Corals switch algae to beat global warming


The ability of corals to change the type of symbiotic algae they contain may allow them to adapt to rising seawater temperatures caused by global warming, scientists have found.

Madeleine van Oppen and Ray Berkelmans of the Australian Institute of Marine Science studied the Indo-Pacific SPS coral Acropora millepora and found that, in some circumstances, adult corals were capable of developing increased tolerance to higher water temperature through switching the type of symbiotic algae held in their tissues.

The study, which used both transplantation and experimental manipulation, has been published today in the Proceedings of the Royal Society and found that the increased thermal tolerance was a direct result of a change in the type of zooxanthellae held in the host coral's tissues from Symbiodinium type C to type D.

Berkelmans and van Oppen said: "Our data suggest that the change in symbiont type in our experiment was due to a shuffling of existing types already present in coral tissues, not through exogenous uptake from the environment. The level of increased tolerance gained by the corals changing their dominant symbiont type to D (the most thermally resistant type known) is around 1-1.5 degrees C."

The study is the world's first to show that the ability to adapt to rising sea temperatures is causally related to the type of zooxanthellae in the host coral. Berkelmans and van Oppen believe that the findings provide a new insight into the ecological advantage of corals that harbour mixtures of zooxanthellae in their tissues, rather than a single form.

"While this increase is of huge ecological significance for many coral species, in the absence of other mechanisms of thermal acclimatization/adaptation, it may not be sufficient to survive climate change under predicted sea surface temperature scenarios over the next 100 years. However, it may be enough to 'buy time' while greenhouse reduction measures are put in place."

For further information on the study see the paper: Berkelmans R, van Oppen MJ (2006) - The role of zooxanthellae in the thermal tolerance of corals: a 'nugget of hope' for coral reefs in an era of climate change. Proc Biol Sci. 2006 Sep 22;273(1599):2305-12.