sex and death on the reef research could help

Published 19 June 2002

New research into when and how corals reproduce themselves to create and repair coral reefs in the South Pacific could help the worldwide coral reef crisis, said study leader and a world expert in coral reproduction at Southern Cross University (SCU).

Director of Marine Studies at SCU, Associate Professor Peter Harrison, and PhD student Andrew Carroll, have just returned from a 15-day research trip to French Polynesia, to the island of Moorea near Tahiti, where they studied coral bleaching and began research into the rare and mysterious phenomenon of coral spawning.

"From a global point-of-view coral reefs are under immense pressure," said Professor Harrison, from SCU's School of Environmental Science and Management.

"It's estimated that around the world, 30 per cent of coral reef systems are seriously degraded," he said. "During the 1998 worldwide coral bleaching event there were groups of islands such as the Maldives, south of India, where some reefs died almost completely."

"Sometimes itís hard to remain optimistic, but coral reproduction, the 'sex on the reef' aspect, is the positive part of the study. That is how we can start to understand how coral communities maintain themselves, so we can know how likely it is that these populations will recover from catastrophic events like coral bleaching."

Bleaching occurs when the corals eject the microscopic algae that normally live within the polyps, making the corals appear white. The main cause is stress from warmer than usual sea temperatures and high light levels, possibly due to global warming.

The project is a French-Australian collaboration, involving the University of Perpignan in France, funded primarily by grants from France. The coral reproduction component led by Professor Harrison is being funded directly by the French embassy in Canberra.

"The aim of the research is to discover when and how the corals in French Polynesia reproduce, because virtually nothing is known about that," Professor Harrison said.

"Our trip also coincided with a coral bleaching event in French Polynesia, so we did some additional underwater video surveys to determine the extent of coral bleaching and what percentage of corals were so stressed that they were dying or had recently died," he said. The results of these surveys are expected within a few months.

Professor Harrison was part of the group of researchers that made the award-winning discovery about mass coral spawning on the Great Barrier Reef in the early 1980s.

"That discovery fundamentally changed our understanding of reef ecology," he said.

Prior to that, researchers thought corals released larvae at an advanced stage of development almost continually throughout the year. Their discovery showed the opposite was true: that most corals spawn together on a only a few nights each year, following full moons in late spring or early summer. The corals spawn eggs and sperm into the water, which fertilise and form coral larvae. The larvae are carried by ocean currents until they find a reef to settle on and develop into coral polyps.

Mr Carroll will return to Moorea for three months from September to November to watch for those few days when the corals spawn, then he and Professor Harrison will return the following year to do more in-depth studies of the event. Once they discover when corals reproduce, they will be able to rear millions of coral larvae, that could be used to regenerate reefs damaged by coral bleaching or human disturbance.

"The major problem is if coral bleaching continues to increase in severity and frequency, which is what weíre seeing on a global scale and what the climate change researchers are predicting, it's going to outpace the coralís ability to recover," Professor Harrison said.

"So we're looking at a knife-edge situation that makes it really interesting but also dramatic, in terms of survival of the world's coral reefs."

Contact: Associate Professor Peter Harrison, Southern Cross University, Ph: 0407 456 249 (M), Ph: 02 6620 3774; or Sara Crowe, Media Unit, SCU, Ph: 02 6620 3144 or 0417 236 154.