The study examined how different concentrations of arsenic exposure affected the feeding habits of hermit crabs. The hypothesis was that hermit crabs exposed to arsenic would retain more arsenic in their tissues and consume less food in a feeding test compared to a control group. The results found that hermit crabs exposed to arsenic absorbed 261% more arsenic and consumed 92.33% less food than the control group. This suggests that arsenic exposure impaired the hermit crabs' feeding abilities and could negatively impact the marine ecosystem by decreasing the health of organisms and disrupting the food chain.

1. The Effect of Arsenic Exposure on Feeding Habits of
Hermit Crabs
Kobayashi, N.K., Kim, C.S.
Kim Environmental Geochemistry (KEG) Lab
Chapman University, Orange, CA
Introduction
Many contaminants that affect marine
ecosystems have origins from manmade processes
including mining and the burning of fossil fuels.
Rainfall and wind patterns help to transport these
substances into delicate habitats, where they are
ingested by the organisms that live there.
This study examines the extent to which arsenic
concentrations affect the feeding patterns of hermit
crabs. Impaired feeding suggests the extent of
impact the substance has on a marine ecosystem.
Exploring the relationship between the amounts of
arsenic exposed to hermit crabs and the amount
retained through respiration defines the
bioavailability of arsenic.
Hypothesis
Analysis of digested crab tissue should yield
greater levels of arsenic in those exposed than in the
control group. Of those who survive the exposure
period, their continual respiration of arsenic-bearing
water will decrease their health as evidenced
through a standard feeding test. In the final feeding
test, the exposed crabs will not be able to consume
up to their potential, which will be measured via the
feeding behavior of the control group. We expect to
see a linear relationship when plotting consumed
pellet as a function of arsenic retention in tissue.
References
1. Nelson. Accumulation of Toxins within a Food Chain. Digital Image.
Organimental Science. N.p., 18 Sept. 2011. Web.
2. Shoshan, D.S., Burns, L.E., Kim, C.S. (2013). Bioavailability of Arsenic in
Hermit Crabs. Poster presented at annual Student Research Day. Orange, CA
3. Takagi, Kimberly K.; wright, William G. “Interspecific Variation in Palatability
Suggests Cospecialization of Antipredator Defenses in Sea Hares.” MARINE
ECOLOGY PROCESS SERIES 4.16 (2010): 137-44. Web.
Figure 1. Schematic showing the accumulation of toxins
such as arsenic in the food chain. (Nelson 2011)
Results
Exposed hermit crabs retained significantly more arsenic than the control group
(Figure 5). The experimental group continually respired 10-4 M arsenic in artificial sea
water for two weeks. Ultimately, they absorbed 261% more arsenic than the control
group, who absorbed a nearly insignificant amount. Sample size is 16.
Although the experiment is still in progress, a statistically significant difference in
the mass of pellet consumed has been established been exposed and control crab
populations (Figure 6). Exposed hermit crabs consumed less than the control group.
The percent difference between the two is 92.33%. Sample size is 16. Because there
are still errors in the feeding test strategy, a visual, but statistically insignificant
difference was found.
Experimental Method
All crabs were captured from the same tide pool in
Laguna Beach, California. Crabs of similar size were fed
pellets made of squid mantle for 30 minutes. Those who
fed continuously throughout the feeding time were
selected for the actual experiment.
The feeding tests were performed on a rolling basis.
Crabs were separated into individual cups containing
artificial seawater. Dried squid pellets were acquired from
the Wright Lab for the feeding test.
• Pellets were soaked for 15 minutes until saturated.
• Pellets were dried on a filter for 2 minutes and weighed.
• Pellets were fed to crab for 30 minutes.
• After their timed feed, tweezers were used to extract
the remaining pellet from the crabs claws.
• Pellets were dried on a filter before measuring the
mass consumed.
• A table (Figure 2) was added to the protocol to ensure
the timeliness of each step (Takagi & Wright).
This data was used in comparison to each crab’s
specific feeding behavior at the end of the trial. Sixteen
crabs were placed into jars. 8 were exposed to a 10-4 M
arsenic solution, while the other half were kept in control
artificial sea water, based on a coin flip. They were
observed and left undisturbed for two weeks.
After the exposure, a final 10 minute feeding test took
place, recording the mass of their meal. The crabs were
instantly frozen using liquid nitrogen. They remained
labeled in a -4°C freezer until the digestion was able to
Figure 4. The digestion process takes place in the fume hood on a level
surface.
Figure 5. Amount of arsenic absorbed in control
and exposed hermit crabs.
Figure 2. A table outlines the time that each step
should be done. It is key in organizing the feeding test.
Figure 3. During a feeding test, the crabs are fed pellets made of
squid mantle. Once the time is up, remaining pellet pieces are
extracted.
Conclusions
The bioavailability of arsenic is
responsible for its retention after ingestion.
The respiration process of hermit crabs leads
to an absorption of 261% in the total mass of
the crab. These unhealthy crabs have been
recorded to have a lower appetite and thus
live shorter lifespans.
The data is significant in understanding
how such contaminants could affect marine
ecosystems. If an environment is polluted
from practices like mining or the burning of
fossil fuels, many organisms will die and all
will have a decreased appetite. Overall, the
unhealthy inhabitants will disorient the food
chain, which can be detrimental to the
environment as a whole. As the predators of
the hermit crabs feed on them, they could
accumulate an even higher concentration of
arsenic or similar chemicals.
occur in sync with sample analysis.
The digestion process consisted of separating the
entire hermit crab body from its shell once ithad fully
thawed. This required crushing the shell, which is difficult.
• Crab bodies were weighed before begin digested in 12
mL 70% nitric acid solution.
• The exoskeletons were stirred for four days.
• After this, 10 mL of acid was filtered and diluted up to
25 mL into borosilicate glass test tubes.
• Samples were sent to Stanford University to be
analyzed for dissolved arsenic using Inductively
Coupled Plasma-Optical Emission Spectrometry.
Future Research
During the study, we were able to adjust the
protocol for a feeding test by conducting a pellet
experiment. It found that it takes 15 minutes of
submergence to reach the maximum saturation
of a pellet. Previously, they were not soaked at all
before they are fed to the crab, which caused
major discrepancies in feeding data. Often, the
final measurement showed that the pellet grew
after consumption. Because pellets are not
homogeneous, there can be a further study on
how to omit the errors that still exist in the
strategy of a feeding test.
Acknowledgements
• Dr. Guangchao Li at Stanford University
• Mikaela Biavati (Kim Environmental
Geochemistry Lab)
• Bill Wright, Marine Invertebrate Lab
• Kim Environmental Geochemistry Lab
Figure 6. Pellet consumed vs. concentration of arsenic