Characterising the 2002 toxic Karenia concordia (Dinophyceae) outbreak and its development using satellite imagery on the north-eastern coast of New Zealand

In spring 2002 there was a significant outbreak of harmful microalgal bloom (HAB) in Hauraki Gulf on the north-eastern coast of New Zealand. With the exception of only a few sites where there was also a build-up of Noctiluca scintillans, the outbreak was largely associated with an almost monospecific bloom of Karenia concordia. At the peak of this bloom, mortalities of fish and abalone were observed. In areas where Noctiluca cells were found dead they had consumed large numbers of K. concordia cells. Laboratory tests showed cell extracts of K. concordia to be haemolytic and cytotoxic and confirmed that this species was responsible for marine life mortality. Satellite sea surface temperature (SST) data, obtained prior to the mid-October 2002 toxic outbreaks in Hauraki Gulf, showed signs of strong, along-shelf upwelling and also cross-shelf advection of warm, offshore, subtropical water into the Gulf through Jellicoe Channel. Time-series ocean colour data retrieved from the same region showed build-up of very high chlorophyll a level in Hauraki Gulf, virtually in same areas where bloom proportions of K. concordia (up to 3.3 × 10⁷ cells l^?1) were recorded. The relationships of this massive bloom to contemporaneous, remotely sensed SST and ocean colour satellite data (SeaWiFS) during the cold phase of ENSO are discussed.