Previous marine heat waves have destroyed corals. If the current rate of climate change is maintained, the future is gloomy for tropical reefs.
A recent study revealed the range of heat stress tolerance among coral species. Corals harvested from a single reef were subjected to an experimental marine heatwave by a team from Newcastle University and the Palau International Coral Reef Center. Surprisingly, the most tolerant 10% required twice as much heat stress to cause bleaching and mortality as the least susceptible 10%.
The scientists discovered that towards the end of the heat stress exposure, all of the least tolerant corals had perished while the most tolerant ones were still alive. They reported their findings in the journal Proceedings of the Royal Society B: Biological Sciences.
Interestingly, this variation did not seem to be influenced by the kind of symbiotic algae the corals were connected to, indicating the coral was more heat tolerant on its own.
It is well known that corals vary in their tolerance to heat stress among species and in different locations, but marine scientists have rarely examined how much variation there is among corals living side by side on the same reef. Despite these corals experiencing the same conditions, we found a remarkable variation in heat tolerance among individuals, suggesting the capacity for adaptation if some of the toughest corals can survive marine heatwaves.
Dr James Guest, Study Co-Author, School of Natural and Environmental Sciences, Newcastle University
Study Lead Authors, Dr Adriana Humanes Schumann and Liam Lachs from the same research group said, “Individual variation in heat tolerance is critical if corals are to adapt to higher temperatures. We show that under an ambitious future emissions scenario, the differences we have found equate to up to 17 years of delay until the onset of annual bleaching and mortality conditions. However, this delay is limited to only 10 years under a high emissions scenario.”
“For coral reefs to persist through the coming century, coral adaptation must keep pace with ocean warming. However, at the same time, the global emissions reductions of greenhouse gasses countries have already committed to need to be realized to give corals a fighting chance,” the researchers said.
The research has the potential to contribute to policy-relevant measures that can directly guide coral reef preservation and restoration initiatives, coupled with future climate projections.
Humanes, A., et al. (2022) Within-population variability in coral heat tolerance indicates climate adaptation potential. Proceedings of the Royal Society B: Biological Sciences. doi.org/10.1098/rspb.2022.0872.