An Experimental Look

In addition to the exciting trips that we have been on and have yet to take, as Three Seas students we have been able to take part in running experiments related to our favorite topic, marine biology!

For our experimental design class (a nice way of saying statistics for scientists), we split into groups to set up and run three different experiments that our professor Geoff Trussell and TA Catherine Matassa (a former Three Seas graduate) introduced us to. Each of them examined the effects of the presence of the green crab (Carcinus maenas), a predator to local Nahant snails. The top down/bottom up group looked at whether chemical cues in the water from the crabs affected how much algae the snails ate, the mechanical damage group looked at differences between the effects of chemical cues and physical damage to snail shells on snail growth, and the respirometry group is still running their experiment on how water temperatures in addition to chemical cues from the crabs affect the snails' respiration rates.


Carcinus maenas, the green crab.

Photo from: uri.edu
Littorina obtusata, the snail used in the damage experiment.

In the damage group, we learned about the time and effort that goes into the care and keeping of an experiment. Multiple times a day, we had to go to the Marine Science Center (MSC) just to make sure the water was flowing into our tanks, so that our snails and crabs would survive. We even had to check on weekends! It became a routine, though, and it was exciting to have something of our own to take care of for 5 weeks. Just last week, it was time to take down our experiment and weigh out all 120 of our snails (yes, 120 of them), to determine how much they grew, or didn't grow, over the length of the experiment. Luckily, with a team of 10, tasks were split up, and the work went quickly and smoothly. By quickly, I mean about 4 hours. A little bit of music on the radio helped keep us entertained while we waited almost two hours for the snails to dry so we could weigh them.

Here are a few pictures documenting the process of taking down our experiment:

Bobby is cleaning one of the jars we used to transport our snails back to the lab.


Josh and Liz are carefully opening the containers with the snails to keep them underwater, so we could record whether they were feeding or not.


Everyone having a good time cleaning the buckets. Want to leave it looking better than when we started.


A demonstration of the buoyant weight technique, to determine the weight of a snail when it is in water. This helps us when we want to determine the weights of the shell and the snail body tissue separately, instead of just the total weight of the snail.


Piper recording the buoyant weights of the snails, then leaving them out to dry.


The set up we used to photograph each snail in the experiment, so we could visually see how much the damaged shells grew back over 5 weeks.

Running and maintaining the experiment was a great experience, and now we get to delve into the statistics. How much did our snails grow when they were exposed to a crab or no crab, and did the damaged snails grow their shells back more or less than the undamaged snails? Crunching the numbers may be difficult, but the results that come out at the end will be the most interesting and will tell us a little bit more about snails that we did not know before.