THE ANNUAL CYCLE OF PLANKTONIC CILIATES IN NEARSHORE WATERS AT SIGNY ISLAND, ANTARCTICA

The abundance and biomass of marine planktonic ciliates in Borge Bay. Signy Island. were determined at monthly intervals between April 1990 and June 1991. At least 24 different ciliate taxa were recorded from s amples preserved in Lugol's iodine. including the tintinnids Codonello psis balechi, Cymatocylis convallaria, Laackmaniella naviculaefera and Salpingella sp., and the aloricate taxa Didinium sp. and Mesodinium r ubrum. Ciliate abundance and biomass exhibited a clear seasonal cycle with high values during the austral summer and low values in the austr al winter. Abundance ranged from 0.3 x 10(3) l-1 in September to 2.3 x 10(3) l-1 in January, while biomass ranged from 0.5 mug C l-1 in Octo ber to 12.6 mug C l-1 in December. Small ciliates dominated abundance throughout the year, and biomass during winter. Larger ciliates contri buted most to biomass during summer. Aloricate ciliates were common th roughout the year, while tintinnids contributed substantially to abund ance and biomass only during summer. Salpingella sp. was the commonest tintinnid, but C.convallaria contributed most to tintinnid biomass. T he seasonal pattern of ciliate abundance and biomass matched that of c hlorophyll a concentration and bacterial biomass, suggesting tight tro phic coupling between ciliates and other components of the pelagic mic robial community.