Biological invaders -- non-native species introduced into areas beyond their historical ranges -- often have an advantage over natives because of the absence of predators. However, in some cases natives can actually prevent these invaders from being established. Such appears to be the case with the European green crab, which can be found along the Atlantic Coast from Nova Scotia to Maryland.

Green crabs eat soft shell clams, oysters, scallops and quahogs, and have had a negative impact on these populations in the Northeast. In some places, green crab bounty programs have been implemented to pay watermen for catching and removing the exotic invaders from waterways.

In our state, however, the green crab is only found in the coastal bays near Ocean City, and has not established itself in the Chesapeake. The reason? Scientists believe our native blue crab – by feeding on its European cousin whenever the opportunity presents itself – is holding claim to its own territory.

When present, the green crab occupies rocky jetties, bulkheads and other structures and forages over open flats and tidal marshes. Growing to a maximum size of 3 inches, it can survive in a wide range of salinity and temperatures.

Green crabs can be purchased as bait in Maryland and should be handled carefully. Leftover baits should be discarded on shore and not returned to the water. The same method of discard should be used for other live bates -- minnows, worms, etc. -- that are not native to the body of water where they are being used.

Photograph of European Green Crab (Carcinus maenas)
courtesy off USGS