The drought
in Africa may be partly to blame for a decline in the coral in
the Caribbean Sea, according to a team of researchers who found
coral-damaging fungi in dust blown across the ocean.
``Coincidental
with the decline of Caribbean coral reefs over the past 25 years,
there has been a sharp increase in the transport of African dust
to the western Atlantic,'' reported the team led by Eugene A.
Shinn of the U.S. Geological Survey Center for Coastal Geology
in St. Petersburg, Fla.
With the long-term
drought in Africa, combined with overgrazing in many areas, the
amount of dust carried across the oceans has been increasing and
is now estimated at several hundred million tons annually.
And the threat
may not be limited to corals, Shinn said in a telephone interview.
``We have
moved into the realm of public health because the dust is bringing
lots of bacteria,'' commented Shinn, who said his research team
has now added a microbiologist to study what types of microorganisms
might be carried on the dust.
In 1989 some
one-inch grasshoppers from Africa made it to the windward islands
in a dust storm. ``If they can make it, think of all the other
things that can make it,'' he said.
``Dust often
reduces visibility in the Virgin Islands, sometimes causes temporary
closing of airports, and is easily verified as African in origin
by tracking dust clouds across the Atlantic with ... satellite
data,'' the scientists reported.
``Our hypothesis
is that some of the decline of the reefs in this region is linked
to the increase in dust transport,'' the team said in a paper
scheduled to appear in the Oct. 1 issue of Geophysical Research
Letters.
Aridity and
decertification in northern Africa began increasing in the mid-1960s,
worsened in the 1970s and 1980s and then began to lessen in the
1990s.
Major episodes
of Caribbean coral mortality occurred in 1983 and 1987, which
were also the two years of the greatest dust movement, Shinn pointed
out. He said iron and other minerals in the dust affected the
water conditions.
In the mid-1990s
an epidemic struck sea fans in the Caribbean and the cause was
found to be the soil fungus Aspergillus, the team noted.
At the time
the presence of Aspergillus was attributed to increased runoff
caused by deforestation on Caribbean islands, but outbreaks also
occurred around isolated islands that had no forests.
Shinn's team
tested dust samples collected from the air arriving at the Virgin
Islands and discovered several species of fungi, including Aspergillus.
``African
dust is an efficient substrate for delivering Aspergillus spores;
spores are absent when the air is clear,'' they concluded.
Coral damage,
including bleaching of corals, has also been attributed to rising
water temperatures and the team agreed that this is probably also
a factor.
Shinn will
be presenting his conclusions next month at an international conference
on coral reefs being held in Bali, Indonesia.
Working with
Shinn on the study were researchers from the University of South
Carolina Aiken, University of Miami, University of South Florida,
Duke University and the Geological Survey office in the Virgin
Islands.
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