Written by Geoff Vivian Thursday, 22 December 2011 12:00
Science Network, Western Australia
RESEARCHERS at Ashmore Reef found shifts in coral diversity after recovery from bleaching events of 1998 and 2003.
Marine ecology consultant Dr Daniela Ceccarelli says, “The scientific consensus is that the causes of severe coral bleaching at Ashmore Reef and on other coral reefs in the region were caused by abnormally high sea surface temperatures associated with an El Nino event”.
Surveys commissioned by the Department of Sustainability, Environment, Water, Population and Communities found the percent cover of hard corals tripled and the percent cover of soft corals doubled over a four-year period from 2005 to 2009.
Dr Ceccarelli, who participated in one of the surveys, attributes the rapid regeneration to two factors: the reef’s relative freedom from human activity, and the success of fast-growing coral species.
“The corals that became dominant over the recovery period were a combination of species that can colonise the reef and grow quickly and species that weren't as heavily affected in the first place, whereas species that were less abundant included slow-growing species that suffered high mortality from the bleaching.
“The fast-growing corals that became abundant in the shallow zone were from the genera Acropora and Pocillopora, and the slower-growing corals that did well in the deep reef zones were from the family Faviidae.”
She said the overall composition of the reef had changed.
“There didn't seem to be any biodiversity loss, and certainly no extinctions, just a shift in species dominance,” she said.
The researchers expect the success of branching corals to promote future biodiversity of other reef species.
“Habitat complexity is a measure of how convoluted the structure of the reef is - corals with branches provide greater habitat complexity than, say, encrusting coral species which grow flat against the substrate.”
Ashmore Reef is a nature reserve with an area of 583 square kilometres on Australia’s Northwest Shelf.
It is located 610km north of Broome and 110km south of Roti in Indonesia, and includes three small islands, sand cays, lagoons and a large flat reef.
Dr Ceccarelli said the last coral survey at Ashore Reef was conducted in 2009.
“Theoretically the monitoring should be repeated every two to three years, but it depends on how much funding is available,” she said.
Dr Ceccarelli is first author of the CSIRO article Ceccarelli et al Rapid increase in coral cover on an isolated coral reef, the Ashmore Reef National Nature Reserve, north-western Australia Marine and Freshwater Research, 2011, 62, 1214–1220