Color
Like size, color can help with identifying these species—especially if you glimpse the sky-blue legs of a blue crab. But green crab coloration can range from dark mottled green or brown to reddish, which makes relying on their hues difficult.
Seasonal Spawning Migration
Swimming plays a crucial part in the blue crabs' life cycle. Their eggs develop best in water with high salinity, so females have to migrate. They use ebb-tide transport, catching the tide as it goes out. Once they're closer to the ocean, they fertilize and brood their egg clutches under their aprons—the flap-like covering on the undersides of their bodies—until the larvae hatch and are swept out to sea. Weeks later, wind and water currents return the older larvae, known as megalopae, to sheltered coastal inlets where they'll mature.
Green crabs, with their lack of swimmerets, can't handle strong waves or deeper water. Females seek out saltier, shallow waters to spawn, while their larvae use the ebbing tides to reach the ocean.
Native vs. Invasive
Blue crabs have been synonymous with the Chesapeake Bay region for centuries, long before colonial settlers arrived. Found along the Atlantic coast from Nova Scotia to the Gulf of Mexico, they are important prey for many fish species and key predators in coastal bays and estuaries.
Green crabs originated in coastal waters from Iceland to Mauritania and were likely transported across the Atlantic on stones used by sailing vessels as ballast. Ballast was often swapped between sailing destinations, leaving hitchhiking organisms behind. By the mid-1800s, green crabs were established around Cape Cod. Within a century, they'd spread and had begun encroaching on the mouth of the Chesapeake Bay. Some green crabs have been spotted in the southern parts of the Bay, but they have not gained a large footing, in part because blue crabs successfully prey on them.
