Vicki Laurie Australian Geographic 16 Sep 10;
Photo of Lyngbya outbreak from Seagrass-Watch Magazine Issue 40 March 2010.
OFF THE COAST OF BROOME, snaking trails are visible at low tide through glistening seagrass meadows. The pathways are a sign that a family of dugongs has swum through the area, pushing through the grassy seabed and grazing on a smorgasbord of tender shoots and roots.
Thriving seagrass meadows are vital for these hefty aquatic mammals, which can eat up to 40 kg of plant matter a day. Fiona Bishop, coordinator of the Broome Community Seagrass Monitoring Project, says dugongs (Dugong dugon) are regular visitors to Broome's Roebuck Bay, a Ramsar-listed wetland with extensive seagrass beds.
"We're lucky to have such low tides so we can walk out and see dugong trails everywhere, sometimes zigzagging back and forth. Two of the dugongs' favourite species of seagrass grow here, and they eat the whole plant, roots, flowers and seeds."
As well as 'mowing' the grass, the dugongs help disperse the seed widely when they expel their waste into the water
But the health of seagrass is this year threatened by an outbreak of toxic blue-green algae, called Lyngbya majuscula, which scientists say the will study in coming weeks to establish whether Roebuck Bay's dugongs, famous migratory bird flocks and marine invertebrates are affected.