Changes in Phytoplankton Biomass and Nutrient Quantities in Sea Ice as Responses to Light/Dark Manipulations during different Phases of the Baltic Winter 2003

The response of Baltic Sea ice communities to changing light climate was studied in three subsequent 3 week in situ experiments on the SW coast of Finland. The investigation covered three different winter periods, short day with low solar angles leading to limited light in the ice, late winter with deep snow cover and early spring with melting snow and increasing light availability. The experimental setup consisted of transparent (no snow) and completely darkened (heavy snow cover) plexiglass tubes in which the ice cores were incubated in situ from 1 to 2 weeks. Changes in the concentrations of inorganic nutrients (NO₃⁻-–N, PO₄³⁻-–P, SiO₄⁻-–Si) and chlorophyll-a concentration in the phytoplankton community composition were recorded as responses to different light manipulations. Changes in inner ice light intensity in untreated ice as well as the temperature both in air and ice were recorded over the entire study period. Increased irradiance in late winter/early spring and during meltdown affected the chlorophyll-a amount in the sea ice. During these periods the phytoplankton community in the top layers decreased possibly as a consequence of photo-acclimation. Closer to the bottom of the ice, however, the increased inner ice light intensity induced algal growth. Complete exclusion of light stopped the algal growth in the whole ice column. Darkening the ice cores also slowed down the ice melting opposite to accelerated melting caused by increased light. The significant differences found in nutrient concentrations between the light and dark treatments were mostly explicable by changes in algal biomass. No obvious changes were observed in the phytoplankton community composition due to light manipulation, diatoms and heterotrophic flagellates dominating throughout the study period.     

Vertical distribution of organic constituents in an Antarctic lake: Lake Fryxell

Vertical distribution of organic constituents, i.e. total organic carbon (TOC), hydrocarbons, fatty acids and hydroxy acids in water and sediment samples from Lake Fryxell (77° 35 S, 163° 15 E) of southern Victoria Land, Antarctica were studied to elucidate their features in relation to stratification of the lake waters and likely distribution of microorganisms. The TOC content of the surface water (5.0 m; just below the ice cover of 4.50 m thickness) was 1.4 mg l^–1. It increased markedly with depth and attained a maximum value of 21.7 mg C l^–1 at a depth of 17.5 m, but decreased to the bottom (13.3 mg C l^–1). The high TOC content of the anoxic bottom layers (> 15 m) is attributable to the concentration of refractory organic substances over long periods following the degradation of labile organic constituents. Hydrocarbons were not found in the water column, but the major constituent of the bottom sediment was n-C_{29 : 2} alkene. Total concentrations of fatty acids in the oxic layers ( 10 m) were highest at 10.0 m and much higher than those in the anoxic layers (> 10 m), probably reflecting the phytoplankton population. The content of branched (iso and anteiso) fatty acids and 3-hydroxy acids in the anoxic layers were much greater than those in the oxic layers which would seem to reflect the distribution of bacterial abundance. The differences of organic composition between the water column and sediments imply that sinking dead organisms were quickly degraded in the lake bottom. Also, the composition of microorganisms in the water column must be very different from that in the sediments.     

Protozooplankton in the Weddell Sea,Antarctica: Abundance and distribution in the ice-edge zone

Summary Protozooplankton were sampled in the iceedge zone of the Weddell Sea during the austral spring of 1983 and the austral autumn of 1986. Protozooplankton biomass was dominated by flagellates and ciliates. Other protozoa and micrometazoa contributed a relatively small fraction to the heterotrophic biomass. During both cruises protozoan biomass, chlorophyll a concentrations, phytoplankton production and bacterial biomass and production were low at ice covered stations. During the spring cruise, protozooplankton, phytoplankton, and bacterioplankton reached high concentrations in a welldeveloped ice edge bloom 100 km north of the receding ice edge. During the autumn cruise, the highest concentrations of biomass were in open water well-separated from the ice edge. Integrated protozoan biomass was <12% of the biomass of phytoplankton during the spring cruise and in the autumn the percentages at some stations were >20%. Bacterial biomass exceeded protozooplankton biomass at ice covered stations but in open water stations during the fall cruise, protozooplankton biomass reached twice that of bacteria in the upper 100m of the water column. The biomass of different protozoan groups was positively correlated with primary production, chlorophyll a concentrations and bacterial production and biomass, suggesting that the protozoan abundances were largely controlled by prey availability and productivity. Population grazing rates calculated from clearance rates in the literature indicated that protozooplankton were capable of consuming significant portions of the daily phyto- and bacterioplankton production.     

