Curbing coral crisis

Mr Marlon drilling coral cores on the reef
Mr Marlon drilling coral cores on the reef

A survey of the health of the iconic Great Barrier Reef has delivered mixed results and heightened the need for research into how to best balance coastal development with a delicate ecosystem

Seaweed is strangling the Great Barrier Reef’s inshore corals, a team of UQ scientists conducting a major health check on the World Heritage-listed ecosystem has found.

On the positive side, the corals of the outer Reef were found to be in excellent condition.

UQ’s Professor Ove Hoegh-Guldberg of the Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies said coral health was in sharp decline close to the Queensland coast.

He said inshore corals had been seriously affected by losing the competition for space with seaweed.

“The increased competitiveness of seaweeds has been triggered by increased nutrients and sediment moving off the land over time and by coral bleaching caused by the hot summer,” Professor Hoegh-Guldberg said.

A nine-day underwater survey by 14 researchers of a 150-kilometre transect of reef running due east from Mackay found that the effects of poor water quality and coral bleaching were plainly evident on inshore reefs.

The survey was part of a three-year project to provide a detailed diagnosis of aspects of the health of the central Reef, both past and present, so that policies and practices can be further developed to ensure that coastal development and reef use is sustainable in the future.

“Our results indicate that stresses to reef health occur along a gradient,” said UQ PhD researcher Guy Marion.

“Inshore, we observed low coral and fish abundance and consistent bleaching across all reefs. However, further offshore we observed intact, healthy reef structure and virtually no bleaching from the stress we saw earlier this year.”

Mr Marion is also working on a novel method for assessing the condition of the reef over the past 200 years.

He is drilling cores from long-lived corals using underwater air tools, with samples then analysed for trace metal elements and nitrogen isotopic “signatures” within the skeleton.

Sections of the core showing an abnormal jump in the nitrogen “signature” can pinpoint past flood events and changes in water nutrient sources – a possible sign of pollution caused by humans.

Each section of the core can be dated, giving a time line of water quality for the region, in some cases extending back to the 1880s and in the early days of European settlement.

Changes in the Reef’s lagoon health can then be matched to records on coastal development, temperature, rainfall and floods, in order to identify the sources of pollution.

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