A normally healthy interaction between fish and coral has turned deadly, scientists have found after a three-year study to understand the impact of overfishing and nutrient pollution on coral reefs.
In typical conditions, parrotfish – like many other species – are essential to the health of coral reefs, nibbling at them to remove algae while causing no permanent damage.
However, a new study conducted by University of California Santa Barbara (UCSB) field ecologist Deron Burkepile and colleagues in the Florida Keys found that 62 per cent of corals weakened by nitrogen and phosphorus pollution died when parrotfish bit them.
The findings were published in the journal Nature Communications.
“Normally benign predation by the parrotfish turned into coral murder,” said Associate Professor Burkepile, of UCSB’s Department of Ecology, Evolution and Marine Biology.
“But it’s not the parrotfish; they’re like the reef janitors, keeping it clean. Those extra nutrients – nutrient pollution – turn parrotfishes into an actual source of mortality by facilitating pathogens in the wounds left by their bites. Excess nutrients turn a coral accomplice into a coral killer.”
The researchers found that multiple local stressors, combined with warming ocean temperatures, weaken corals to such an extent that opportunistic pathogens build to levels that kill them.
“The solution will be to help those corals recover their health by ensuring that their local environment is free of nutrient pollution and fish stocks are not depleted,” said corresponding author Rebecca Vega Thurber, an assistant professor in the College of Science at Oregon State University.