DV-13-14 Invasive Green Crab Impacts on Salt Marshes

Dan Belknap
School of Earth and Climate Sciences
University of Maine

The current explosive population growth of the non-native European green crab (Carcinus maenus) is implicated in the widespread destruction of juvenile clams, eelgrass beds, and possible impacts on mussels and lobsters in Maine. Each of these effects has critical consequences for seafood industries as well as ecosystem health, prompting increased attention from fishermen, coastal communities, and scientists. In Belknap’s case, he recently noticed severe dieback of low salt marshes in some parts of Maine, along with dozens of green crab carapaces (discarded molts) lying nearby. Consultations with colleagues about other observed salt marsh degradation raised the idea that green crabs could explain the widespread clipping of the salt marsh grass, resulting die-off and denudation of the low-marsh surface, and potential increased erosion. Salt marshes are critical in the bluff erosion-stability cycle in Maine. Loss of marsh grass and consequent marsh erosion could lead to greater extents of bare bluff exposed to wave and ice erosion, resulting in land loss.

In this pilot project, Belknap will establish monitoring stations in the Damariscotta River and a control site at the Wells National Estuarine Research Reserve. Graduate student Eliza Cronkite will monitor the marsh surface, crab presence, and crab burrow density, along with other parameters. The sites include locations that were part of coastal erosion studies in the 1980s (and funded by Sea Grant), providing insight into short- and long-term changes in marsh structure.

Sea Grant funds: $3,800
Additional support provided by Casco Bay Estuary Partnership, Wells National Estuarine Research Reserve, and US Geological Survey.