Document Type

Honors Thesis

Publication Date

Spring 5-2017

Abstract

The blue mussel, Mytilus edulis, is a commercially important species along the Gulf of Maine. Its rapid decline in population size over the last forty years has led many researchers to question if the invasive green crab, Carcinus maenas, is affecting its distribution. The increase in annual mean water temperature, due to global climate change, has led many to fear an expansion of the green crab’s range and an increase in population density among areas they currently inhabit. The Damariscotta River in Walpole, Maine offers a unique thermal gradient to study the effects of temperature on green crab distribution, abundance, and size. I conducted field surveys to measure the abundance and size of both Carcinus maenas and Mytilus edulis within the intertidal zone of ten sites along the river. Results showed the highest abundance of both species occurred along the outer coast at sites dominated by cobblestone habitat. Sites with the highest abundance of green crab recruits also had the highest sample size and population density. In addition to intertidal surveys, green crabs were caught off the dock at the Darling Marine Center. Size frequency data from these traps suggest larger adult green crabs can be found both within the intertidal zone and in shallow subtidal waters. Green crabs caught within the subtidal and intertidal zone at the Darling Marine Center were used to conduct feeding trials to study the feeding capabilities, rates, and limitations of green crabs on blue mussels. Results showed that mussels 25 mm or greater are immune to green crab predation from crabs with a carapace width <50 mm. Size frequency data collected on the blue mussels show that despite large mussels being relatively immune to green crab predation, they are found in historically low numbers. The increased demand of blue mussels by humans over the last century could offer one explanation for the lack of large adult mussels along the Damariscotta River.

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