Alicia Vinocur

Periphyton flora of some lotic and lentic environments of Hope Bay (Antarctic Peninsula)

A taxonomic study was made of the periphytic algal flora of some freshwater environments at Hope Bay, Antarctic Peninsula (63°27′S; 56°59′W), during summer 1992–1993. Seven lakes and two pools that are characterized by different trophic levels were studied. The largest, Boeckella Lake, has an important outflow (Prasiola Stream) that was also analyzed. Ninety-seven algal taxa, including specific and infraspecific entities, are recorded. Thirty-one new records for the Antarctic continent are described and illustrated. The flora comprises 44.4% Cyanophyceae, 21.6% Bacillariophyceae, 18.5% Chlorophyceae, 9.3% Tribophyceae, 4.2% Chrysophyceae and 2% Zygophyceae. The epilithic flora of Hope Bay shows a high species richness. Phormidiumfragile and Lyngbya lagerheimii were the most abundant species among the Cyanophyceae. In the algal mats we also found Chrysophyceae (mainly Hydrurus foetidus and Chrysococcus rufescens) and the macroscopic chlorophycean Prasiola crispa. Tribonema australis sp. nov. (Tribonematales, Tribophyceae) is put forward as a new species. Hormidium fluitans (Gay) Heering is renamed Klebshormidium fluitans.

Phytoplankton communities in relation to trophic status in lakes from Hope Bay (Antarctic Peninsula)

Nine lakes and ponds of Hope Bay (Antarctic Peninsula), with different trophic status were surveyed during four summer periods between 1991 and 1996. Some limnological features and the structure of their algal assemblages were strongly influenced by the eutrophication caused by sea-birds activity in their areas. Such differences among lakes were evidenced by the results of Principal Component Analyses, based on both physico-chemical and phytoplankton data. Oligotrophic lakes showed a scarce phytoplankton, commonly dominated by small flagellated Chrysophyceae, and a well developed phytobenthos. Water bodies enriched by ornithogenic nutrients revealed an abundant phytoplankton usually dominated by Chlorophyceae (Volvocales) and planktonic Cyanobacteria. A study on one particular lake showed that summer changes in the phytoplankton community were mainly affected by physical phenomena such as variation in light intensity, and thawing, mixing and freezing processes.

Cyanophyta of lakes and ponds of Hope Bay, Antarctic Peninsula

This paper presents the results of the floristic inventory of the freshwater Cyanophyceae found in plankton samples from nine lakes and ponds at Hope Bay (Antarctic Peninsula). Forty taxa were recorded, among which nine are new records for Antarctica. All the taxa are illustrated, and their distribution in Antarctica as well as the ecological characteristics of the sampling sites are given. The main morphological features and the geographic distribution are also given for the new records.

Ecology of algal communities of different soil types from Cierva Point, Antarctic Peninsula

During summer 2005/2006, we characterized three sampling sites on mineral soils and four on ornithogenic soils from Cierva Point, Antarctic Peninsula, in terms of topographic and abiotic features (altitude, slope, magnetic direction, temperature, texture, pH, conductivity, organic matter, moisture and nutrient concentrations), and compared their microalgal communities through taxonomic composition, species richness, diversity, chlorophyll a content and their variation in time. Average values of pH, moisture, organic matter and nutrient concentrations were always significantly lower in mineral than in ornithogenic soils. Low N/P mass ratio showed potential N-limitation of biomass capacity in the former. On the other hand, the results suggested that physical stability is not as a key stress factor for mineral soil microalgae. Chlorophyll a concentration was not only higher in ornithogenic soils, but it also showed a wider range of values. As this parameter was positively correlated with temperature, pH, nutrients, organic matter and moisture, we cannot come to conclusions regarding the influence of each factor on algal growth. Communities of mineral soils were significantly more diverse than those of enriched ornithogenic soils due to higher species richness as well as higher equitability. Also, their structure was steadier over time, as shown by a cluster analysis based on relative frequency of algal taxa. Although Cyanobacteria and Bacillariophyceae dominated almost all samples, Chlorophyceae represented 34% of the 140 taxa recorded, and most of them observed only in cultures. The detection under controlled conditions of a high latent species richness in harsh mineral soil sites shows that the composition and equitability of these microalgal communities would be more prone to modification due to the manifold local consequences of climatic change than those of ornithogenic soils.

