Great Barrier Reef coral communities may not be able to recover from bleaching as easily as previously proposed, according to new UQ research.
A two-year study by a team of UQ researchers, in the Centre for Marine Studies, has found that contrary to popular theory, it is not possible for bleached corals to recover or become more resistant to bleaching by taking up more heat tolerant species of their micro-algae partners.
All corals have a symbiotic (sharing relationship) with single-celled dinoflagellates, commonly referred to as zooxanthellae.
The coral provides a habitat for the zooxanthellae, which in turn produce essential nutrients for the corals.
Under stressful conditions, such as high or low water temperatures, the symbiotic zooxanthellae are expelled from their host, causing a whitening of the coral tissue or bleaching.
Coral bleaching events have caused significant mortality of corals worldwide and the frequency as well as intensity of bleaching events is predicted to increase as a result of climate change.
Dr Eugenia Sampayo, who performed the research as part of her PhD, said past research had suggested that bleached corals could take up new, more tolerant symbionts, which would make them less susceptible to future bleaching events.
“Our research, however, shows that this may not be possible for all corals” she said.
“This study is one of few that follows individual colonies over a two-year period and shows that individual colonies of the stony coral, Stylophora pistillata, do not change their symbionts as a response to temperature stress.”
The research team, which included Dr Eugenia Sampayo, Dr Tyrone Ridgway, PhD student Pim Bongaerts and Professor Ove Hoegh-Guldberg, found that individual colonies of the same coral species on the same reef are differentially sensitive to bleaching depending on the type of zooxanthellae present inside the corals.
“The sensitivity to bleaching conditions and survival appears tightly linked with fine scale differences in the genetic identity of the zooxanthellae that were present within the coral colonies,” Dr Sampayo said.
“Because corals with sensitive zooxanthellae suffer high mortality after bleaching we see a shift in the symbiont community towards more tolerant types.
“The important message here is that this shift is not due to the uptake of different symbionts by individual colonies but by differential mortality between sensitive and tolerant colonies.
“The result is a decrease in diversity of both the coral host and their symbionts.
“The reduced diversity will have a negative effect on reef resilience since it makes the ecosystem more vulnerable to fluctuations in other environmental factors.
“This is worrying since coral reefs are likely to face a suite of stressors in the future.”
The research paper “Bleaching susceptibility and mortality of corals determined by fine-scale differences in symbiont type” was published in the journal Proceedings of the National Academy of Sciences.
Media: Eugenia Sampayo on (e.sampayo@cms.uq.edu.au) or Eliza Plant at UQ Communications on (07 3365 2619).
