The genus Pseudo‐nitzschia (Bacillariophyceae) in New Zealand: analysis of the last decade's monitoring data

Abstract

The diatom genus Pseudo‐nitzschia blooms throughout New Zealand's coastal waters. More than a decade of monitoring data were analysed in this study and seasonality was a significant factor in the appearance of Pseudo‐nitzschia blooms. Austral spring and summer were the main bloom periods, although there were regional differences. Between January 2000 and August 2011, 8.4% of 29,000 seawater samples analysed for Pseudo‐nitzschia exceeded the voluntary trigger level for biotoxin testing (10×10 4 cells l −1 ), and these were analysed by fluorescent in situ hybridisation (FISH) assays. Pseudo‐nitzschia fraudulenta and P. pseudodelicatissima (low domoic acid [DA] producers) were the dominant bloom formers throughout New Zealand (each contributing 25%) followed by the highly toxic P. australis (10%). Shellfish flesh testing for DA was triggered on 8477 occasions between 2000 and 2011, but no samples exceeded the regulatory limit (20 mg/kg); the maximum concentration was 13 mg/kg (Marlborough Sounds, mid‐winter 2010).

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