Researchers from the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Sciences identified that certain reefs in the tropical Pacific Ocean could retain high coral cover into the second half of the century by shuffling the symbiotic algae they host. The observations provide a ray of hope in an otherwise desolate picture of the future of global coral reefs.
While global warming is inducing the loss of coral reefs worldwide, researchers believe that certain corals are raising their heat tolerance by switching the symbiotic algae communities they host, which provides them with the energy they need to thrive through photosynthesis.
Our results suggest that some reefs in the eastern tropical Pacific, which includes the Pacific coasts of Panama, Costa Rica, Mexico, and Colombia, might be able to maintain high coral cover through the 2060s. However, while this may be seen as good news for these reefs, their survival may not continue past that date unless we reduce global greenhouse gas emissions and curtail global warming on a larger scale.
Ana Palacio-Castro, Study Lead Author and Coral Biologist, University of Miami
Ana Palacio-Castro is an alumna of the Rosenstiel School and a Postdoctoral Associate at the school’s Cooperative Institute for Marine and Atmospheric Studies.
Shallow coral reefs in the eastern tropical Pacific Ocean are primarily built by branching corals of the genus Pocillopora, which are vital to the region’s reefs. The microscopic algae that live in their tissue harvest light to assist the coral in producing energy to grow. When these symbiotic algae die, the coral turns white or bleaches and struggles to meet its energy needs, which can be fatal.
The researchers examined over 40 years of coral reef monitoring data from Panama, one of the world’s longest datasets of its kind, to understand how corals advanced their tolerance to heat stress. They looked at temperature, coral cover, bleaching, and mortality data from three ocean heatwaves: 1982–1983, 1997–1998, and 2015–2016, as well as algal symbiont community data from the last two.
The 1982–83 heatwave considerably lowered coral cover on the reef, however, the impacts of the 1997–98 and 2015–16 El Niño were relatively mild, particularly for corals in the genus Pocillopora, also known as cauliflower coral, which is the dominant reef-building coral in the eastern tropical Pacific.
Researchers also confirmed that during intense ocean heatwaves, the heat-tolerant alga Durusdinium glynnii becomes more prevalent in this lineage of corals, enabling them to better withstand periods of high temperatures.
When combined with climate projections of future heat stress, it was discovered that reefs primarily composed of Pocillopora corals and hosting this heat-tolerant alga were best suited to survive and maintain high levels of coral cover well through the second half of the present century, implying that certain reef systems may be more robust to warming than previously assumed.
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. “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.
Andrew Baker, Study Senior Author and Professor, Marine Biology and Ecology, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami
Andrew Baker adds, “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.”
The research was published on February 13th, 2023, in the journal PNAS. The authors of the study are Ana M. Palacio-Castro, the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, Cooperative Institute for Marine and Atmospheric Studies and NOAA Atlantic Oceanographic and Meteorological Laboratory; Andrew C. Baker, Grace A. Snyder and Peter W. Glynn, University of Miami Rosenstiel School.
Other authors include Tyler B. Smith and Viktor Brandtneris, Center for Marine and Environmental Studies, University of the Virgin Islands; Ruben van Hooidonk, Cooperative Institute for Marine and Atmospheric Studies and NOAA Atlantic Oceanographic and Meteorological Laboratory; Juan L. Maté, Smithsonian Tropical Research Institute; Derek Manzello, Coral Reef Watch, NOAA and Peggy Fong, the University of California Los Angeles.
Palacio-Castro, A. M., et al. (2023) Increased dominance of heat-tolerant symbionts creates resilient coral reefs in near-term ocean warming. Proceedings of the National Academy of Sciences. doi.org/10.1073/pnas.2202388120.