“I got out here and read more than I ever thought I would about snails,” Liam said as we stood by his snail tubs on West Beach. While snails are less charismatic than storm petrels or sparrows, it turns out they are fascinating research subjects. The species of snail that dominates on Kent Island and along the New England coast are Littorina littorea, the common periwinkle. These periwinkles are actually an invasive species introduced from Europe in the early 19th century, one of the many species that have grown so commonplace that it’s hard to imagine North America without them. Periwinkles were originally introduced because they are a popular food in Western Europe, where they are steamed with garlic and butter. Snails are also a delicacy enjoyed in this area, and Sam, our cook, has made periwinkle fritters that were surprisingly palatable.
Liam’s project builds off of research by a previous Kent Islander Kevin Wu, who looked at why the snails on the island are so big, and how size affects their distribution in the intertidal zone. Initially, Liam was curious about the parasitic worms (trematodes) that infect and castrate snails. He wanted to know if the trematodes increased or decreased snail growth. On the one hand, lab studies have shown that castrated snails grow larger, probably because they don’t invest energy into reproduction. On the other hand, field studies have found the opposite trend of infection and decreased growth. Real-world conditions are different from controlled lab experiments. In the lab, snails are provided with all the food that they need, like livestock, whereas in the wild, infected snails may not be healthy enough to forage and grow. Experiments are highly dependent on the situation in which they are conducted, and you have to ask very specific questions to account for all of the variables that you cannot control. “You can’t ask, ‘Why are the snails on Kent Island so big?’ within the short time frame I have and expect a quantifiable answer,” Liam told me. Instead, Liam is asking a more specific, measurable question related to snail size: “What food makes them grow the most?”
Liam’s project was initially fraught with logistical difficulties, leaving him a few weeks behind in his research. He decided to contain his snails in forty plastic tubs, which rest inside holes in the intertidal mud that took a long afternoon of teamwork to dig. There wasn’t enough wire mesh on the Island to cover the tubs, so there was a mass exodus of snails, which Liam had to collect all over again. He lost a tub to a storm, and there is a very real possibility of another snail jailbreak if crashing waves dislodge the window screening (specially purchased on Grand Manan) from his tubs. Fieldwork can be messy, and many of the scientists that I’ve followed have had to accept the unpredictability of nature and focus on the parts of their experiment that they can control.
Now that he has his project set up, Liam is restricting his 400 test snails, each painted with an orange nail-polished number, to a strict diet of algae. He has filled half of his snail tubs with sea lettuce [Ulva sp.], which is fluorescent green, soft, and digestible, the gourmet salad of the intertidal. The other half contain Laminaria [sp.], a tough brown kelp that is far less appetizing, which studies have shown is a “low preference food” for these snails (Lubchenko, 1978). Each tub contains five large and five small snails, because Liam wants to test the effect of size on their growth. He postulates that small snails may be unable to digest Laminaria, and therefore might grow less than small snails eating sea lettuce. Understanding the optimal food for snail growth will make one dimension of intertidal ecology more clear. For example, if Laminaria is optimal for growth, but snails prefer sea lettuce, there are other factors that determine their food preferences, a piece of the puzzle for a future Kent Islander to fit in to the picture.
Lubchenco, Jane. “Plant species diversity in a marine intertidal community: importance of herbivore food preference and algal competitive abilities.” American Naturalist (1978): 23-39.