Population ecology of Noctiluca scintillans Macartney, a red-tide-forming dinoflagellate

The population ecology of the large heterotrophic dinoflagellate Noctiluca scintillans Macartney was examined in the coastal ocean and two estuaries in south-eastern Australia from July 1996 to June 1997. High concentrations (>100 cells L–1) occurred in spring and again in late summer, and low concentrations (<5 cells L–1) in mid summer and mid winter. Abundances were greater in coastal waters than in the estuaries during all months in which concentration exceeded 1 cell L–1. During the spring bloom, Noctiluca cells from coastal stations had small diameters (340–450 µm), a high nutritional status and a high proportion of division stages, indicative of good condition. During the late summer blooms, poor-condition cells were found in coastal waters and especially in the near-surface concentrations of red tides (>104 cells L–1), and were characterized by large diameters (400–1200 µm), cell lysis and uniformly low nutritional status; at this time, Noctiluca cells from estuaries were generally fewer, smaller and in better condition. Overall, cell concentrations were higher in coastal waters than in the estuaries, and red tides of Noctiluca probably developed along the local coast (in spring) or were advected into the area from northern regions (in late summer).