Whenever Cornell junior Kate Allen studies seagulls at Shoals Marine Laboratory, she wears a construction hat with three dowels projecting from the top like a tall wooden mohawk. The reason: herring gulls and great black-backed gulls protecting their chicks dive-bomb people and even fire droppings at their heads.

Allen risks such attacks for the sake of science. For years now, faculty researchers and undergraduates in the summer Research Experience for Undergraduates (REU) fellowship program at the lab on Appledore Island, six miles off the northern New Hampshire coastline, have worked to build an understanding of the island's interconnecting biology. These connections range from the ecology of marine species that live near the shore, and how gulls interact with those species, to studying the gulls themselves.

Researchers have learned over the years, for example, that gulls play a critical role in propagating a parasite that castrates snails, turning them into parasite-manufacturing factories, and that mussels have developed thicker shells in response to a new crab in town.

Allen, an archaeology and preveterinarian studies major and an REU fellow this summer, is completing a project to study the effects of human habitation on the reproduction of the island's gulls. So far, she has found that the nests of gulls that live closer to people are more evenly spaced with fewer neighbors than those that live away from humans. The gulls that live near people also appear to be more tolerant of humans and of such potential chick predators as other gulls, allowing them to get closer before showing an aggressive response.

"Herring gulls and great black-backed gulls nest all up and down the New England Coast," said Allen. "I am hoping to get a good idea of the average number of chicks fledged per nest by the end of the summer."

In the intertidal spaces where ocean meets the island's shores, the seagulls prey on crabs, snails, clams, mussels and other creatures from the subtidal areas. In another area of study, the researchers have learned that trematode parasites (flatworms) benefit from these interactions.

The trematodes' complicated life cycle takes place in seagulls, periwinkles (snails) and crabs. Their sexually reproductive stage, for example, takes place in the gulls' digestive tracts. Fertilized eggs are then passed on through guano (gull feces) to the shorelines where foraging periwinkles ingest them while grazing. The trematodes then hatch within the snails and take over their gonads, where the parasites reproduce asexually, turning the gonads into a "trematode factory," castrating the snails in the process. The trematode then enters a swimming stage, where it swims and enters fish and crabs, which are in turn eaten by gulls.

It turns out that gulls forage on Jonah crabs and keep their numbers low. Since Jonah crabs eat periwinkles, the gull actually helps support the spread of trematodes by lowering crab numbers.

Faculty and undergraduates also have studied the impacts of a few of the island's introduced species of crabs, namely the European green crab that arrived on the island about 150 years ago and Asian shore crabs, whose larvae may have floated in plankton to Appledore Island within the last 20 years. Due to the presence of Asian shore crabs, researchers have already observed evolutionary adaptations in the local mussels, a common prey for crabs. Experiments reveal that these mussels develop thicker shells in the presence of Asian crabs, an adaptation already seen in response to green crabs. But mussels on the island's shorelines without Asian crabs do not develop thicker shells when exposed to them, while chemical cues from green crabs do cause shells to thicken.