Long-term study of bloom-forming cyanobacteria in a highly fluctuating vegetated floodplain lake: a morpho-functional approach

This study portrays the frequency and intensity of bloom-forming cyanobacteria in relation to highly changing environmental conditions in a floodplain lake from the Chaco-Pampean region and identifies the factors promoting the growth of different species along a 15-year period marked by important drought and flood periods. Phytoplankton in Laguna Grande was increasingly dominated by cyanobacteria represented by eight bloom-forming species bearing different eco-physiological traits. The bloom development showed strong inter-annual variability in correspondence with the depth of the lake that was affected by local rainfall and the ENSO regional phenomenon. The water level of the lake strongly influenced the species composition, favoring non-heterocystous filaments in deep turbid waters and nitrogen fixing in very short well lit, nitrogen-depleted water columns. Species morphology, dimensions and occurrence of akinetes in the filaments also varied in relation to water level. We suggest that the akinete pool of the sediments played a key role on the occurrence of recurrent Anabaenopsis cf. elenkinii and Sphaerospermopsis cf. aphanizonemoides blooms.

Landscape-driven environmental variability largely determines abiotic characteristics and phytoplankton patterns in peat bog pools (Tierra del Fuego, Argentina)

Ombrotrophic peat bogs from Tierra del Fuego are characteristically raised, dome-shaped, fed by precipitation, and nutrient-poor. Their landscape pattern consists of a Sphagnum magellanicum matrix encompassing pools with different morphometric and trophic features. Within the framework of a 2-year limnological survey in five pools from Rancho Hambre peat bog, we analyzed phytoplankton communities under the hypothesis that taxonomic composition would show a spatial pattern driven by ultimately landscape-controlled environmental features such as pH and trophic status, while temperature and weather-dependent features would account for seasonal changes in abundance and structure. Among the 305 taxa recorded, most were Conjugatophyceae and Bacillariophyceae, and were strongly associated to circumneutral pH and minerotrophic conditions, though limited superficial connectivity among pools accounted for dissimilar taxonomic compositions. Despite such differences, phytoplankton of pools with similar morphometry and trophic status showed similar dominant and richest taxonomic groups undergoing paralell changes over time. Seasonal temperature fluctuations were modulated by pool size and modified not only abiotic properties but also phytoplankton abundance, with different taxa showing strong summer peaks in different pools. An interpretative model is proposed which will be tested as a tool for predicting community strategy and temporal variation patterns as responses to different environmental templates.

Phytoplankton structure and dynamics in a volcanic lake in Deception Island (South Shetland Islands, Antarctica)

This work constitutes the first floristic and ecological analysis of the phytoplankton community of a volcanic freshwater lake in Deception Island (62°57′S, 60°38′W, South Shetland Islands, Antarctica). The main limnological features and phytoplankton size fractions were analyzed. Samples were taken during the austral summer of 2002 at two opposite sites. According to ANOVA results performed with abiotic variables, no significant differences between sites were found. The phytoplankton community showed low algal species richness, with an important contribution of the tychoplanktonic taxa. In terms of species number, Bacillariophyceae was the dominant class. Autotrophic picoplankton registered the highest densities from the second sampling date onwards. Nanophytoplankton was represented by unidentified chrysophycean organisms, which showed different distribution patterns between sites. The net phytoplankton abundance remained low during the sampling period and was strongly correlated with chlorophyll a concentration. Both nutrient concentrations and chlorophyll a values indicated oligotrophic conditions.