CHARLOTTE, N.C. – A heavy metal believed to be benign in the state’s coastal waters does in fact pose a threat to the health and survival of oysters, a University of North Carolina at Charlotte scientist says. The heavy metal cadmium, combined with warming coastal waters, can kill the shellfish or weaken their resistance to disease, according to research led by assistant biology professor Inna Sokolova and published this month in the Journal of Experimental Biology.
Oysters in North Carolina·s sounds are already in decline due to pollution, overfishing and damaged habitat.
Because the shellfish take in nutrients by filtering the water in which they live, oysters from tainted water are dangerous to eat because toxins accumulate in the meat.
Cadmium·s impact is magnified by warming water, and coastal waters near Wilmington have warmed by 1 to 1.5 degrees since 1949, Sokolova said. Climate scientists expect that trend to continue in shallow waters.
“Temperature is a really key player in determining how toxic cadmium is to an organism,” Sokolova said.
Confronted by both the toxic metal and warm water, the oysters must invest all their energy in staying alive rather than growing or fighting off toxins, she said, and the same thing is probably happening with fish, crabs and other cold-blooded animals.
Mike Marshall of the state Division of Marine Fisheries in Morehead City said recent warm winters have allowed a longer growing season for Dermo, an oyster-killing parasite that has attacked the shellfish for decades.
“What (Sokolova) is saying is borne out time and again in the literature, that heavy metals do reduce oysters· ability to resist infection and their ability to reproduce,” Marshall said.
North Carolina·s oyster harvests peaked in the 1960s at about 300,000 bushels a year. By the 1990s the catch had plummeted to about 40,000 bushels.
Restoring the population will be difficult, Sokolova said. The filter feeders cleanse water remarkably well, but the oysters· dwindling numbers have limited their effectiveness.
“It·s very hard to restore oysters in polluted water,” she said. “They just don·t live there.”
