| 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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