The study, published June 18 in Nature Ecology & Evolution, comes at a time when scientists are deeply divided over whether local efforts to protect and manage coral reefs are enough to help stem the global tide of thermal bleaching that’s decimating corals worldwide as ocean temperatures continue to warm.
To test whether local actions can make a difference, the Duke-led team focused on one threat to reefs that is often controlled by local managers—populations of coral-eating animals like snails and starfish that have become too abundant.
“At high densities, these coral-eating animals, or ‘corallivores’, can cause low-grade but chronic stress to corals. Some of them are like Dracula, constantly sucking the energetic reserves out of corals and leaving them less equipped to deal with harsh environmental conditions like extreme warm temperatures and bleaching,” said Elizabeth Shaver, a 2018 doctoral graduate of Duke’s Nicholas School of the Environment.
To get a global sense of how managers deal with this threat, the researchers surveyed more than 30 coral reef management agencies worldwide, finding that many agencies reduce local corallivore populations in their sites. The researchers then mimicked managers by manually removing a voracious and common coral-eating snail from corals in the Florida Keys during a three-month spike in ocean temperatures in 2014. That warmup caused widespread coral bleaching across much of the eastern Caribbean and Gulf of Mexico.
The researchers focused their efforts on brain corals, which were found in a survey of six corals reefs in the Florida Keys to be particularly susceptible to predation by the snail.
“The idea was to see if removing these snails helped corals withstand and recover from warm temperatures and bleaching compared with corals that had average or naturally high densities of snails. And it did,” said Shaver.