planet which includes oceans,coral reefs,and estuaries.
Since it is large and a complex one, it is very difficult to deal with as a whole.
 This makes the oceanographers divide the ocean into zones according to physical characteristics,mainly based on
depth, light and temperature.
 The two major zones of the ocean are the sea floor, or bottom region, called the benthic realm and the watery
region above the sea floor called the pelagic realm.
PELAGIC REALM
• The ocean’s pelagic realm is divided horizontally into two zones,
1. neritic zones :The neritic zone, also called coastalzone, is the region which lies above the continental shelf. This is a
shallow part of the ocean and is very close to the land mass.
2. oceanic zone :The oceanic zone, is the pelagic zone which lies above the sea floor beyond the depth of continental
shelf, i.e. the water mass that lies beyond the depth of 200 meter to the deepest part of the ocean.
pelagic realm is also divided into different zones, based on the penetration of light and depth of water.
The pelagic realm is further subdivided vertically into five zones
i. Epipelagic zone - 0 - 200 meters deep from the surface of the ocean (Photic zone; all light rays are seen here initially)
ii. Mesopelagic zone - from 200 -1000 meters deep (dysphotic zone; only blue light is seen here:also referred as "twilight
zone"); its lower boundary in the tropics is the 10º C isotherm.
iii. Bathypelagic zone - falls below 1000- 4000 meters deep (aphotic zone; no light reaches this depth, total darkness);
lying between the boundaries of water with 10 and 4º C isotherm layers.
iv. Abyssopelagic zone - lies below 2000 - 6000 meters deep (aphotic zone).
v. Hadal pelagic zone - has a depth of 6000-10000 meters (aphotic zone).
epipelagic,or euphotic zone :
• It is the top layer of the ocean zones. This is the ideal place for about 90 % of all ocean life to live because of
warm temperature and sunlight that goes down about 660 feet.
• This is the only zone to support plant life because it has the light needed for photosynthesis.
• As this region is diverse in plant life, there is a variety of animals including zooplankton, crustaceans,molluscs,
sharks, sting rays, mackerels, tuna, seals, sea lions, sea turtles, etc.
mesopelagic zone
• Though some sunlight penetrates through this zone, it is not enough for photosynthesis to occur and plants to
grow.
• This zone has some animals including octopus, squid, and hatchet fish.
• The animals living in this zone must survive cold temperatures,increased water pressure,and dark water.

2.
POWER RANGERNOTES MARINE BIOLOGY
2
• Some fish have extra big eyes to help them see,while others produce their own light called bioluminescence
using special organs in their bodies called photophors.
• Most fish don’t chase their food but they either wait for it or stalk it. Some have sharp fangs or big mouths to
help them catch their food
bathypelagic zone
• It can be as deep as 20,000 feet. No sunlight reaches this zone so it is freezing and completely dark.
• It also has a very intense water pressure which can be as great as two tons per square inch.
• Just like the mesopelagic zone, there are no plants and even fewer organisms.
• Some organisms in this zone are vampire squid, giant squid, amphipod, slime stars,snake dragon fish, anglerfish,
oarfish, gulper eel
Hadal zone
• It is the deepest parts of the ocean,causing it to be totally dark, and constantly cold, with a very intense pressure.
• The deep-sea creatures have adapted to the darkness by reducing their use of eyesight.
• The fish do have eyes,though, and they are usually enormous, which indicates enough flashes of bioluminescent
light to keep their eyes from totally deteriorating.
• The animals that live near the bottom have a reddish or pinkish coloration, possibly because the red light waves
are absorbed in the topmost layers of the ocean.
BENTHIC REALM
 Benthic, a term meaning bottom is the name of the ocean zone ranging from the deepest parts of the ocean to the
tidal affected areas.
 The most productive region of the benthic zone is the area over the continental margin, which is unaffected by the
tides.
 Many groups and varieties of animals live here, a few are
worms, sea pens, crustaceans,stars,and protozoa.
 The life in this zone is mostly made up of bottom
dwellers which get most of their food from dead and
decaying organisms.
 Therefore most of the organisms in the benthic zone are
scavengers because they depend on dead flesh as their
main food source.
 The benthic environment is further divided by depth into
five zones
 i. Intertidal zone – the area between the lowest low tide
and highest high tide markings, it is sometimes called the
littoral zone.
 ii. Sub littoral zone – from the lowest low tide mark to the shelf break, about 200 m deep. This area essentially
coincides with the continental shelf.
 iii. Bathyal zone – from the shelf break to 4000 m. This area coincides with the continental slope and rise.
 iv. Abyssal zone – from 4000 to 6000 m. This includes the average depth of the deep ocean floor.
 v. Hadalzone – sea floor deeper than 6000 m. This includes the trenches,the deepest part of the sea floor.

3.
POWER RANGERNOTES MARINE BIOLOGY
3
Life in the Oceans
• The average depth of oceans is about 3,800 meters,which means that they represent 99 percent of the living space
on the planet.
• Despite having 99 percent of the planet’s living space,only 250,000 of approximately 1.8 million described living
species (14 percent) are marine.
• While the oceans lack diversity at the level of species,they are home to members of thirty-one of the thirty-four
animal phyla, about twice the number of phyla that are found on land or in freshwater.
• Because of its vastness and humans’ inability to easily visit deep waters,the oceans remain the least studied
habitats on earth.
The organisms of these marine habitats are generally divided into pelagic and benthic organisms based on their selection
of habitats.
Pelagic organisms
• living in the water column .
• The pelagic zone can be divided into photic and aphotic zones.
• The photic zone is the shallow part of the ocean that receives enough sunlight to support photosynthesis, which is
about two hundred meters deep in the clearest waters,and as shallow as three meters in turbid coastal waters.
• The aphotic zone is where there is no light to support photosynthesis, and extends from the bottom of the photic
zone to the ocean floor.
• Pelagic organisms include plankton, which float along with currents,and nekton, which are active swimmers.
Plankton
Plankton are divided into two types
Phytoplankton: which include photosynthesizing species such as algae.
zooplankton:which are consumer species. Zooplankton consist largely of copepods (tiny crustaceans).
• Although plankton generally drift with ocean currents,some plankton have limited mobility.
• For example, certain zooplankton species move towards the water surface at night to feed, when there is less
danger of predation, and return to deeper waters during the day. This type of migration is termed vertical
migration.
• Although most planktonic species are small, some are large, such as Sargassum and jellyfish.
NEKTON
 Nekton are active swimmers that use diverse means to propel themselves through the water.
 Some species swim using fins, tails, or flippers.
 Other species,such as cephalopods, move by shooting out jets of water,known as jet propulsion.
 Nektonic species include fish, octopus, sea turtles, whales, seals, penguins, and many others.

4.
POWER RANGERNOTES MARINE BIOLOGY
4
 Many nektonic species eat high in the food chain, although there are plankton-eating species (e.g., some fish) and
herbivorous species (e.g.,sea turtles) in addition to carnivorous ones (e.g., seals and killer whales)..
 It is common for sea creatures (especially animals live at the intermediate depths) to house luminescent bacteria
within their tissues, which are able to produce light for communication, as a lure to attract prey, or to light their
bottom surface to conceal their silhouette against the dimly lighted background from above.
 Anglerfish are deep-sea predators that attract prey near their mouths by dangling a bioluminescent lure in front of
their head.
 The density of organisms in the deep sea is low.
 Because of this low density, a long period of time can pass between meals, or between encounters with the
opposite sex.
 To deal with the problem of infrequent meals, deep-sea creatures are often gigantic compared to shallow-water
relatives.
 Large size allows for storage of food reserves that sustain the animals between meals.
 Predatory fish also have large mouths and stomachs that allow them to take full advantage of any meal, regardless
of size.
BENTHOS
 Organisms that live in, on, or near the ocean floor are appropriately called benthic organisms, and represent 98
percent of all marine creatures.
 They occur in such familiar marine habitats as intertidal rocky shores, mud flats, sandy beaches,coral reefs,and
kelp forests.
 The main primary producers in benthic habitats are macroscopic seaweeds that grow attached to the bottom or
microscopic algae that grow within the tissues of animals such as corals, sponges, and bryozoans.
 Benthic animals include mobile creatures such as fish, crabs, shrimp, snails, urchins, sea stars,and slugs
 Additionally, there are numerous animals that never move around as adults.
 These sessile animals include barnacles, sponges, oysters, mussels, corals, gorgonians, crinoids, hydroids, and
bryozoans.
 These animals’ lifestyle combines facets of plant and animal lifestyles.
 Sessile invertebrates are plant like in that they obtain some of their energy from sunlight (the animals themselves
do not photosynthesize, but they house photosynthetic symbionts), they are anchored in place, and they grow in a
modular fashion just as the branches of a tree do.
 They are animal-like in that they capture and digest prey and they undergo embryonic development, often
involving metamorphosis. I
• In fact,nearly all benthic animals start life in the pelagic realm, drifting around as planktonic larva, dispersing to
new habitats as they develop and feed.
• After a few hours to weeks of pelagic living, they sink to the ocean floor to complete life as adults.
• Being stuck in one place presents special challenges for sessile animals, including food acquisition, predator
avoidance, and mating.
• Sessile animals feed by having symbiotic algae and by filtering organic particles from passing water currents.
• Like plants, sessile animals use structural and chemical defenses against predators, and have tremendous
regenerative abilities to recover from partial predation events.

5.
POWER RANGERNOTES MARINE BIOLOGY
5
• Most benthic animals reproduce via external fertilization.
• Sperm and eggs are spawned into the water column and fertilization occurs outside the body of the female.
• Certain deep-sea habitats can be highly diverse. In the deep-sea vents,for example, chemosynthetic bacteria
(rather than photosynthetic species) form the basis of the food chain.
• These bacteria obtain energy from chemical sources such as hydrogen sulfide instead of from sunlight.
PLANKTON
 The term ‘plankton’ was first used by a German Scientist, Victor Hensen (1887).
 The word plankton is derived from the Greek word ‘planktos’, meaning for wanderer or drifters.
 These organisms are free floating with limited locomotory powers and are transported horizontally with the
mercy of the prevailing water movements such as tides, waves and currents.
 Plankton are often used as indicator of environmental and aquatic health because of their high sensitivity to
changes such as eutrophication and pollution with their short life span.
CLASSIFICATIONOF PLANKTON
I. Based on nutrition
• Plankton are classified into phytoplankton and zooplankton based on nutrition.
1. Phytoplankton
• Phytoplankton are the free floating organisms of the sea that are capable of photosynthesis and synthesise organic
matter as their food i.e. primary producers.
• Phytoplankters are microalgae, which includes diatoms, dinoflagellates, blue-green algae, silicoflagellates, etc.
•
2. Zooplankton
• zooplankon are the various free floating animals, i.e. heterotrophic or primary and secondary consumers.
• They are heterotrophic in nature as they depend on the already formed organic matters for their source of food.
• Their food materials include phytoplankton, smaller or micro zooplankton and detritus.
• Zooplankton encompasses many different groups of animals that range in size from microscopic crustaceans to
jellyfish up to a few feet across
• zooplankton forms an important and intermediate link in the food web between primary producers and the higher
trophic levels.
• E.g., copepods, foraminiferans, siphanophores, eggs and larvae of fishes, veligers of molluscs etc.
II. Based on life history
Zooplankton are further classified into two types based on their life history stages viz. holoplankton and meroplankton.
1.Holoplankton- These are organisms that spend their entire lives in the plankton. These are the permanent plankton
organisms.

