Mutually-assured destruction in heated coral-algae war
by Kristen Brown 24 Mar 2019 17:34 PDT
Global warming and acidifying oceans are creating an intense competition between coral and algae. New research reveals both are deemed to lose under future climate predictions.
Dr Kristen Brown, from the University of Queensland (UQ) School of Biological Sciences, said it was previously thought that human-induced stressors like climate change would result in an algal takeover. But experiments conducted on the southern Great Barrier Reef suggest otherwise.
Competition on coral reefs is a major factor defining benthic community composition, with reef-building corals and macroalgae naturally competing for space and light. "Coral and macroalgae mostly compete through direct physical or chemical mechanisms, and the increase in algae can lead to an increase in coral bleaching and mortality," Dr Brown said.
"So far, our warming and acidifying oceans have led to a shift in competitive advantage between macroalgae and coral, generally in favour of algal species," she said.
"But in our experiments – using the branching coral Acropora and the green algae species Halimeda – we looked even further into the future, using mid-late century climate predictions, to see if macroalgal competitive mechanisms will increase at the expense of the coral.
"It turns out, both the algae and coral examined here fail to thrive in our business-as-usual climate predictions."
The experiment was conducted at UQ's Heron Island Research Station on the southern Great Barrier Reef. Coral and algal fragments were collected on the reef slope, where they were incubated for two months under different climate change scenarios simulating mid-late century conditions.
"We then measured physiological functions to determine how competition with algae under these stressful conditions might affect the growth of coral reefs," Dr Brown said.
"And the results were clear – the combined effects of ocean warming and acidification reduced survival, and photosynthesis of coral.
"Coral reefs are among the most threatened ecosystems on Earth, with an estimated 50 per cent of reef-building corals lost in the last few decades due to human influences.
"These results show that we must do all we can to better understand of the processes that govern the structure, function and recovery of coral reefs in a changing climate, in order to protect these invaluable ecosystems."
The research is published in Coral Reefs: Brown, K.T., Bender-Champ, D., Kenyon, T.M. et al. Coral Reefs (2019). doi.org/10.1007/s00338-019-01775-y