This document discusses plankton, including their ecological importance and role in the food web. It describes phytoplankton and zooplankton, how they are sampled using nets and bottles, and their importance as a food source. It also discusses how plankton sampling is conducted and has evolved over time, from the use of silk nets to modern techniques like continuous plankton recorders and optical plankton counters.

1. M.Aishwarya
17393022
M.Tech(EE&M)
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2. • Planktons in the open ocean
• Phytoplanktons and
Zooplanktons
• Ecological importance
• Planktons in the food web
• Sampling of Planktons
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3. • Plankton (singular plankter) are the diverse collection
of organisms that live in large bodies of water and
are unable to swim against a current. They provide a
crucial source of food to many large aquatic
organisms, such as fish and whales.
• These organisms include
bacteria, archaea, algae, protozoa and drifting or
floating animals that inhabit for example—the pelagic
zone of oceans, seas, or bodies of fresh water.
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4. • Planktons spend at least a part of their life cycle
suspended in water.
• The term plankton is actually a Greek word,
meaning that which is made to wander or drift.
• Planktons are further divided
as phytoplankton and zooplankton, meaning plant and
animal drifters respectively.
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5. • Planktonic organisms may have a limited ability to control their
fine-scale distribution in the water column, but are otherwise at
the mercy of oceanic currents and water movements.
• Holoplantkon refers to those organisms that spend their entire
life in the plankton, as opposed to the meroplantkon, which are
only planktonic for a part of their lives.
• Organisms that are capable of resisting the powers of currents,
such as fish and squid, are referred to as neckton.
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7. Phytoplanktons
Diatoms Dinoflagellates coccolithophorids cyanobacteria
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8. Zooplanktons
Protozoa Crustacea Jellies Chaetognaths
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9. • The zooplanktons feed on phytoplanktons through 3 modes. They
are,
– Pallium feeding, Tube feeding, Direct engulfment
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Fig: Protoperidinium sp. pallium-
feeding on a chain-forming
diatom. Dinoflagellates capture
prey (at times even larger than
their own size) by 3 different
raptorial mechanisms: pallium
feeding, tube feeding, and
direct engulfment. They can be
active predators during diatom
blooms.

10. Some of the organic molecules produced by phytoplankton
are exuded as dissolved organic matter (DOM). Similarly, DOM is
released due to ‘sloppy feeding’ as zooplankton graze on
phytoplankton cells.
Each ml of seawater contains approximately 1 million
bacterial cells, many of which utilise DOM as a source of energy
and nutrition. The abundance of these bacteria is, to a large
extent, regulated by the grazing effects of heterotrophic nano-
flagellates (2 – 20 μm in diameter).
In turn, the heterotrophic nanoflagellates are grazed by
larger heterotrophic organisms such as dinoflagellates and ciliates.
Thus, DOM released by primary producers is channelled back into
the food chain by what is known as the ‘microbial loop’.
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13. • All planktonic organisms were traditionally sampled with a fine-
mesh net, the exact size and nature of which depending on the
target organisms.
• Silk, such as the ‘bolting cloths’ originally used by millers to
sieve flour, was used for net manufacture prior to the advent of
nylon meshes.
• Plankton nets are typically conical in shape. They are towed or
hauled through the water, funnelling organisms towards the ‘cod
end’ where they remain trapped.
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14. • Contemporary studies interested in the vertical distribution
of phytoplankton species typically collect seawater samples with
Niskin bottles.
• The constituent phytoplankton cells are subsequently preserved
with Lugol’s iodine for later examination with a microscope. The
chlorophyll content of seawater is frequently used as an
indicator of phytoplankton abundance and biomass.
• Broad-scale (km) surveys of chlorophyll can be achieved by
towing a fluorimeter through the water.
• The colour of the surface of our oceans can now be accurately
measured from space. These ‘ocean colour’ measurements enable
global-scale monitoring phytoplankton growth patterns.
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Fig: A Niskin bottle about to be
lowered into the water.
The Niskin bottle is a development of the Nansen bottle
patented by Shale Niskin in March 1966. Instead of a metal
bottle sealed at one end, the 'bottle' is a tube, usually
plastic to minimize contamination of the sample, and open to
the water at both ends. Each end is equipped with a cap
which is either spring-loaded or tensioned by an elastic rope.
The action of the messenger weight is to trip both caps shut
and seal the tube.

16. The plankton net is used for phytoplankton Sampling.
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Fig: Microscopic view
of phytoplankton.

18. • Modern biological oceanographers have a suite of nets and sampling
arrays to help them collect and count zooplankton from discrete depths
of the ocean. Broad-scale surveys can be undertaken by towing an
optical plankton counter (OPC) behind a research vessel.
• Zooplankton are funnelled into a narrow corridor and through a beam of
light. A computer counts the number of times that the beam of light is
broken, and thus the number of zooplankton.
• The larger types of zooplankton reflect sound and can thus be surveyed
by using acoustic techniques. This type of survey uses techniques
identical to those used by fishermen to locate fish.
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Fig: Shape profiles obtained from an LOPC mounted
on a Batfish vehicle towed at 8 knots. Silhouettes
show profiles of euphausiids and copepods of a
variety of sizes.

21. • The development of the Continuous Plankton Recorder (CPR), by
Sir Alistair Hardy and colleagues in the 1920’s and 30’s,
represents one of the major milestones in plankton
biogeography.
• Each CPR is a self-contained sampling device that collects
animals on to an array of ‘silks’. They are designed to be
deployed by merchant ships crossing the oceans.
• This enables a far greater number of observations than would be
achievable using dedicated research vessels alone.
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22. • CPR samples are analysed as given below.
– The Phytoplankton Colour Index (PCI) is determined for each sample. The
colour of the silk is evaluated against a standard colour chart and given a
'green-ness' value based on the visual discoloration of the CPR silk produced
by green chlorophyll pigments; the PCI is a semi quantitative estimate of
phytoplankton biomass.
– In this way the PCI takes into account the chloroplasts of broken cells and
small phytoplankton which cannot be counted during the microscopic analysis
stage.
– After determination of the PCI, microscopic analysis is undertaken for each
sample, and individual phytoplankton and zooplankton taxa are identified and
counted. Nearly 500 phyto- and zooplankton taxa have been identified on
CPR samples since 1948.
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24.  Sieburth, J. Mn., Smetacek, V. & Lenz, J. 1978. Pelagic ecosystem structure:
Heterotrophic compartments of the plankton and their relationship to plankton
size fractions. Limnology and Oceanography 23(6): 1256-1263.
 http://planktonnet.awi.de/
 Marine insect home page: http://cgi.unk.edu/hoback/marineinsects/home.html
 Hansen, P.J. & Calado A. J. 1999 Phagotrophic mechanisms and prey selection in
free-living dinoflagellates. J. Eukaryot. Microbiol. 46(4) 382-389.
 Sir Alistair Hardy, 1959. The open sea – its natural history: Part I The world of
plankton, 2nd Edition. Readers Union, Collins, London
 MAR-ECO: http://www.mar-eco.no/
 https://www.gvsu.edu/wri/education/instructors-manual-plankton-sampling-
32.htm
 https://en.wikipedia.org/wiki/Continuous_Plankton_Recorder
 http://www.icm.csic.es/bio/projects/gezm/microzoo/microzoo.htm
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