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by Matthew Cimitile

For five decades, coral reefs in the Florida Keys have experienced hurricanes, coral diseases, bleaching, die-off events, and boat groundings. And for five decades, U.S. Geological Survey (USGS) geologist Gene Shinn (retired) has been there to chronicle changing conditions at seven coral reef sites, creating an unprecedented 50-year photographic record of changes to coral reef ecosystems in what eventually became the Florida Keys National Marine Sanctuary. A new video podcast produced at the USGS office in St. Petersburg, Florida, highlights this one-of-a-kind photographic record of changes.

Shinn began work on reefs in the Florida Keys in 1960 as a support diver with scientists Ed Hoffmeister and Gray Multer, who were looking at growth rates of corals to better understand the origin of the emergent reef that forms the middle and upper Florida Keys. They measured coral growth rates by taking live corals out of the water, cementing them on tiles, and putting them back in the water—a method used since the early 1900s.

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The photographic record also began in 1960, when Shinn started exploring new ways of measuring coral growth without removing corals from the water. One technique involved measuring branching coral growth by attaching a plastic ring to the branches as a reference point and using a millimeter scale to periodically measure the distance from the ring to the tip of the growing branch (see scientific report). Another technique involved inserting stainless-steel rods into the coral as a reference point and measuring how fast the coral grew up around them.

"I started this work, putting stainless rods in coral heads, in 1960, and I thought it might be a good idea to take photographs. I didn't realize what a good idea that was at the time," said Shinn.

What began as a coral experiment turned into 50 years of photographic documentation. Sequences of photos spanning the years 1960 to 2010 show alterations to the size, types, and structure of corals at Carysfort Reef and at another site called Grecian Rocks. Shinn's images of Carysfort Reef capture the appearance of coral disease that began in the late 1970s and the resulting deterioration of reef growth and structure that continues today. At Grecian Rocks, he documented the die-off of staghorn corals that were prolific until the early 1980s.

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"Staghorn began to die in the late 1970s, but most died between 1980 and 1988," said Shinn. "Historically throughout the Caribbean, coral deaths started in the mid-80s due primarily to coral disease, and from then on there is practically no more staghorn. Soft corals like gorgonians and sea fans have taken over."

Currently, there are approximately 30 types of coral diseases or disease-like states recognized worldwide. These include seafan disease (or gorgonian aspergillosis), black-band disease, white plague, white pox, and bacterial-induced bleaching.

"Diseases were first reported on coral reefs in the Caribbean in the late 1970s, and today disease is considered the primary factor causing mortality in corals," said Ginger Garrison, a USGS ecologist in St. Petersburg. "Caribbean coral reefs were the first ones that were hit and were hit hardest, but the problem today is global and is very serious."

One source of the deterioration of Caribbean reef health by diseases and other factors may be found halfway around the world (the subject of another USGS video podcast). 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. Although African dust has been carried out of the Saharan Desert and Sahel region 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.

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"Larger amounts of dust began to be carried out of the Sahara in the early 1970s due to a number of factors, including global climate, changes in regional meteorology, and local human activities," said Garrison. "During this same period, the composition of the dust changed. Toxic chemicals produced by the combustion of biomass, fossil fuels, and the burning of garbage and plastics in the source region have been carried along with the dust particles from Africa into the Caribbean. In addition, the source region is using more pesticides on crops as well as to fight mosquitoes (which transmit malaria and other diseases to humans) and crop-eating desert locusts. The pesticides appear to be coming across with the dust as well."

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Changes in the quantity and composition of dust correlate with increased mortality from Caribbean coral diseases; however, causation has not been shown. To test the hypothesis that African dust is a factor in the deterioration of Caribbean coral reefs, scientists analyzed air samples from a dust-source area in Mali, West Africa; from a site off the west coast of Africa in Cape Verde; and at downwind sites in Trinidad and Tobago in the southeastern Caribbean and the U.S. Virgin Islands in the northeastern Caribbean.

It has been discovered that viable bacterial and fungal spores are transported long distances across the ocean in African dust events. Scientists have also found very fine particles that can be easily inhaled into the lungs of humans. According to USGS geologist and public-health specialist Suzette Morman, fine particulate matter has been correlated with increased rates of heart attack and stroke and exacerbations of asthma and other respiratory diseases. (For example, see "Cardiovascular mortality and long-term exposure to particulate air pollution," in the journal Circulation, v. 109.)

So far, carcinogens, neurotoxins, endocrine disruptors, and suppressors of immune systems have been identified in African dust air masses. Some of these chemicals may have long-term effects on ecosystems because they persist in the environment for years, accumulate in organisms, are toxic and (or) carcinogenic, and interfere with physiological processes in low concentrations. Plumes of pollutants originate in industrialized as well as developing areas throughout the world and can have global impacts when transported long distances through the atmosphere.

Scientists are now 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, if so, how they do so. And Shinn continues to monitor the health of coral ecosystems in the Keys, while moving into a sixth decade of documenting changing environmental conditions.