E‐mail: J.Laybourn‐Parry@nottingham.ac.ukAnnual plankton dynamics in an Antarctic saline lake

Abstract

Summary 1. The plankton dynamics of Ace Lake, a saline, meromictic basin in the Vestfold Hills, eastern Antarctica was studied between December 1995 and February 1997. 2. The lake supported two distinct plankton communities; an aerobic microbial community in the upper oxygenated mixolimnion and an anaerobic microbial community in the lower anoxic monimolimnion. 3. Phytoplankton development was limited by nitrogen availability. Soluble reactive phosphorus was never limiting. Chlorophyll a concentrations in the mixolimnion ranged between 0.3 and 4.4 μg L−−1 during the study period and a deep chlorophyll maximum persisted throughout the year below the chemo/oxycline. 4. Bacterioplankton abundance showed considerable seasonal variation related to light and substrate availability. Autotrophic bacterial abundance ranged between 0.02 and 8.94 × 108 L−−1 and heterotrophic bacterial abundance between 1.26 and 72.8 × 108 L−−1 throughout the water column. 5. The mixolimnion phytoplankton was dominated by phytoflagellates, in particular Pyramimonas gelidicola. P. gelidicola remained active for most of the year by virtue of its mixotrophic behaviour. Photosynthetic dinoflagellates occurred during the austral summer, but the entire population encysted for the winter. 6. Two communities of heterotrophic flagellates were apparent; a community living in the upper monimolimnion and a community living in the aerobic mixolimnion. Both exhibited different seasonal dynamics. 7. The ciliate community was dominated by the autotroph Mesodinium rubrum. The abundance of M. rubrum peaked in summer. A proportion of the population encysted during winter. Only one other ciliate, Euplotes sp., occurred regularly. 8. Two species of Metazoa occurred in the mixolimnion; a calanoid copepod (Paralabidocera antarctica) and a rotifer (Notholca sp.). However, there was no evidence of grazing pressure on the microbial community. In common with most other Antarctic lakes, Ace Lake appears to be driven by ‘bottom‐up’ forces.

Role of lipid in the life cycles of ice-dependent and ice-independent populations of the copepod Paralabidocera antarctica

“…In Ace Lake, diatoms are a small component of the phytoplankton assemblage (Burch 1988, Bell & Laybourn-Parry 1999, consistent with the observation that 16:1(n-7) was a minor component (3 to 9%) of the fatty acid profile of the lacustrine population. The 16:1/16:0 ratio was always much less than 1 (0.22 to 0.35), indicating that other, non-diatom species were more important in the diet of lacustrine Paralabidocera antarctica.…”

“…Alternative food sources include the benthic algal mats which fringe the lake; however, nothing is known about the contribution of this material to the diet of Paralabidocera antarctica. The 4 dominant protists present in the oxic zone of the water columnPyramimonas gelidicola, Mesodinium rubrum, an unidentified microflagellate possibly belonging to the family Prymnesiophyceae, and an unidentified cryptomonad -have a vertically stratified distribution as a response to gradients in light levels and nutrient concentrations (Burch 1988, Bell & Laybourn-Parry 1999). An unarmoured dinoflagellate has also been recorded, although in low abundances (Burch 1988).…”

“…Common phytoplankton species present in Ace Lake include Pyramimonas gelidicola, an unidentified cryptomonad, and an unidentified prymnesiophyte (Burch 1988, Bell & Laybourn-Parry 1999, and these species could contribute to the copepods' diet. P. gelidicola is high in 16:4 and 18:3, with less 18:4 fatty acids, while cryptomonads are high in 18:4 and 18:3, with less 16:4 (Volkman et al 1989, Skerratt et al 1995.…”

Adaptation and Acclimation of Photosynthetic Microorganisms to Permanently Cold Environments

“…Phytoplankton populations employ a number of survival mechanisms for winter survival, such as mixotrophy, cyst formation, and breakdown of metabolic reserves, such as starch (12). One of the keys to survival of the microorganism populations in the dry valley Antarctic lakes is to enter the short summer season with an actively growing population (119).…”

Life cycle plasticity and differential growth and development in marine and lacustrine populations of an Antarctic copepod

“…It is uncertain whether the patterns we observed in Ace Lake, including the January mass mortality, also occur in the other lacustrine populations. One other study that examined the P. antarctica distribution in Ace Lake also observed the presence of most stages throughout the year and recorded a decline in abundance of nauplii and copepodites in late January (Bell and Laybourn-Parry 1999).…”