6.
POWER RANGERNOTES MARINE BIOLOGY
6
• This includes both phytoplankton and zooplankton, covering the whole spectrum of plankton sizes and types.
• E.g. most phytoplankton, some seaweeds,copepods,salps, jelly fishes etc.
2.Meroplankton - These are organisms that spend only part of their life in the plankton.
• These are temporary planktonic organisms.
• These include the larval forms of majority of benthic invertebrates and nektonic forms.
• Often benthos have an early stage of the life history which is planktonic, followed by a stage during which the
plankton metamorphoses into an organism which settles to the bottom .
• This includes species of seaweeds and kelps, and also crabs,lobsters, clams, oysters,and worms among many others..
III. Based on size
• Based on size, these organisms are classified into seven groups as follows.
• 1.Megaplankton - are organisms above 20 cm in size
• 2.Macroplankton - are organisms of 2-20 cm in size range
• 3.Mesoplankton - fall between 0.2-20 mm in size range
• 4.Microplankton - are organisms of 20-200 µm in size range
• 5.Nanoplankton - are very small organisms ranging from 2-20 µm in size.
• 6.Picoplankton - are minute organisms of 0.02-2.0 µm in size
• 7.Femtoplankton - are still smaller organisms of 0.02-0.20 µm in size.
PHYTOPLANKTON
• The free-floating plant plankton are called phytoplankton and wide range of photosynthetic organisms are
included under this category.
• Generally, phytoplankton are grouped under algae.
• Phytoplankton also contribute a significant portion of the oxygen found in the air we breathe.
• There are severaltypes of phytoplankton viz., diatoms, dinoflagellates, blue-green algae, etc.
1.Diatoms (Class: Bacillariophyceae)
Diatoms with their characteristic yellow-brown pigment that masks their green chlorophyll are also called golden
algae. They are unicellular and either solitary or chain forming. The cell contents are enclosed in a unique glass (pill
box), which is called as frustules and have no visible means of locomotion. The frustule is made of two parts, much like a
petridish /petriplate, one valve fitting over another. The upper part (largest part) is called as epitheca and the smaller part
is called as the cell wall (frustule) is made of silicon dioxide. The valves or the frustules are highly ornamented with
species-specific designs, pits and perforations, which make the frustule a lot lighter in weight and also provide a place for
materials to move in and out of the cell.

7.
POWER RANGERNOTES MARINE BIOLOGY
7
Diatoms may occur singly or they may occur in chains of various kinds. Many species have flotation mechanisms
(spines, internal oil droplets or disc shaped). Some of these are holoplanktonic and some are not planktonic at all i.e
benthic. When conditions are bad they dieand sink. The cell decomposes and the frustule breakes up and mixes with sand
and mud. This combination of sediments and glass frustules makes the siliceous ooze called diatomaceous earth. It is
mined by human beings and used as filtering as well as insulating materials.
Diatoms belong to two orders viz. Centrales and Pennales. Some bloom forming species of diatoms are known to
produce harmful chemicals (i.e domoic acid) which got concentrated in animals which feed on such plankton (i.e. filter
feeders). Large amounts of domoic acid consumed by mammals such as seals, sea lions and human beings by eating the
shell fishes caught from the polthese may exhibit erratic behaviour and finally die. , If the accumulation of domoic acid
exceeds certain level in human beings it is known to cause amnesia and this poisoning is called Amnesic Shellfish
Poisoning (ASP).
Reproduction
: Diatoms reproduce mainly by simple fission i.e. each diatom divides into two halves.
• Each half will then develop a new inner valve so that the typical box is recreated.
• The very tiny ones can no longer undergo divisions and at that time they cast off both valves and become a
structure called an auxospore.
• Within this spore, new valves are secreted that re-establish the original size of the diatom species.
• Though this is the general mechanism of diatom reproduction and reestablishment of size, there are some diatoms
which undergo division of cells without reduction of valve size and hence, without auxospore formation.
• Diatoms belong to two orders viz. Centrales and Pennales.
• Some bloom forming species of diatoms are known to produce harmful chemicals (i.e. domoic acid) which can
concentrate in animals who feed on such plankton (i.e. filter feeders).
• The toxin attacks the human central nervous system causing vomiting, abdominal cramps and diarrhoea.
• Some species of diatoms can be mass cultured under controlled conditions and used as larval feed in the shrimp
and finfish hatcheries. E.g. Skeletonema costatum, Chaetoceros sp., etc.
2.Dinoflagellates (Class: Dinophyceaea)
Dinoflagellates are unicellular and very abundant next to diatoms. They have characteristics of both plants and animals.
Like plants, they prepare their food materials by converting sunlight and nutrients in water into food and however, like
animals, many varieties of dinoflagellates eat microscopic particles of organic matter found in the water. Some
dinoflagellates even eat each other, the condition of which is known as phagotrophy. They have two whip-like

8.
POWER RANGERNOTES MARINE BIOLOGY
8
appendages, called flagella, which provide some mobility. They lack an external skeleton of silicon but are impregnated
with armored plates of the carbohydrate, cellulose. These generally small organisms usually solitary and rarely chain
forming ones They reproduce by simple fission, as the diatoms. Each daughter cell of diatom retains half the original
cellulose armor and forms a new part to replace the missing half without any reduction in size; hence, successive
generations do not change in size. Some dinoflagellates are also capable of producing toxins that are released into
seawater. At times, dinoflagellates become extremely abundant, the condition is known as bloom (2-8 million cells per
liter), and the toxins released by these forms may affect other organisms of higher trophic levels, causing mass mortality.
Such extreme concentrations, or blooms of dinoflagellates are called red tides and are responsible for massive localized
mortality in fishes in various places.
Some dinoflagellates have non-motile stages called Zooxanthellae, which are symbionts in the tissues of many
invertebrates such as corals, sea anemones, and giant clams. The dinoflagellate species like Noctiluca scintillans is highly
bioluminescent.
3.Other phytoplankton
Constituents of the nanoplankton and picoplankton size classes (sometimes collectively called nanoplankton) include a
number of photosynthetic microalgal organisms. These organisms are important in primary productivity as well as in
oceanic food webs, which has only been recently realized. The important groups among these organisms are the
prochlorophytes, the haptophytes (Coccolithophoridae, Haptophyceae) and the blue-green algae, also called the
cyanobacteria (Cyanophyceae) . The cyanobacteria are prokaryotic cells that possess chlorophyll-a, but this is not in
plastids and occurs in single cells, filaments, or chains. Cyanobacteria are abundant in the tropics, where they
occasionally form dense mats of filaments and discolour the water (red tide) brownish or saw-dust coloured by
Trichodesmium erythraeum. The abundant haptophytes are the coccolithophores, easily distinguished by the tiny
calcareous plates (coccoliths) on their outer surface. They have complex life histories, with several morphologically
different cells present in the same species, and several modes of reproduction. Coccolithophores are now recognized as a
major source of primary production in many ocean areas. Other less abundant microalgae include the silicoflagellates
(Chrysophyceae), the cryptomonads (Cryptophyceae), and certain motile green algae (Chlorophyceae).
Pelagic bacteria or bacterioplankton, are also found in all oceans. They are most abundant near the sea surface and
are now thought to equal or exceed the total biomass of phytoplankton. They are usually found in association with
organic particles in the water column, collectively called Particulate Organic Carbon (POC), or on various gelatinous

9.
POWER RANGERNOTES MARINE BIOLOGY
9
zooplankton pieces known as marine snow. They decrease markedly with depth, and their role in the microbial loop of the
oceanic food web is now clearly recognised.
ZOOPLANKTON
Zooplankton comprise many microscopic and macroscopic animals represented by almost all the major taxa of the
Kingdom Animalia. The zooplankton are ubiquitous. They eat other smaller sized zooplankton as well as phytoplankton.
Almost all zooplankton are invertebrates , however some belong to the vertebrate groups ( e.g. salps) .Zooplankton
include both unicellular ( protozoans) and multicellular forms.
Zooplankton play an important role in the aquatic food web, having the potential to affect water transparency, levels of
suspended algae (phytoplankton),and the fishery. Many economically important fish depend on a diet of zooplankton
during some stages in their life cycle. Some of the zooplankton species include those of copepods and krills. The krills
(Euphausiids) are serving as an indicator organism for the presence of baleen whales in the polar waters.
Holoplankton (Permanent plankton)
• The holoplankton are composed of forms representing nearly every phylum of the animal kingdom with the
exception of the sponges, bryozoans, and phoronids.
• Among the echinoderms, only the sea cucumbers have members, Pelagothuria with two species and Planktothuria
with one species,which are planktonic throughout their life.
• However,no plankton animals play so vital role in the economy of the sea as do the crustacea of the phylum
Arthropoda.
• Among these,the copepods rank first in most parts of the ocean although in many instances euphausiids are of
equal or greater importance as food for the larger plankton-feeding animals.
Meroplankton (Temporary plankton)
• The temporary plankton is characteristically seasonal in occurrence as it is dependent upon the spawning habits
of the benthic parental stock.
• This variation in time of spawning of the various benthos i.e. some spawn in different times of the year or some
spawn throughout the year,the occurrence of meroplankton is always there in the seawater.
• meroplanktonic forms are abundant mostly in the inshore waters or neritic waters as this region is in close
proximity to the littoral region, where more benthos known to live
ADAPTATIONS
Floatation by increasing surface of resistance
• Plankton, show severalimportant morphological and ecological adaptations crucial in their survival.
• For this many plankton have flattened body shapes,for example some are bladder like, ribbon like, needle like, or
branched types.