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

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.     

Water temperature and stratification depth independently shift cardinal events during plankton spring succession

In deep temperate lakes, the beginning of the growing season is triggered by thermal stratification, which alleviates light limitation of planktonic producers in the surface layer and prevents heat loss to deeper strata. The sequence of subsequent phenological events (phytoplankton spring bloom, grazer peak, clearwater phase) results in part from coupled phytoplankton–grazer interactions. Disentangling the separate, direct effects of correlated climatic drivers (stratification‐dependent underwater light climate vs. water temperature) from their indirect effects mediated through trophic feedbacks is impossible using observational field data, which challenges our understanding of global warming effects on seasonal plankton dynamics. We therefore manipulated water temperature and stratification depth independently in experimental field mesocosms containing ambient microplankton and inocula of the resident grazer Daphnia hyalina. Higher light availability in shallower surface layers accelerated primary production, warming accelerated consumption and growth of Daphnia, and both factors speeded up successional dynamics driven by trophic feedbacks. Specifically, phytoplankton peaked and decreased earlier and Daphnia populations increased and peaked earlier at both shallower stratification and higher temperature. The timing of ciliate dynamics was unrelated to both factors. Volumetric peak densities of phytoplankton, ciliates and Daphnia in the surface layer were also unaffected by temperature but declined with stratification depth in parallel with light availability. The latter relationship vanished, however, when population sizes were integrated over the entire water column. Overall our results suggest that, integrated over the entire water column of a deep lake, surface warming and shallower stratification independently speed up spring successional events, whereas the magnitudes of phytoplankton and zooplankton spring peaks are less sensitive to these factors. Therefore, accelerated dynamics under warming need not lead to a trophic mismatch (given similar grazer inocula at the time of stratification). We emphasize that entire water column dynamics must be studied to estimate global warming effects on lake ecosystems.     

Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica)

The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 g l^–1 . Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 mol l^–1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation.     

Some aspects of the seasonal distribution of flagellates in mountain lakes

In a larger regional survey in Tyrol, phytoplankton species composition and biovolume of mid-altitude and high-mountain lakes was studied. Results from eight lakes showed that flagellates (mainly Chrysophyceae, Dinophyceae, and Cryptophyceae) are important components of the phytoplankton.In the mid-altitude lakes a spring and an autumn maximum of Chrysophyceae as well as a summer maximum of large dinoflagellates are observed, whereas Cryptophyceae and Dinophyceae show irregular distributions. In the high-mountain lakes the seasonal variations of phytoplankton, including flagellates, are limited by the long duration of the winter situation. However similar sequences of phytoplankton assemblages as in the midaltitude lakes can be observed. Flagellates in high-mountain lakes are important to sustain phytoplankton standing crop under the winter snow and ice cover.In order to show similarities and differences of high-mountain and mid-altitude lakes, vertical profiles of phytoplankton from three lakes and seasonal patterns of Gymnodinium uberrimum from two lakes are compared. In addition the patterns of cryptomonads differing in their ecological requirements (Cryptomonas spp. and Rhodomonas minuta) are shown for a meromictic mid-altitude lake.     

Overwintering populations of Mesodinium rubrum (Ciliophora: Haptorida) in lakes of the Vestfold Hills, East Antarctica

 The autotrophic ciliate Mesodinium rubrum Lohmann was observed during winter and spring in saline lakes ranging in salinity from 2 to 78‰ in the Vestfold Hills, Antarctica. The ciliate remained active during winter, and contained chlorophyll even though the level of light available for photosynthesis was minimal. No evidence of encystment as a means of survival during winter was observed. A seasonal study in one of the lakes, Ace Lake, revealed that M. rubrum was present throughout the year at abundances ranging from 1×10⁴ to 3.5×10⁵ cells l^-1. During the winter period, when little light penetrated the lake’s ice cover, cells were most common immediately under the ice at 2 m, where cell numbers were typically 8×10⁴ cells l^-1. Received: 3 January 1996/Accepted: 21 April 1996     

Summer phytoplankton succession in Ellis Fjord, eastern Antarctica

Spring phytoplankton communities in the water column of EllisFjord are characterized by diatoms originating from the bottomsea-ice strand community. Upon ice breakout in early summer,these are replaced by blooms of the phytoflagellates, Phaeocystispouchetii, Cryptomonas cryophila, Pyramimonas gelidicola, silicoflagellatcsand dinoflagellates. The narrow entrance of the fjord and thedevelopment of summer stratification is probably limiting theavailability of nutrients and containing the magnitude of thesmall bloom (maximum 2.8 10⁶ cells l^–1).     

