November 22, 1999
SAVANNAH, GA. -- A fatal blood disease is killing some of Georgia's blue crabs before they ever make it to market.
It's not clear what effect hematodinium, which is caused by a parasite, could have on the state's crab harvest. But some crabbers are worried. Blue crabs are valuable for Georgia, bringing in about $2.3 million annually to the state's 159 licensed crabbers.
Hematodinium leaves the infected crabs weak and lethargic. No one knows for certain what causes the parasitic infections, but environmental factors such as higher-than-normal salinity and warm weather seem to provoke parasite activity in the crabs.
Although the disease carries no external symptoms, crab retailer James Holland has no trouble spotting the sick crabs. He scoops them out of his bins, saying they just don't look or act properly.
Infected crabs have milky-colored blood, which leaves their meat bitter tasting. The disease has no known impact on humans who may eat the infected crabs.
Holland believes development along the coast and its impact on fresh water could play a role in the disease.
"The environment is a mess and it's getting worse," he said. "It's killing the crabs."
Scientists aren't as sure. Dick Lee is one of several scientists trying to unravel the mystery of hematodinium in Georgia.
"The big thing is that the crabs are not being wiped out," said Lee, a professor of marine biotechnology and environmental toxicology with the Skidaway Institute of Oceanography. "The disease has been around for a long time, it may be that this fall with little rain and warm weather triggered it. Diseases are a part of nature."
Lee, along with the Department of Natural Resources, the National Marine Fisheries Service and the crabbers, have been studying the disease all summer. Researchers have learned that the disease is widespread -- occurring from Canada to Scotland to the Chesapeake Bay and now to Georgia. It can affect all types of crabs, not just blue crabs.
Death seems more likely to occur when in warm water with a high salinity. Mortality rates peak in Georgia in the fall, when estuary waters are the temperature of a comfortable bath. While the disease can be found all over the world, it's distribution is patchy -- occurring in one creek but not another.
As crab harvests vary year-to-year, determining whether the disease will have an economic impact isn't easy, said Susan Shipman, chief of marine fisheries with the Coastal Resources Division of Georgia's Department of Natural Resources. The disease proves most fatal in small, young crabs, which often are large enough to be sold anyway.
"But with young crabs dying, you're going to have decreased production and it's going to take a toll," Ms. Shipman said.
To get an idea of the disease's possible impact, the Coastal Resources Division will monitor crab harvests in areas where it is known to be present. Those figures will be compared to harvests from non-infected areas.
Some of Georgia's crabs are also suffering from chtinoclastic, a disease that deforms their shells and makes them look ugly and unappetizing. Although people will not get sick from crabs infected with either disease, Holland worries people may be afraid and not buy them.
"We have no idea how all this is affecting the yearly (harvest), but you put it all together and it's bound to take a toll," he said.