Some reefs in the tropical Pacific Ocean could maintain high coral cover into the second half of this century by shuffling the symbiotic algae they host. The findings, made by scientists at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, offer a glimmer of hope in an often-depressing outlook for coral reefs worldwide.
Shallow coral reefs in the eastern tropical Pacific Ocean are predominantly built by branching corals in the genus Pocillopora, which are extremely important for the reefs in the region. The microscopic algae they host in their tissue harvest light to help the coral produce energy to grow. The loss of these symbiotic algae causes the coral to turn white, or bleach, and the coral struggles to meet their energy needs, which can often prove fatal.
To better understand how corals improved their tolerance to heat stress, the researchers examined over 40 years’ worth of coral reef-monitoring data from Panama, one of the longest datasets of its kind in the world. This analysis showed that the 1982-83 heatwave significantly reduced coral cover on the reef, but the effects of the 1997-98 and 2015-16 El Niño were milder. They also confirmed that during strong ocean heatwaves, the heat-tolerant alga Durusdinium glynnii becomes increasingly common in this particular lineage of corals, allowing them to better withstand periods of elevated temperatures. When combined with climate projections of future heat stress, the reefs that were predominantly composed of Pocillopora corals and that hosted this heat-tolerant alga were found to be better equipped to survive and maintain high levels of coral cover well into the second half of the current century, indicating that some reef systems may be more resilient to warming than previously thought.
“This study shows that there are some unusual reefs that may be able to survive for several decades as a result of their ability to shuffle symbionts,” said Andrew Baker, professor of marine biology and ecology at the Rosenstiel School, and senior author of the study. “While we don’t think that most reefs will be able to survive in this way, it does suggest that vestiges of our current reefs may persist for longer than we previously thought, although potentially with many fewer species. Coral reefs are incredibly valuable natural assets, providing coastal protection and fisheries benefits, and supporting many local communities. We can still make a difference by protecting them.”
Feature image: Ana Palacio, Ph.D., lean author of the study. surveys a coral reef in the eastern Pacific dominated by Pocillopora corals. Credit: Viktor Brandtneris
More information: Palacio-Castro, Ana M., Increased dominance of heat-tolerant symbionts creates resilient coral reefs in near-term ocean warming, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2202388120. doi.org/10.1073/pnas.2202388120
