Tainted African dust clouds harm U.S., Caribbean reefs

From an article by Brian Handwerk on the Web site of National Geographic:

Coral reefs in the United States and the Caribbean may be under siege—from a surprising source half a world away.

Scientists say tons of dust from Africa's arid Sahara and Sahel regions could be polluting oceans in the Caribbean and southeastern U.S.

The dusty clouds carry contaminants like metals, pesticides and microorganisms—potentially disastrous news for coral reefs and other marine animals already stressed by warming waters.

"We're trying to actually look at what is in these African dust air masses when the get over to the Caribbean," said Virginia "Ginger" Garrison, an ecologist with the U.S. Geological Survey in St. Petersburg, Florida, who studies how the dust travels.

"We're at the baby-step stages of trying to see how this dust and this stew of things may be affecting organisms—including humans—in downwind areas."

Something in the Air

Air-quality data from a network of sampling sites have revealed intriguing results, Garrison and colleagues said recently at the International Coral Reef Symposium in Fort Lauderdale, Florida.

For instance, Caribbean air samples during African dust events may hold two to three times as many microorganisms, such as bacteria and fungi, as samples taken from the same spot during other periods.

In Florida the Africa-influenced air conditions sometimes deteriorate below U.S. air-quality standards.

Air-quality testing in Mali, the U.S. Virgin Islands, and Trinidad and Tobago has also revealed traces of pesticides, including DDE—a breakdown product of DDT, which is still used as an insecticide in some African countries.

Pesticides are of particular concern to coral reefs because they can interfere with the tiny animals' reproduction, fertilization, or immune function. . . .

Winds of Change

Atmospheric systems such as the Africa-Americas pathway have functioned for thousands of years.

A similar system delivers Asian dust to the western United States, where it accounts for up to an estimated 40 percent of local air particles.

In recent times, however, humans have caused some significant changes.

Desertification and changing land-use patterns can put more dust into the air. Industrialization, pesticide use, waste burning, and other practices have produced air pollutants that ride with that dust to far-flung locales.