Hurricane Island Hermit Crab Habitat and Substrate Preference Alexa Skrivanek & Emilio Hernández 2018 ch. 7 pg. 1 Skrivanek & Hernández
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Chapter 7
Hurricane Island Hermit Crab Habitat and Substrate Preference
Alexa Skrivanek & Emilio Hernández
2018 ch. 7 pg. 1 Skrivanek & Hernández
Hurricane Island Hermit Crab Habitat and Substrate Preference
The main objective of this experiment was to record the substrate preference of
Hurricane Island’s two hermit crab species, Pagurus acadianus (Acadian hermit crab), and
Pagurus arcuatus (hairy hermit crab), through a two test process in a simulated environment.
Throughout this experiment, five tide pools were utilized for collecting specimens and within those
tide pools, a number of surprising results were discovered. In the end, the data seemed to
support the second half of the hypothesis and allowed for a deeper look into hermit crab instinct
and behavior.
Hurricane Island is a small island in the Gulf of Maine that used to be a granite quarry.1
Located in Penobscot Bay, ME, Hurricane is home to numerous intertidal organisms, some of
which are the Paguridae (also known as hermit crabs), a specific group of creatures that have
evolved to endure this an ever-changing environment.
Figure 1: Aerial view of Hurricane Island, Vinalhaven, ME2
On Hurricane Island, there are two species of hermit crabs; Pagurus acadianus (Acadian
hermit crab) and Pagurus arcuatus (hairy hermit crab) which frequent Maine’s ocean-based
substrates. The hermit crab belongs to the family Paguridae, the order Decapoda of the class
Crustacea. The hermit crab possesses two pairs of antennae and five pairs of legs. The first pair
of legs is modified to form chelae, or pincers (the right claw is usually larger) that are shaped so
as to cover the shell entrance in order to protect itself from predators.3
1
Page “Island History” paragraph 1 Hurricane Island Foundation. (n.d.). Island History. Retrieved from Hurricane
Island Foundation website: http://www.hurricaneisland.net/history/
2
Google, & TerraMetrics. (n.d.). Retrieved May 31, 2018, from https://goo.gl/maps/Xi6X6e5mpMG2
3
Page 1 paragraph 1 Hermit crab. (2018). In Encyclopædia Britannica. Retrieved from
https://library.eb.com/levels/youngadults/article/hermit-crab/40167
2018 ch. 7 pg. 2 Skrivanek & Hernández
Figure 2: Anatomy of Paguridae (also known as “hermit crabs”).4 The diagram above gives an overview of
a couple of the more prominent body parts of a hermit crab.
Unlike most crustaceans, hermit crabs do not have a hard protected carapace but they
have adapted to living in deserted gastropod shells such as Nucella lapillus (Dog whelk),
Littorina obtusata (Smooth Periwinkle), or Littorina littorea (Common periwinkle) or other hollow
objects.5
Figures 3a, 3b & 3c: (from left to right) Littorina obtusata (Smooth Periwinkle) (3a), Littorina littorea
(Common periwinkle) (3b)6 & Nucella lapillus (Dog whelk ) (3c)7 Note how the dog whelk shell is larger
than either of the periwinkles and is rounded with a pointed spire and a short, straight siphonal canal. The
4
Free Printable Hermit Crab Coloring Pages For Kids. (2014, August 05). Retrieved June 1, 2018, from
http://www.bestcoloringpagesforkids.com/hermit-crab-coloring-pages.html (modified)
5
Page 1 paragraph 1 Hermit crab. (2018). In Encyclopædia Britannica. Retrieved from
https://library.eb.com/levels/youngadults/article/hermit-crab/40167
6
Photograph taken by Steve Scrimshaw
7
Photograph taken by Adam Jamal
2018 ch. 7 pg. 3 Skrivanek & Hernández
easiest way to differentiate the two types of periwinkle shells is that the common periwinkle shell has a
pointed spire while the smooth periwinkle shell does not have a spire at all, and is much flatter.
The environment of Hurricane Island’s Two Bush Island falls into the category of rocky
intertidal. By definition, a rocky intertidal is a region of extremes, as it is the area that intersects
between the tides. The rocky intertidal can take the form of rocky cliffs, boulder rubble, or in the
case of where the study was conducted, rocky shores. The Pagurus acadianus and Pagurus
arcuatus were found in the tide pools and shores among the lower intertidal, where they
generally wandered about in the still waters, feeding on detritus and bits of dead organisms.