10.
POWER RANGERNOTES MARINE BIOLOGY
10
• Certain phytoplankton like Chaetoceros,which possess hair like setae on its cell and zooplankton, phyllosoma (
larva of lobster) have long projected appendages help these forms in creating surface of resistance,hence aids in
floating in the surface.
Floatation by reducing over weight
• For reducing the weight of the organisms so as to live as plankton in the surface layers of the water,these
organisms simply change their body fluid composition so as to make the body less dense than the seawater
without affecting the salt balance/ osmotic conditions.
• The most common way for this is the replacement of heavy ions in the body fluids with lighter ones.
• This is seen in Noctiluca, by having ammonium chloride in its internal body fluid with the specific gravity of
1.01 against the seawater value of 1.025.
• Some plankton will have more water contents in their body to reduce the specific gravity, thereby increasing the
buoyancy e.g. jelly fish.
• Some animals like foraminiferans have many perforations in their test or shells so as to reduce the weight of the
animal to increase the buoyancy.
• Some are having oil globules or droplets in their body to reduce the specific gravity so as to increase the
buoyancy e.g. fish eggs and diatoms.
• Another mechanism that is employed to reduce density is the possession of a gas float of some sort. Some
siphonophores have air filled sacs called pneumatophores in its body.
IMPORTANCES OF PHYTOPLANKTON
. Beneficial effects
• They are very much important in the aquatic environments as these are the basis of the life in any aquatic system
.About 80 % of the oxygen on the earth is known to be produced by these marine phytoplankton .
• They are also playing a major role in the cycling of biogeochemical in the marine environment and hence these
are of great significance on the aspects of global warming.
• Phytoplankton cycles major nutrients in aquatic habitats.
• Phytoplankton are used as indicators of water quality
• Phytoplankton species are known to serve as indicators of some commercially important fishery .
• For example, the abundance of diatom , Fragillaria oceanica in the plankton samples is very high, then it is the
indication of the presence of oil sardine fishes ( Sardinella longiceps) in that location . Similarly, the species of
diatom Hemidiscus hardmanianus is observed to indicate the choodai fishery (lesser sardine) in the west coast of
India.
• They are also known to serve as a food for the fish larvae in the hatcheries.
• E.g. diatoms(Chaetoceros, Skeletonema), silicoflagellates (Isochrysis galbana) and green algae (Chlorella).
ii.Harmful effects
• Some red tide causing dinoflagellates ( Gonyaulax and Gymnodinium ) are toxic to the organisms of higher
trophic levels of the aquatic systems when they form bloom .
• They are responsible for the localized mass mortality of fishes in the marine ecosystem .

11.
POWER RANGERNOTES MARINE BIOLOGY
11
• Besides the mass mortality of fishes, they are also responsible for the transmission of some diseases to human
beings particularly, PSP,when the shell fish harvested from the red tide affected coastalwaters is consumed by
human beings.
IMPORTANCES OF ZOOPLANKTON
i. Beneficial effects
• Zooplankton are playing a pivotal role or as serving as an intermediate links in the aquatic food chain and
transfer the energy to the higher trophic levels.
• Most of the zooplankton are serving as a very good food source to the larval and adult fishes of the commercially
important marine fishes.
• The abundance of the rich shoal of herrings and mackerels is indicated by the abundance of copepod species
Calanus.
• The presence of abundant krills (Euphausia superba) will indicate the presence of baleen whales.
ii.Harmful effects
• Some zooplankton are known to have some adverse effects on the fishery as they are the voracious predators on
the fish eggs and larvae, which may leads to the poor fishery of that location.
• E.g., Sagitta sp. (arrow worm)
• It is worth mentioning here that the abundance of jelly fishes in the sea is considered as a menace or hindrance to
the fishing operation as these are known to clog the fish nets.
• Apart from this, the area rich in jelly fishes are also invariably observed to be devoid of fishes.
NEKTON
• Nekton comprises all the fast and free swimming animals of the pelagic waters.
• The term "nekton" was coined by Ernst Haeckel(1890) and it is derived from the Greek word nekton, which
means "swimming".
• They are provided with efficient locomotory organ and hence they are not at the mercy of currents.
• Most nekton are carnivores (meat eaters) and predators (organisms that kill and eat other animals) and some are
scavengers (meat eaters that don’t kill what they eat).
• A few nekton are carnivorous filter feeders (animals that filter large volumes of water to obtain their food, which
is usually zooplankton) e.g. baleen whales.
TYPES
There are three types of nekton viz.
• chordates
• molluscs

12.
POWER RANGERNOTES MARINE BIOLOGY
12
• Arthropods
Chordates
• Nekton belonging to the chordates are the largest groups, which have bones or cartilage.
• This group includes bony fish, sharks,whales, porpoises, dolphins, seals, turtles, snakes,and sea birds.
• There are almost 25,000 species of fishes, more than any other group of vertebrates.
i. Fishes
• Among the nektonic vertebrates,fishes represent the major constituent of the nekton.
• Based on the habitat they inhabit, these are grouped into holoepipelagic and meroepipelagic.
• Holoepipelagic fishes are those that spend their entire lives in the epipelagic region. These fishes include most of
the tropical and subtropical fishes and often lay floating eggs and have epipelagic larval life.
• meroepipelagic fishes spend only part of their life in the epipelagic region and visit this region to find their prey.
They may spawn in inshore or fresh water regions.
ii.Reptiles
• The nektonic marine reptiles include sea snakes and turtles. These are cold blooded animals.
• Though the turtles are the true pelagic animals they often visit the shores for breeding .
• The leathery turtle (Dermochelys) and the hawk- billed turtles (Chelonia imbricata) are carnivores
• The green turtle (Chelonia mydas) feeds largely on seaweeds and eel-grass.
• The sea-snakes are represented by more than sixty species distributed abundantly in the Indo-Pacific region.
• Important genera include Enhydrina, Pelamis, Microcephalophis and Laticauda.
iii.Seabirds (Aves)
• Seabirds, which are warm blooded nektonic animals, play a significant role in the investigation of marine
ecosystems and food chain dynamics.
• Especially their interaction with marine fishes and the fishery are regarded of growing economic importance.
• They typically breed on offshore or coastalareas like cliffs, dunes, skerries or remote islands.
• Some 274 species belong to seabirds, comprising mainly penguins, albatrosses, fulmars, petrels, shearwaters,
pelicans, cormorants, skuas, ducks, terns and auks.
iv.Mammals
• The mammals include the seals, dugongs, manatees,dolphins, porpoises and whales, of which the whales are the
most important.
• These are the largest members of the nekton. The blue sulphur-bottom whale, a plankton feeder,attains a length
of 25 metres and a weight of 60-80 tons.
• The toothed whales (sperm whale, Physeter catodon, and killer whale, Orcinus orca) are predators feeding on
squids and large fish.
• The whalebone whales (baleen whales) on the other hand feed on plankton, mainly sieving euphausids and others
from surface waters.

13.
POWER RANGERNOTES MARINE BIOLOGY
13
INVERTEBRATES
i)Molluscs
• Nektonic molluscs include octopus and squid. Unlike clams and oysters, squids have no shells on the outside of
their bodies.
• There are about 375 species of squid. Squids are very fast swimmers and they use a kind of jet propulsion to
move.
• Squids have some unique adaptations. Some can change colour, some use bioluminescence to create light, and
some shoot ink to cloud the water and escape from predators.
• There are two large groups of octopus.
• The cirrata or finned octopuses live in the deep sea at depths of between 1000 and 24,000 feet.
• About 85% of octopuses are in the incirrata group.
• They have eight tentacles. The tentacles have suction cups on them and are used to hold onto prey.
• The tentacles also have taste sensors that let the octopus know if what it grabbed is worth eating.
• Some species may also inject prey with a toxic substance.
ii)Arthropods
• Among arthropods, shrimps are the major nektonic organisms.
ADAPTATIONS
1.Fishes
i. Buoyancy
• Most fish have a gas-filled swim bladder. Most fish can regulate the amount of gas in the bladder and thus
control their buoyancy.
• Gas filled cavities (lungs) help float all air-breathing nektonic animals.
• Marine mammals to increase buoyancy are bone reduction and the presence of a layer of lipids (fats or oils).
• Large amounts of lipids are also present in nektonic fish that do not have swim bladders (sharks, mackerels,
bonito).
ii.Musculature
• The fishes those living in the deep sea areas have suitable adaptations to withstand the prevailing high pressures
and to the dark conditions. These fishes are fragile and weak with soft and loose muscle.
iii.Colour
• They develop black or dark brown colourations to minimise the problem of predation.
iv.Eyes

14.
POWER RANGERNOTES MARINE BIOLOGY
14
• Many deep sea nekton have reduced eyes or no eyes.
v.Bioluminescence
• Some fishes have bioluminescence organs in their body to attract their prey as well as to find their mates (e.g.
angler fish)
2.Reptiles
• Turtles possess a special adaptation to marine life by having buccal respiration in which a highly vascularised
mucous epithelium takes up oxygen from water in the mouth.
• The mucous epithelium of the buccal cavity of sea-snakes is known to be supplied with numerous capillaries
which enable these snakes to take oxygen form the water.
• This would explain the records of sea snakes seen resting in the bottom and remaining submerged for several
hours.
3.Seabirds
• Seabirds swim at the sea surface and under water; they use their webbed feet, their wings, or a combination of
wings and feet.
• They float by using fat deposits in combination with light bones and air sacs developed for flight.
• Their feathers are waterproofed by an oily secretion called preen, and the air trapped under their feathers helps
keep the birds afloat, insulates their bodies, and prevents heat loss.
• When diving, the birds reduce their buoyancy by exhaling the air from their lungs and air sacs and pulling in their
feathers close to their bodies to squeeze out the trapped air.
4. Marine Mammals
i. Temperature Maintenance
•Large size - less loss of body heat (reduces surface to volume ratio)
•Insulating layers of blubber or fat
•Adaptations of the circulatory system for reducing heat loss
ii. Respiratory modifications for diving
•Have the ability to hold their breath for extended periods of time making deep dives possible.
•They are able to dive with their lungs empty avoiding problems of buoyancy and bends (nitrogen bubbles in the blood)
•Their blood is rich in haemoglobin and other respiratory pigments, and the muscles are rich in myoglobin (another
respiratory pigment in the muscles).
•During deep dives, sphincters in arteries shut off blood to parts of the body so it only goes where it is needed.
•The heart slows, and the muscles can tolerate a greater oxygen debt than terrestrial animals.
•When the animal surfaces and breathes,a very rapid O2-CO2 exchange occurs.
iii. Osmotic Adaptations
• The kidneys reabsorb water and they excrete a very concentrated urine
• Fatty insulating layers may also play a role in water storage.
• Most water intake comes from the fish they eat.

