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 i n 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 conce ntrations (<5 cells L-1) in mid summer and mid winter. Abundances were grea ter in coastal waters than in the estuaries during all months in which conc entration exceeded 1 cell L-1. During the spring bloom, Noctiluca cells fro m coastal stations had small diameters (340-450 mu m), a high nutritional s tatus and a high proportion of division stages, indicative of good conditio n. During the late summer blooms, poor-condition cells were found in coasta l waters and especially in the near-surface concentrations of red tides (>1 0(4) cells L-1), and were characterized by large diameters (400-1200 mu m), cell lysis and uniformly low nutritional status; at this time, Noctiluca c ells from estuaries were generally fewer, smaller and in better condition. Overall, cell concentrations were higher in coastal waters than in the estu aries, and red tides of Noctiluca probably developed along the local coast (in spring) or were advected into the area from northern regions (in late s ummer).