Figures 4a & 4b: Pagurus acadianus (Acadian Hermit Crab) (4a)8 & Pagurus arcuatus (Hairy Hermit Crab)
(4b).9 The easiest way in which to tell the two species of hermit crab apart is that the Acadian hermit crab
has distinct white stripes on their claws and legs while the hairy hermit crab has bristly hairs on their
claws and legs.
When the Pagurus acadianus and the Pagurus arcuatus are posed with four different
substrate choices, it would choose the substrate most similar to that of their original location; It
was also hypothesized that the second test run would take less time than the first. Before
heading off to Hurricane, we looked into studies on hermit crab behavior, done by both previous
Cambridge School of Weston marine bio students, professional marine biologists and other
scientists. We found that there were only four previous studies done by former CSW students
that focused on hermit crabs. Three of the four studies were behavioral, but they focused on
different topics then we did, such as how far the crabs would retract into their shells. We mainly
used these studies for inspiration, getting a sense of the hermit crab population and other
peer-edited journal articles about hermit crabs. We found Rachel Hennessy’s study titled Hermit
Crab Species, Size, and Shell Type Distribution on Hurricane Island, Maine10 to be particularly
8
Photograph taken by Steve Scrimshaw
9
Photograph taken by Emilio Hernández
10
Hennessy, R. (2014). Hermit Crab Species, Size, and Shell Type Distribution on Hurricane Island, Maine. 1-8.
Retrieved May 31, 2018.
2018 ch. 7 pg. 4 Skrivanek & Hernández
helpful in terms of helping to develop a hypothesis. We also looked at five peer-reviewed journal
articles regarding hermit crabs, but at this point in time, our hypothesis was on shell type rather
than substrate preference. Due to this change, our previously selected journals no longer
applied to the study. Because we were on the island, changes could not be made. Upon
returning, we found more studies that applied to the final study.
Our study looks into the behavioral habits of hermit crabs that are native to Hurricane
Island. Hermit crabs are an integral part of the rocky intertidal community as they play a part in
picking up and eating the detritus from the ground, which in turn keeps the ecosystem clean. By
studying their substrate and their “preference” (for lack of a better scientific term), one can
further delve into the lives of hermit crabs, and their impact on the ecosystems and
mini-ecosystems in which they dwell. Such studies, in turn, benefit those studying food chains
and ocean ecology, as the creatures that consume detritus are the ones that keep the ocean
floor clean. A study that is particularly similar to ours in nature, Substrate use and Selection in
Sympatric Intertidal Hermit Crab Species,11 focuses on the recorded sequences of substrate
preferences among different hermit crab species. From this article, we are able to see that the
study is similar to that of others, particularly the focus on the relationship between the rocky
intertidal habitats, and how the hermit crabs dwell and live within them.
11
Turra, A., & Denadai, M. R. (2002). Substrate use and selection in sympatric intertidal hermit crab species.
Brazilian Journal of Biology. Retrieved June 5, 2018.
2018 ch. 7 pg. 5 Skrivanek & Hernández
Materials
Test Bucket:
● Five gallon bucket
● Shell hash (for the bottom of the bucket)*
● Seawater (enough to go a quarter of the way up the side of the bucket)*
● A small bunch of Bladderwrack-Fucus seaweed*
● 8 Rocks*
○ (3) Rocks for structure*
○ (4) Rocks for crevice*
○ (1) For holding down seaweed*
● Assorted number of …
○ Periwinkles (common and smooth) (both vacant and occupied)*
○ Dog whelks (both vacant and occupied)*
○ Detritus*
● 1 Mussel or clam*
Holding Bucket:
● One gallon bucket
● Seawater (enough to go about halfway up the side of the bucket)*
Everything Else:
● GPS (longitude/latitude)
● Stopwatch
● Data chart
● Pencil(s)
● Waterproof Journal
● Computer
*Collect at site
2018 ch. 7 pg. 6 Skrivanek & Hernández
Methods
Location: The experiment was conducted on the rocky intertidal zone of Two Bush
Island, Hurricane Island, ME. But more specifically...
● Day 1: Rock Crevice 19 T 059266 UTM 4875301
● Day 2: Shell Environment 19 T 0509265 UTM 4875294
● Day 3: Rock Crevice 19 T 0509270 UTM 4875300
● Day 4: Rock crevices around seaweed 19 T 0509272 UTM 4875306
● Day 5: Open seaweed area 19 T 0509279 UTM 4875327
Figure 5: Two Bush Island, Hurricane Island, Vinalhaven ME12 An aerial view of Two Bush Island and the
general location of where the hermit crabs used in this study were collected.
We chose these specific locations on Two Bush Island because when Emilio was out
looking for specimens, he selected the areas that fit the desired simulated substrates, and that
had an abundant amount of hermit crabs.