15.
POWER RANGERNOTES MARINE BIOLOGY
15
BENTHOS
 All the organisms living or inhabiting in the bottom regions of the aquatic environment are termed benthos.
 These benthos/benthic organisms live in a variety of bottom environments of the aquatic ecosystems and are as
diverse as the plankton.
 These bottom living organisms have direct contact with the substrate,which limits the distribution of these
organisms.
 The factors such as the composition, size of the particles, its firmness or resistance to penetration, its mobility and
the food they contain, are all known to have major influence on the distribution of organisms.
CLASSIFICATION OF BENTHOS
BASED ON SIZE
• Macro benthos are organisms that are larger than one millimeter
E.g. oysters, starfish, lobsters, sea urchins,
shrimps, crabs and corals.
• Meio benthos are between one tenth and one millimeter in size.
E.g. ciliates, annelids , kinorhynchs, copepods
• Micro benthos are very tiny organisms. They are smaller than one tenth of a millimeter.
E.g. bacteria and ciliates
TYPES OF MEIOBENTHOS
Meiobenthos are also called as interstitial organisms (mainly fauna) which live in the spaces between the sand grains or
particles of the substratum or live on the individual particles. However, meiofauna is the preferred term to refer to the
organisms that live interstitially. Meiobenthos and meiofauna are synonymous terms to each other. These organisms
include all animals that pass through a 0.5 mm screen but are retained on a 62 µm screen mesh. This term meiofauna is
mainly based on size of the benthic organisms and it does not explain about the location of the organisms or their
movements within their habitats. In order to indicate their location and to refine the classification of these forms, some
other terms have been introduced as, endobenthic, mesobenthic and epibenthic.
Endobenthic organisms are the meiofaunal sized organisms which move within the sediment by displacing particles (i.e as
they are the bigger than the interstitial spaces of the sediment(sand) particles).
Mesobenthic organisms are the meiofaunal organisms living and moving within the interstitial spaces of the sand grains.
Epibenthic organisms are those that living at the sediment-water interface.
BASED ON MOBILITY
1. Sessile organisms: are those that do not have any mobility, attached or fixed with the substratum or bottom of the
aquatic environments and rely on currents or other mechanisms to bring food to them.
E.g. benthic algae (seaweeds) ,sea grasses ,corals ,barnacles, oysters etc

16.
POWER RANGERNOTES MARINE BIOLOGY
16
2. Vagrant benthos :are those that have locomotory powers and either they can move rapidly or slowly. E.g. Only animals
are included under this category.
Based on the mode oflife
 Epifaunal organisms : animals which live on the substratum.
 infaunal organisms : are those that animals live into the substratum.
 Burrowers : Organisms that penetrate or burrow into the unconsolidated bottom sediments are called burrowers.
 Borers : organisms those that penetrate or bore the hard rock or substrate materials are called borers.
Benthic plants
Bottom living plants include varieties of algae and angiosperms or flowering plants, particularly sea grasses. The algae
include the Cyanophyta (blue-green algae), Chlorophyta (green), Phaeophyta (brown) and Rhodophyta (red),in
increasing order of diversity. All range from microscopic to large except the blue-green algae, which are all microscopic.
They commonly have filamentous character and occur in clusters or mats.
Green algae include severalcalcareous species that are important contributors to the sediment substrate, especially in the
shallow waters of the low latitudes.
The brown algae include the largest varieties of seaweeds i.e. the kelps, which are very abundant in shallow cold waters
Most of them are of commercial value as they contain algin, a gelatinous material that is used as an emulsifier in ice-
creams,paints, drugs, and cosmetics.
The red algae are represented by more species of seaweeds than all other classes of algae. They may inhabit relatively in
the deep waters of the subtidal regions of the sea. Some are calcareous and an important constituents of low-latitude reefs.
There are very few common types of marine grasses. Some of these occupy the intertidal marsh environment. For
example, Juncus sp, is known to occupy the higher level and Spartina sp occupy the lower level of the intertidal marsh
regions. The sea-grasses are known to occupy the sub-tidal regions, which are included by the species such as Thalassia
spp. (turtle grass), and Halodule spp. live in shallow waters of the low-latitudes. In the higher latitudes, Zostera spp (eel-
grass) are the dominant type of seagrasses.
Benthic animals (zoo benthos)
Sedentary or Vagrant epifauna: They may live on rigid substrate,firm sand or soft mud. While some move very slowly,
others move very quickly.
foraminifera: These tiny animals are typically less than a millimetre in diameter with different shaped tests or shells and
most of which are multichambered
shelled invertebrates : arthropods (crabs and lobsters), molluscs (clams, gastropods, chitons, and octopuses) and
echinoderms (sea urchins, sand dollars, star fishes and sea cucumbers).
Arthropods : The crabs and lobsters are the largest and fastest of the vagrant benthos. In addition, they have some
swimming ability, using either their tails and/or specially adapted legs.

17.
POWER RANGERNOTES MARINE BIOLOGY
17
• Many species in this group live in the shelter of rocks, ledges or other cover.
• They are scavengers and will eat almost anything that is available.
Echinoderms : They have numerous appendages in the form of sucker feet or spines that are used for locomotion.
• The sea urchins live on hard substrates where they feed on debris.
• Sand dollars have the poorest mobility but they can move slowly by the whisker-like feet that surround their
body.
• Nearly all vagrant benthic molluscs have external shells and move slowly, on the order of millimetres or
centimetres per minute.
• Some, such as the chitons, are completely protected by their shell and will move across a hard substrate rasping
and scraping food from the surface.
• A few gastropods move slowly through the sediment, ingesting whatever material they encounter, with little or
no selection. They digest the nutrient material and excrete the mineral sediment.
• Generally, these animals have thick, heavy shells to protect them from predators and from the enemies.
• Most have somewhat bulbous shapes,those that live on soft sediment may have special adaptations in shell
morphology to prevent sinking into the mud. e.g. Murex sp with spines.
Sedentary or Vagrant epifauna
This group of animals is the largest in terms of both the number of individuals and the diversity of types. They have two
common primary features:all live on the surface of the sea floor and all have at least some ability to move. They may
live on rigid substrate, firm sand or soft mud. They range in size from microscopic to over a meter in length. While some
move very slowly, others move very quickly. The smallest and probably the slowest of the benthic animals are the single
celled animals, which include the foraminifera. These tiny animals are typically less than a millimeter in diameter with
different shaped tests or shells and most of which are multichambered. Most foraminiferans tests are composed of
calcium carbonate,although some are comprised of sediment particles held together by organic material. They are a
significant contributor to marine sediment. Mobility is nearly nonexistent in foraminiferans; however, the individual
foraminiferan can extend its protoplasm through pores in the test and then contract it to pull the test,thus moving slowly.
They feed by engulfing particulate organic matter. Most vagrant benthos are shelled macro-invertebrates,although there
are some worms thatcrawlover the substrate. The shelled invertebrates are dominated by three groups viz. arthropods
(crabs and lobsters), molluscs (clams, gastropods, chitons, and octopuses) and echinoderms (sea urchins, sand dollars, star
fishes and sea cucumbers).
Except the octopuses, the crabs and lobsters are the largest and fastest of the vagrant benthos. These jointed-leg
animals can move rapidly; they use this ability along with their hard exoskeleton for protection from enemies. In
addition, they have some swimming ability, using either their tails and/or specially adapted legs. Many species in this
group live in the shelter of rocks, ledges or other cover. They are scavengers and will eat almost anything that is
available.
Nearly all vagrant benthic molluscs have external shells and move slowly, on the order of millimeters or
centimeters per minute. Some, such as the chitons, are completely protected by their shell and will move across a hard

18.
POWER RANGERNOTES MARINE BIOLOGY
18
substrate rasping and scraping food from the surface. A few gastropods move slowly through the sediment, ingesting
whatever material they encounter, with little or no selection. They digest the nutrient material and excrete the mineral
sediment in the form of pellets which become an important contributor to the volume of sediment. Generally, these
animals have thick, heavy shells to protect them from predators and from the enemies. Most have somewhat bulbous
shapes,those that live on soft sediment may have special adaptations in shell morphology to prevent sinking into the
mud. e.g. Murex sp with spines.
The echinoderms, or spiny-skinned animals have bulky shapes,such as the various sea-urchins, sea cucumbers,
and many of the starfish. They have numerous appendages in the form of sucker feet or spines that are used for
locomotion. The sea urchins live on hard substrates where they feed on debris attached to the rocks (or) they may live on
the unconsolidated sediment. Sand dollars have the poorest mobility but they can move slowly by the whisker-like feet
that surround their body. These animals may be partially in faunal in that they can burry themselves just under the
sediment surface for protection.
Sessile Epifauna
Many organisms are attached to the substrate throughout their maturity and have no mobility at all. Included are both
solitary organisms and colonial ones, with as many as hundreds of individuals merged into large condominium-style
skeletal complexes. Some can torn up and moved, then reattached and still carry on, where as others expire when
uprooted. Virtually, all sessile epifauna are filter feeders,relying on currents to carry their food to them.
There is a variety of sessile solitary invertebrates that attaches to hard substrates, typically bedrock. These include
barnacles, oysters, some brachiopods, and mussels; sponges, sea anemones,and sea-lilies. Although all are macroscopic,
there is some range in size, from sponges only a few millimeters across to large sea lilies with arms that may be meters
long.
Brachiopods and mussels (Pelecypoda) are both bivalves and filter feeders. Brachiopods (lamp shell) attach with a stem
like foot that extends from near the hinge line that holds the shells together. Mussels are about the same size and they
attach themselves to a hard surface with strong thread like structures,called byssus threads which develop at the hinge
line. The mussels are especially well attached and can withstand vigorous wave and current action.
Anemones (Coelenterata) and lilies (Echinodermata, crinoid) belong to different phyla and have markedly contrasting
anatomies, but there are some similarities in their feeding activities. Both have multiple appendages that serve as the
primary food gathering mechanisms. Anemones are carnivores; they grasp their prey, then envelop and digest it. Some
have sticky substances or toxins in their appendages to aid in capture and submission of their pray. By contrast,the sea
lilies have sophisticated system of circulating plankton and organic debris to their centrally located mouth.
Barnacles are crustaceans (Arthropoda) that exist in two different forms, both sessile. Encrusting barnacles have their
calcareous shells attached directly to the hand substrate,their soft part extended during feeding and retracted for
protection. These are the barnacles that encrust boats, bridges, and other marine structures. The goose-necked barnacles
have fleshy, stalk like structures that attach to the substrate and emanate from the shell that contains the soft parts of the
organism. Both feed by removing small particles of organic debris from the water.
There are also colonial varieties of sessile benthic animals. Primary members of this group are the corals, sea whips, sea
fans and bryozoans. Bryozoans are small and may be encrusting or delicately branching. They have calcareous external
skeletons forming lacy structures that have given this phylum the nick name “moss animals”. The corals, sea whips and
sea fans are all coelenterates,the same phylum as the sea anemones. Sea whips and fans do not have hand, articulated
skeleton and so they disintegrate upon expiration, where as the corals have massive calcareous skeletons that house
numerous individuals. All feed by filtering plankton and organic debris from the water.
Infaunal Organisms

