Two hydrothermal vent fields have been described at the ultra-slow spreading ridge of the Mid-Cayman Rise (MRC), including the world’s deepest (Piccard ~4985m) and the nearby Von Damm vent field (~2300m). Both vent fields support a localized high-biomass. The food web has chemoautotrophic bacteria at the base and includes bacterivorous shrimp as well as carnivores: shrimp and anemones. The alvinocaridid shrimp Rimicaris hybisae is abundant at both vent fields and shows spatial variability in population structure. So far it has been considered bacterivorous. Large variations in tissue δ13C values remained largely unexplained, and it has been argued that δ13C values are not a good food web tracer in hydrothermal vent ecosystems. We observed that shrimp tended to be either in dense aggregations on active chimneys, or more sparsely distributed and peripheral in (near) ambient temperatures. With the hypotheses that varying δ13C values show real differences in food sources and that shrimp in different locales might have different diets, we collected shrimp from both environments at the Von Damm site during an Ocean Exploration Trust Expedition with E/V Nautilus (NA034, 08/2013) and examined their gut contents. Gut contents of all shrimp from dense aggregations consisted of white, amorphous material that resembled bacteria. Sparsely distributed shrimp (~1m from dense aggregations) had guts filled with fragments of crustacean exoskeleton, a mixture of bacteria-like material and crustacean exoskeleton, or bacteria-like material only. We analyzed stable isotope compositions of the shrimp and their gut contents. Shrimp δ13C, δ15N and δ34S values reflect those of their gut contents +1 trophic level. Sparse shrimp have dramatically lower δ13C and δ34S values, and slightly elevated δ15N values, in comparison to dense shrimp. Sparse and dense R. hybisae clearly have different diets. Ongoing work is determining what exactly is this crustacean food source, whether diet changes occur during life history, and if this is linked to the molting cycle.

1. Emma
Versteegh,
Cindy
Van
Dover,
Max
Coleman
NASA
Jet
Propulsion
Laboratory,
California
Ins9tute
of
Technology
Copyright
2014
California
Ins9tute
of
Technology.
U.S.
Government
sponsorship
acknowledged.

3. Life
without
sunlight
NASA/JPL/Ted
Stryk
NASA/JPL
Photosynthesis:
6
CO2
+
12
H2O
+
sunlight
→
C6H12O6
+
6
H2O
+
6
O2
Chemosynthesis:
6
CO2
+
6
H2O
+
3
O2
+
3
H2S
→
C6H12O6
+
3
H2SO4
Would
work
on
Europa
too
Quan9fy
biomass
expected?
→
look
on
Earth
How
much
new
biomass/9me?
→
food
web

4. • Piccard
vent
field,
world’s
deepest:
4985m,
basal9c
• Von
Damm
vent
field:
2309m,
ultramafic
Mid-­‐Cayman
Rise
(MCR)
Jack
Cook,
WHOI
NOAA
Okeanos
Explorer

5. Von
Damm
Vent
Field

6. A
shrimp
world

7. Rimicaris
hybisae
• Abundant
at
MCR
• Spa9al
variability
in
popula9on
structure:
dense
~
sparse
• Bac9vorous
(un9l
now)
• Unexplained
varia9ons
in
δ13C
values
• δ13C
not
a
good
food
web
tracer?

8. Previous
work
Bennee
et
al.
(under
review)
~10‰

9. What
is
the
structure
of
the
food
web
around
MCR
vent
fields?
Who
eats
whom
(or
what)?
Ques9ons
1. What
causes
the
wide
range
of
δ13C
values?
2. Are
δ13C
values
related
to
dense
and
sparse
assemblages?
3. Do
dense
and
sparse
have
different
diets?
4. Do
dense
and
sparse
differ
in
δ15N
and
δ34S
values?
5. How
do
δ15N
and
δ34S
relate
to
diet?
Hypotheses
1. Dense
and
sparse
Rimicaris
have
different
diets
2. They
are
metabolically
different
You
are
what
you
eat:
• +1
(δ13C
‰
vs.
VPDB)
• +3
(δ15N
‰
vs.
AIR)
• +?
(δ34S
‰
vs.
VCDT)

10. Methods
E/V
Nau9lus
Expedi9on
August
26,
2013
• Von
Damm
vent
field
• Remotely
operated
vehicle
Hercules
• Dense
and
sparse,
separated
by
~1m
• R.
hybisae
dissected,
frozen
on
board
In
lab:
• Freeze
dried
&
homogenized
• Stable
isotope
analyses:
Costech
ECS
4010
&
MAT
253
IRMS
www.nau9luslive.org

11. Shrimp
tail
δ13C,
δ15N
&
δ34S
values
® Rimicaris hybisae tail (sparse)
¯ R. hybisae tail (dense)
˜ Lebbeus virentova whole
p R. hybisae gut (crustacea)
p R. hybisae gut (bacteria & crustacea)
r R. hybisae gut (bacteria)
£ R. hybisae gill covers (dense)
~3‰
<<3‰
~6‰
~7‰
~15‰

12. Gut
contents
• Dense:
– bacteria
• Sparse:
– crustacea
(5
out
of
13)
– bacteria
and
crustacea
(3
out
of
13)
– bacteria
only
(5
out
of
13)
® R. hybisae (crustacea)
® R. hybisae (bacteria & crustacea)
¯ R. hybisae (bacteria)

13. Tails
&
gut
contents
® R. hybisae (crustacea)
® R. hybisae (bacteria & crustacea)
¯ R. hybisae (bacteria)

14. Results
• Sparse
/
crustacea-­‐ea9ng
shrimp:
– Lower
δ13C
values
(-­‐2.4
‰)
– Elevated
δ15N
values
(+0.3
‰)
– Lower
δ34S
values
(-­‐2.2
‰)
• Lebbeus
virentova
δ13C
and
δ15N
overlap
with
R.
hybisae,
differ
from
sparse
in
δ34S
only
• Exoskeleton
of
R.
hybisae
same
δ15N
and
δ34S
as
guts,
but
different
δ13C

15. Results
• Tail
δ13C
and
δ34S
reflect
gut
content,
no
enrichment
• Tail
δ15N
enriched
by
+3.4‰
vs.
gut
• Bacteria
in
gut:
higher
tail
δ13C
and
δ34S
• Crustacea
in
gut:
lower
tail
δ34S

16. Conclusions
• Dense
and
sparse
R.
hybisae
use
different
food
sources.
• Dense
Rimicaris
eat
/
absorb
episymbio9c
bacteria
only.
• Sparse
shrimp
eat
bacteria,
crustacea,
and
possibly
gastropods.
• They
might
have
different
episymbio9c
bacterial
communi9es.
• Diet
switch
possibly
related
to
mol9ng
cycle.

17. Implica9ons
/
future
work
• DNA
analysis
on
dense
/
sparse
R.
hybisae
• Gut
contents
vs.
stage
in
mol9ng
cycle
• Analogous
dense
and
sparse
assemblages
in
Rimicaris
exoculata
and
Rimicaris
kairei
–
do
they
differ
in
diet?

18. Thank
you!
Ques9ons?
Acknowledgements
• NASA
ASTEP
Oases
for
life
• E/V
Nau9lus
&
ROV
Hercules
team
• Kenneth
Williford
&
Michael
Tuite
(JPL)
• JPL
ISOLAB
team:
Bethany
Theiling,
Kathrin
Streit,
Emma
Gar