Bleaching tolerance and adaptation

Variation in bleaching resistance within and among coral species depends on many factors connected to both the host and their algal symbionts. These include the thermal stability of certain membranes in the symbiont cell, the ability of the zooxanthellae to dissipate excess light energy and the amount of anti-oxidant enzymes that the coral can produce.

AIMS researchers are characterising the genes that underlie some of these factors by comparing the amount of gene product that corals from warm and cooler environments make, as well as that from heat-stressed versus non-stressed corals. If the amount of gene product in the cell changes during bleaching stress, it is believed that this gene plays a role in the bleaching response.

Once such genes have been identified, the distribution of certain variants of these genes in coral populations living in warm and cooler regions may point to those variants that confer the highest heat tolerance.

This can be tested in aquarium-based studies of thermal tolerance using colonies with known variants of the genes that are suspected or known to play a role in heat tolerance. This information can then be used to identify bleaching sensitive and tolerant reef coral populations and will feed into the risk mapping of coral reefs.

Evolution is the change in the inherited traits of a population from generation to generation. These traits are the expression of genes that are copied and passed on to offspring during reproduction. Evolution occurs when these heritable differences (the gene variants) become more common or rare in a population. If this happens non-randomly and is mediated by natural selection, the population is adapting.

Whether corals can adapt quickly enough to cope with climate change is hotly debated. AIMS is examining whether there is sufficient heritable variation in thermal tolerance of corals for selection to lead to adaptation over the next several generations.

Acclimatisation through changes in zooxanthellae

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October 19, 2007