19.
POWER RANGERNOTES MARINE BIOLOGY
19
This group includes various meiofauna and macrofauna such as snails, clams, worms, sea urchins, and crustaceans. Some
groups are entirely infaunal, such as the tusk shells (scaphopods). Infaunal organisms occupy two different models of life.
Some graze or plow through the sediment (sediment destabilizers) and others construct extensive burrow complexes that
they occupy and in which they move about (sediment stabilizers). There are also those that burrow or bore near the
surface and simply occupy that place; they do not move from place to place unless uprooted by waves,currents, or other
organisms.
Grazing or plowing organisms include some sea urchins, snails, and clams. These organisms have shells that are stream
lined for this type of activity. In the case of the sea urchins, they have short, stubby spines. Such animals ingest large
quantities of sediment, extract the organic debris, and them excrete the sediment in pellet form.
A few types like the ghost shrimp, have great burrowing abilities and may be found over 2 m beneath the substrate. They
take in suspended particles and digest the organics, then excrete the mineral sediment. This feeding style is also used by
the numerous clams that burrow near the surface. They have an inhalant siphon and an exhalent siphon that are used for
circulating the water through their digestive systems. Numerous varieties of worms also occupy this mode of life. These
types of infaunal organisms typically move only when they are exhumed from their burrow.
The types of meiofaunal organisms are represented by a broad range of invertebrate phyla. These meiofaunal organisms
have a size range similar to that of some of the smaller mesoplankton and the microplankton. These include the members
of the phyla Ciliophora, turbellarians of the Platyhelminthes, Gastrotricha, Kinorhyncha, Tardigrada, Annelida, and
Arthropoda. These organisms are very abundant only in the intertidal beaches and their biomass decreases with increasing
depth in the oceans. The abundant groups are nematodes and harpacticoid copepods. These meiofauna forms a very good
food source to most of the macrofaunal deposit feeders like larger polychaetes, holothurids, fishes such as young ones flat
fishes, gobies and mullets. The role of these as food of the macrofaunal organisms mainly depends on the nature of
sediments. That is the muddy sediment is known to harbour more meiofaunal biomass in the top layer, which is more
accessible to the predators than the sandy sediment.
These infaunal meiobenthos are also known to exhibit a variety of feeding habits viz. herbivores- feeds on the attached
diatoms; detritus feeders, suspension feeders and predators. Suspension feeders are quite rare,due to lack of plankton
availability. They prefer to feed on bacteria and microalgae attached to the sand grains. Large bodied animals and sessile
benthos are poorly represented in the marine meiobenthos, for example, members of the phyla Echinodermata and
Cnidaria. The members of the phyla such as Phoronida, Pogonophora, Porifera, Ctenophora, Hemichordata and
Chaetognatha are totally absent in the meiobenthic communities.
There are some organisms, such as certain clams and sponges that can bore into solid rock or shells. This is done through
a combination of physical rasping and chemical reaction between substances secreted by the organisms and the substrate.
ENVIRONMENTAL FACTORS AFFECTING THE LIFE IN THE OCEAN
TEMPERATURE
• Temperature is a measure of the condition caused by heat and it expresses the intensity of the warmth and is
measured by 0C.
• To be more precise, it is defined ‘as the energy in molecular motion and expresses the intensity of warmth, which
is measured by 0 Celsius’.
• Temperature is a factor of prime important in the marine environment because of its action.
• 1.Directly upon the physiological process of the animals especially upon the rate of metabolism and the
reproductive cycle.
• 2.Indirectly through its influence on the other environmental factors such as gases in solution, viscosity of water
and distribution.

20.
POWER RANGERNOTES MARINE BIOLOGY
20
• The range of temperature in the sea varies from about –30 C to 420C depending on season and locality, but in the
open ocean, the maximum temperature does not exceed 300C. (Whereas air temperature from –650 C to + 650 C
may be found)
Ocean is the largest store house of the sun’s heat and it occupies much space. This stored heat of the ocean is able to
regulate the temperature of the world. The extremes of temperature range from – 3 to 40º C, while in the Indian seas the
temperature ranges between 18 to 25º C at the surface. Seasonalvariations of temperature in tropical waters are not much.
There is always a direct stratification in sea and the temperature of the bottom water of the deep sea may be about – 1º C.
The density of the sea water increases with decrease in temperature. Similarly the solubility of oxygen also increases
generally with a lowering of temperature.
Seawater temperature affects marine organisms by changing the reaction rates within their cell(s). Although each species
has a specific range of temperature at which it can live, the warmer the water gets the faster the reactions and the cooler
the water the slower the reactions. An organism's response to water temperature is considered to be cold blooded (or
poikilothermic) or warm blooded (homiothermic) depending on their ability to control their internal body temperature. If
any species is moved out of its temperature tolerance range, it may die in a short time although temperatures on the cool
side of the range are easier for organisms to tolerate than temperatures on the warm side because cell reactions just slow
down in the cold but may speed up over six times the normal levels for each 10º C of heat.
Cold blooded (poikilothermic) marine organisms lack any body temperature regulatory controls. These include marine
plants, invertebrates, most fish and marine reptiles. These species each have their specific temperature tolerance range
within which they must live (some are adapted to polar temperatures,some to tropical temperatures). Some have a narrow
range (and are thus very restricted) and some have a wide range (and are thus less restricted).
Warm blooded (homiothermic) marine organisms have some type of internal temperature controls to maintain a constant
body temperature. These organisms include a few fish, all sea birds and mammals. This ability allows these warm
blooded marine species to migrate over vast distances through various temperatures without problems and include some
of the animals on Earth with the longest migrations.
Marine animals show a varied response to temperature. The stenothermal animals like reef corals, salps and heteropods
are always found around 20º C. Eurythermal animals like Cardium and Arenicola are able to withstand wide ranges of
temperature. Temperature difference in the sea though not very conspicuous yet acts as effective barrier for the
distribution of animals.
Marine animals present certain structural variations in relation to temperature. The number of vertebrae in fishes of colder
regions is more. The fish species of flounders have 35 vertebrae in the warmer regions while in the colder regions they
may have up to 50. The cold water forms also show an increase in size. This is because it takes a longer time for the cold
water forms to attain sexual maturity and thus they get a chance to grow till then. There are however a few exceptions to
this rule. The sea urchin, Echinus esculentus, and the gastropod Urofolpinx cinerea, show a larger maximum size in
warmer waters.
There is also an increase in respiratory rates in many marine organisms. In Mytilus edulis , the respiratory rate increases
with temperature up to the optimum limit and then it slowly decreases. A similar behaviour is found in Calanus
finmarchicus and Emerita sp.
The animals are commonly divided into large groups with reference to their tolerance to temperature namely,
• Stenothermic
• Eurythemic.
Within the temperature limits tolerated by an animals there are three fundamental categories.

21.
POWER RANGERNOTES MARINE BIOLOGY
21
• Optimum, minimum and maximum
Response of an organism to varying temperature in the marine environment can be described as
• Structural response
• Functional response
• Behavioural response
Structural Responses:
• There are much direct evidences that frequently cold water animals grow to a large size than the similar animals
in warm water.
• Jesperson (1939) reports that Calanus finmarchicus in Greenland waters forms two size groups, larger being
found particularly in waters of low temperature and the smaller size population in warmer surface layers.
• Three explanations have been given for the increased size of the cold water planktonic form.
• 1.Lowered temperatures lengthen the time required for poikilothermal animal sexual maturity. Hence in cold
water forms, the delay permits longer growing period with resultant large size at maturity.
• 2.It has been shown that, the oxygen consumption of certain non- locomotary warm water benthic species is
higher than that of related colder water species and this difference in metabolism may have a bearing on the
question.
• 3.Increased density and viscosity of cold waters enables large forms to keep afloat more successfully in cold than
warm water.
FUNCTIONAL RESPONSES
Metabolism:
• The rate of metabolism (measured by O2 consumption and production of CO2) of all poikilothermic organisms is
very much increased with rise in temperature.
• According to Vant-Hoff’s rule, the increase is 2-3 times for each 100C rise in temperature within favourable
limits.
• Hence,it serves,as one of the factors in rapid and abundant production in warmer regions.
• During winter, when production is less, Calanus finmarchicus sinks down to deeper waters where the metabolic
rate declines.
• Among the coastal forms Penilia and Evadne survive the low winter temperature as resistant resting eggs and are
therefore able to appear suddenly in abundance in spring, when warming of water takes place.
• Therefore,parthenogenic activity in marine cladocerons is largely depend on temperature fluctuation.
• It could be noted that, the optimum temperature for life activity is considered to be nearer the maximum than the
minimum limit, for which reason a small rise in the temperature from the optimum is more disastrous to cold
blooded animals than is a greater lowering.
Calcium Precipitation:
• Temperature influences to a marked degree of which CaCO3 can be precipitated by the animals in the formation
of skeletal parts, shells and spicules.
• Therefore,organisms that utilize calcium compounds in their supporting, protective structures are notably
abundant in warm water. Because of this, deep water molluscan shells is not large and heavy as in warm water.

