Award: OCE-2017626

This project examined 1) how recent temporal changes in the geographic distribution of an invasive predatory crab (the green crab) have shaped the evolution of snail shell thickness and shell thickness plasticity, (2) whether there is geographic variation within the Gulf of Maine in how snail populations respond plastically to predation risk and ocean temperature, (3) how such geographic variation may alter predator-prey interactions to influence rocky shore community structure.

In terms of intellectual merit, the project produced several key findings. First, a historical comparison (late 1990s vs late 2010s) of clinal variation in snail shell thickness, an important trait in deterring shell crushing predators like the green crab, revealed that both northern and southern snail populations have increased shell thickness with northern populations exhibiting a more substantial change. In the 1990s, southern populations were considerably thicker than northern populations, but by the 2010s regional differences in shell thickness had substantially decreased. These changes in shell thickness are associated with recent changes in the distribution of the green crab in the Gulf of Maine. Second, comparison of plasticity experiments conducted 20 years ago with similar experiments as part of this project revealed that past geographic variation in shell thickness plasticity (populations in the northern Gulf were much more plastic) has disappeared. Thus the relatively recent range expansion and establishment of the green crab in the northern Gulf appears to have produced an evolutionary loss of plasticity. This result is consistent with theory predicting that as environments (i.e., predation pressure) become more predictable natural selection should favor fixed over plastic traits. The results of the experiment were verified with a more extensive experiment involving 12 snail populations throughout the Gulf of Maine which also revealed no evidence of shell thickness plasticity.

Our laboratory and field experiments found that regional differences in other anti-predator treats (e.g., refuge seeking) affected how much snails forage on basal resources (e.g., barnacles and mussels), which are important drivers of rocky shore community dynamics. The foraging of northern snails was less sensitive to the negative effects of predation risk than southern snails suggesting that risk effects on communities are much stronger in the southern Gulf. In addition, these effects appeared to operate independent of regional differences in ocean temperature, which was surprising because past work has shown that ocean temperature can also influence snail foraging.

To explore this issue further, an experiment examining the independent and combined effects of ocean temperature and predation risk on snail development and morphological defense is ongoing and should help to resolve the longstanding debate regarding the effects of ocean temperature on molluscan shell traits.

Finally, the project also produced a fully annotated genome for one of the key snail species involved in our experiments. This resource will be essential to our goal of exploring the connection between trait and genomic variation and will be useful to all researchers examining the ecological significance of genomic variation in marine systems.

Thus far, the project has produced 4 published manuscripts in top-tier journals (e.g., Science Advances, Ecology, Proceedings of the Royal Society) and we expect at least two more papers to result from both completed and ongoing work. 

In terms of broader impacts, this project supported the professional development of three PhD students (James Corbett, Matthew Baker and Meghan Ford). James’ dissertation was fully aligned with the goals of this project and he successfully defended his dissertation in December 2023. Matthew, who contributed to the project in its first year has migrated to studying the ecological effects in old field communities. Meghan Ford (NSF GRFP recipient in 2024) matriculated into Northeastern’s PhD program and the Trussell lab in September 2022, and joined the project to explore potential connections between trait plasticity and snail performance with genomic variation. All three PhD students involved with project have developed excellent experimental design and analysis skills and continue to perfect their writing skills. James Corbett is presently applying his analytical skills at a private, green investment firm. Matthew Baker will defend his PhD in December 2025 and hopes to obtain a tenure-track faculty position at either a teaching college or research university. Meghan Ford continues her PhD studies and also hopes to obtain a tenure-track faculty position at either a teaching college or research university.

 

Last Modified: 10/16/2025
Modified by: Geoffrey C Trussell