An Invasive Species on Martha’s Vineyard

By Katherine Donegan

The aliens have invaded. They can be found strutting around Martha’s Vineyard waters, gobbling up our scallops, limiting biodiversity, and causing fishermen everywhere much grief. In fact, they are so hated that they have a bounty price on their head. These are the European Green Crabs (Carcinus maenas), and these foreign pests have intruded on our ecosystems.

The Green Crab is an omnivore, eating various prey from over 104 families. Most offensively the crab preys on soft-shell clams, quahogs, oysters and scallops. Female Green Crabs can reproduce twice in one season, producing up to 185,000 eggs at a time. Unfortunately, this crab can be abundantly found all over New England in shallow waters, including estuaries. Their lives can span from 3-5 years, and they progressively move from intertidal zones to sub tidal zones. Its five, evenly spaced, spines found behind the eyes on the shell can identify the Green Crab. Color is not a reliable trait to identify them with because their name is almost a misnomer; they can have coloration ranging from red to yellow to green.

True to its name, the European Green Crab originates from the North, East Atlantic, and Baltic Seas, and can be commonly found in Europe from Norway all the way down to Mauritania and Northern Africa. The Green Crab has arrived on

Martha’s Vineyard, and North America, through ship ballast water, currents, the hulls of ships, and aqua cultural activities, among others. The crab was first discovered in North America in 1817 on the East Coast, and has moved west there on, arriving in San Francisco Bay from 1989-1990.

These intrusive crabs have a very negative impact on the local ecosystem. It’s ability to displace native species, specifically through competition, is very threatening. The Green Crab has also significantly impacted the scallop industry on the island, by being partially responsible for the declined population of scallops. From 1992-1996 the fleets dwindled from 100 boats down to less than 20. Their characteristically broad niches, maneuverability and adaptability increase their chances of survival, and decrease their vulnerability.

The European Crab threatens shellfish populations and is a long-term predator to native bird and marine organism species. Although it is nearly impossible to eliminate this crab, methods have been employed to try and decrease the threat. These methods include a bounty program, trapping, and efforts to prevent new migration. A European barnacle is also under consideration for importation, as it is a natural predator for the crab that weakens exoskeletons and causes sterility. Although it appears like the barnacle would be a very effective measure to take, ecologists must consider the toll these foreign barnacles would have on native species.

“Invasive ecology” is a growing threat affecting everyone all over the world, including our small island of Martha’s Vineyard. To limit its effects on our ecosystem, we must take precautions such as thoroughly cleaning our boats, and trapping these crabs, so we can continue to enjoy our garlic and butter scallops that our island as so perfected.