Common South Florida pollutants from sewage, agricultural practices and other sources can lead to a rapid increase in coral disease and bleaching among nearby coral reefs, a new study finds.
A three-year study in the Florida Keys examined the effects of increased exposure to nitrogen and phosphorous in a controlled testing site. It was one of the largest and longest experiments ever conducted to evaluate nutrient loading on coral reefs. The study determined these common pollutants doubled the prevalence of disease and more than tripled the amount of coral bleaching, according to Deron Burkepile, FIU assistant professor and co-author of the study.
“Coral bleaching is a common sign of stress among corals in response to high temperatures,” Burkepile said. “To see such a dramatic increase in bleaching and disease among the corals is a definite concern, as the levels of pollution we simulated are common in areas impacted by rural and urban development, including areas of South Florida.”
The findings were published Nov. 26 in “Global Change Biology” to shed light on the problems that have crippled coral reefs around the world. In the Caribbean Sea, more than 80 percent of the corals have disappeared in recent decades. These reefs, which host thousands of species of fish and other marine life, are a major component of biodiversity in the tropics and a major source of food and income for many developing nations.
While a variety of factors contribute to the loss of corals, the study offers some hope when it comes to nutrient loading. According to the findings, once the addition of pollutants was stopped, the corals recovered within months.
“The results of our study actually offer hope that local decisions to mitigate nutrient pollution can help corals survive the increasing stress of rising sea surface temperatures as a result of climate change, “ said Burkepile. “While slowing climate change will take coordinated, international action over decades, reducing nutrient pollution on coral reefs can have immediate effects on reef health and conservation.”
Burkepile said central sewer lines, like the ones installed in the Florida Keys in recent years, are a good start in reducing nutrients that move from the land into the marine environment. Reducing fertilizer in agriculture is another way to minimize nutrient pollution. The ultimate goal is to lower the stress levels on corals so they can better deal with the stresses that are more difficult to regulate, such as the warming oceans.
“However, taking these local actions, while important, is no substitute for taking global action to address our carbon emissions and the coming climate crisis,” Burkepile said.
Researchers have observed for years the decline in coral reef health where sewage outflows or use of fertilizers, in either urban or agricultural areas, have caused an increase in the loading of nutrients such as nitrogen and phosphorus. But until now almost no large, long-term experiments have actually been done to pin down the impact of nutrient overloading and separate them from other possible causes of coral reef decline.
In addition to researchers from FIU’s College of Arts & Sciences, the study includes researchers from Oregon State University and the University of Florida. The work was supported by the National Science Foundation.