ANNAPOLIS — A mysterious parasite sickening Asian oysters in waters off North Carolina likely holds no threat to future habitats of similar nonnative oysters in the Chesapeake Bay, preliminary tests show.
An unknown species of parasite, belonging to the genus Bonamia, is infecting thousands of experimental Asian oysters growing in Bogue Sound, near Moorehead City, N.C. Within three weeks of putting the bivalves into the sound last year — in cages and in aquaculture tanks — 60 percent were sick and many died, said Charles Peterson, a professor at the University of North Carolina Institute of Marine Sciences who is overseeing the project.
But Mr. Peterson recently found the parasite infected only the Asian oysters, called Crassostrea ariakensis, that were in areas of high salinity in Bogue Sound. The Bonamia didn’t affect the oysters in the low- and medium-salinity areas of the sound, water with salinity levels similar to those in Maryland’s portion of Chesapeake Bay and most of the Virginia section.
Mr. Peterson’s early tests are good news for Chesapeake Bay watermen, who are counting on an infusion of ariakensis to revive the reefs and the fishery.
“Maryland looks like she gets a free pass, along with most of the Virginia territory of the Bay,” Mr. Peterson said.
Scientists still have a key question to answer: Where is the parasite coming from? Until they find out what animal is hosting Bonamia in North Carolina, they won’t know for sure if the Chesapeake Bay is safe for the oyster.
There still is a chance a reserve of the parasite exists in the Bay but hasn’t shown its deadly nature. That is because Bonamia isn’t fatal for every marine species; the nature of a parasite is to live off its host, not kill it. For example, scientists likely will find Bonamia has been living off native oysters of North Carolina for years, Mr. Peterson said.
Mr. Peterson’s results mean that even if the parasite does exist in the Bay, it likely wouldn’t be able to spread or survive except in the highest-salinity waters — those close to the mouth of the Bay.
Mr. Peterson’s preliminary findings are consistent with what scientists have long known about Bonamia, which is partially blamed for the collapse of native flat oyster populations in France. Officials there were forced to introduce a Pacific oyster related to ariakensis to bolster its industry.
Scientists warn that because the Bogue Sound species of Bonamia is new and unknown, they can’t make definitive conclusions about it until more tests are conducted.
The Virginia Institute of Marine Sciences (VIMS) is performing experiments to find the natural hosts of Bonamia and whether the parasite can survive in lower-salinity waters such as those in the Chesapeake Bay, said VIMS researcher Ryan Carnegie.
Mr. Peterson’s tests also showed the Bonamia did not originate with the young Asian oysters bred in VIMS labs — more good news for Maryland and Virginia scientists, who are using the same brood stock for their experiments.
“In terms of the animals we have now, and whether we’re going to move this [parasite] around, I have good confidence that we’re not going to do that,” said Kennedy Paynter, who is overseeing a University of Maryland experiment that soon will put sterile ariakensis in the Chesapeake Bay to test their survival rates.
VIMS scientists already have begun a “million oyster march” of sterile ariakensis in Virginia bay waters.
Maryland and Virginia are collaborating to finish research on ariakensis by early 2005, when Maryland Gov. Robert L. Ehrlich Jr. hopes to introduce the breeding nonnative oysters into the Bay. State environmental officials say the new bivalves can be a “lung transplant” for the Bay, which is choking on pollution and diseases the native oyster beds no longer can filter.
Oysters native to the Chesapeake have been devastated by overharvesting and disease; Maryland’s harvest has dropped to an all-time low and now makes up less than 2 percent of the nation’s total.
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