Plagues,
Pestilences and Diseases
Mystery Die Off: Oysters disappearing worldwide: study
WASHINGTON (AFP) - – A survey of oyster habitats around the world
has found that the succulent mollusks are disappearing fast and 85
percent of their reefs have been lost due to disease and
over-harvesting.
Most of the remaining wild oysters in the world, or about 75
percent, can be found in five locations in North America, said the
study published in BioScience, the journal of the American
Institute of Biological Sciences.
An international team of researchers led by Michael Beck of the
Nature Conservancy and the University of California, Santa Cruz,
examined the condition of native oyster reefs in 40 ecoregions,
including 144 bays.
"Oyster reefs are at less than 10 percent of their prior abundance
in most bays (70 percent) and ecoregions (63 percent)," said the
study.
"They are functionally extinct -- in that they lack any
significant ecosystem role and remain at less than one percent of
prior abundances in many bays (37 percent) and ecoregions (28
percent) -- particularly in North America, Australia and Europe."
By averaging the loss among all regions, the researchers came up
with an estimate that 85 percent of oyster reef ecosystems have
been lost, but said that figure was likely low because some areas
lacked historical records for comparison.
The study also did not include oyster reefs in parts of South
Africa, China, Japan, and North and South Korea.
Other studies and observations in those areas "suggest that wild
oyster abundance was much higher in the past and that reefs have
declined greatly in abundance or have disappeared altogether," the
authors said.
The one bright spot in the oyster world was in the Gulf of Mexico,
where native oyster catches are "the highest in the world despite
significant declines in abundance and reefs," according to the
study.
Five regions where oyster catches were globally the highest were
located in eastern North America, from the Virginia coast
southward and also in the Gulf of Mexico.
Oysters are important to ecosystems because they filter impurities
from water and provide food and employment for people living in
coastal communities.
The decline in oyster population often begins when trawling or
dredging destroys the structure of parts of the reef, leaving
surviving oysters vulnerable to stresses in the environment.
In some cases, non-native species of oysters are introduced after
a population decline, and they bring with them diseases that
further kill off the native oysters.
The authors recommended that any reefs with less than 10 percent
of their former abundance be closed to further harvesting until
the oysters can build up their numbers again.