Bleached Acropora coral (foreground) and normal colony (background), Keppel Islands, Great Barrier Reef. Image: Wikimedia
Some coral species may be able to survive ocean heat waves through ecological memory. According to research from Oregon State University, these corals are able to survive heat waves by “remembering” how they lived through previous ones. The discovery could point to means of aiding in the conservation of coral reefs in the face of threats from human-caused climate change.
In the study, funded by the National Science Foundation, OSU researchers teamed up with colleagues from the University of California, Santa Barbara, Arizona State University, and the University of Essex to spend five years studying 200 coral colonies at a reef on the north shore of Mo’orea, French Polynesia. Their findings, published today in Global Change Biology, contain evidence that the ecological memory response is likely linked to the microbial communities that live symbiotically with corals.
Corals are made up of hundreds to hundreds of thousands of animals called polyps. However, these corals also house microscopic algae within their cells, alongside an entire ecosystem of bacteria, viruses, archaea and microeukaryotes, called the coral microbiome. Though these symbiotic relationships are key to the survival of coral reef ecosystem, they can be threatened by warming oceans, which can cause coral to expel the algae living in their tissues and become bleached.
However, the corals observed by the study’s lead author, Alex Vompe, and his colleagues, appeared to be surprisingly resilient to this climate-change induced damage. “Acropora retusa, a prevalent coral species in the Mo’orean coral reef that we studied, appears to have a powerful ecological memory response to heat waves that the microbiome seems to play a role in,” said Vompe to the Oregon State newsroom. “This means some coral species may be more resilient to climate change than previously thought.”
The reef in question had gone through multiple traumatic events, making it a unique subject of study. In 2010, crown-of-thorns starfish and a cyclone destroyed more than 99 percent of the corals. After the colonies were reestablished, they then went through minor heat wave events in 2016 and 2017. Then in December 2018 and July 2019 the reef went through the area’s most severe marine heat wave in recorded history, followed by the second-most severe heat wave from February to July of 2020.
“We observed that some species of coral seem to remember exposure to past marine heat waves and maintain a higher level of health in subsequent heat waves,” microbiology professor Rebecca Vega Thurber told OSU. “And Acropora retusa’s memory response was strongly linked to changes in its microbiome, supporting the idea that the microbial community has a part in this process.”
“Members of coral microbial communities have unique biological features that make them more adaptable and responsive to environmental change – short generation cycles, large population sizes and diverse metabolic potential,” added Thurber. “In two of the three coral species we focused on, we identified initial microbiome resilience, host and microbiome acclimatization, or developed microbiome resistance to repeated heat stress. The latter two patterns are consistent with the concept of ecological memory.”
This new information could help aid in future conservation efforts. Understanding microbial processes and the organisms responsible for ecological memory can help with various strategies for saving corals, from development of probiotics, to monitoring protocols, to coral gardening and planting projects.
