David Baugh and Dr. Lee F. Braithwaite, Integrative Biology
Limpets are one-shelled marine mollusks that live on rocky beaches in the intertidal zone. The limpet species Collisella scabra is also found living on the shell of the limpet species L. gigantea. C. scabra exhibits an interesting phenomenon known as homing. This means that while not feeding, C. scabra are always found on the same spot on the rock or shell where they live. The C. scabra leave this spot, known as a home scar, to feed, but always return to it after they are done feeding. In this research, Chris Miller, Bryant Low, Christian Armstrong, and I examined the homing behavior of C. scabra limpets that are found living on the shell of L. gigantea. The research was performed at the Monterey Bay Marine Life Refuge in Monterey, California.
There have been many studies performed on the homing behavior of C. scabra that live on the rocks, but not much has been done on the homing behavior of those limpets that live on the shell of L. gigantea. We examined the homing behavior of C. scabra living on L. gigantea and hypothesized that C. scabra would have to move off the shell of the L. gigantea to feed to find enough food to support its needs.
Another focus of our research was to provide further support for previous research that C. scabra uses a knowledge of the topography of the shell of L. gigantea to return to its home scar as opposed to a mucous trail. We also wanted to see if we could observe any specific homing patterns displayed by C. scabra.
The research site that we chose was a sheer rock face, exposed to heavy wave action. The site was 5.07 meters wide by 1.14 meters high. We selected eighteen L. gigantea for the study. Each L. gigantea had one to four C. scabra living on its shell, for a total of thirty-two C. scabra in the study. We labeled all the limpets and recorded their widths and heights.
The movements of the limpets were observed during five consecutive nighttime high tides. Direct observations were performed by using a spotting scope placed on a rock perch approximately seven meters from the research site and three meters above the water level. After sunset two flashlights were used to view the research site. The position of each C. scabra noted and recorded at one-hour intervals over the course of a four-hour period surrounding high tide. Two additional experiments were performed which we called Collisella transfer and dog pile. In the Collisella transfer experiment we moved C. scabra living on L. gigantea from their home scar to another spot on the shell. Their position at the next low tide was recorded to see if they had returned to their home scar. We also had a control group where C. scabra were lifted off their home scar and then placed back on the home scar. The dog pile experiment involved placing multiple C. scabra on the shell of different L. gigantea to observe the reaction of the C. scabra. In one group we used only C. scabra living on the rock face and in another group we used C. scabra living on the shell of L. gigantea.
Our research led to some interesting conclusions about the interactions between C. scabra and L. gigantea. Our observations showed that C. scabra do not leave the shell of their host L. gigantea. Our study showed that this is not due to their inability to leave, but that there is enough food on the shell of L. gigantea to support the C. scabra that lived on its shell. We saw that the C. scabra exhibit linear, triangular, and even figure eight homing patterns. Each limpet tends to follow the same pattern every time it feeds.
From our Collisella transfer experiment we found further proof that C. scabra uses the topography of the rocks to find their way back to the rock as we observed the limpets that we moved were able to find their way back to their home scar.
From our observations we collected a lot of data on how far each C. scabra moved while feeding. We performed statistical tests on this data to see if we could find any correlations between how far the limpets moved and their characteristics, such as size. One characteristic we chose was the number of C. scabra on the L. gigantea host to see if this affected movement. The t-test we performed showed that there was no significant difference in distance moved. When we divided the limpets into two different size classes, the t-test showed that the larger-sized group moved significantly more than the smaller-sized group. But a regression analysis test showed that no correlation could be found between the size of a limpet and the distance it moved while feeding.
Further research needs to be conducted with a larger sample size and larger variation in size of the C. scabra. This may prove that there is in fact a correlation between the size of C. scabra and the distance it moves while feeding.
My research group had a few obstacles to overcome before we were able to collect relevant data. We knew we wanted to observe the limpets to see if we could find any new information about the way the limpets interacted. Observing the limpets was difficult, however, because most of the time the limpets do not move. When they do move it is when waves are crashing up over them. We finally devised a way to observe the limpets at these times of heavy wave action. We used a spotting scope from a good distance away and high enough that we stayed dry for the most part. When a wave subsided we noted the movements of the limpets. Using this method we were able to observe most but not all of the limpets at a given time. Another obstacle was figuring out a way to affix labels to the limpets without them falling off in the heavy waves. We tried a few different glues, but Super Glue worked the best.
This experience was valuable to me because I learned how to conduct a research project and deal with the problems that research entails. I am graduating in April and will then attend medical school where I will use what I learned from this project to conduct other research