Mutually assured destruction in a war of coral and fiery algae

Global warming and ocean acidification create intense competition between coral and algae that both will lose.

Dr. Kristen Brown of the School of Biological Sciences at the University of Queensland said that it was previously thought that human-induced stressors, such as climate change, would lead to algae control, but experiments conducted in the southern part of the Great Barrier Reef suggest the opposite.

"Corals and macroalgae are mainly competing by direct physical or chemical mechanisms, and more algae can lead to increased bleaching and coral mortality," said Dr. Brown.

"Until now, the warming and acidification of our oceans have resulted in a shift in the competitive advantage between macroalgae and coral, generally in favor of algal species," he said. she said.

"But in our experiments – using the branched coral Acropora and Halimeda species of green algae – we looked further into the future, to see if the competition mechanisms of macroalgae would increase at the same time. costs of coral.

"It turns out that the algae and corals examined here are failing to thrive in our usual weather forecasts."

The experiment began at the UQ Heron Island Research Station, in the south of the Great Barrier Reef, with divers who recovered fragments of coral and algae from the reef slope.

The specimens were then returned to the research station, where they were incubated in 24 tanks for two months under different climate change scenarios simulating the conditions of the mid-end of the century.

"We then performed several physiological laboratory measurements to determine how competition with algae under these stressful conditions could affect coral reef growth," said Dr. Brown.

"And the results were clear: the combined effects of ocean warming and acidification have reduced the survival, calcification and photosynthesis of coral.

"Coral reefs are among the most endangered ecosystems on the planet.It is estimated that about 50% of coral reef-building corals have been lost in recent decades due to the influence of the coral reefs. man.

"We must do everything in our power to better understand the processes that govern the structure, functioning and recovery of coral reefs in a changing climate to protect these valuable ecosystems."

The search was published in Coral reefs.

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More information:
Kristen T. Brown et al. Temporal effects of ocean warming and acidification on coral-algal competition, Coral reefs (2019). DOI: 10.1007 / s00338-019-01775-y