Local efforts to reduce pollution on coral reefs is not enough to save the world’s coral reefs, as a global effort to reduce global warming is needed to help these reef ecosystems, according to a National Science Foundation study put out by Oregon State University and University of California, Santa Barbara researchers.

The researchers collected Pocillopora meandrina cauliflower coral samples off the coast of Moorea in French Polynesia and exposed them to stressors that affect them in the wild. They examined how the dinoflagellates, fungi, bacteria and archaea that comprise a coral microbiome reacted.

“We subjected the corals to three stressors: increased temperature, nutrient enrichment—meaning pollution—and manual scarring,” Rebecca Maher, lead author of the study and a graduate research fellow in the OSU College of Science, said in a statement released to the media. “We scarred the corals with pliers, which was meant to simulate fish biting the coral.”

They then examined how these coral stressors interacted to negatively affect the coral microbiome and 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.”

The researchers determined that stressing the corals with two stressors didn’t necessarily result in twice the stress on the coral, as there was less stress in some instances, but they determined that all three stressors together fueled each other to the detriment of the corals.

“Two stressors did not always compound each other’s negative effects but instead interacted antagonistically to produce less-than-additive effects on changes in microbial community distinctness, instability and diversity,” Maher said. “However, when three forms of stress were experienced by corals, the microbiomes dramatically changed, showing that stress can act synergistically to amplify the negative effects of single stressors.”

While the simulated fish bites definitely stressed the corals, the high temperatures were the death knell for the marine organisms.

“There is no magical number of stressors, but multiple stressors may interact in ways that we would not expect and that can depend on the type of stressor – human vs. environmental – or the severity of the stress,” Maher said. “Therefore, we should take care to understand these interactions before attempting to manage them with conservation actions. Our work is an important step in informing those actions by providing insights into how the coral and its microbiome will change under increasing human impacts.”

While we as ocean lovers can do our part to reduce the effects of global warming, it is imperative that people around the world continue to pursue a path to reduce our carbon footprint, so our coral reefs can recover from a warming planet.