Extending from an earlier taxonomic survey of Pseudo-nitzschia species occurring in Australian water by Hallegraeff (1994), phytoplankton samples were collected from Tasmanian, South Australian, Victorian, New South Wales, Western Australian and Queensland marine and estuarine waters. Single cells of Pseudo-nitzschia spp. were isolated from samples and grown in culture. Using a combination of light microscopy, TEM, and rRNA fluorescent probes, cultures were identified and then tested for domoic acid production. Alternatively, preserved field samples were cleaned and observed using TEM.

This study has identified for the first time the presence ofPseudo-nitzschia australis (a known domoic acid producer) in Tasmanian, Victorian and New South Wales waters. The occurrence of P. multiseries at six sites along the New South Wales coast was noted. Other species identified include P. pseudodelicatissima, P. pungens, P. delicatissima, P. fraudulenta, P. subfraudulenta, P. subpacifica, P. heimii and P. cuspidata. The present survey confirmed earlier results that the dominant bloom-forming species in Australian waters are P. pseudodelicatissima and P. pungens. Preliminary analysis using ELISA has confirmed significant levels of domoic acid in extracts from all four P. australis cultures tested. Of the five P. pseudodelicatissima cultures tested, one produced detectable levels of domoic acid. No toxin was detected in any of the cultures of P. pungens, P. delicatissima and P. fraudulenta tested. Efforts to isolate cultures of P. multiseries have thus far been unsuccessful.

The regular presence in Southern Australian waters of low concentrations of P. australis and P. multiseries highlight the need for Pseudo-nitzschia and domoic acid monitoring programs to be set up in marine farm areas.