22.
POWER RANGERNOTES MARINE BIOLOGY
22
• Calcium precipitating organisms are present in all seas,but their numbers are much reduced in the fauna of cold
polar seas and the shells of these present are relatively more weakly constructed.
• Calcareous shelled species are replaced in cold northern waters by the arnaceous types, which build shells of
sand, fragments of shells, spicules and so forth, cemented together with non calcareous cement. This type is
characteristic of deepwater foraminifera.
• Low temperature is apparently a major cause of the limited production of calcareous structures,although a great
hydrostatic pressure in deep water,may be of great importance.
• effect of temperature on biological deposition of CaCO3 provides a key to the interpretation of temperature
conditions and water depths that mush have prevailed.
BEHAVIOURAL RESPONSES
Bipolarity:
• It has long been known that the fauna’s of the cold waters,the north and south latitude contain many elements in
common.
• The animals or animal group that form these elements may be wanting in the intervening tropical region. A break
of continuity of distribution of species is called ‘discontinuous distribution’.
• This discontinuous distribution occurring in the meridonial direction resulting in the absence of species in the
tropical belt is known as ‘bipolarity’.
There are three hypotheses to support the theory of bipolarity.
• (i) Theory ofextinction: This hypothesis holds that the fauna were cosmopolitan and is now extinct along the
tropical belt.
• (ii) Theory oftropical submergence: This hypothesis is associated with the sinking of eurybenthic and
eurythermic fauna to a greater depth along the tropical belt, thus involving discontinuous distribution.
• (iii) Theory ofParallel Evolution: This hypothesis states that, the species of the fauna developed simultaneously
along both the poles resulting in the presence of same species of the fauna and their absence in tropical belt.
SALINITY
The salinity of the open ocean at about 300 metres depth is about 3.5%. There is a slight variation in salinity in some seas,
as in the Mediterranean where it is 3.9% while in the red sea it is 4.6%. The salinity of the sea is due to the two elements
sodium and chlorine which account for 80% of the salts of the sea. The composition of chemicals contributing to seawater
salinity is given in the following table.

23.
POWER RANGERNOTES MARINE BIOLOGY
23
In the sea water,cations and anions are not balanced against each other. As a result, sea water is weakly alkaline (pH 8 to
8.3) and strongly buffered. This factor possesses much biological importance. The various salts of the sea are
indispensable to the marine life. Animals absorb and utilize many substances like Ca, Na,K, Mg, S, C l etc. They also use
many inorganic materials like Na, Mg, Ca,and silicic acid to build their bodies. A few animals even use and store rare
elements. Strontium sulphate is utilized by some radiolarians. Bromine and iodine is stored by horny corals and vanadium
is used by ascidians.
An increase or decrease of salinity brings about changes in the specific gravity of the sea water. All marine animals are
affected by changes in specific gravity. Only some animals like the teleostean fishes have the swim bladders which are
used for hydrostatic control. Animals with hard skeletal materials of calcium and silicon face the problem of sinking.
These animals however have various adaptations developed to keep themselves afloat, which include reduction of
calcium contents by having perforations in the shell of foramnifers and thin shell in radiolarians. Some pelagic molluscs
have thin and uncalcified shells, which aids in floatation.
Osmotic properties of the seawater present another problem to some of the marine animals. Most of the marine animals
are isotonic with seawater and when they come across any change in salinity, they are put to much difficulty. The
stenohaline animals have a restricted distribution. These animals are usually found in the open oceans far away from
estuaries and below the level of tidal variation and only a few metres below the surface.
Euryhaline animals include the coastalforms found between tide levels. Arenicola, Mytilus, Sagitta and Oikopleura are
some good examples. Some animals like the shore crab,Carcinus, can tolerate lower salinity at higher temperature. The
younger organisms have lesser tolerance for lower salinity than their adults.
Salinity has a profound effect on the respiratory activities of marine animals. The respiratory rates increase with a
reduction in salinity. The animals spend much of their energy in osmoregulation, when salinity falls and this leads to a
higher rate of oxygen consumption and higher respiratory rates. The highest respiratory rates are found in estuarine forms
like Hydrobia, Carophium and Pygospio.
More calcium carbonate is deposited in the skeleton of molluscs, crustaceans and other animals living in the water with a
high salinity content. The molluscs found living in lower salinity have thinner shells. Animals can tolerate lower salinity
when the temperature is high.
Definition ofSalinity:
• Salinity is defined as the total amount of dissolved material in gms per kg of sea water with an assumption of the
organic matter is completely oxidized, the bromide and iodide are replaced by an equivalent amount of chlorine
and all carbonates are oxidized.
• The physical property of seawater depends in general on 3 factors, temperature,salinity and pressure.
• In the open ocean, the surface salt content varies between 32 and 38 ppt. (one can take the mean value as 35 ppt).
The considerable differences in surface salinities are caused by variations in the extent of evaporation, quantity of
rain and inflow of freshwater. So the salinity fluctuation is seen from 0 to 41 ppt.
Density and Viscosity:
• Changes in salinity lead to respective changes in density and viscosity of the ambient water.
• This may be importance in regard to movement and maintenance of position in planktonic invertebrates.
• Variations in density can affect the amount of energy, which must be expended for migrations and other activities
of planktonic communities.
• The density of the protoplasm of most marine invertebrates ranges between 1.0400 and 1.0500. This range lies
slightly above the density of seawater (1.028 at 100
C and 35 ppt).
FUNCTIONAL RESPONSES

24.
POWER RANGERNOTES MARINE BIOLOGY
24
a) Tolerance:
• Animals, which can tolerate the wide range of salinity, are referred to as ‘euryhaline’ and those animals which
have a limited salinity tolerance range are ‘stenohaline’.
• In marine invertebrates, the degree of tolerance to salinity variations often varies during the embryonic stages.
• Developing eggs and newly hatched larvae of some invertebrates may not tolerate extremely wide range of
salinity.
• Eggs of shore crab develop normally in salinities between 28 ppt and 40 ppt, while adults tolerate salinity down
to 4 ppt.
b) Metabolism and Activity:
• Rates of metabolism and activity are functionally correlated; changes in metabolic rate tend to alter the scope for
activity.
• The amount of oxygen and carbon dioxide, which can be held in solution decreases in increasing salinity.
(1) Many aquatic invertebrates respire at most economic rates in salinities to which they are genetically adjusted or to
which they have been acclimatized over longer time.
(2) Respiratory demands due to salinity stress can be reduced by reductions in muscular activity.
• Salinity may influence the metabolic rates in multiple ways.
• Ex. Via stimulation or diminution of locomotary activity, increases or decreases of water or salt contents of body
fluids.
c) Reproduction:
• Salinity may effect decisively reproduction in areas where it undergoes pronounced changes .Changes in salinity
have been shown to modify rates of reproduction and to bring about a shift from asexualto sexual reproduction.
• Amphipod lays more eggs in brackish water than in freshwater.
• Theodoxus sp. produces smaller egg capsules containing pure eggs than in freshwater.
• Salinity variations may also modify time and length of breeding season.
• Salinity may affect functional and structural response of invertebrates.
STRUCTURAL RESPONSES
 Among euryhaline animals, individuals living in reduced salinities frequently have smaller size than do those of
the same species inhabiting more saline waters. Ex: oyster, Mytilus.
 It is very strange to note that, with few exceptions, marine animals from groups with fresh water representative
and larger than the fresh water relative and usually size difference is enormous.
 Respiration is more difficult in fresh water hypotonic is another factor for which it has to spend energy more.
LIGHT
The availability of light in the marine ecosystems plays a major role , mainly in the process of photosynthesis by plant
communities in the sea. Light that is falling or penetrating into the seawater is absorbed by the microscopic as well as
macro vegetation like seaweeds and synthesise organic matter . This is called primary production, with which the
consumers of the higher trophic levels of the marine food chain depends for their food. When there is good light, then
there will be a good amount of plants and hence good organic matter, which determines the distribution of animals in the

25.
POWER RANGERNOTES MARINE BIOLOGY
25
sea. The vision of the marine animals is also controlled by the light availability and also light plays an important role in
the breeding cycles of the many marine animals.
Of all the light rays emitted by the sun is not fully reaching the ocean surface and only 50% of it striking the ocean
surface. The rest of the sun light is scattered,absorbed or reflected back into the atmosphere. The reflection of the same
depends up on the various factors like angle of incidence of sun light on the ocean surface,seasons of the year, the time of
the day and the location or latitude. In the equator, the sun light radiation is fairly constant throughout the year when
compared to the higher latitudes. That is at near the poles, the availability of sunlight is continuous during the summer
and a continuous darkness in winter seasons.
Of all the light falling on the surface ,only 1% of the falling light will be penetrating down the sea and the remainder is
absorbed and is scattered by the particles suspended in the water. The penetration of light also varies with the wave
lengths of the light. Not all the rays are penetrating deep in the water and some of them are absorbed in the top few meters
of the water column. Red light is absorbed in the top few meters depth whereas the blue light rays penetrates up to a depth
of about 150 meters in the sea. The penetration of light is also influenced much by the turbidity or clarity of the water. If
the water is more turbid in nature, the most of the light will be absorbed in the top few meters of depth whereas in the
clear waters it will penetrate to the deeper levels of the sea i.e about 1000 m depth.
Zonation of sea on the basis ofintensity oflight
On the basis of the penetration of light, the ocean is vertically divisible into three zones:-
a. Euphotic stratum – This extends from 0-80 meters. This may also be called as “illuminated zone” of “Producing zone”.
This zone is very rich in phytoplankton and primary consumers and secondary consumers.
b. Dysphotic stratum – This zone extends from 80 to 200 meters and is weakly lighted. Animals here are mostly
secondary consumers and a few primary consumers. Plant life is rare.
c. Aphotic stratum – This zone extends below 200 meters where light is completely absent. The producers are absent as
photosynthesis cannot take place. The animals in this region are secondary consumers and also feed on other animals. The
only light available in this zone is mainly of light produced by the bioluminescent animals (living light or cold light).
Harmful Effects oflight
Light which is very essential for the photosynthesis of plants and generally beneficial to animals may sometimes be
harmful. The violet and ultra-violet parts of the spectrum have harmful effect on animals. In order to avoid these harmful
effects,many animals become nocturnal. By taking up a nocturnal habit, these animals also avoid the predators which can
easily spot them in good light.
Diatoms react to excessive light by clumping. Many animals avoid excessive illumination by diurnal migrations. Animals
like corals which cannot move about, open their polyps only in dim light and close them when there is bright light.
Intertidal animals also become nocturnal. Ligia oceanica comes out from crevices only in night. Mytilus edulis closes its
shells in excess of light and opens only in night. Chiton also lives in areas where shade is available. It is negatively
phototropic when young. As regards the zooplankton, the young stages do not live at the same level as their adults.
Light as a Biological Factor