Preparation for the experiment:
A friendly tip, before heading out into the field to make sure any data charts are written
out. After arriving at Hurricane Island, ME, we set out to the rocky intertidal zone at Two Bush
Island with two buckets, a GPS, stopwatch, premade data chart, waterproof journals, and
pencils. We scouted out a flat rock near a tide pool on the far side of Two Bush Island for us to
place our supplies and then set out to collect test subjects and the materials for the substrate
simulation. We divided up preparation for the experiment. Emilio went to procure the test
subjects from either a rock crevice or an open space and made sure to bring his camera and the
GPS with him in order to record the location, as well as get the longitude and latitude. When
Emilio found an area with some hermit crabs, he took a couple pictures of the location and
12
Google, & TerraMetrics. (n.d.). Retrieved May 31, 2018, from https://goo.gl/maps/Xi6X6e5mpMG2
2018 ch. 7 pg. 7 Skrivanek & Hernández
recorded the longitude and latitude using a GPS function. This information was later recorded
by Alexa. Emilio then returned to the location, and collected as many hermit crabs as he could
find, with a minimum of ten individual crabs. Once there was a satisfactory amount was
collected, Emilio returned to Alexa.
While Emilio was collecting hermit crabs, Alexa was preparing the simulation bucket.
The preparation included finding enough shell hash to cover the bottom of the bucket in a light
layer, collecting enough seawater to go a quarter of the way up the side of the bucket, this water
was from whichever tide pool the crabs were found in. A note on the water, make sure to
change the water in the holding bucket and simulation bucket roughly every twenty minutes or
so in order to keep the water oxygenated. If it was a particularly sunny/hot day, we made sure to
change the water more often. After the base was finished Alexa set about making the four
substrate choices. The goal was to make the four sections as equal as possible, roughly 25%
per substrate with the center of the bucket empty except for shell hash.
Construction of each substrate:
Rock Crevice: Find 4 small rocks and place them in a crevice shape.
Rock Structure: Find three small rocks, place 2 rocks on the bottom level and 1 resting
on top of the others to make an overhang.
Seaweed: Find a small bunch of Bladderwrack-Fucus seaweed and weigh it down with a
small rock so it does not disturb the other substrates.
Shells: Collect periwinkles (both smooth and common), dog whelks, and a mussel or
clam to make up the shell area. It is okay if the periwinkles and dog whelks move, just make
sure they do not obstruct the test.
The Actual Experiment:
To begin the experiment, one must pick out one hermit crab at random from the holding
bucket. One person records the data about the species of each hermit crab, the species of the
shell it is dwelling in, and anything else of interest about the hermit crab itself regarding its
appearance. The recorder then must prepare the stopwatch as the collector places a hermit
crab into the bucket for the first test run. As soon as the hermit crab is placed into the simulation
bucket for the first test (facing the rock structure), start the stopwatch. Be sure to stop the
stopwatch as soon as the hermit crab touches and stays on one of the four substrates. This
point in the experiment is a great time to note any behavior, as the hermit crab is in the midst of
2018 ch. 7 pg. 8 Skrivanek & Hernández
selecting a substrate, and may begin to pick at detritus or stay in one place for three minutes.
When the hermit crab makes its decision, remove the hermit crab from the bucket. Record
which substrate the hermit crab chooses and how long it took. Then reset the stopwatch, and
prepare for the second test run.
Figure 6: The test rig.13 Designed by A. Skrivanek. The test bucket pictured above contains four different
choices of substrates for our experiment.
The second test run follows the same procedure as the first with the only two differences
being the orientation of the hermit crab (in this case facing the shells) and releasing the hermit
crab after this test is over. The reason we chose to have two test runs, each facing a different
substrate choice, was to minimize the chance of bias in our data. We thought that if we faced
each hermit crab towards only one of the substrate choices with only one test run, someone
could argue that we were heavily influencing the hermit crab’s choice. At one point we were
asked why we didn’t do four test runs per crab, each test run facing each substrate. The reason
we didn’t and decided on only two test runs was that the time spent on each hermit crab would
not make sense with the amount of field time we had to work. Also, with four test runs, we ran a
greater risk of overstressing the hermit crabs.
Once the hermit crab chooses a substrate, stop the watch, record which substrate the
hermit crab chooses and how long it took. Then release the crab and repeat the entire process
with the remaining specimens.
13
Emilio’s lovely photography Hurricane Island, Maine 2018
2018 ch. 7 pg. 9 Skrivanek & Hernández
Disclaimer: For this results section, only the data for the hairy hermit crabs will be
discussed, due to the small sample size of Acadians collected.