The primary production of phytoplankton in Lake Vechten

The primary production of the phytoplankton of Lake Vechten (The Netherlands) (area, 4.7 ha; mean depth, 6 m), an unpolluted and stratified sandpit was investigated from 1969 to 1980 (except in 1971, 1975 and 1976) by the in situ ¹⁴C-technique. Other data collected include: solar radiation, transparency, oxygen and thermal structure. In winter and spring diatoms, Cryptophyceae and Chlorococcales were important algal groups, while in summer Dinophyceae and Chrysophyceae were important. The chlorophyll-a concentration was compared to the cellular biovolumes (= fresh weight) of the most abundant phytoplankton species. The primary production maxima occurred in winter, spring and during the summer stratification. The vertical profiles of photosynthesis exhibit light inhibition at surface to a maximum of 4 m. The maximum of zooplankton grazing in May–June caused a sharp decrease in the phytoplankton biomass and seston concentration accompanied by the highest transparency (clear water phase).The values for cellular C-fixation range from 10 to 1307 mg C · M^–2 · day^–1 (annual mean of 280 mg C · m^–2 · day^–1). High dark fixation (up to 100%) was encountered in the metalimnion and hypolimnion from July to October together with peaks of ¹⁴C-fixation due to a crowding of phytoplankton and phototrophic anoxic bacteria. Extracellular excretion by phytoplankton, investigated in 1977 to 1979, was 15% of the annual mean of the total C-fixation. The photosynthetic efficiency, turnover rates, and activity coefficients were low, particularly in the summer months when Ceratium hirundinella was predominant. The seasonal variations were controlled mainly by solar radiation and probably phosphate, the former being more important in the non-stratification period and the latter during the stratification period.     

The phytoplankton of Lake Liddell,New South Wales: chlorophyll a concentrations,species seasonal succession,and covariation with nutrients

Samples of the phytoplankton in a freshwater lake, Lake Liddell, New South Wales (Lat: 32° 22 S, Long. 150° 1 E) were collected every 4 weeks between October 1987 and November 1988. Chlorophyll a concentrations ranged from 1.8 g 1^–1 to 9.1 g 1^–1 and were positively correlated with the following nutrient parameters: total and nett mass additions of nitrate/nitrite-N and total-N, total additions of Kjeldahl-N, and nett mass addition N-P ratios. There was no correlation between lake nutrient concentrations and chlorophyll a. Factors other than nutrient concentrations appeared to be effecting chlorophyll a concentrations as summer levels were low despite nutrient concentrations being at a maximum. In spring and summer the phytoplankton was dominated by chlorophytes, with dinoflagellates and diatoms most abundant in autumn. During winter cyanobacteria were the most abundant. The relative abundance of chlorophytes was positively correlated with in lake nitrate/nitrite-N concentrations whereas the relative abundance of cyanobacteria was negatively correlated with this parameter. Based on chlorophyll a concentrations and the phytoplankton flora Lake Liddell can be classified as mesotrophic.     

Annual primary productivity of an antarctic continental lake: Phytoplankton and benthic algal mat production strategies

Primary production in Watts Lake, Vestfold Hills, Antarctica (68°36S, 78°13E), was measured from March 1981 to February 1982. Phytoplankton production peaked in autumn and spring, with a September maximum (340 mgC m^–2 d^–1), then declined in summer and was not detectable in winter. Benthic algal production peaked in summer at 74 mgC m^–2 d^–1), Production strategies differed, with the more efficient phytoplankton adapted to growth at low light, while benthic production increased with increasing light in summer. Estimation of annual production was 10.1 gC m^–2 and 5.5 gC m^–2 for the phytoplankton and benthos respectively.     

