Nahant

Introduction
    At the Northeastern University Marine Science Center one can find a wonderful example of what the New England rocky intertidal zone should look like. Timing it so that we get there at low tide is a bit tricky, but when we do what we find is a diverse community that has managed to survive despite the harsh conditions (the cold winters and the storms that accompany them) that are associated with the New England coast line. Tide pools themselves are subject to the tides and can be separated from the sea for hours or even weeks at a time. Temperatures can change dramatically over time, and evaporation can change the salt concentrations in the water significantly. The fact that any organism can survive these conditions is a testament to their durability.
    Hermit Crabs (Pagurus spp) are one such organism that toughs it out in the intertidal zone and can range anywhere from shallow waters to upper intertidal, depending on species and location. The two species that I was most likely to find on the shoreline of Nahant were Pagurus longicarpus and Pagurus. Typically Hermit crabs find their homes in the vacant shells of various species of snails that they inhabit tide pools with, but if the need arises they aren't above evicting the previous owner of the shell. What I wanted to find out was if there was a species preference in the shells that Hermit crabs look for. Do Hermit crabs prefer Littorina littorea shells or do they want Littorina saxitillus shells or is there no preference at all? Previous studies(Sato & Jensen, 1996) suggest that there are indeed shell preferences when it comes to hermit crabs choosing their shells. I wanted to see if the same trend was present in Nahant among the hermit crab species found there with the snails that live with them.

Methods
    Originally the plan was to test the hermit crabs in both the field and in the lab, but with limited time and resources I decided it was best to use field measurements only. I proceeded to search the tide pools for any hermit crabs I could find and using a plastic container to hold them until I was finished measuring them. Measurements consisted of shell size and color as well as identification of the species of Pagurus that was in the shell. I also counted the number of each species of snail in the tide pool where I found the hermit crabs in order to see what the resource pool for the hermit crabs looks like. Measurements for the hermit crabs were separated by tide pool. For example hermit crab A was found in tide pool 1 and hermit crab B was found in tide pool 2. To see if my results were signifcant I used a Chi-Square test to see if I could obtain the number of shells that I obtain by random chance alone (given that p=.05). In other words if there is no preference for shell type then we would expect to see shells appearing at about an equal rate, which is our expected value for the test.