Figure 7: The graph shows the distribution of hairy hermit crabs that chose each substrate by
percentage. No hermit crabs chose the rock crevice in test run one and only a couple chose the rock
crevice in test run two.
Figure 8: The graph shows the distribution of hairy hermit crabs that chose each substrate by
percentage for day two. For both test runs, the shell substrate was the most popular among the hermit
crabs.
2018 ch. 7 pg. 10 Skrivanek & HernándezFigure 9: The graph shows the distribution of hairy hermit crabs that chose each substrate by
percentage on day three. For test run one, the most popular choice was the rock structure, while for test
run two the most popular choice was the rock crevice.
Figure 10: The graph shows the distribution of hairy hermit crabs that chose each substrate by
percentage for day four. The preference for test run one was the rock structure while in test run two the
most popular choice was the shell substrate.
2018 ch. 7 pg. 11 Skrivanek & HernándezFigure 11: The graph shows the distribution of hairy hermit crabs that chose each substrate by
percentage for day five. In test run one, the rock crevice was the most chosen, while test run two, the
shell substrate was selected most, and the seaweed not selected once.
Figure 12a: The graph shows the distribution of hairy hermit crabs that chose each substrate by
percentage of all five days. Overall the rock crevice was the most selected of the substrate choices.
Shells were the second most selected.
2018 ch. 7 pg. 12 Skrivanek & HernándezFigure 12b: This graph compares the distribution of hairy hermit crabs by the observed substrate
preference of all five days vs hypothesized substrate preference. In the hypothesized version there should
be no hermit crabs that chose the rock structure but in the observed part of the graph that is not the case
at all.
Figure 13: The graph shows the probability versus the reality of the number of hairy hermit crabs
that chose each substrate. The result is of the chi-squared test is not significant, as it is above 0.05.
2018 ch. 7 pg. 13 Skrivanek & HernándezFigure 14: This graph shows the distribution of hermit crabs by test run times. For test run one,
most took between 20-30 seconds, while in test run two most took between 10-20 seconds.
Figure 15: The averages of the test runs, utilizing the Wilcoxon Signed-Ranks Test. Results show
that the data is significant, as it is below 0.05.
2018 ch. 7 pg. 14 Skrivanek & HernándezDiscussion
For the first part of the hypothesis, on an individual level, we did not see many crabs
selecting the same substrates as those they were initially found in (see figures 7-11). Rather, we
witnessed our test subjects going to all sorts of substrates, without a clear pattern. These
graphs show the percentages of which hermit crabs chose which substrate, separated by test
run for days one through five in the field.
Unlike figures 7-11, figure 12a isn’t broken down by individual days or by test run,
instead, this graph combines all the days and both test runs. By looking at our data in this way,
we were able to notice some slight trends in our overall data. The most selected substrate was
the rock crevice. In contrast, the least chosen substrate was seaweed. Interestingly enough, the
seaweed substrate had the highest rate of hermit crabs return to it during both test runs. We
also noticed that the individuals that selected seaweed often consumed detritus that was
surrounding the seaweed or they would crawl around the area for a while for an unknown
reason.
In the end, we found that it is not possible to come to a definite conclusion since the
result of our chi-squared test (see figure 13) was not statistically significant as the result was
above 0.05. Aside from the chi-squared test, the other reason the first part of our hypothesis
can’t be considered fully supported by our results is that the rock structure was chosen by the
hermit crabs. We specifically chose to not collect any hermit crabs from what we considered to
be a rock structure in order to have a more definite way to figure out the meaning of our results.
Figure 12b shows what our observed value is compared to our hypothesized value would be in
order to really drive the point home. And lo and behold, the hermit crabs did choose the rock
structure 25% of the time (see figures 12a and 12b). We believe this to be a result of the
structure offering a texture and hiding place similar to that of the crevice.
In terms of the second part of our hypothesis, we thought that the second run would be
faster due to the crabs having the necessity to find a substrate ingrained. Figure 14 shows that
on average, the second run took less time than the first for the crab to make a choice. This
suggests that the hermit crabs were undergoing a form of adaptive learning. By being placed in
the same situation twice, it is likely that the hermit crabs became accustomed to the simulated
situation, and were more quick to move to a hiding area. Figure 15 shows the averages and the
standard deviations, which make for an easier visual description of our data, including the
deviation within our data. Figure 15 represents the collected data input using the Wilcoxon
Signed-Ranks Test. The result of the Wilcoxon Signed-Ranks Test is that our data was
2018 ch. 7 pg. 15 Skrivanek & Hernándezsignificant, as it is below 0.05. From what we can understand, the second part of our hypothesis
is in fact supported by our results.
