James Cook University, ScienceAlert 8 Jul 09;
Hope some of the world’s corals may be able to escape destruction under climate change has emerged from a study by an international team of scientists working in French Polynesia in the Pacific.
The researchers found that corals off Moorea, in the central Pacific, have rebounded on five occasions despite sustaining heavy damage from four bleaching events and one cyclone in the past 18 years.
In particular they were able to recover even after the reef had been swamped by weeds, says team member Dr Lucie Penin of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.
“We conclude from this that coral reefs may not completely disappear as a result of climate change – as some people fear they might,” she says. (In the earth’s past history corals have become either nearly or totally extinct on five separate occasions, and some researchers warn that conditions under global warming may prove similar to those previous events.)
However Dr Penin notes that the corals studied lie on the outer reef slope of an island that is not heavily populated, and that the main human impact on them is fishing. “The lack of human pressure on the reef makes it more resilient,” she says. “This research suggests that, if left alone, coral reefs have the possibility to recover and re-grow.”
However the addition of further human disturbances such as silt, nutrients and chemicals from the land or physical destruction of corals compounds the impact of natural events such as bleaching and storms, making it all the more important to keep these in check.
Researcher Loïc Thibaut adds: “One of the salient feature of this reef is that the fish community, and in particular herbivorous fishes have remained at high levels of abundances throughout the study. This might well explain why the coral community recovered so quickly despite the catastrophic events it had to face.”
Dr Penin said the Tiahura Outer Reef Sector of Moorea had been closely studied for four decades by scientists, and the corals responses to natural disturbances was now well understood.
The five major disturbances had reduced coral cover at the time from over 50 per cent of the area to as little as 22 per cent while, in the early nineties sea weeds known as turf algae had taken over more than half of the area in the wake of cyclone and bleaching. However key coral species were able to re-colonise the reef in subsequent years.
“Our results support the idea that a rapid recovery from a weed-dominated reef to a coral dominated one is possible – but it will depend on what other pressures the corals are facing,” Dr Penin says. “It also shows that a fast recovery, in just a decade, is possible under the right conditions.”
However since the study was completed the Tiahura reef has come under a new threat – Crown of Thorns starfish have mounted a severe attack on the corals, slashing coral cover to as little as two per cent in some areas.
“We are keeping a very close eye on this outbreak. Right now the reef is in a very bad condition, but there are signs of recovery and we are hoping it will come back from this as it has from the damage caused by bleaching and cyclones,” she says.
The paper 'Recurrent disturbances, recovery trajectories, and resilience of coral assemblages on a South Central Pacific reef' by Adjeroud M and colleagues, appeared in the online journal Coral Reefs in early June.
