As part of our Diving Research Methods class, we surveyed Pumphouse Beach and Canoe Beach for hermit crabs (Pagurus spp.) to analyze their abundances and see if there was a difference between beaches.
Pumphouse Beach is exposed to more wave action than Canoe Beach and also has a rockier substrate compared to Canoe Beach which has a cobble bottom. We thought that these differences might contribute to more hermit crabs being present at one site than at another.
To find out, we split into two groups and went SCUBA diving at each site taking along transect tapes, T-bars, and rugosity chains. Each dive team swam along the 30-meter transect and and used the T-bars to count the number of hermit crabs seen in the one meter to either side of the tape. We used the rugosity chain to figure out how complex the substrate was. A pre-measured chain is laid on the bottom and is conformed to any variations in substrate, such as rocks or valleys. We compared the length of the conformed chain to the actual length to find out if it was the same (sandy bottom) or shorter (rocky bottom).
There was a lot of variation in the number 0f hermit crabs that we found; some groups found only 14 0r 18, but one group found over 100! We looked at the data using methods that we've learned in our Experimental Design statistics course, but found that there wasn't really a difference in where hermit crabs live. This might be because they don't have to worry about finding the perfect home, since they carry their homes with them.
Although bottom type and beach location didn't affect the number of hermit crabs, we still got to combine what we've been learning in our classes to carry out an observational experiment.
To find out, we split into two groups and went SCUBA diving at each site taking along transect tapes, T-bars, and rugosity chains. Each dive team swam along the 30-meter transect and and used the T-bars to count the number of hermit crabs seen in the one meter to either side of the tape. We used the rugosity chain to figure out how complex the substrate was. A pre-measured chain is laid on the bottom and is conformed to any variations in substrate, such as rocks or valleys. We compared the length of the conformed chain to the actual length to find out if it was the same (sandy bottom) or shorter (rocky bottom).
There was a lot of variation in the number 0f hermit crabs that we found; some groups found only 14 0r 18, but one group found over 100! We looked at the data using methods that we've learned in our Experimental Design statistics course, but found that there wasn't really a difference in where hermit crabs live. This might be because they don't have to worry about finding the perfect home, since they carry their homes with them.
Although bottom type and beach location didn't affect the number of hermit crabs, we still got to combine what we've been learning in our classes to carry out an observational experiment.
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