Climate change may have major impacts on the reproduction of the world’s corals, by changing some of the cues which trigger corals to spawn.

This is one of the major issues being explored by the world’s leading coral scientists at the International Coral Research Symposium (ICRS) in Fort Lauderdale, Florida from 7 July - 11 July 2008.

It follows the recent discovery that the world’s biggest orgasm – the synchronized mass-spawning of corals on major reef systems – may in fact be far more widespread than previously thought, to the point of being almost global.

“Previously it was thought that mass spawning events were mainly confined to a few major reef systems such as Australia’s Great Barrier Reef and Ningaloo but not more tropical reefs like in the Coral Triangle/Indonesia,” says Dr Andrew Baird of the ARC Centre of Excellence for Coral Reef Studies and James Cook University, who is co-chairing the conference session on coral reproduction.

“However new research is revealing these mass spawning events occur throughout the Indo-Pacific – from French Polynesia to the Red Sea – wherever there large numbers of coral species present, and even to a degree in the Caribbean.”

Dr James Guest, of the University of Newcastle and co-chair of the session said: “We’re still in the process of working out exactly what the cues are which prompt many different coral species to spawn together, on the same night.

“But it is clear that water temperature is a significant factor – and under climate change that is likely to change.

“This raises the risk that corals will become confused under climate change, start spawning all over the place at different times, reducing fertilization success and leading to less effective replenishment of coral populations.”

The failure of reefs to regenerate properly – as has been the case in the Caribbean – makes them less resilient to withstand human impacts such as overfishing and pollution or climatic impacts such as hurricanes or bleaching.

Dr Baird said that there were many factors, such as moonlight-sensing genes, solar radiation, tides and possibly other seasonal cues such as daylength, which prompt corals to spawn en masse. However it is now clear that mass spawning is a feature of all diverse coral assemblages – particularly those dominated by Acropora and favid corals.

“This is one of the many paradigms about coral biology that has changed with the wider geographic focus of recent research, and it is evoking great scientific interest as we come to grips with the implications,” Dr Baird said.

A second paradigm challenged by recent findings is the view that coral species hybridize (or cross-breed) extensively during mass spawning.

“Most researchers now agree this is not the case, hybridization is both rare and is not a major force in coral evolution,” Dr Baird says.

“For example researchers have found that while the corals may all shed their gametes at the same time, these little packages of eggs and sperm in fact open at slightly different times, even a few minutes is enough to stop the gametes from different species meeting. Also many gametes are incompatible and when in competition, the right sperm usually wins. All this makes hybridisation between different coral species much less likely

“Bother these paradigm shifts, or changes in scientific perspective, will be among the issues warmly debated at the symposium,” Dr Baird says.