The current paper analyses the micro and mesozooplankton in Ushuaia and Golondrina Bays, the first research on these plankton fractions of these areas in wintertime (August 2004). The number of microzooplankton and mesozooplankton taxa was higher in Ushuaia Bay than in Golondrina Bay. Aloricate ciliates predominated over tintinnids in microzooplankton and holoplankton over meroplankton in mesozooplankton in both bays. Ctenocalanus citer, Drepanopus forcipatus and Clausocalanus brevipes presented the highest frequency of occurrence. Among the meroplankton, Halicarcinus planatus and Munida gregaria were the most frequent decapod larvae in both bays. The distribution of the different sampling station groups of microzooplankton and mesozooplankton as determined by cluster analysis suggests the influence of natural conditions in each bay and anthropogenic environmental differences between the two bays. RESUMOEste trabalho analisa o micro e o mesozooplâncton das Baías Ushuaia e Golondrina, constituindo a primeira pesquisa realizada nessas áreas sobre estas frações do plâncton no inverno (agosto 2004). O número dos taxa do microzooplâncton e do mesozooplâncton foi mais elevado na Baía Ushuaia do que na Baía Golondrina. Os ciliados aloricados foram dominantes sobre os tintinídeos, enquanto que no mesozooplâncton o holoplâncton foi dominante nas duas baías. Ctenocalamus citer, Drepanopus forcipatus e Clausocalamus brevipes foram as espécies mais freqüentes. No meroplâncton, Halicarnus planatus e Munida gregaria foram as larvas de decápodes mais freqüentes em ambos os locais. Os diferentes grupos de estações formados em função do microzooplâncton e do mesozooplânkton, e detectados na análise de agrupamento, sugerem a influência de condições naturais em cada baía e de diferenças ambientais antropogénicas entre as duas baías.Descriptors: Microzooplankton,

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Since ciliates rarely possess structures that easily fossilize, we are limited in our ability to use paleontological studies to reconstruct the early evolution of this large and ecologically important clade of protists. Tintinnids, a group of loricate (house-forming) planktonic ciliates, are the only group that has a significant fossil record. Putative tintinnid fossils from rocks older than Jurassic, however, possess few to no characters that can be found in extant ciliates; these fossils are best described as 'incertae sedis eukaryotes'. Here, we review the Devonian fossil Nassacysta reticulata and propose that it is likewise another incertae sedis eukaryote due to the lack of any unambiguous ciliate characters. Future tintinnid fossil descriptions would be most helpful if: (i) neutral terminology is used in the descriptions but ciliate-specific terminology in the interpretations; (ii) the current ciliate classification is used, although fossil data may expand or modify classifications based on modern forms; (iii) close collaboration with specialists studying extant ciliates is done; and (iv) editors include an expert of extant ciliates in the review process.

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The specific composition and abundance variation of the ciliate community from a wastewater discharge zone in the Bahía Blanca estuary, Argentina, were studied all throughout a year, from June 1995 to May 1996. The polluted area exhibited high values of particulate organic matter and nutrients, particularly phosphates. Aloricate ciliates were represented by 15 species belonging to the genera Strombidium Claparède & Lachmann, 1859; Strombidinopsis Kent, 1881; Cyrtostrombidium Lynn & Gilron, 1993; Strobilidium Schewiakoff, 1983; Lohmmanniella Leegaard, 1915 and Tontonia Fauré-Fremiet, 1914. Tintinnids were represented by nine species belonging to the genera Tintinnidium Kent, 1881, Tintinnopsis Stein, 1867 and Codonellopsis Jörgensen, 1924. The total abundance of aloricate ciliates reached a peak of 1,800 ind. l -1 and the total abundance of tintinnids reached a peak of 9,400 ind. l -1 . Tintinnidium balechi Barría de Cao, 1981 was the most abundant ciliate in the community. Considerations on the presence and abundance of ciliates are made in relation to physicochemical and biochemical parameters.

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Eutrophication is the most widespread effect of urban development in coastal areas. To elucidate how nutrient loading affects the carbon pathways at the base of food chains, we quantified the carbon transfer among microbial components, from prokaryotes to microzooplankton. For this purpose, we performed two size-fractionation feeding experiments during late summer under moderate (N: 28.5 μM, P: 0.92 μM, Si: 45.8 μM) and severe (N: 173.9 μM, P: 3.5 μM, Si: 67.2 μM) cultural eutrophication in the Bahía Blanca Estuary (Argentina). In both experiments, prokaryotes were largely dominated by heterotrophic forms, small diatoms dominated among autotrophs, and heterotrophic nanoflagellates were the most abundant among protistan grazers. Under severe eutrophication, however, the average biomass was 75% lower for all autotrophic and heterotrophic components. Nutrient loading sustained a higher growth rate of heterotrophic bacteria and phytoplankton but implied poorer trophic transfer. Under moderate eutrophication, daily productivity of nanoplankton and bacteria grazed was 157% and 154%, respectively, while under severe eutrophication, this percentage dropped to 3.54% and 33.7%, respectively. In addition, under excess nutrient conditions, microzooplankton evidenced an active prey switching toward the most abundant prey (diatoms). Weak top-down control of bacterial biomass along with trophic decoupling between microzooplankton and nanoflagellates, constituted a dead-end of bacterial biomass under severe cultural eutrophication. This inefficient carbon transfer can potentially produce a positive feedback by exacerbating organic matter accumulation.