Lord Howe Island coral reef shows signs of recovery

Southern Cross University researchers investigating the impact of a significant coral bleaching event at Lord Howe Island, which occurred early last year, have found signs of recovery at most sites and are continuing to monitor the impact of the bleaching event on the world’s southern-most coral reef.

The Northern Rivers Catchment Management Authority (NRCMA) funded research project is being led by Dr Steve Dalton and Dr Andrew Carroll, from Southern Cross University’s National Marine Science Centre, with support from the NSW Marine Park Authority.

Dr Dalton said there were encouraging signs of coral recovery at most sites observed during their September trip to the island.

The project aims to address high priority knowledge gaps identified in the NRCMA’s Marine Knowledge Review. In collaboration with Professor Peter Harrison, director of Southern Cross University’s Marine Ecology Research Centre and Dr Anya Salih and Dr Sandra Diamond (University of Western Sydney), the project will further the understanding of the distribution of Lord Howe Island’s nearshore reefs; determine the full extent of the 2010 coral bleaching episode; and evaluate the recovery capacity of the coral community.

The reef lies within the Lord Howe Island Marine Park and is part of the Lord Howe Island World Heritage site located in the Tasman Sea, 600 kilometres east of the northern NSW coast.

During summer 2010, warmer than usual seawater temperatures in combination with a period of light winds and little cloud cover led to mild to moderate bleaching in some parts of the reef system and almost total coral bleaching in other areas.

“Coral bleaching occurs when the special symbiotic relationship between the coral animal and the microscopic algae that live within the coral tissue becomes stressed and disassociates,” Professor Harrison said.

“The coral reef at Lord Howe Island is globally significant because of its unique combination of tropical, subtropical and temperate species so the recovery of many corals is very good news.

"Lord Howe Island corals are also relatively geographically and genetically isolated, which will increase the time taken for recovery."

The researchers visited the island in March, May and September 2010 and will return again in March this year to assess the capacity of the coral community to recover from the bleaching event.

“During the height of the bleaching event in March 2010, bleaching levels ranged between 60 and 95 per cent at sites within the lagoon, with some minor bleaching (less than 30 per cent) on the outer slopes and deeper reefs,” Dr Dalton said.

“During May and September coral pigment recovery was obvious with bleaching levels declining by 30 per cent at most sites within the lagoon. We did however find some complete coral mortality, with up to 25 per cent mortality associated with bleaching stress at the most affected shallow sites.”

As part of the research project, the researchers have also provided tools to the marine tourism operators on the island to be able to assess and monitor coral health throughout the year.

Photo: Steve Dalton and Andrew Carroll assessing the recovery of corals in the Lord Howe Island Marine Park. Photo by Sallyann Gudge, Marine Ranger Lord Howe Island Marine Park.