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The Campaign - Values


How Important is Exmouth Gulf?


Exmouth Gulf is one of Australia's most productive marine ecosystems. Because it is located in the tropical arid zone it functions most of the time as a 'reverse estuary' where seawater salinity increases slightly upstream away from the ocean gulf due to evaporation.

However, during intermittent heavy rainfall events, usually the result of tropical cyclones, the extensive Yannarie delta system floods out transporting terrestrial sediment and nutrients into the marine environment along the entire length of the eastern shore of the Gulf.

Flood waters from cyclone Vance

Red floodwater from Cyclone Bobby (300 mm [12 inches] of rain) illustrates that the whole region along the east side of the Exmouth Gulf is one delta system.

The floodwater fingers out into the blue waters of the Gulf through dark mangrove island.

This image was taken March 3, 1995. Image Science and Analysis Laboratory, NASA-Johnson Space Center. 18 Jul. 2005.
" Earth Sciences and Image Analysis Debriefing with Crew members, 9 April, 2002.”

(20 Feb. 2006).

Larger image available here

At least some of the sediment is trapped by the mangrove system. It is highly probable that the nutrient flush from such events is captured through the growth of marine plants, including the mangroves, seaweeds, seagrasses and mats of micro-algae that grow in the shallow, silty environment on the eastern side of the Gulf.

The relative importance of the regular marine and intermittent terrestrial inputs of nutrients to the productivity of Exmouth Gulf is not well understood. The adjacent oceanic environments are nutrient poor and relatively unproductive and it is difficult to conceive at inputs from the sea alone could sustain the productivity of the Gulf ecosystem.

It is likely the mangrove, seaweed and seagrass habitats of the eastern Gulf function like a battery, fixing and gradually re-supplying nutrients and energy after re-charge from the intermittent flood-out events.

The mangrove system on the eastern side of Exmouth Gulf is a vital nursery for crustaceans and fish, including species utilised by significant commercial and recreational fisheries established in the region.

© Photograph courtesy Tony Howard

Exmouth Gulf is bio-diverse meaning many different species in a single area. For example a recent study of the biodiversity of the prawn trawl grounds identified onsiderably more species than in the comparable Shark Bay Gulf system.

At the Muiron Islands at the head of the Gulf, museum studies identified 482 species of fish. Even in the simple muddy bottom habitats trawled for adult king and tiger prawns there are 289 species of fish and at least 365 species of marine invertebrate. Many more species would be expected to occupy the protected mangrove, seagrass, seaweed and reef habitats within the Gulf.

The shallow water habitats on the eastern side of the Gulf are an important feeding ground for both adult and juvenile green turtles. The area is a major dugong habitat and an important sheltered resting area for humpback whales which may be critical for the survival of young calves on the southward migration.

The Yannarie mangrove system on the eastern side of Exmouth Gulf has been universally recognised as requiring a high level of protection. It is completely closed to trawling and has been proposed as a marine conservation reserve under the Conservation and Land Management Act, as a fish habitat protection area under the Fish Resources Management Act and as part of a Ningaloo/Cape Range World Heritage Area.


The Residents

World Heritage






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