Winter distribution and overwintering strategies of the Antarctic copepod species Calanoides acutus,Rhincalanus gigas and Calanus propinquus (Crustacea,Calanoida) in the Weddell Sea

During the Winter Weddell Gyre Study in September–October 1989, the horizontal and vertical distribution, stage composition and feeding condition of the three antarctic copepod species Calanoides acutus, Rhincalanus gigas and Calanus propinquus were studied. The data indicate that C. acutus and R. gigas have the bases of their distributional ranges (sensu Makarov et al. 1982) in the Antarctic Circumpolar Current (ACC) and in the Warm Deep Water (WDW) entering the Weddell Gyre (WG). C. propinquus lived mainly in the cold WG south of the ACC. C. acutus overwintered mainly in the WG as stage IV copepodites (C). The species mainly inhabited the layers below the T_max stratum and down to 2000 m, but C V and females occurred slightly higher than C III and IV. Males prevailed over females and were confined to a rather narrow layer between 500 and 1000 m. Feeding experiments suggested all deep-living stages to be resting. However, if this species spawns in late autumn the younger C I–II can stay in the Winter Water (WW). R. gigas inhabited mainly the T_max stratum. In the eastern part of the WG, R. gigas breed in the WDW in autumn and hibernate as C I–III and C V–VI in the first and second winter, respectively. In the ACC zone, however, its life cycle is different and winter breeding of overwintered adults occurs. Most of the C. propinquus population overwintered in the WG as C III–V, inhabiting the WW. In the upper water layers in the interior of the WG, C III dominated with upto 18,000 individuals 1,000 m³. Shallow living C. propinquus were in the active, feeding state. Persistence of active feeding zooplankton populations in the WW of the WG can be an important factor influencing processes of phytoplankton development and the particle flux.