In a major checkup of the health of the central Great Barrier Reef, scientists report that while corals on the outer reef are in excellent condition, coral health is in sharp decline close to the Queensland coast.
Inshore corals have 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 many years) and now coral bleaching caused by the hot summer, reports UQ`s Professor Ove Hoegh-Guldberg of the ARC Centre of Excellence for Coral Reef Studies.
A nine-day underwater survey by 14 researchers covering 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.
“Our results indicate that stresses to reef health occur along a gradient,” Guy Marion, a University of Queensland PhD researcher working on the project, said.
“[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.
His research involves drilling cores from long-lived corals using underwater air tools, which are then analysed for trace metal elements and nitrogen isotopic “signatures” within the skeleton.
The cores, which can be up to 2.5m long, can take over an hour of patient drilling underwater to collect. They are then transported to the lab and sliced into thin sections where analysis of the organic matter – just 0.01% of the skeleton– begins.
Sections of the core showing an abnormal jump in the nitrogen “signature” can pinpoint past flood events and changes in nutrient sources in the water – a possible sign of man-made pollution.
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 – prior to European settlement. These changes in the Great Barrier Reef lagoon health can then be matched to records on coastal development, temperature, rainfall and floods, in order to identify the sources of pollution.
“The project is trying to put numbers on the steady, long-term change in Great Barrier Reef water quality, in order to gauge current conditions relative to baseline, pre-European water quality. We want to know how inshore reef health has changed in response to coastal land clearing for city building and farming,” Mr Marion said.
Mr Marion’s work will be combined with the work of his supervisors and colleagues, who are each using new techniques to provide fresh insights into the historical relationship between water quality and reef health in the Great Barrier Reef.
“We hope that this approach of integrating multiple land, satellite, and coral-based techniques can become a blueprint study for reef studies worldwide,” Mr Marion said.
The survey is part of a three-year project which, on completion, will provide a detailed diagnosis of aspects of the health of the central Great Barrier 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.
It is part of a collaborative research project between leading members of the ARC Centre of Excellence and Stanford University in California.
More information:
Guy Marion, CoECRS and The University of Queensland, 07 3365 3548; g.marion@uq.edu.au
Ove Hoegh-Guldberg, CoECRS and The University of Queensland, 07 3365 1156
oveh@uq.edu.au
Jan King, UQ Communications Manager, 07 3365 1120
Jenny Lappin, CoECRS, 07 4781 4222
http://www.coralcoe.org.au/.
