The green crab is an efficient forager capable of learning and improving upon its food-gathering skills. Studies have shown that the green crab is quicker and more dextrous than most crabs, and readily opens bivalve shells. One adult crab can eat 40 half-inch clams a day and can devour a crab as large as itself. Green crab prey on numberous other organisms, making them competitors for food with native fish and birds. These crabs are also the intermediate host for a marine worm that can harm local shore birds.
Green crab can thrive in many coastal habitats and in wide temperature and salinity ranges.
Larval green crab can live up to 80 days drifting on ocean currents. Human activities have almost certainly contributed to the spread of green crab to Pacific Northwest and British Columbia waters. Discharge of ballast water from ships is also thought to be a source of green crab larvae to the region.