In our study, the biggest issue we came across was a lack of Acadian hermit crabs when
we were collecting data. While we found 57 hairy hermit crabs, we only found 13 Acadian, all
through the five days we were in the field. We felt that a bigger sample size would be beneficial,
as more hermit crabs collected means more data to work with. Another source of error was the
number of tide pools used, which would increase sample size along with the individual crabs.
Another issue we found is that having four different options did not match well with our chosen
tide pools, as we found crabs in shells, seaweed, and rock crevices, but no structures.
For future studies, we advise that anyone who would like to continue our experiment to
consider a few options. First, seeking out more Acadian hermit crabs, as the lack of a near
equal amount of the two species skewed our data. In addition, more photo/video documentation
would be helpful, as it allows for visual reference when there is a need to delve into more heavy
detail in discussions and description. Importantly, look into the population diversity in the
Hurricane Island tide pools beforehand, so as to be aware of the apparent difference in hairy
and Acadian populations. Regarding the experiment and simulation, removing the rock structure
and allowing for the crab to have three tests that reflect their original location would allow for
extra data collection, albeit resulting in more work.
Making inferences and observations about these animals allows for scientists to tap into
the crab’s “umwelts”, and from there make another step towards an understanding of arthropod
behavior. In the case of substrate preference, observing the area the crab selects allows for a
glimpse into their behavior and instinct. While behavioral experiments do not directly benefit the
short term population statistics that marine biology generally focuses on, studying the behavior
of hermit crabs is still important for the science.
Figures 16a & 16b: (left to right) Alexa & Emilio in the field in the midst of collecting data on Two Bush
Island, ME14
14
Photographs taken by Steve Scrimshaw, CSW faculty, 2018
2018 ch. 7 pg. 16 Skrivanek & HernándezReferences/Citations
Bousvaros, G. (2015). Chapter 4: Observations on the Defensive Behavior of Hermit Crabs on
Hurricane Island. 1-12. Retrieved June 1, 2018.
Bresnahan, A., & Scozzafava, A. (2016). Chapter 4: Hermit Crab Defensive Behavior in Relation
to Shell Depth. 1-16. Retrieved June 1, 2018.
Folino, N., & Yund, P. (1998). The Distribution of Hydroid Sibling Species on Hermit Crabs in
Estuaries in the Gulf of Maine. Estuaries, 21(4), 829-836. Retrieved from
http://www.jstor.org/stable/1353284
Google, & TerraMetrics. (n.d.). Retrieved May 31, 2018, from
https://goo.gl/maps/Xi6X6e5mpMG2
Grant, W. (1963). Notes on the Ecology and Behavior of the Hermit Crab, Pagurus acadianus.
Ecology, 44(4), 767-771. doi:10.2307/1933025
Hazlett, B. (1981). The Behavioral Ecology of Hermit Crabs. Annual Review of Ecology and
Systematics, 12, 1-22. Retrieved from http://www.jstor.org/stable/2097103
Hennessy, R. (2014). Hermit Crab Species, Size, and Shell Type Distribution on Hurricane
Island, Maine. 1-8. Retrieved May 31, 2018.
Trott, T. (2004). Cobscook Bay Inventory: A Historical Checklist of Marine Invertebrates
Spanning 162 Years. Northeastern Naturalist, 11, 261-324. Retrieved from
http://www.jstor.org/stable/60225658
Turra, A., & Denadai, M. R. (2002). Substrate use and selection in sympatric intertidal hermit
crab species. Brazilian Journal of Biology. Retrieved June 5, 2018.
Turrigiano, R., & Blumenthal, W. (2015). CH.3 Hermit Crab Response and Habituation to
Repeated Negative Stimuli. 1-8. Retrieved June 1, 2018.
Walker, S. (1989). Hermit Crabs as Taphonomic Agents. PALAIOS, 4(5), 439-452. Retrieved
from http://www.jstor.org/stable/3514588
Images
Adam Jamal, CSW Student, 2018
Cameron Nayeri, CSW Student, 2018
Free Printable Hermit Crab Coloring Pages For Kids. (2014, August 05). Retrieved June 1,
2018, from http://www.bestcoloringpagesforkids.com/hermit-crab-coloring-pages.html
(modified)
Steve Scrimshaw, CSW faculty, 2018
Emilio Hernández, CSW Student, 2018
2018 ch. 7 pg. 17 Skrivanek & HernándezYou can also read
