A study by researchers at the University of Guam found that shade can lessen the effects of heat stress on corals. The study, which was funded by the university’s National Science Foundation EPSCoR grant, was published in February in the peer-reviewed journal Marine Biology Research.
“We wanted to see what role light plays in coral bleaching,” said UOG assistant professor Bastian Bentlage, supervisor and co-author of the study. “Usually people talk about temperature as the cause of whitening, but we show that light and temperature work together.”
Previous UOG research led by Laurie J. Raymundo found that more than a third of all coral reefs in Guam were killed from 2013 to 2017 during multiple bleaching events. Coral bleaching is the process by which corals stressed by environmental changes expel essential symbiotic algae that live in their tissues, causing them to bleach and often die.
This latest study examined the resilience of staghorn corals (Acropora cf. pulchra) to high seawater temperatures. This coral species is one of Guam’s major reef builders and its habitats experience temperatures of up to at 97 degrees Fahrenheit during the hottest months of the year, making it vulnerable to bleaching episodes and population decline.
A team of researchers – including lead author Justin T. Berg, a UOG graduate student studying biology; Charlotte M. David, an undergraduate student at Plymouth University (England), and Melissa Gabriel, a UOG graduate student studying environmental science – collected coral samples from the Hagåtña Reef and examined their health in the UOG marine laboratory under normal and normal conditions. high temperatures.
“One group was subjected to constant reference temperatures seen on the Guam reef flats,” Bentlage said, “and another was set to temperatures that are expected to become the new normal over the next two decades.”
Researchers found that corals took three weeks to recover from a week-long heat stress event. The experiment was then replicated to see how the corals would react if they received shade when subjected to warmer temperatures.
“We found that when we put shading on coral with high seawater temperatures, it dramatically increased the photosynthetic yield of the symbiotic algae. The shade made a huge difference to the health of the corals when the temperatures were down. high, ”said Berg.
Implications for reef management
Shading is a practice already used in coral nurseries, Bentlage said, but it may not be practical to shade entire reefs in the ocean. Future studies may examine practical ways to reduce the impact of light on corals, especially when recovering from periods of high temperatures.
“We saw the corals recover quite slowly,” Berg said. “The length of recovery indicates that corals are vulnerable during this time and that management efforts may be particularly needed during this time to reduce coral mortality.”
Berg said the new knowledge could also help inform the best places to successfully transplant corals.
“For example, slightly cloudy water could provide some shade for corals, making them less likely to bleach during periods of high sea surface temperatures,” Berg said.
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