26.
POWER RANGERNOTES MARINE BIOLOGY
26
• Light is defined as radiant energy roughly covering the range 380-780 nm (1 nm = 10-9m) which is capable of
simulating a human eye so as to produce the sensation of vision.
• Further, the extent of scattering and absorption depends upon dissolved substances,suspended particles and
molecular processes in the water.
• Light serves animals for visual orientation and stimulant for locomotion. In addition, there are other living
processes that are controlled by light.
Light and Colour:
Colour changes in marine invertebrates are brought about for mainly three reasons.
1.To match the colour with the surrounding.
2.To scare the predator
3.To protect itself from harmful rays of the sun.
• The pigments of chromatophores produce degrees of shade and colour by the concentration or depression of
pigments within the irregularly shaped chromatophores cells.
• The content of chromatophores are either activated directly by intensity of incident light or medicated through
the eyes and nervous system in response to colour.
• I) On the open coast of California, Holothuriods are darkly pigmented, while specimens from Mytilus bed have
very little body wall pigment. Interestingly darkly pigmented individuals do not contact when a strong light
directed on their body, whereas,pale individuals are sensitive to strong light and move rapidly away.
• ii) Population of crab found on the white sandy beach of Oahu are pale in colour when compared to that of crabs
found on the black sandy beaches of Hawaii. Hawaii beach crabs process approximately 12 times as many black
chromatophores as Oahuan beach crabs.
• iii) In cephalopods, colour intensity may quickly shift from pale grey to rich chocolate as the mollusc passes over
a lighter or darker surrounding. Here,light appears to be the stimulus activating the changes, but in addition
nervous reaction related to feeding or presence of enemies may also produce the temporary colour changes in
cephalopods.
• iv) Summer and Doudoroff showed that Guppy was nearly independent of the intensity of light, but was
dependent upon albido of the background.
The responses of marine invertebrates towards light can be described as:
Functional Responses:
• Under laboratory conditions, calcium deposition in corals was higher in higher light intensity, while it was
significantly less in lower light intensity.
• In severaldecapods, especially freshwater crabs,it was observed that darkness enhances the rate of moulting and
promotes growth, while in constant light condition, the decapods enter into a irregular moulting leading to
inhibition of growth
• In planktonic copepod, Calanus finmarchicus decreased in the heart rate and sharp increase in respiratory rate
when exposed to light.
• The ascidian, Corella parallelograma which normally spawns during the early morning hours, can be induced to
spawn after exposure to light for 2 mins. following a period of dark adaptation.

27.
POWER RANGERNOTES MARINE BIOLOGY
27
• Diurnal vertical migration of planktonic and benthic marine invertebrates represents one of the most widespread
and conspicuous phenomenon in the oceans and coastalwaters.
• Many of the benthic animals produce pelagic larvae, which are generally positive photo taxis. After the
metamorphosis, they show negative response to light (negative photo taxis) during settlement at the bottom.
Structural Responses:
• Body size and form (i.e. sexual and asexual) in reef building corals depend primarily upon water movement and
conditions of illumination.
• Ex: Gorgonia and Madreporaria produce more branches in colonies in calm and higher intensity of light.
• Ascidian growing under eel algae in shallow water grows smaller than that of the ascidian present in deeper
waters. Similarly, Balanus belanoid grows bigger settle in shade than the one settle in high illumination.
• The absence of light indirectly plays a more remarkable stamp on structure than on colour.
• This is manifested by the strange and varied anatomical adaptations, especially of many abyssal fauna.
• These adaptations are concerned with structural modifications fitting the animals better to survive in utter
perpetual darkness.
• They are mainly along three lines:
(1)Tactile structure
(2)Food procuring devices
(3)Light production
• Development of tactile devices is an important feature in numerous instances and is well illustrated in Macro
pharynx. Sensory structures may involve modification of the whole body where by it is elongated and ends in
disproportionately long thread like tail.
• The film rays grow to a length of severaltimes that of the body.
• The prawns of deepwater also possess extremely long tactile antennae. Some of which may be 12 times the length
of the body as in Aristeus sp.
• The food procuring devices of deep sea fishes consists commonly of an extraordinarily immense mouth in
proportion to body size.
• The stomach and abdominal wall may be so elastic that it is possible for some of these Malanocetus, for ex
swallow other fishes 3 times their own size and many times their own weight. In addition, they are provided with
formidable teeth.
• As if these were not sufficient, some species of deep sea angler fishes possess a tectile organ, ‘illicum’ useful as
rod and line and provided with terminal luminous lure, which in some cases be armed with hooks.
• The number of animal species emitting light distributed among such group has the radiolarians, dinoflagellates,
hydroids, jelly fish, ctenophores, bryozoans, polychaetes, brittle stars,many crustaceans (ostracods,copepods and
decapods), gastropods, cephalopods, protochordates and true fishes
• In many luminescent organisms, the light results from luminous slime secreted over parts of the body are thrown
out as glowing cloud.
• Ex: Squids, which produces this secretion in a gland corresponding to ink sac.
• In many of the fishes and crustaceans highly specialized luminescent organs are present,which in some cases are
under nervous control as in dinoflagellates, bacteria.

28.
POWER RANGERNOTES MARINE BIOLOGY
28
• There appears to be no possible utility, but in the higher forms those with specialized light organs capable of
flashing under nervous control and arranged in a definite pattern and even specific colours, utility seems clear.
• Bioluminescence seems to be of greater significance in abyssal benthic animals.
• The biochemical activities involved in bioluminescence are only in part understood.
• It is highly efficient, since the light is practically devoid of heat and there being no infra and ultra violet rays.
• The light is produced by oxidation of substance,probably a simple protein known as luciferin, that is produced by
a living cell.
• However,before light can be produced by union of oxygen, it is necessary that another substance luciferase be
present as catalyst to accelerate the oxidation.
Pressure
• Pressure affectsmarine animals in various ways. The deposition of calcium is difficult at heavy pressure. Carbon
dioxide accumulates in high pressure and makes calcium carbonate more soluble. Animals that have a great
vertical range in the sea are referred to as eurybathic. On the other hand, animals which are limited to a narrow
range of depth are called stenobathic animals. The fish, Chimaera and the snail, Turris are stenobathic.
•
Waves
• The waves are caused by wind. They have their maximum effect in the intertidal zones. The maximum height that
is normally reached by the waves in the oceans is 17 metres. When the waves strike, the impact is very heavy and
can even turn huge stones. The force of impact of the waves is roughly about 1.5 kg. per cm2. Animals unless
well attached will easily be dislodged from the substratum and thrown away or dashed against rocks. Wave action
is also beneficial to animals. It helps in the mixing of oxygen with water. The breaking waves that cause spray,
wet many animals and save them from drying. The shape of reef corals is modified by wave action.
TIDES
• The tides are caused by the gravitational pull of the moon and sun on the waters of the ocean. As the earth is
continuously rotating, the water is heaped in some areas causing a rise in water level in some places and reduction
in other areas. The tides may appear once in 12 and half hours. These tides are called diurnal tides. The lunar
tides are almost double the size of the solar tides and normally mask them except on two days viz. full moon and
new moon when the pulls work together and increase the height. This is the reason why tides on the full moon
and new moon days have larger amplitude. Those on full moon will be larger than on new moon. The tidal range
in most of the places is in between 5 and 7 metres.
• The ecological effect of tides depends on two factors:(1) the duration of exposure or immersion, and (2) the
time at which the exposure occurs. If the duration of exposure is very long, it will affect the intertidal fauna very
much by causing desiccation and osmotic problems. Exposure during midday and that too in summer will also
affect the fauna adversely.
Currents
• The sea is in continuous circulation. Air temperature differences between poles and equator set up strong winds
which create definite currents in the oceans. Due to currents, the cool dense water from the pole moves towards
the equator and it gradually becomes warmer as it reaches the equator. From the equator, water again moves
towards the pole and becomes cooler and dense as it reaches the pole. Because of the circulation, oxygen
depletion or stagnation so common in freshwater lakes,is rare in the oceans.

29.
POWER RANGERNOTES MARINE BIOLOGY
29
• Currents transport food materials and remove waste materials. Currents also distribute the planktonic
larvae to the different parts of the world. They also break the temperature barriers in the ocean by constantly
circulating the waters.
• Currents can be divided into three kinds:-
• a. Density currents
• b. Tidal currents
• c. Wind currents
• Density currents are produced by the heating action of sun on the ocean water. As the warm water rises up
and spreads on the surface,the cold water sinks down for the cold region and spreads downwards. Tidal currents
are produced by the gravitational pull of moon and sun on oceanic waters. Wind currents are caused by the effect
of winds blowing on the waters in a slanting manner. These currents affect only the surface waters.
Dissolved Gases
• The concentration of dissolved oxygen and carbon dioxide are very important for marine life forms. Although
both oxygen and carbon dioxide are a gas when outside the water,they dissolve to a certain extent in liquid
seawater. Dissolved oxygen is what animals with gills use for respiration (their gills extract the dissolved oxygen
from the water flowing over the gill filaments). Dissolved carbon dioxide is what marine plants use for
photosynthesis.
• The amount of dissolved gases varies according to the types of life forms in the water. Most living species need
oxygen to keep their cells alive (both plants and animals) and are constantly using it up. Replenishment of
dissolved oxygen comes from the photosynthetic activity of plants (during daylight hours only) and from surface
diffusion (to a lesser extent). If there are a large number of plants in marine water mass then the oxygen levels
can be quite high during the day. If there are few plants but a large number of animals in marine water mass then
the oxygen levels can be quite low. The amount of dissolved gases in seawater depends more on the types of life
forms (plants and animals) that are present and their relative proportions.
Dissolved Nutrients
• Nutrients, like nitrogen (N), phosphorous (P),and potassium (K), are important for plant growth. The level of
dissolved nutrients increases from animal faeces and decomposition (bacteria,fungi). Surface water often may be
lacking in nutrients because faeces and dead matter tend to settle to the bottom of the ocean. Most decomposition
is thus at the bottom of the ocean. In the oceans,most surface water is separated from bottom water by a
thermocline (seasonalin temperate and marginal polar regions, constant in tropics) which means that once surface
nutrients get used up (by the plants there), they become a limiting factor for the growth of new plants. Plants must
be at the surface for the light. Nutrients are returned to surface waters by a specialtype of current called
'upwelling' and it is in these areas of upwelling that we find the highest productivity of marine life.
• Silica and iron may also be considered important marine nutrients as their lack can limit the amount of
productivity in an area. Silica is needed by diatoms (one of the main phytoplankton that forms the base of many
marine food chains). Iron is just recently being discovered to be a limiting factor for phytoplankton.
pH
• pH is a measure of the acidity or alkalinity of a substance and is one of the stable measurements in seawater.
Ocean water has an excellent buffering system with the interaction of carbon dioxide and water so that it is
generally always at a pH of 7.5 to 8.5. Neutral water is a pH of 7 while acidic substances are less than 7 (down to
1, which is highly acidic) and alkaline substances are more than 7 (up to 14, which is highly alkaline). Anything
either highly acid or alkaline would kill marine life but the oceans are very stable with regard to pH. If seawater is
out of normal range (7.5-8.5), then something would be horribly wrong.

