Competition between invasive green crab (Carcinus maenas) and American lobster (Homarus americanus)

Green crab (Carcinus maenas) have recently invaded the southern Gulf of St. Lawrence, Canada. Although these invasive crabs have coexisted without appreciable impact on American lobster (Homarus americanus) populations in northeastern United States, Bay of Fundy, and the southern shore of Nova Scotia, Canada, the green crab in the southern Gulf of St. Lawrence likely represents a new introduction of crab from northern Europe. The southern gulf is ideal habitat for green crab, and the crab are commonly captured subtidally, increasing the potential for overlap with juvenile lobsters. To complement previous experiments with green crab versus small (28-57 mm carapace length, CL) and medium (55-70 mm CL) sized lobsters in food competition trials, this paper reports findings from trials with large (72-80 mm CL) lobsters. The lobsters were first to gain possession of the food in an equal number of trials as green crab. The large lobsters fed for 62% of the total feeding time, versus 38% for the green crab, and initiated a significantly greater number of aggressive interactions than green crab. It appears that a reversal of dominance with adult green crab occurs once lobsters exceed 72 mm CL.