TITLE: Fish woes linked to oysters' decline; Shellfish remove Pfiesteria from water
BYLINE: Frank D. Roylance
CREDIT: SUN STAFF
EST. PAGES: 2
DATE: 09/27/97
DOCID: BSUN535486
SOURCE: The Baltimore Sun; BSUN
EDITION: FINAL; SECTION: NEWS; PAGE: 1A
(Copyright 1997 @ The Baltimore Sun Company)
Decimation of the Chesapeake Bay's once-abundant oyster population
over the past century may have removed one of the bay's natural
mechanisms for controlling organisms such as Pfiesteria piscicida,
scientists say.
Percy Donaghay of the University of Rhode Island Graduate
School of Oceanography said yesterday that oysters are a kind
of marine "grazer." They remove algae and other microscopic
phytoplankton such as Pfiesteria -- and the nitrogen they contain
-- from the water.
The oysters' feces are then processed by bacteria in bottom
sediments. The bacteria convert the nitrogen to a gas and remove
it from the ecosystem.
"They're the equivalent of sewage-treatment plants," said Roger Newell, a professor at the University of Maryland's Center for Environmental Science at Horn Point.
By nearly wiping out the Chesapeake's oysters, Donaghay said, humans -- and more recently oyster parasites -- have created a bay in which the nutrients stored in one-celled algae are no longer removed from the ecosystem when the algae die. Instead, they are left to be consumed by the next well-fed generation of algae.
Chesapeake is an Algonquian Indian word meaning "great
shellfish bay." The bay was once studded with oyster reefs
so large that they rose above the surface in places.
In the past century, over-harvesting has reduced the bay's oyster population by 99 percent.
The 1996-1997 harvest was about 130,000 bushels, down from annual harvests of 2 million bushels two decades ago.
Newell said oysters once were abundant enough to filter the
bay's water in three to five days. Today it takes them 300 to
400 days.
The bay's waters are rich in nutrients, making them ripe for the growth and frequent "blooms" of a variety of phytoplankton. Some of those organisms can be expected to be harmful or toxic.
Scientists investigating the recent Pfiesteria outbreak don't know whether high nutrient levels in the Pocomoke River and two other bay tributaries contributed to the Pfiesteria-related fish kills and human illnesses there, but that is possible.
Harmful algae blooms occur when a variety of factors converge to produce a favorable combination of environmental conditions.
Scientists think the one-celled Pfiesteria organism usually spends its time eating other algae. Something caused it to release toxins that stun fish and then dissolve the fish flesh so that it can be eaten by the Pfiesteria.
Increased inflows of nutrients from farm runoff, chicken manure and human waste might be part of the reason. The absence of oysters to remove the nutrients from the water also might have played a role.
"The point you need to make to readers is that lots of changes in the Chesapeake Bay have occurred because of man's activities," Newell said.
"One of the most marked has been the removal of oysters, and inputs of nutrients generally that are thought to allow algal blooms to reach levels they didn't before."
If scientists determine that the Pfiesteria problem could be addressed by reducing the flow of man-made nutrients into the bay, they might also find they have another reason to try to restore the Chesapeake's shellfish.
There are no known cures for the parasites MSX and Dermo, which have destroyed many of the bay's oyster beds. Efforts to restore productive oyster reefs, and to raise native oysters that are resistant to Dermo and MSX, have been disappointing, Newell said.
If those efforts fail, the answer could lie in the introduction
of foreign oyster species that are more resistant to disease.
"It's a really contentious issue, because history is littered with examples where some do-gooder scientists like me have brought something in and made the problem much worse," Newell said. But with oysters playing such a key role -- in filtering nutrients from the bay and in providing fish habitat around their shell reefs -- "bringing in a resistant oyster species is perhaps beneficial from both a food and commercial, and an ecological point of view," he said.
In agreement yesterday were a number of other experts in
the study of harmful algal blooms such as Maryland's Pfiesteria
outbreak: Dr. Sandra E. Shumway of Southhampton College at Long
Island University, Dr. Katherine Richardson of the Danish Institute
for Fisheries Research and Dr. Patrick Gentien of the French Institute
for Sea Research.
Pub Date: 9/27/97
ART: COLOR PHOTO;
Caption: Conference: Kathryn Richardson talks about Pfiesteria at a meeting of experts on ocean resources.;
Credit: DOUG KAPUSTIN : SUN STAFF