Fringe dwellers hold secrets of survival

by ARC Centre of Excellence for Coral Reef Studies on 4 Jul 2010 Corals right out on the exposed edges of the world’s great coral reef zones may hold an important clue to the survival of coral ecosystems facing intensifying pressure from human activities and climate change.

In a paper in the international journal Science, researchers Professor John Pandolfi of the ARC Centre of Excellence for Coral Reef Studies and University of Queensland and Professor Ann Budd of the University of Iowa have released new evidence showing that the evolutionary action on coral reefs is not in their ‘hot spots’ – but out on the fringes, where corals struggle to survive.

Their trailblazing research is calling for a re-think about how to protect corals and other at-risk species under climate change.

'We think we may have to pay just as much attention to protecting the edges of the ranges of coral species, where corals are fewer and less diverse, as we are currently paying to the places of rich coral biodiversity,' Prof Pandolfi says.

'There are two main reasons. First, this appears to be where corals are evolving most quickly, giving rise to new species, in response to all the challenges they encounter, and where they appear to hybridize with one another most readily, potentially as a survival tactic.

'And second, it is on the edges of their ranges that the corals are likely to encounter significant impacts from climate change – and hence, where we need to act to protect them.'

In their research Prof Pandolfi and Prof Budd have pioneered a new approach to assessing the conservation significance of a population of species – not simply looking at how many species are present, but also the rate of evolution going on among them.

'Evolution is the key to survival for life on Earth, and we feel it makes good sense to assess an area or ecosystem by its evolutionary potential rather than just the number of species it holds,' he said.

'In terms of species richness, these fringe areas can’t compete with the spectacular hotspots of biodiversity which we normally protect with Marine Parks and other important measures. But in terms of evolutionary innovation, our work suggests they can be way out in front.'

The researchers argue that there is a need to anticipate the evolutionary potential of populations at the edge of their inhabited ranges when considering likely effects of climate change on the species. 'You’d really hate to lose the populations that are really showing high levels of adaptation and change,' Prof. Pandolfi says.

In order to compare the rates of evolution in corals, the team studied existing and fossil corals, going back for several hundreds of thousands of years, collected across the Caribbean.

'One thing we noticed was that not only speciation but also hybridization – inter-breeding among coral species – was going on at the edges much more than in the heart of their range. Both mechanisms are ways that the rate of coral evolution speeds up and generates evolutionary novelty over time, in order to cope with the more hostile conditions the corals encounter on the fringes of their distributions,' Professor Budd says.

'Our data suggest that species edge zones play an important role in evolutionary innovation,' the researchers say.

'As such, we believe that species edge zones and peripheral areas, together with population connectivity, should play a prominent role in the future design (number, placement, size) of marine reserves.'

Their paper 'Evolutionary novelty is concentrated at the edge of coral species distributions'; by Ann F. Budd and John M. Pandolfi, is published in the current issue of Science, June 18, 2010.

For more information, please go to: www.coralcoe.org.au