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Friday, January 28, 2022

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SDSU-led Team Finds Microbes Endanger Coral Reefs

By Lorena Nava Ruggero

While fish populations have been decimated by overfishing worldwide, a research team led by San Diego State University biology professor Forest Rohwer have recently found how the practice can also endanger coral reefs.

According to the team’s research in the Line Islands, located in the Central Pacific, overfishing leads to an excess of microbes that kill off coral. As fish populations decline, algae, which is usually eaten by fish, flourishes and potentially leaches organic matter that feeds the excess microbes which decimate coral. The four islands studied had a range of no inhabitants to human populations of about 5,500. Researchers found that as human populations increased, so did overfishing and the presence of coral-decimating microbes and coral reef damage.

"Coral reefs are globally degraded, but the causal links between human impacts and the loss of coral reef biodiversity are poorly understood," Rohwer said. "We examined reef condition in relation to fishing, water quality and variances in the Central Pacific and found that healthy coral reefs were negatively correlated with human population density."

According to Elizabeth Dinsdale, a post-doctoral researcher at SDSU, there were ten times as many microbial cells and virus-like particles in the water surrounding the island of Kiritimati, which had the largest population density at nearly 5,500 inhabitants, as compared to Kingman, with a population of zero.

"The Kiritimati microbial community was dominated by heterotrophs, micro-organisms that feed off of organic matter, many of which were disease-causing organisms," Dinsdale said. "The fact that Kiritimati also had the highest prevalence of coral disease and the lowest coral cover led us to believe that the microbes were likely related to declining coral health."

Stuart Sandin and Enric Sala from the Scripps Institution of Oceanography at the University of California San Diego organized the expedition and other researchers included colleagues from the University of Queensland, Australia and the computer science department at SDSU. The findings are published in the Feb. 27 issue of the peer-reviewed journal PLoS ONE. To read the article, visit

The research study was supported by the Marine Microbial Initiative of the Gordon and Betty Moore Foundation. Further support came from the Fairweather Foundation, the National Geographic Society, the Marine Managed Areas Science Project of Conservation International, the Scripps Institution of Oceanography and the SDSU College of Sciences, among others.