New theory of corals' ability to adapt to climate change

4 December 2007

A new paper, published in the leading evolutionary journal, The American Naturalist, investigates the potential for corals to evolve greater resistance to bleaching.

The joint study, carried out by scientists from Queen's University in Canada and the Australian Institute of Marine Science (AIMS) presents a new way of examining how coral reefs may respond to climate change.

The mutualistic relationship between corals and the algae that live within their tissues can break down in response to stress, leaving the white calcium carbonate skeleton of the coral visible and hence a bleached appearance. In this new study, population genetic models were developed that explore factors that could affect the rate at which resistance to bleaching might evolve.

The study examined the effects of four factors on the evolution of bleaching resistance: (i) the existence of tradeoffs where an evolutionary advantage conferred by one trait is accompanied by a disadvantage conferred by another (ii) whether the zooxanthellae are expelled from the coral tissue or die during bleaching (iii) the nature of the genetic control of bleaching resistance and (iv) the mode of reproduction, sexual or asexual, of the corals and their symbionts.

This research does not indicate that corals are safe from climate change. Instead it provides a framework for assessing the potential for corals to evolve a greater ability to cope with such changes. "These models demonstrate for the first time that in spite of the complex nature of the interactions between these algal symbionts and their coral hosts, there is no necessary impediment to them evolving greater bleaching resistance. However, predicting the precise rates at which this may occur, or whether the rate will be sufficient to outpace projected sea temperature rise as a result of climate change, will require much more information about many aspects of the biology of these species," said Dr. Troy Day of Queen's University.

"Prior to this study, we had a theory about the conditions under which mutualistic relationships were likely to form and breakdown, but not how they evolve once established", said Dr Julian Caley of AIMS. "It is also likely that the theory developed in this study can be applied to understanding evolution in other mutualistic relationships which are a common component of biodiversity".

Although these results open up a new line of inquiry for how corals might be evolutionarily buffered from temperature stress, there is no reason to become complacent about human impacts on the environment. "While this study helps us to understand how coral reefs might evolve in response to climate change, these icons of biodiversity are still under threat from it," said Dr. van Oppen of AIMS. As Dr. Laura Nagel put it, "This project is important for providing a more complete understanding of the risks of climate change faced by coral reefs, and to help us to start thinking about how knowledge of these evolutionary dynamics might help to us to better manage these risks".

This research was conducted with part funding support from the Australian Government's Marine and Tropical Sciences Research Facility.

Media contacts:

Dr Julian Caley , Principal Research Scientist
Phone: 07 4753 4148
Mobil: 0439 472 148

Wendy Ellery, AIMS Media Liaison
Phone: 07 4753 4409
Mobil: 0418 729 265