Temporal abundance patterns of the red tide dinoflagellate Noctiluca scintillans along the southeast coast of Australia

Noctiluca scintillans was seasonally abundant during the austral spring and summer with typical values of 16 cells l–1, but depleted in autumn and winter, with values of <1 cell l–1. Peaks in abundance of up to 79 cells l–1 were observed, at the same time or subsequent to diatom blooms which were caused by episodic uplifting events during the spring and summer. The diatom blooms were dominated by the small centric diatom Thalassiosira partheneia, which was also the dominant food item found within the Noctiluca cells. A high proportion (>80%) of Noctiluca cells contained food particles in their vacuoles during the diatom blooms, suggesting that the increase in abundance of Noctiluca was most likely stimulated by food availability. Pulses of small-sized Noctiluca cells during the diatoms blooms were indicative of this population growth. The δ15N isotopic similarity of the red tide cells collected from spatially and temporally distant water masses suggests that the prey of Noctiluca were derived from a single nutrient source, most likely uplifted slope water. This study shows that the predominant underlying mechanism regulating population growth of Noctiluca along the southeast coast of Australia is the uplifting of nutrient-rich slope water. The uplifting events stimulate phytoplankton blooms which in turn stimulate Noctiluca blooms.