Risk reduction strategies in <Emphasis Type="Italic">Branchipus schaefferi</Emphasis> (Crustacea: Anostraca: Branchiopoda) as adaptation to a variable environment

The effect of long-term changes in total precipitation on physical and chemical parameters of the water and the structure of phytoplankton community during a year were studied in a deep hard water lake. With respect to total precipitation, two different periods were distinguished: dry and wet. In the wet period, the water level rose and caused an increase in the water colour and a decrease in the electrolytic conductivity and concentration of nutrients. These changes were reflected in the composition and amount of phytoplankton. Certain phytoplankton groups, e.g. Cryptophyceae, Dinophyceae, Chrysophyceae, Bacillariophyceae and Chlorophyta/Charophyta, were positively affected by the environmental changes; instead, these effects were not observed in Cyanobacteria and Euglenophyta. The development of flagellates, such as Cryptomonas curvata, Plagioselmis nannoplanctica and Ceratium hirundinella, was enhanced during the wet period, whereas the dry period favoured non-flagellates, such as Planktothrix agardhii, Planktothrix rubescens and Limnothrix planctonica. Hence, the long-term variability in total precipitation can be a switch from non-flagellate- to flagellate-dominated phytoplankton in lakes. Moreover, a short time of ice cover duration in winter linked with the wet period promoted phytoplankton groups typical for spring and autumn, e.g. Cryptophyceae and Bacillariophyceae.     

Phytoplankton dynamics in the stratified water column of Lake Bonney,Antarctica

Phytoplankton populations in perennially ice-covered Lake Bonney, Antarctica grow in a unique non-turbulent environment. The absence of turbulence generated by winds or major streams, combined with strong vertical gradients in temperature and nutrients, create vertically stratified environmental conditions that support three discrete phytoplankton populations in the east lobe of this lake. Phytoplankton biomass and photosynthesis were measured in the east lobe of Lake Bonney during the winter-spring transicion (September) to mid-summer (January). During this period, irradiance beneath the ice increased from 0.03 to 1.9 mol quanta m⁻² d⁻¹. Chlorophylla concentrations ranged from 0.03 to 3.8 μl⁻¹ within the trophogenic zone (just beneath the permanent ice cover to 20 m) and photosynthesis ranged from below detection to 3.2 μg Cl⁻¹ d⁻¹. Our results indicate: (1) phytoplankton photosynthesis began in late winter (before 9 September, our earliest sampling date); (2) maxima for phytoplankton biomass and production developed sequentially in time from the top to the bottom of the trophogenic zone, following the seasoral increase in irradiance; and (3) the highest photosynthetic efficiencies occurred in early spring, then decreased over the remainder of the phytoplankton growth season. The spring decrease in photosynthetic rates for shallower phytoplankton appeared to be related to nutrient availability, while photosynthesis in the deeper populations was solely lightdependent.     

Comparative seasonal changes,and inter-annual variability and stability,in a 26-year record of total phytoplankton biomass in four English lake basins

Long-term sequences of total phytoplankton biomass are described and analysed in relation to environmental conditions and species composition. They are based on largely weekly sampling of mean concentrations of chlorophyll a ([Chl]) in the euphotic zones of four English lake basins over 26 years. More restricted sampling is used to illustrate the regulation of vertical distribution, and a comparison with several chemical indices of seston abundance.The seasonal variation of [Chl] is predominantly constructed from two peaks in spring and summer-autumn. These are separated by a universal and light-limited winter minimum that is accentuated in the deeper basins and a more variable early summer minimum to which diatom sedimentation, species replacement and grazing by Cladocera contribute. In some years or year-sequences additional peaks of varied origin may be interpolated (frequency modulation), especially in the shallower basins. Some variability of maxima with nutrient enrichment and particular species-crop failure or success (e.g. Ceratium spp.), and of minima with growth limitation, loss modes and species replacement, exists within and between basins (amplitude modulation).Depth-colonization is primarily controlled by restrictions on vertical mixing associated with the seasonal temperature/density stratification. Relative timings can be important for areal biomass development. Though [Chl] is mainly epilimnetic in summer, metalimnetic and hypolimnetic accumulations can also arise by growth in situ, flagellate migration, or sedimentation. Variations in the content of Chl below unit area, for entire lake column or euphotic zone, are less sensitive to trophic state than are mean euphotic concentrations because of compensating influences of morphometry and light penetration.Correspondences exist between temporal sequences of [Chl] and some chemical components of seston (C, N, reducing capacity), but ratios to P show much variation.Comparison is made with other observations of seasonal phytoplankton biomass, with reference to latitudinal influence and to proposed generalisations regarding seasonal pattern.     