30.
POWER RANGERNOTES MARINE BIOLOGY
30
PRIMARYPRODUCTION
 The primary producers are green plants which convert carbon dioxide and water into organic matter using
sunlight as the energy source (photosynthesis).
 In simplified form, the photosynthetic reaction is written as follows:
 6CO2 + 6H2O + sunlight → C6H12O6 (carbohydrate) + 6O2
 In this reaction, carbon dioxide and water vapour are converted to simple sugars and oxygen.
 The energy required for metabolic activity is derived by reversing this reaction (respiration)
 There are severaltypes of productivity.
 Primary productivity is the conversion of inorganic compounds into organic compounds.
 Gross primary productivity is the total amount of organic material synthesized during photosynthesis or
chemosynthesis.
 Net primary productivity is the difference between the gross productivity and the amount of organic material used
during respiration.
 Net productivity = Gross productivity - Respiration
Primary productivity can be determined in a number of ways.
1.Light and dark bottle technique
 A water sample is collected from a particular depth in the ocean. The oxygen content of the water sample is
measured.
 The water from the sample is then placed in two bottles, one is transparent (light bottle) and the other is opaque
(dark bottle).
 The two bottles are submerged at the original depth of the water sample for a period of time.
 Both photosynthesis and respiration will occur in the light bottle while only respiration will occur in the dark
bottle.
 The bottles are then retrieved and the oxygen content of each bottle is measured.
 Gross photosynthesis = increase in oxygen in light bottle + decrease in oxygen in dark bottle
 Net photosynthesis = increase in oxygen in light bottle
2. 14C method
 A known amount of radioactive carbon in the form of bicarbonate is added to a water sample.
 The uptake of carbon by the primary producers is determined by measuring their radioactivity.

31.
POWER RANGERNOTES MARINE BIOLOGY
31
3.Standing crop of phytoplankton
 Phytoplankton are free-floating microscopic plants which are the primary producers of the oceanic system.
 In this method, either the number of plankton or the total weight of plankton per unit volume or unit area is
measured.
FACTORS INFLUENCING PRIMARY PRODUCTION
1.Light
 One of the most obvious variable factors influencing primary production is the amount of solar energy reaching
the surface of the sea.
 The light that penetrates the water is rapidly absorbed by inorganic and dead organic matter present in it.
 Thus, nearly 80% of the total solar radiation is absorbed in the upper 10 metres
 only 1% of incident visible light reaches 120 meters in clear tropical waters and 10 to 20 meters in turbid inshore
waters of the incident light that falls over the sea
 only 0.02 to 2.0% or 0.1% on an average alone is utilized for the production of organic matter.
 In the tropical regions of the earth, the sun is directly overhead at midday (or) virtually perpendicular to the sea
surface,giving an angle for maximum penetration of light into the water column.
 In the temperate regions, the sun may be directly overhead during the summer months, but may be far from this
position at the other times of the year
 In the polar regions, the sun is absent during the winter or is so low to the horizon that no light can penetrate the
water. The presence of ice in these areas also reduces light penetration into the water.
 The portion of light that enter the water column is subject to further reduction from two additional processes
acting on it within the water.
 The first is reflection from various suspended particles in the water column. Suspended living or dead particles
intercept the light and either absorb it (or) reflect it back to the surface.
 Secondly, water itself absorbs light, making it unavailable for the plants
 Sunlight spectrum includes all the visible colours ranging from violet to red or wavelengths from about 400 -
700 mm.
 The green and blue components are absorbed less rapidly and hence penetrate most deeply.
 The rate of photosynthesis is high in high light levels and decreases as the light intensity decreases.
 The rate of respiration of the phytoplankton cells is essentially constant at all depths.
 At some point, the photosynthetic rate equals the respiration rate. At this point, there is net production of organic
material and this depth is called Compensation depth
 The compensation depth also changes with season,due to the change in the position of the sun and it may be
absent during the winter months in high latitudes.
2.Temperature
 Temperature acts along with other factors in influencing the variation of photosynthetic production.

32.
POWER RANGERNOTES MARINE BIOLOGY
32
 The rate of photosynthesis increases with an increase in temperature but diminishes sharply after a point is
reached.
 Temperature has some important indirect effects on production, particularly in relation to its role in the
establishment of a thermocline and also in the mixing of water, resulting in the supply of nutrients to the euphotic
zone.
3.Salinity
 Besides light and temperature, salinity also is known to influence primary production.
For example, Skeletonema shows an optimum rate of photosynthesis at salinities ranging from 15 and 20%, although the
process could go on in a much wider range of 11 - 40 %.
 Many species of dinoflagellates such as Ceratium, Peridinium and Prorocentrum reproduce actively at lower
salinities.
4.Nutirents
 The concentration of phosphates and nitrates, which are the two major plant nutrients
 During photosynthesis phytoplankton absorb these nutrients for the formation of particulate organic matter
 A certain amount of nutrients utilized by phytoplankton are however,regenerated by bacterial activity within the
euphotic zone itself
 Thus, much of the nutrients absorb from the euphotic layer are transferred to the deeper zones of the aquatic
systems where they are regenerated..
 The nutrients that accumulate in the deeper levels, particularly in the oceans,are mostly returned to the surface
waters by vertical mixing process such as upwelling, eddy diffusion, vertical convection and wind mixing.
 Seasonal and regional variations of primary production are often attributed to the influence of these plant
nutrients.
 The cycle of phytoplankton in temperate latitudes, with marked peak in spring and decrease in production during
summer, has been correlated with the changes in nutrient levels
 During winter, owing to vertical mixing, the euphotic zone is enriched with nutrients which result in high
productivity during spring
 In summer, owing to the increase in temperature and the consequent formation of the thermocline, the nutrient
replenishment in the euphotic zone by vertical mixing is prevented and this results in the decrease of production.
 In the tropical waters,a permanent thermocline is present throughout the year and consequently, replenishment of
nutrients by normal mixing process does not take place.
 Thus, short supply of nutrients in the tropical waters seems to impose a restriction on the rate of primary
production.
Grazing by zooplankton
 The grazing rate of herbivorous zooplankton, consisting mainly of copepod species, euphausids, pteropods,
cladocerans, appendicularians, salps.
 The inverse relationship in the distribution of phytoplankton and zooplanktons is usually common,
 where phytoplankters are abundant, zooplankters are few and where zooplankters are abundant, phytoplankters
are few

33.
POWER RANGERNOTES MARINE BIOLOGY
33
 Hence, herbivorous zooplankton affects primary production to a greater extent.
Geographical variations in productivity
• The environmental factors such as light , temperature and nutrients interact with each other in the marine
environment and play a major role to produce the geographical and latitudinal variations in productivity.
TEMPERATE SEAS
In the temperate zone seas,the amount of light varies seasonally.
• As a result, the amount of solar energy entering the water varies, which alters the temperature in the upper water
layers.
• The thermal structure of the water column, therefore,changes seasonally. In the summer months, the sun is high,
days are long, and the upper layers heat up and become less dense than underlying layers.
• In contrast to the tropics, all the major factors that-at affect productivity change seasonally in temperate seas.
• In the spring, the increased light and solar energy increase the temperature of the upper layers.
• With increasing temperature come increasing differences in density between upper and lower layers.
• Under such conditions the wind cannot mix the water to as great a depth as in winter; at some point, algal cells
are no longer carried below the critical depth.
• Since nutrients in upper layers have been replenished during the winter mixing, conditions are good for
phytoplankton growth, and we observe the spring bloom.
• As spring passes into summer, the water column becomes more thermally stratified, mixing with lower levels
ceases,and light conditions reach optimal levels.
• Because mixing cases due to stratification, nutrient replenishment ceases and production falls, even though light
levels are optimal.
TROPICAL SEAS
• In the tropical seas,the upper waters are well lighted throughout the year because the sun does not show marked
changes in height above the horizon.
• This means there is a great difference in density between surface and deep waters; hence,mixing does not occur.
• This thermal stratification extends throughout the year.
• In the tropical seas,the light conditions are optimal for high productivity.
• Tropical seas are very clear and have the deepest compensation depths, but they are that way because there are
few phytoplankton in the water column due to the low nutrient content.
POLAR SEAS
• In Polar areas,productivity is restricted to a single short period in the polar summer, usually July or August in the
Arctic.
• At this time, the snow cover on the ice has disappeared, allowing sufficient light to enter the water through the
ice to permit phytoplankton growth.

34.
POWER RANGERNOTES MARINE BIOLOGY
34
• Following this single burst of growth, the production quickly declines.
• Nutrients are not limiting and the water column is never strongly stratified.
• The reason for the lack of production at other times is due primarily to lack of light.
• Light intensity is insufficient for a fall bloom, and during the long winter, light is either absent or prevented from
reaching the water column by a layer of snow over the ice pack.
PRODUCTIVITYIN INSHORE AND COASTALWATERS
• The situation in the water masses adjacent to land is somewhat different. There are severalfactors that contribute
to this difference.
• First factor is, inshore waters tend to receive a considerable input of the critical nutrients, PO4
-3
and No3
-1
,due to
runoff from the adjacent land.
• Because of this input, inshore waters usually do not show nutrient depletion.
• A second factor contributing to the difference is the water depth. Most inshore waters are shallower than the
critical depth; thus, the phytoplankton cannot be carried below this depth in any kind of weather.
• A third factor is that shallow inshore waters rarely have a persistent thermocline; hence, no nutrients are locked
up in bottom waters
• A final influencing factor is the presence of large amounts of terrigenous debris in the water,
• which may act to restrict depth of the photic zone and counteract the high nutrient concentration and shallow
depth.
• Nutrients are not limiting due to runoff from land and lack of a permanent thermocline.
• Yearly average production in inshore temperate waters is higher than in offshore waters due to the greater
nutrient concentrations and lack of critical depth problems.
• The production is not even higher inshore probably is due to the presence of large amounts of light-absorbing
debris in shallow water,and the fact that in offshore water,production can occur to a greater depth.
PRODUCTION FOR SEVERAL DIFFERENT GEOGRAPHICAL AREAS
• Location:Productivity in g C/m2
/year
• Long Island Sound (temperature inshore):380
• Continental shelf:100 160
• Tropical oceans:18 50
• Temperate oceans:70 -120
• Antarctic oceans:100
• Arctic Ocean:<1
Energy Flow