DISTRIBUTION AND ABUNDANCE OF POSTLARVAL AND JUVENILE PLEURAGRAMMA-ANTARCTICUM (PISCES, NOTOTHENIIDAE) OFF TERRA-NOVA BAY (ROSS SEA, ANTARCTICA)

During the Italian Antarctic Expedition of 1987-1988 zooplankton was c ollected in Terra Nova Bay (Ross Sea) by a multinet BIONESS (250-mu m or 500-mu m net mesh size). The early life history of Pleuragramma ant arcticum was described from 268 samples. More than 98% of a total of 3 4,436 fish larvae belonged to P. antarcticum. The mean relative abunda nce in the whole area for positive 0 to 150-m hauls was 434 ind./100 m (3) (+/-720 SD). Postlarvae were most abundant and frequent in the sam ples (99.8%) while low concentrations of juveniles were found (n = 67) . Length of age group 0 ranged from 8 to 20 mm and age group 1+ were f rom 36 to 53 mm. Average growth rate over a period of 1 year was 0.08 mm per day. Based on modal values, the mean daily increment of P. anta rcticum postlarvae in the period 5 January to 2 February (29 days) was about 0.21 mm. Highest abundances occurred near Cape Washington (mean : 2,108 ind./100 m(3)) while lower densities were recorded in the nort hern basin of the self (31 ind./100 m(3)). Horizontal and vertical dis tribution patterns in Terra Nova Bay seem to be strictly correlated to hydrographic features and different water masses with highest densiti es associated with the westward flowing current of the limb of the Ant arctic coastal current and southern limb of the Ross Sea Gyre. These c urrents become part of the clockwise gyre in Terra Nova Bay. More than 62% of the postlarvae were collected in well-stratified warm surface water (0-50 m) near the summertime thermocline (20-70 m). The northern part of Terra Nova Bay seems to represent nursery ground of early sta ges of P. antarcticum and the presence of permanent polynya could prov ide favourable food conditions for development of the first stages of life. Differing distribution patterns probably reflect an interaction of various parameters including bathymetry, floating ice shelf, hydrog raphic features such as currents, local eddies and frontal systems, wi th P. antarcticum postlarval biology (spawning) and ecology (feeding, horizontal and vertical distribution patterns).