Phytoplankton distribution in relation to sea ice,hydrography and nutrients in the northwestern Weddell Sea in early spring 1988 during EPOS

Summary Phytoplankton biomass and distribution of major phytoplankton groups were investigated in relation to sea ice conditions, hydrography and nutrients along three north-south transects in the north western Weddell Sea in early spring 1988 during the EPOS Study (European Polarstern Study), Leg 1. Three different zones along the transects could be distinguished: 1) the Open Water Zone (OWZ) from 58° to 60°S with high chlorophyll a concentrations up to 3.5 g l^–1; 2) the Marginal Ice Zone (MIZ) from 60° to about 62.5° with chlorophyll a concentrations between 0.1 and 0.3 g l^–1, and 3) the closed pack-ice zone (CPI) from 62.5° to 63.2°S with chlorophyll a concentrations below 0.1 gl^–1. Nutrient concentrations increased towards the south showing winter values under the closed pack-ice. Centric diatoms such as Thalassiosira gravida and Chaetoceros neglectum forming large colonies dominated the phytoplankton assemblage in terms of biomass in open water together with large, long chain forming, pennate diatoms, whereas small pennate diatoms such as Nitzschia spp., and nanoflagellates prevailed in ice covered areas. Fairly low concentrations of phytoplankton cells were encountered at the southernmost stations and many empty diatom frustules were found in the samples. The enhanced phytoplankton biomass in the Weddell-Scotia-Confluence area is achieved through sea ice melting in the frontal zone of two different water masses, the Weddell and the Scotia Sea surface waters.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Perennially ice-covered Lake Hoare,Antarctica: physical environment,biology and sedimentation

Lake Hoare (77° 38 S, 162° 53 E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3–5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30–60 years. Therefore, the lake environment responds to changes on a 10–100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.     

Phytoplankton composition in the Weddell-Scotia Confluence area during austral spring in relation to hydrography

During the EPOS leg 2 cruise of the RV Polarstern, carried out in late austral spring of 1988–1989, the composition of phytoplankton in relation to the distribution of hydrographic parameters was studied in four successive transects carried out along 49°W and 47°W, across the Weddell-Scotia Confluence (WSC) and the marginal ice zone (which overlapped in part). In all transects, a maximum of phytoplankton biomass was found in the WSC, in surface waters stabilized by ice melting. Different phytoplankton assemblages could be distinguished. North of the Scotia Front (the northern limit of the WSC) diatoms with Chaetoceros neglectus, Nitzschia spp. and (Thalassiosira gravida) dominated the phytoplankton community. This assemblage appeared to have seeded a biomass maximum which occupied, during the first transect, an area of the WSC, south of the Scotia Front. The southernmost stations of the first transect and all the stations to the south of the Scotia Front in the other transects were populated by a flagellate assemblage (with a cryptomonad, Pyramimonas spp. and Phaeocystis sp.) and an assemblage of diatoms (Corethron criophilum and Tropidoneis vanheurkii among others) associated to the presence of ice. During the last three transects, the flagellate assemblage formed a bloom in the low salinity surface layers of the WSC zone. The bulk of the biomass maximum was formed by the cryptomonad which reached concentrations up to 4×10⁶ cells l^–1 towards the end of the cruise. Multivariate analysis is used to summarize phytoplankton composition variation. The relationships between the distribution of the different assemblages and the hydrographic conditions indicate that the change of dominance from diatoms to flagellates in the WSC zone was related to the presence of water masses from different origin.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

AN ENCYSTMENT STAGE,BEARING A NEW SCALE TYPE,OF THE ANTARCTIC PRASINOPHYTE PYRAMIMONAS GELIDICOLA AND ITS PALEOLIMNOLOGICAL AND TAXONOMIC SIGNIFICANCE1

Cysts of the Antarctic prasinophyte Pyramimonas gelidicola McFadden were found in water samples from a fjord and a saline lake in the Vestfold Hills, Antarctica Unialgal cultures of P. gelidicola from Ace Lake produced cysts. After ca. five weeks, tile cysts settled and adhered to the bottom of the culture flask. The cyst wall was covered by a scale type not seen on the flagellated cells; however, the base of the cyst scale was similar to the box scales of P. gelidicola motile cells. Cyst scales were also found off the continental shelf in Prydz Bay. In a 1.7 m sediment core taken from Ace Lake, both cyst scales and box scales of P. gelidicola occurred at most depths. Differences in the ratio of these two scale types at different depths in the core may indicate past ecological changes in the lake. Upper sediments of the core were dated at 5310 ± 90 yrs B.P., indicating that prasinophyte scales may be recognizably preserved for extended periods. P. gelidicola was widely distributed in saline lakes of the Vestfold Hills with salinities of 3.2–133% and temperatures ranging from – 5.0 to 10.4°C. This is the first report of encystment of P. gelidicola and, to our knowledge, is the first record of a prasinophyte with two distinctly different scale types occurring on cells during different stages of the life history.