Coral bleaching reaches Coral Sea

Scientists say the effect of coral bleaching in the Coral Sea is similar to that recently experienced in the Great Barrier Reef.

Dr Hugo Harrison from the ARC Centre of Excellence for Coral Reef Studies spent the past month with colleagues surveying coral bleaching at 21 sites across seven reefs in the Coral Sea Commonwealth Marine Reserve. These included Saumarez, Wreck, and Kenn (southern reefs) and Mellish, Coringa-Herald, Lihou and Holmes (central reefs).

Preliminary advice suggests between 10-35 per cent of the Central reefs have been heavily impacted and while all Central reefs assessed showed degrees of stress not all coral colonies within those reefs were affected.

No bleaching was observed in the southern reefs of the Coral Sea.

Dr Harrison will take time to assess observations and the full results of these surveys, including the degree of mortality, should be finalised in six to eight weeks.

These surveys provide valuable data which once analysed will contribute to the National Coral Bleaching Taskforce database and provide an enhanced picture of this threat within the Coral Sea Commonwealth marine reserve and adjacent Great Barrier Reef.

This research provides a basis on which Parks Australia will continue to build future monitoring and manage the health of the Coral Sea Commonwealth marine reserve.

Key points:

• No coral bleaching was observed in the southern reefs of the Coral Sea Commonwealth Marine Reserve.
• The findings are consistent with other studies which demonstrate the extent of bleaching is higher in more northerly reefs.
• These surveys provide valuable data which will contribute to the National Bleaching Taskforce database and provide an enhanced picture of this threat within the Coral Sea CMR and adjacent Great Barrier Reef.
• The bleaching event has been tied to the combination of unusually high water temperatures in the Coral Sea and GBR and a strong El Nino event in the Pacific.

Observations by reef:

• The reefs in the southern section were unaffected by coral bleaching (Saumarez, Wreck, Kenn).
• At Mellish Reef in the far east, coral bleaching was observed on 45% of corals surveyed and of those <10% were fully bleached or dead.
• At Lihou Reef in the middle of the Coral Sea CMR, approximately 60% of corals were bleached and of those 20% were fully bleached and 10% dead.
• At Coringa Herald, in the same area, approximately 70% of corals were bleached, and of those 35% were totally bleached and 20% dead.
• At Holmes Reef, the most northern of the reefs surveyed, almost 80% of corals show some sign of bleaching, and of those 40% were fully bleached and 25% dead. It lies approximately 200 km east from some of the worst affected reefs of the Great Barrier Reef.
• There was a clear north – south gradient in the severity of bleaching across these reefs which is similar to what has been reported in the Great Barrier Reef.