Identification and seasonal occurrence of potentially toxic Pseudo-nitzschia diatoms in oyster growing estuaries of New South Wales, Australia

Species belonging to the potentially toxic diatom genus Pseudo-nitzschia are a significant component of the phytoplankton community in south-east Australian waters. Toxigenic representatives of this genus produce domoic acid and are responsible for the majority of regulatory exceedances in New South Wales (NSW) oyster-growing estuaries. This toxic genus has been implicated in 6 toxic events during the sampling period 2005-2009 (max. concentration of 34 mg DA kg^-1 oyster tissue). However, identification to species level is difficult and requires both electron microscopy and molecular techniques for unambiguous identification. Detailed analyses revealed 10 different species in NSW coastal waters, Pseudo-nitzschia americana, P. arenysensis, P. calliantha, P. cuspidata, P. fraudulenta, P. hasleana, P. micropora, P. multiseries, P. multistriata and P. pungens, including two confirmed domoic acid producers, P. cuspidata (25.4 pg DA cell^-1) and P. multistriata (11 pg DA cell^-1). Species diversity and the seasonal occurrence of regulatory Pseudo-nitzschia groupings have important implications for monitoring and management of shellfish harvest areas in NSW. The ubiquitous species, Pseudo-nitzschia cuspidata, represents the greatest challenge for coastal shellfish culture in NSW.