A TOXIC microalgae has been confirmed as the cause of a large fish kill on the NSW South Coast which saw thousands of dead fish wash up on beaches in Jervis Bay last month. Residents reported dead and dying fish at a number of locations including Honeymoon Bay, Hare Bay and Callala Bay in early January. Fish affected by the kill included a large range of species and size classes including flathead, whiting, mullet, luderick and catfish.
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Test results by Industry & Investment NSW have revealed that Karlodinium micrum, a toxic microalgae, was present in sufficient excess quantities in water samples taken in and near the Carama Creek area.
Industry & Investment NSW (I&I NSW) Manager (Fisheries Ecosystems) Sarah Fairfull said the results confirmed earlier tests which showed a natural biological cause was most likely.
“I&I NSW has worked in conjunction with the Department of Environment, Climate Change and Water and Marine Parks Authority to ascertain the cause of this fish kill,” Ms Fairfull said.
“Harmful algae species do occur naturally in estuarine and marine environments.
“It is important to note that there is no link between the algae reported in the water samples and the macro green algae Microdictyon that has been reported in the bay previously. “
K. micrum is a dinoflagellate (microalgae) that occurs naturally in estuarine and brackish waters worldwide and is known to be toxic to fish and shellfish and has been linked to large fish kills in Australia and overseas, including Sydney Harbour (1991), Lake Illawarra (2000) and the Swan River in Perth (2003-2006 and 2010). Kills have also been reported in the US and the north west Mediterranean.
Densities of the microalgae can increase from mid summer to autumn and high densities can colour the water reddish-brown (referred to as a mahogany tide) and can leave an oily sheen on the surface in calm conditions. When the algae dies and its cells break down it releases toxins into the water.
The exact cause of the bloom in Jervis Bay is unclear, but is thought to have been due to nutrient rich ocean currents and warm, clear shallow water which provide ideal conditions for algae to grow.
No reports of dead fish have come from the area since January 14.
