A National Science Foundation study of factors that cause corals stress suggests that localized attempts to curb pollution on reefs won’t save them without a worldwide effort to reduce global warming.
Findings by researchers at Oregon State University and the University of California, Santa Barbara were published today in Scientific Reports.
Rebecca Maher, a graduate research fellow in the biology department, led the Oregon State study, which involved coral samples collected off the coast of Moorea, a South Pacific island that’s part of French Polynesia. The corals examined in tank experiments by biologists Rebecca Vega Thurber and Ryan McMinds, were Pocillopora meandrina, commonly known as cauliflower corals.
Coral reefs are found in less than 1 percent of the ocean but are home to nearly one-quarter of all known marine species. Reefs also help regulate the sea’s carbon dioxide levels and are a crucial hunting ground that scientists use in the search for new medicines.
Corals are home to a complex composition of dinoflagellates, fungi, bacteria and archaea that together make up the coral microbiome. Shifts in microbiome composition are connected to changes in coral health.
“We subjected the corals to three stressors: increased temperature, nutrient enrichment – meaning pollution – and manual scarring,” Maher said. “We scarred the corals with pliers, which was meant to simulate fish biting the coral.”
The scientists then studied how these stressors can interact to negatively affect the coral microbiome and thus coral health.
“We found that with every form of stress, the amount of ‘friendly’ bacteria decreases in the coral and the amount of ‘unfriendly’ or disease-related bacteria increases,” Maher said. “Stressed corals had more unstable microbiomes, possibly leading to more disease and coral death.”