Previously unsuspected dietary habits of hydrothermal vent fauna: the bacterivorous shrimp Rimicaris hybisae can be carnivorous

1. Previously unsuspected dietary habits of hydrothermal vent fauna:
The bacterivorous shrimp Rimicaris hybisae can be carnivorous
Emma Versteegh1
*, Cindy Van Dover2
, Max Coleman1,3
*emma.versteegh@jpl.nasa.gov
1
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA, USA; 2
Duke Marine Lab, Duke University, Beaufort NC, USA; NASA Astrobiology Institute
Research questions
• What causes the previously observed wide range of δ13
C values in
R. hybisae tissues?
• Are the different δ13
C values related to differences between dense
and sparse shrimp aggregations?
• What can δ15
N and δ34
S values tell about ecological or
physiological differences between dense and sparse shrimp?
Hypotheses
With the aim to investigate diet & trophic shifts of dense and sparse R. Hybisae, we tested the
following hypotheses:
• Dense and sparse Rimicaris differ in diet: varying δ13
C values show real differences in
food sources between individuals.
• They are metabolically different.
Preliminary conclusions
Dense and sparse R. hybisae use
different food sources. Dense shrimp eat
bacteria only, while sparse shrimp appear
to eat crustacea, and possibly other
animals.
The switch between diets might be
related to the molting cycle, as the shrimp
temporarily lose their episymbionts when
molting.
Ongoing and future work
More δ13
C and δ15
N analyses of gut
contents are under way to complete the
picture on isotopic composition of food.
NASA/JPL/Ted Stryk
Mid-Cayman Rise
hydrothermal vents
In 2009 two hydrothermal vent fields
were discovered at the ultra-slow
spreading Mid-Cayman Rise. These
include the world’s deepest, the
Piccard Vent Field at 4960m, which
vents fluids at extremely high
temperatures (398°C). The nearby Von
Damm vent field (2309m deep) is an
off-axis vent field, located on the upper
slopes of an oceanic core complex,
with diffuse venting at up to 226°C.
Life in the dark:
the food web
The Von Damm vent field supports a complex
food web, which includes bactivorous shrimp
and carnivorous anemones. There is probably
some influx of photosynthetically produced
carbon as well.
Rimicaris hybisae
The shrimp species Rimicaris hybisae is
abundant at both known MCR vent fields and
shows a high degree of spatial variability in
population structure and reproductive
features. In previous work it has been
considered bacterivorous.
Dense and sparse
We observed that shrimp tended to be either
in dense aggregations on active chimneys, or
more sparsely distributed, peripheral in
ambient or near-ambient temperatures.
δ13
C and δ15
N values
Stable isotopes of carbon (δ13
C values) and
nitrogen (δ15
N values) have been proven to be
useful tools in determining trophic positions
and disentangling food webs. Generally an
animal is enriched by about 1‰ in 13
C and
about 3.4‰ in 15
N relative to its diet.
Large variations in R. hybisae tissue δ13
C
values have so far been unexplained, and it
has been argued that δ13
C values are not a
good food web tracer in hydrothermal vent
ecosystems.
Results
Gut contents of all shrimp from dense aggregations at the Von Damm field consisted of white,
amorphous material that resembled bacteria. Sparsely distributed peripheral shrimp had
stomachs filled with fragments of crustacean exoskeleton (5 out of 13), a mixture of
bacteria-like material and crustacean exoskeleton (3 out of 13), or bacteria-like material only
(5 out of 13).
The range of δ13
C values of sparse R. hybisae partially overlaps with, but tends to be lower
than for dense individuals. δ15
N values all fall in a narrow range and are slightly elevated in
some sparse shrimp in comparison with dense individuals. δ34
S values of sparse shrimp are
lower by up to 5‰ than dense shrimp. Carnivorous Lebbeus virentova shrimp are isotopically
more similar to dense than to sparse R. hybisae.
Tail tissue isotopic compositions reflect those of the gut contents. No enrichment was found
between gut content and tail tissue for δ13
C and δ34
S values. With respect to δ15
N values, tail
tissue was enriched by 3.3‰; the expected amount for 1 trophic level.
These results suggest dense and sparse R. hybisae use different food sources.
Methods
Samples were collected during the E/V
Nautilus Expedition on August 26 2013 at
the Von Damm vent field. Individual shrimp
were sampled with the remotely operated
vehicle Hercules from dense and sparse
assemblages, separated by ~1m. R.
hybisae were dissected and gut contents
identified.
Samples were analyzed using a combined
analysis for δ13
C and δ15
N values and a
separate setup for δ34
S values on a Thermo
MAT 253 isotope ratio mass spectrometer,
connected to a Costech ECS 4010
elemental analyzer.
Abstract
Dense and sparse assemblages of
the shrimp species Rimicaris
hybisae were sampled at the Von
Damm hydrothermal vent field
(Mid-Cayman Rise).
Although previously considered
bacterivorous, examination of gut
contents show differences in diet
between dense and sparse shrimp.
This is corroborated by stable
isotope analyses of tail tissues and
gut contents. The switch in diet
might or might not be a life-history
trait related to the molting cycle. www.nautiluslive.org
Location of the Mid-Cayman Spreading Center, in the
middle of the Cayman Trough, south of Cuba.
(Jack Cook, WHOI)
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8Life in the dark: Europa?
Jupiter’s moon Europa has a metallic core
and a further rocky composition like the
terrestrial planets. It is covered by a deep
ice-covered ocean (together ~100km).
Due to Jupiter’s tidal heating, there is
potential hydrothermal activity. Oxygen can
be produced by breaking down of water
molecules under the influence of Jupiter’s
radiation field. Thus, Europa could support a
chemosynthetically-based ecosystem
hosting species similar to, but not the same
as Rimicaris hybisae.
Several other moons in the Solar system,
e.g. Enceladus, are thought to have
subsurface oceans and might harbor similar
life-supporting conditions.
The ocean on Europa
could potentially drive
hydrothermal circula-
tion. Image coutesy of
NASA (Europa Jupiter
System Mission Report,
2010)
NASA/JPL/Ted Stryk
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