Annually recurrent diatom blooms in spring along the New South Wales coast of Australia

Abstract

Blooms of phytoplankton (100-280 mg chlorophyll a m^-1) occur on the continental shelf off Sydney in the spring of most years. These sudden chlorophyll increases (more than 10 times the normal algal biomass) are due to short-lived diatom blooms that evolve in a predictable sequence from small chainforming species (Nitzschia, Thalassiosira) to large centric species (Lauderia, Rhizosolenia) and eventually to large dinoflagellates (Protoperidinium). Two research cruises (October 1981, September 1984) were conducted to define the longshore extent of this phenomenon. Diatom blooms were widespread along the whole New South Wales coastline, occurring in the 700-km-long region from Cape Hawke in the north (32°S), where the East Australian Current separates from the coast, to Maria Island off Tasmania in the south (43°S). Hydrological mechanisms of these annually recurrent enrichments are related to the action of the East Australian Current and are unlike those triggering spring blooms in temperate European waters. Implications of these diatom blooms for coastal fisheries along the New South Wales coast are briefly discussed.