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Shellfish Conference Panel Explores Link Between Climate Change and Oyster Disease

Mar 24, 2015 | News

Many regions around the world have lost their oyster resources to overharvesting, disease, pollution, or salinity changes, but the South Carolina coast has managed to sustain its fishery and oyster populations better than most. The state, moreover, has successfully restored many oyster beds with new techniques and knowledge.

Now, though, an expanding threat to oyster fisheries is emerging as coastal waters warm because of climate change, according to a panel presentation at the 16th International Conference on Shellfish Restoration, December 10-13, 2014, in Charleston.

The U.S. conference is a biennial event that brings together researchers, industry figures, regulators, coastal advocates, and others. The idea is to see “what’s been working and what hasn’t been working in shellfish management and restoration around the world,” said Rick DeVoe, executive director of S.C. Sea Grant Consortium, which organized the conference.

Over 200 attendees participated in conference sessions, which included practices of restoring shellfish ecosystems, rehabilitation of shellfish populations, and protection and improvement of water quality for shellfish survival, growth, and harvest.

Elizabeth Fly, coastal climate extension specialist with the S.C. Sea Grant Extension Program, organized and chaired a panel called “The Future of Shellfish Restoration in the Face of a Changing Climate.”

Fly has followed trends of increasing ocean temperatures and shifting distributions of species as organisms adapt to warmer waters. One such organism is the bacterium Vibrio parahaemolyticus. Vibrios are saltwater bacteria that prefer warm water.

As the climate changes, scientists are seeing outbreaks of this vibrio in locations where they have never been previously documented, according to S.C. Sea Grant researcher Charles R. Lovell, a microbial ecologist at the University of South Carolina.

“We’ve been seeing major outbreaks of this organism at high latitudes since 1998,” Lovell said, “and we continue to see them today. They are in places that historically have been considered too cold. The connection to global change is pretty obvious.”

V. parahaemolyticus is the number-one cause of seafood-associated food poisoning. There are 4,500 cases estimated per year in United States.

“That’s certainly an underestimate, because lots of cases go unreported,” said Lovell. “Diarrhea [that you get from this pathogen] won’t kill you, but you might wish it would.”

Lovell and his colleagues are studying conditions under which a virulent strain of this bacterium would be magnified very rapidly and create
a “hot” oyster.

“This pathogen is extremely fast-growing,” said Lovell. “It has a doubling time as low as 8 minutes. Escherichia coli (E. coli), which people think of as extremely fast-growing, has a doubling time of 20 minutes at best.”

But what’s the trigger that allows this vibrio to grow so quickly? It appears that the vibrio stresses the oyster’s immune system. Lovell’s research suggests that the vibrio attaches to the outer membrane tissue of the oyster and begins growing rapidly in population while also battering the oyster’s immune system. The vibrio in an immune-compromised oyster can grow without opposition and can outnumber all other organisms, growing to a size that creates a “hot” oyster.