A recent report by the Science Program at the South Slough Reserve says European green crab populations have steadily grown in the Coos Bay estuary over the last five years. Their population is now large enough that they could start negatively impacting native species, including Dungeness crabs, an economic staple for this region.
“The public around here are seeing more green crabs and are linking it with declines in recreational shellfish harvesting as well,” says state researcher Shon Schooler.
Green crabs have long been invasive along the Northeastern seaboard, where they threaten native crabs, clams, oysters, and mussels. In Southern Oregon, they’re eating and boring into eelgrass, a protective habitat for juvenile Dungeness crabs and many other native species.
The crabbing industry was already struggling with domoic acid appearing in Dungeness crabs at levels that could be poisonous to humans. Domoic acid is a biotoxin that’s produced by marine algal blooms, which are increasing in size and intensity because of warming waters and land runoff. The toxin has caused state agencies in California and Oregon to delay crabbing seasons in recent years.
European green crabs likely got to North America through seaweed used as packing material more than a century ago. Since then, ocean currents have carried them from San Francisco to northern estuaries like Coos Bay. Some have appeared as far north as Alaska.
Despite their name, green crabs are not always green. Their shells and underbellies could have bits of red or orange.
“The best way to tell them apart from other crabs is there are five spines on each side of the eyes,” Schooler says. “All our other crabs don't have that.”
Researchers don’t yet know how to control the invasive species, but one option is to develop a consumer market for green crabs. That could prove difficult since many crabbers consider them too small for manual shucking — although they apparently make for a decent empanada. Softshell green crabs are considered a delicacy in parts of Italy and Portugal, but it’s difficult to catch them during that short span of their life cycle.
Another option is to limit red rock crab harvesting near Coos Bay. Researchers found that where there are more red rock crabs, there are fewer green crabs — and the adult green crabs are often missing limbs. That suggests that the red rock crabs are eating them. While red rock crabs tend to prey on most juvenile crabs, including Dungeness, they’ll pick on green crabs of any age because they’re small.
