African Dust Harming Corals?
Filed under: Discovery,News & Resources
Clansmen are silhouetted amid dust as they herd cattle in northern Mali. Research suggests dust traveling across the Atlantic from Mali may be harming Caribbean corals. (Credit: AP/Jerome Delay)
Dust that blows across the Atlantic and settles in the Caribbean may be laced with toxins.
(From Discovery News / by Micahel Reilly) — African dust that billows across the Atlantic Ocean and settles in the Caribbean Sea is laced with toxic pollutants, and could be sickening the region’s coral reef ecosystem.
Hundreds of millions of tons of it comes from Mali each year, when the vast Niger River Valley dries out and its fine clay sediments are lofted into the air. It’s a process that gone on for eons, supplying parts of the ocean with much-needed nutrients like iron.
But in the last four decades something has gone wrong.
Coral throughout the Caribbean have started dying. Some researchers blame rising ocean temperatures, or damage from growing local populations.
A few, like the group led by Virginia Garrison of the United States Geological Survey in St. Petersburg, Fla., think it’s the dust.
Garrison’s team have found trace amounts of dozens of noxious pollutants strewn across islands from Trinidad to the U.S. Virgin Islands, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and a variety of pesticides that have been banned in the United States for years.
“These are organic contaminants that are known to persist in the environment, are toxic at low concentrations, and can bio-accumulate in organisms,” Garrison said.
So far the team has only found tiny concentrations of the chemicals, which for the most part look like the same suite of chemicals Garrison found when she traveled to Mali to take air samples. Recent studies have shown that some of these compounds, including the pesticides endosulfan and chloropyrifos, prevent coral larvae from settling and building reefs.
Garrison presented their research last month at the Society of Environmental Toxicology and Chemistry annual meeting in New Orleans.
“People living there have really bad air to breathe,” she said. “There are just these constant fires where they burn everything; tires, plastic and biomass that includes pesticides.”
“We’ve done a couple of papers on pesticides and dust, and these sorts of chemicals are all over the place, particularly in the northern hemisphere. They’re transported very long distances,” Joseph Prospero of the University of Miami in Florida said. He added that he’s skeptical of the team’s conclusions, because they have yet to directly sample dust plumes as they waft into the Caribbean.
“The question is, how much of these chemicals are there, and is it enough to impact corals? It’s a critical question,” and one that the team’s work doesn’t answer, he said.
Garrison admits her team’s case is circumstantial. The chemicals are in the environment, but it doesn’t prove that they are what’s damaging the reef ecosystem. Rising ocean temperatures, acidity in the water, and invasive species could all be combining with pollutants from the dust to stress the delicate organisms.
“The next step is to see if these chemicals are present in the tissues of fish, coral, and other organisms,” she said.
