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The Kimberley coastline: what lies beneath?

26 February 2015

early morning low tide exposed corals

The ocean bottom supports communities as diverse as those of any habitat on land but learning about what lies beneath the sea off Australia’s remote and hazardous Kimberley coast is presenting many challenges for marine scientists.

One project, which aims to explore and describe the nature of seabed life in the far northwest, is beginning to reveal the diverse nature of life beneath the sometimes swirling, turbid waters.

The results will form the basis for sound decision making to support conservation and sustainable development of marine parks as part of the Western Australian Marine Science Institution’s (WAMSI) Kimberley Marine Research Program.

Project leader, The Australian Institute of Marine Science’s (AIMS) Dr Andrew Heyward explained how the researchers are collecting data where ships carrying scientists and a range of equipment will survey the seabed areas in the southern, central and northern Kimberley.  

“This work is the major field activity for the project and consists of five expeditions over the next couple of years. The first, undertaken last November, focussed on mapping the very large area contained within the boundaries of the recently declared Lalang -garram/Camden Sound Marine Park.”

“We mainly used acoustic mapping of depth and seabed shape using multibeam echo sounders combined with direct assessment of habitats on the seabed using towed video cameras,” Dr Heyward said.

Along with researchers from CSIRO and the WA Museum, the scientists will also work with Indigenous groups of the Kimberley coasts, including the sea rangers, who will provide additional information about shallow near shore areas.

“The initial survey has revealed very complex seabed shapes in some places, particularly close to island edges and narrow channels, where the extreme tides caused strong currents,” Dr Heyward said. “In those places the seabed was fairly hard, being either exposed rocky ground or pavement with a veneer of coarse sand.

Those sorts of places often supported low to medium density patches of filter feeding organisms like sponges and sea fans.”

High resolution photos also revealed very diverse life was often present on submerged rocks and ledges, but many of the organisms were small or encrusting. The researchers anticipate that many new species, both large and small, will be discovered once samples are identified back at the WA Museum.

In the northern part of the Lalang -garram/ Camden Sound Marine Park, an archipelago of islands provides a range of different habitats, including fringing reefs where, at low tide, abundant areas of coral can be seen exposed on the edges of the reef flats.

In contrast the deeper and more open bay areas of Camden Sound typically had fewer exposed rocky areas of seabed, but were frequently large areas of sand, including in a few places, large underwater sand dunes formed by the strong tidal currents.

“So the large open part of the Lalang -garram/Camden Sound zoned for whale sanctuary, is kind of like a big sandpit for them to frolic in,” Dr Heyward said.

Mixed brozoans soft corals sponges & seafans on rock

The researchers found that during spring the tidal currents caused increased turbidity, making camera work very challenging. The turbid water also greatly reduced the amount of light reaching the seabed.

“When we measured this it was quite common for little or no light to reach below depths of 10-15m below low tide,” Dr Heyward said. “This observation explains why organisms that rely on light for growth were not found in the broader parts of the bay which were typically 20-40m deep. So things like seaweeds and reef building corals tend to be close to the edges on hard rocky ground that is not too deep.”

A second expedition back to Camden Sound will commence this March. While further mapping of the seabed will continue, that expedition will also allow the scientists from AIMS, CSIRO and WA Museum, to collect samples of the biota. These samples will form the basis of the Kimberley project’s biodiversity reference collection at the WA Museum.

 

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley. 

 

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Kimberley Marine Research Program