Recognising the importance of the coastal embayments, such as Exmouth Gulf to the prawn industry, a team of AIMS scientists from the major scientific disciplines mounted a collaborative effort to learn more about carbon cycling and the ecological and physical conditions supporting prawn yields in Exmouth Gulf.

As is true for large areas of the northwest Australian coastline, the Gulf is fringed with mangroves on the southern and eastern edges. Saline flats and sand ridges lie inland. Rainfall and river run off are very low, and depend on rare floods associated with cyclones. Coral reefs dot the entrance to the northwest, human habitation is sparse, and the area holds tremendous interest for tourism. There is little published information on marine habitats within the Gulf, despite its area (~3,000 km2) and the presence of a highly productive prawn fishery (over 1,000 tonnes per year). The region provides an interesting contrast to wet tropical coasts bordering the Great Barrier Reef, which have larger freshwater inputs of nutrients and sediments. The program team’s working hypothesis was that ecosystem production in Exmouth was dominated by marine processes, tightly coupled with physical forces such as tides, surface waves and internal waves impinging the Shelf. Is the Gulf and the surrounding shelf area an erosional coast? And what does this imply for its response to potential perturbations by storms or industrial mishaps?

The Institute’s mangrove ecologists and geomorphologists set up long-term monitoring sites which were accessible from land. They sought to estimate growth, production, and the rates of critical microbial cycles for nutrient turnover. Are these mangrove forests stressed by their arid environment? Do they contribute significantly to the export of nutrients and carbon to the coastal embayment?

Shiptime was coordinated to support the offshore studies and those along the inaccessible east coast. Physical oceanographers placed current meters, wave and tide gauges and other instruments with the aim of describing the water and sediment movement within the Gulf. Benthic ecologists surveyed the distributions of seagrasses and attached algae, and deployed benthic respirometers; biological and chemical oceanographers measured pelagic and benthic production and community respiration; geologists characterised the sediments to ascertain their sources, and organic chemists analysed carbon and molecular marker compounds.

Future studies planned for 1996-1997 will extend this team approach to estimating carbon and sediment budgets for the Exmouth Plateau area further offshore.