The effects of blue and green crab grazing on eelgrass transplants in Sage Lot Pond, Waquoit Bay

Eelgrass, Zostera marina, has been disappearing from the Atlantic coasts of North America and Europe since the 1930s. Within Massachusetts, Cape Cod and Buzzards Bay have lost 65% of their seagrass within the past three decades. To assess the feasibility of seagrass restoration in Waquoit Bay, seagrasses from a local donor site, Little Pond, were transplanted into Sage Lot Pond in Waquoit Bay. Over the course of a month, transplants had only a 4% survival rate. It was hypothesized that crabs were grazing on the transplants. To test this, exclusion cages and open plots with seagrass transplants were placed into Sage Lot Pond. Seagrass loss was high in open plots while seagrasses in the cages were left untouched. To further investigate the feeding behavior of crabs in the Bay, blue (Callinectes sapidus) and green (Carcinus maenas) crabs were placed in tanks with seagrass transplants and monitored. Over four days, crabs were found to graze rhizome and sheath tissue. This study shows that both native blue crab and invasive green crab grazing can have a negative effect on attempted seagrass restoration and that measures need to be taken to prevent crab grazing on transplants in future restoration projects in the region. 

For more information: arkauke@eckerd.edu

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