Corals are marine animals typically living in compact colonies of many identical individual polyps. The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton. Coral reefs are under stress around the world often due to climate change issues. Researchers have uncovered a pattern of gene activity that enables some corals to survive in higher temperatures. The finding suggests a way to predict how different corals will fare in the warmer waters expected to result from climate change over the coming decades. Such information could help to focus future conservation efforts, the researchers say.
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Some of the Acropora hyacinthus corals in the back reef of Ofu Island, American Samoa, are able to thrive in pools that experience daily heat fluctuations of up to 6 °C. To find the molecular basis of this resilience, the researchers compared gene activity in heat-resistant and heat-sensitive A. hyacinthus corals by measuring their transcription — the complement of RNA molecules transcribed from the genes — under different temperatures.
The Hyacinthus Acropora are very beautiful species that will add a variety of color. Many of the brightly colored Hyacinthus Acroporas will even fluoresce.
The findings, published in the Proceedings of National Academy of Sciences today1, reveal a suite of genes that — though present in both populations — are more highly expressed in the temperature-resilient corals. These genes code for antioxidants and other proteins that organisms deploy in response to heat shock.
“We’re applying techniques that were basically developed for human-disease diagnosis to wild coral”, says the study’s lead author Daniel Barshis, a marine molecular ecologist now at the Institute of Marine Science at the University of California in Santa Cruz.
The authors found that the expression of hundreds of the corals’ genes changed in response to their tank water being heated from the control temperature of 29.2 °C to 32.9 °C. But in the heat-resilient corals, around 60 of these genes were already more highly expressed at the control temperature. The authors think that this front-loaded gene expression could be what gives these corals a survival edge in changeable conditions.
Study co-author Stephen Palumbi, a marine ecologist at Stanford University’s Hopkins Marine Station in Pacific Grove, California, describes the back reef of Ofu Island as a training ground for climate change. “The corals here are exercised by low tides and high temperatures, and as they experience those high temperatures, they become tougher and tougher.”
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“Climate change is happening rapidly, so it’s important to understand how organisms can respond to rapid change,” comments Ove Hoegh-Guldberg, a marine biologist at the Global Change Institute at the University of Queensland in Brisbane, Australia. He says that the results are a useful confirmation of the complexity of genetic response to thermal stress. But that complexity, he warns, “suggests that we’re not going to see corals rapidly evolving over the next decades in response to 1—2 °C changes in temperature.”
The team is now investigating whether the pattern of front-loaded genes is shared by other temperature-resilient coral species, with the aim of better understanding the process and potentially developing a diagnostic test to identify sites around the world where coral might stand a better chance of surviving global warming.
For further information see Fighting Corral.
Coral image via Diversity of Stanford by Daniel Barshis.