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How are the seagrasses faring?

Play  Sharon Ferguson reports on the seagrasses of Roebuck Bay
  sharon ferguson seagrass.mp3  
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Sharon Ferguson, who heads the Nature Conservation Unit of the Department of Environment and Conservation in Broome, looks at some of the impacts on sea grass at Roebuck Bay.     
The sea grass on Roebuck Bay grows mainly to less than 10cm tall and is a significant food source for dugongs, turtles and juvenile fish as well as being important as a nursery for some fish. The sea grass is present along the intertidal zone at Roebuck Bay.

There are two main types. One is oval shaped, Halophila ovalis and one is a strap sea grass (think blade of grass), Halodule uninervis. The seagrass are covered by water at high tide and at low tide it can be seen if you look on the mudflats, along Roebuck Bay the tide variations are up to 10m.

Haolphila ovalis (oval shaped leaf), Halodule uninervis (strap leaf), Lyngbya with feeding trail.    

Roebuck Bay is listed as a Ramsar wetland of international significance. The Roebuck Bay sea grasses seem to be healthy but are potentially under some threats associated with their proximity to an urban centre. In recent years a blue-green algae, Lyngbya, has occasionally appeared on the sea grass, although what causes it is unknown. It has been known to smother sea grass in other areas of Australia and may be toxic at certain stages of its lifecycle. So far the Lyngbya found in Roebuck Bay has not been identified as toxic.

Lyngbya in clumps     

A monitoring program for Lyngbya is in place and aims to form a picture of when, when and why the Lyngbya appears in the Bay. Generally the Lyngbya seems to bloom mostly in the wet season and can often be found in large clumps. These clumps are mostly broken down and scattered by the huge tides but among the mangroves and on the mudflats may create an unpleasant and smelly eyesore as well as potentially impacting on the flora and fauna on the Bay.
The Roebuck Bay Working Group, a local community organisation, is developing a Lyngbya Contingency Plan which aims to engage the local stakeholders and work out a response plan to potential Lyngbya blooms. Environs Kimberley hosts a community sea grass coordinator, who coordinates an ongoing program to monitor the sea grass and providing information to stakeholders, land managers and this information is lodged and managed through Seagrass- Watch, a QLD based organisation.

Text: V.B. September 2009

Images from Sharon Ferguson

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