Pollution Impact On Coral Reefs Leading to Coral Disease And Bleaching Can Be Reversed In a Year
A study published today in Global Change Biology confirms that pollution from agricultural practices, sewage or other sources leads to coral disease and bleaching. The research that forms the basis of the study, conducted in the Florida Keys from 2009 to 2012, is the largest ever to investigate the impact of pollution on coral reef. The controlled exposure of corals to elevated levels of nitrogen and phosphorous for three years, according to the study, reveals that the prevalence of disease doubled, while coral bleaching tripled. Coral bleaching is an early sign of stress.
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"We were shocked to see the rapid increase in disease and bleaching from a level of pollution that's fairly common in areas affected by sewage discharge, or fertilizers from agricultural or urban use," said Rebecca Vega-Thurber, an assistant professor in the College of Science at Oregon State University, in a press release."
However, the study also found that coral could make a swift recovery when the injection of the pollutants was stopped. Within 10 months after an overload of nutrients like nitrogen and phosphorous was stopped, the deterioration of the coral began to reverse, said Vega-Thurber. This provides real evidence, according to Vega-Thurber, that while nutrient overload leads to coral problems, the programs to reduce or eliminate nutrients can be hugely successful in restoration of coral health.
The findings offer a great solace and hope to environmentalists worried over crippled coral reefs around the world. In recent decades, over 80 percent of the corals have disappeared in the Caribbean Sea alone. Thousands of species of fish and other marine life rely on coral reefs for their survival, and the coral are a major component of biodiversity in the tropics.
While decline in coral reef health with increased loading of nutrients like phosphorous and nitrogen has been observed for years, this is the first large scale, long term experiment conducted to study the nutrient overloads impact as distinguished from other possible causes. More than 1200 corals in the study plots near Key Largo, Fla. were examined for the effects of nutrient pollution, including signs of bleaching and coral disease. Other factors that had complicated earlier surveys like temperature, salinity, and water depth were excluded. The level of bleaching and coral disease surged following regular injection of nutrients. Among the diseases, the one most commonly observed was "dark spot syndrome" found on about half of the diseased corals. On the positive front, however, the level of "dark spot syndrome" had receded to the same level as control study plots, about a year after nutrient injections wee stopped.
The exact mechanism of nutrient-induced disease is not yet known. However, there are theories that nutrients introduce pathogens or provide nutrients that help existing pathogens to grow or make corals vulnerable to pathogens or some combination of these factors.
"A combination of increased stress and a higher level of pathogens is probably the mechanism that affects coral health," Vega-Thurber said. "What's exciting about this research is the clear experimental evidence that stopping the pollution can lead to coral recovery. A lot of people have been hoping for some news like this."
"Some of the corals left in the world are actually among the species that are most hardy," she said. "The others are already dead. We're desperately trying to save what's left, and cleaning up the water may be one mechanism that has the most promise."
The best aspect of the study findings is that the solution offered is easily applicable on a local basis in comparison to factors like global warming or human population that could be difficult to control, according to Vega-Thurber.
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