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St. Petersburg Coastal and Marine Science Center > Effects of African Dust on Coral Reefs and Human Health

The Effects of African Dust on Coral Reefs and Human Health

Documentary

African Dust, Coral Reefs and Human Health presents how recent changes in the composition and quantities of African dust transported to the Caribbean and the Americas might provide clues to why Caribbean coral reef ecosystems are deteriorating and human health may be impacted. The documentary features work done by scientists at the U.S. Geological Survey in St. Petersburg, Florida, and Denver, Colorado, and at the Department of Energy in Berkeley, California.

Movie length: 9:52

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Documentary Transcript

Narrator – Coral reefs worldwide are in decline. Over the last three decades, coral reefs throughout the world have been damaged by human activities, powerful storms, abnormally high water temperatures, and diseases. Where coral has died, algae have quickly grown in its place. Scientists are particularly concerned because, once damaged, these key marine ecosystems are not recovering.

Ginger Garrison – Diseases were first reported on coral reefs in the Caribbean in the early 1970s. But today disease is considered probably the primary factor causing mortality in corals. Today, there are more diseases on coral reefs. There are more coral species that are affected by disease and disease is causing more mortality. Caribbean coral reefs were the first ones that were hit and hit hardest, the problem today is global and it is very serious.

Narrator: Currently, there are around 30 types of diseases or disease-like states recognized. Thus far, scientists have identified the causes of six coral diseases: sea-fan disease (or Gorgonian aspergillosis), black band disease, white plague, white pox, bacterial-induced bleaching, and pink-spot disease.

Why are the diseases on an increase? Why are they so widespread? Why are reefs worldwide in decline? What large-scale processes could be at work?

Hundreds of millions of tons of dust are carried each year from the Sahara and Sahel regions of Africa to the Caribbean, the eastern United States, and beyond. At times, these dust air masses cover the tropical Atlantic and the entire Caribbean Sea. Is this large-scale system having an effect on coral reefs throughout the Caribbean?

African desert locusts are known to be periodically carried along with the dust and arrive alive on several Caribbean islands. If a two-inch locust can survive the trip across the Atlantic, can smaller organisms such as the disease-causing microbes survive as well? Scientists at the U.S. Geological Survey are trying to determine whether downwind ecosystems are being harmed by nutrients, microbes, or chemical contaminants carried with African dust.

Suzette Mormon - By the time the African dust reaches the Caribbean, the particles are very small, about one micron in diameter. These fine particles are easily inhaled and less easily exhaled. The compositions of these particles are primarily clay with some other smaller amounts of gypsum and iron oxides. The iron oxides are important because they work as a sponge for other metals and they carry with them things, in particular arsenic.

Narrator – To test the hypothesis that African dust is a factor in the deteriorating state of Caribbean coral reefs, air samples were collected from the source region of Mali in Africa, off the western coast of Africa in Cape Verde, and at downwind sites in Trinidad and Tobago in the southeastern and the U.S. Virgin Islands in the northeastern Caribbean.

Suzette Mormon: The dust in the downwind sites had slightly lower concentrations of total metals but the bio-accessibility of these metals was higher. This may be related to the very fine particle size in these iron oxide coatings, which tends to absorb these metals on them and release them very easily. The very fine particles are very easy to inhale. We know that the less than 5-micron particles will travel further into the lungs. We know that these very fine particulate matters have been correlated health wise with increased rates of heart attack and stroke and exacerbations of asthma and other respiratory diseases.

Chris Kellogg: What we wanted to know is whether viable bacterial and fungal spores could be transported long distance across the ocean in African dust events, and the answer is yes. We found much higher numbers of microbes, say 10 to 100 times more cultured bacteria, when we tested air samples from Mali, West Africa, a source region, compared to downwind sites in the Caribbean. The downwind samples are complicated, because you have local aerosolized microbes and then you have microbes that have come in the dust and as of now there is no good way to tell the source of a microorganism. For example, Garriet Smith isolated Aspergillus sydowii, which is a fungus that causes disease in sea fans, from a dust event in the Virgin Islands, but the question remains is the source of that fungus local or long distance?

Narrator - Microarray technology recently developed at the Lawrence Berkeley Lab in California is using molecular techniques to identify microorganisms in dust samples.

Eoin Brodie: At Lawrence Berkeley National Lab, we have developed a microarray technology called the folic chip, which can be used to simultaneously detect up to 30,000 different types of bacteria in any environmental sample. Working with researchers at the USGS, we have been attempting to identify the microorganisms present in African dust samples, and we hope to correlate the presence of those organisms with coral disease and changes in human health in the Caribbean. We receive a filter sample containing dust. We extract the DNA and apply the DNA to this microarray device, the folic chip. Within 24 hours, we can identify the organisms present in a sample and then inform researchers at USGS which organisms are associated with dust and which organisms may be associated with coral disease.

Narrator – Although African dust has been carried out of the Sahara and into the Caribbean and the Americas for hundreds of thousands of years, there have been significant changes in the past 40 years: the quantity of dust has increased and the composition has changed. Scientists have identified carcinogens, neurotoxins, endocrine disruptors, and suppressors of immune systems.

Ginger Garrison – Greater amounts of dust have been carried out of the Sahara since the 1970s due to a number of factors: global climate, changes in regional meteorology, and local human activities. During that same time, the composition of the dust has changed. Toxic chemicals are produced by the combustion of biomass, fossil fuels, the burning of garbage, and things like plastics in the source region. These have been carried along with the dust particles from Africa into the Caribbean. At the same time in the source region, they are using pesticides for things such as malaria from mosquitoes, on their crops, and also against locust plagues, and those pesticides are also coming across.

Narrator –These chemicals can travel around the globe and have long-term effects on ecosystems because they persist in the environment, accumulate in organisms, and are toxic in low concentrations.

Ginger Garrison – The question is, can we really point our finger at any one source for this load of inorganic contaminants that we are finding in the atmosphere, both in Mali and also in the Caribbean, and we think not. We think that there is an underlying burden of contaminants. If you look at the pollution plume that will come out of the northeast United States, crosses the Atlantic into Europe, mixes with air pollution from Europe, that can conceivably be brought down south, especially with a cold front in winter, into Africa where it mixes with the African and Saharan air layer and then everything comes over into the Caribbean, comes around again.

Narrator - Scientists are beginning to test the toxicity of African dust and associated chemical contaminants on the life stages of many kinds of marine organisms, including corals, to see if they harm marine life and how they do so. Preliminary laboratory research has found some disturbing results. Two of the pesticides most commonly found in dust air samples from source and downwind sites were found to interfere with the settlement of coral larvae – an important stage in the life of a coral.

The movement of small particles of dust, metals, and toxic chemical pollutants through the air, across the oceans, and among continents is occurring. USGS research continues on this global issue.


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