"Dedicated partnership may be corals weakness"

(Sampayo et al 2008, PNAS 105[30] 10444-10449)

"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" (Read more)

"New indicator uncovered that can predict coral health"

(Stat et al 2008, PNAS 105[27] 9256-9261)

A new indicator of coral health has been discovered in a community of microscopic single-celled algae called dinoflagellates. The study, released in the July 8th edition of the journal Proceedings of the National Academy of Sciences, reveals that a particular type of these algae renders corals more susceptible to disease. "Corals are fascinating organisms whose survival is dependent on dinoflagellates that live inside the coral’s tissue," says lead author Michael Stat, an assistant researcher at the Hawaii Institute for Marine Biology (HIMB) at the University of Hawaii at Manoa. "The relationship between these dinoflagellates and corals has long been considered mutually beneficial, with the dinoflagellates supplying the coral with food via photosynthesis in return for recycled nutrients and shelter. Over the last 20 years it has been made clear that there are many different types of dinoflagellates in corals and that the unions or symbiosis between a given coral and their dinoflagellates can be very specific." It had previously been considered that all dinoflagellates found in coral are equally beneficial to their coral host, but in this study Stat, along with HIMB researchers Ruth Gates and Emily Morris, present evidence that a particular type of dinoflagellate can be found in corals that are diseased or show evidence of having had a disease. (Read more)