Marine scientists are gaining a better understanding of coral bleaching caused by climate change, rising ocean temperatures, pollution, and sediment runoff.
When coral bleaching occurs, corals release unique organic compounds and bacteria that promote bacterial growth, putting further stress on coral reefs, according to a new study led by the University of Hawaii at Manoa and the Royal Netherlands Institute of Marine Research. , which could put coral reefs at further risk. damage.
“Our findings show how the effects of short-term heat stress and long-term bleaching extend beyond corals and into the water column,” said co-first author and University of Manoa College of Tropical Agriculture. said Wesley Sparragon, a postdoctoral researcher. He is a human resources professional and a doctoral student at the University of Mānoa’s School of Ocean, Earth Science and Technology.
The research team included scientists from UH Mānoa, NIOZ, Scripps Institution of Oceanography, and the University of California, Santa Barbara. They conducted experiments on bleached and unbleached corals collected during a 2019 bleaching event on the French Polynesian island of Moorea.
“Although coral bleaching is a well-documented and increasingly widespread phenomenon on coral reefs around the world, there is relatively little research into its effects on the water column microbiology and biogeochemistry of coral reefs.” said Craig Nelson, senior author of the study and a professor at the university.Department of Marine and Earth Sciences
Through heating experiments, the researchers showed that both heat-stressed and bleached corals exude different compositions of organic matter in response to heat stress compared to unbleached corals. These unique compounds nourished the microbial community in the surrounding water bodies, causing an increase in their abundance.
“Interestingly, the microbes that responded to exudates from bleached corals (complex coral exudates) were different from those that grew in exudates from healthy corals,” Sparragon said. “And there were more abundant fast-growing opportunists and potential pathogens. As microbial communities proliferate around stressed corals, they can negatively impact corals through suffocation and disease introduction. there is.”
The biggest surprise, the scientists say, is that this change in the compounds released by the corals occurred at the beginning or end of coral bleaching in the corals that underwent some form of stress in the study. These included corals that had warmed but had not yet bleached. Coral bleached by heating. and corals that had previously bleached in the field.
“This suggests that this process occurs throughout the entire period of coral bleaching, from the onset of heat stress to recovery,” said co-lead author Milou Arts from NIOZ. “Importantly, this phenomenon is most pronounced in healthy corals under heat stress, and this phenomenon is most impactful at the onset of heat stress, leading corals to more severe bleaching and ultimately mortality. This suggests that it may lead to
Researchers are working to identify compounds and microorganisms in the water column that act as early warning systems for coral reefs under stress. This could enhance or complement other reef conservation efforts, especially in terms of identifying reef stress before catastrophic damage occurs.
