TEMPORAL PATTERNS OF PROTOZOOPLANKTON ABUNDANCE AND THEIR FOOD IN ELLIS FJORD, PRINCESS-ELIZABETH-LAND, EASTERN ANTARCTICA

The abundance and biomass of ciliates, dinoflagellates and heterotroph ic and phototrophic nanoflagellates were determined at three sites alo ng an ice-covered Antarctic fjord between January and November 1993. T he water column showed little in the way of temperature and salinity g radients during the study period. In general, the protozooplankton exh ibited a seasonal variation which closely mirrored that of chlorophyll a and bacterioplankton. The fjord mouth, which was affected by the gr eatest marine influences, consistently had the highest densities of ci liates and the most diverse community, with up to 18 species during th e sampling period. Small aloricate ciliates were present throughout th e year with Strobilidium spp. being dominant during the winter. Larger loricate and aloricate ciliates became more prominent during January and November, along with the autotrophic ciliate Mesodinium rubrum and two mixotrophic species (Strombidium wulffi and a type resembling Ton tonia) suggesting evidence of species successions. Data on dinoflagell ates were less extensive, but these protists showed greatest species d iversity in the middle reaches of the fjord. A total of 13 species of dinoflagellate was recorded. Ciliates made a significant contribution to the biomass of the microbial community in summer, particularly in t he middle and at the seaward end of the fjord. In winter, heterotrophi c flagellates (HNAN) and phototrophic nanoflagellates (PNAN) were the dominant component of protistan biomass. In terms of percentage contri bution to the microbial carbon pool, bacteria dominated during winter and spring. To the authors' knowledge, this is the first seasonal stud y of an Antarctic fjord. The Ellis Fjord is very unproductive compared to lower latitude systems, and supports low biomass of phytoplankton and microbial plankton during most of the year. This relates to severe climatic and seasonal conditions, and the lack of allochthonous carbo n inputs to the system. Thus, high latitude estuaries may differ signi ficantly from lower latitude systems, which generally rank among the m ost productive aquatic systems in the world. (C) 1997 Academic Press L imited.