VALERIE DEPRAETERE

Caribbean coral reefs are shrinking because of a doubling in the amount of dust carried in westbound winds across the Atlantic from the Sahara Desert each year, thanks to global warming, US scientists suggest.

The African dust brings with it a fungus, Aspergillus sydowii, that attacks coral reefs, and minerals, such as iron and silicates, that promote the growth of algae in the normally nutritionally poor waters of the Caribbean sea. The algae colonize the same environment as the reef and suffocate it.

"We now know that the inorganic species associated with dust, especially iron, have a very important impact on primary productivity in the ocean", Joseph M. Prospero, an atmospheric scientist comments. "As for the role of biological materials, that is highly speculative, but it certainly warrants further research."

These fluxes of African dust across the Atlantic tend to coincide with prolonged drought in the Sahara, Eugene A. Shinn of US Geological Survey, St Petersberg, Florida, and his colleagues now show1. So global warming, they say, is responsible for these increased transatlantic dust fluxes.

Disease in the Caribbean reefs also coincides with these peak dust loads and droughts, so the scientists explain in Geophysical Research Letters1 that African dust may be responsible for choking the Atlantic coral reef. The reef has been shrinking for the past 25 years.

"The Caribbean seems to be in worse shape than the other coral reef areas", says Ernest H. Williams, a coral conservationist at the University of Puerto Rico. It has been struck by disease, invaded by weed, polluted and bleached. "I have not heard any other suggestions explaining this situation", Williams adds.

"Dust could be involved as a contributing factor", he says, "but this does not always fit. Why for example was the last bleaching event far worst in the Indo-Pacific than in the 'dusty' Caribbean?", Williams wonders.

The study of Shinn and co-workers suggests that rather than combating the death of coral reefs locally, the solution may come from limiting the increase in atmospheric temperature by reducing gas emissions.

References Shinn, E. A. et al. African dust and the demise of Caribbean coral reefs. Geophysical Research Letters 27, 3029 - 3032 (2000)

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