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Certain physical factors, substrate type and ice action appear to be important determinants for ascidian distribution. Three different substrate types were sampled at depths between 0–30 m by SCUBA diving: soft bottoms, hard bottoms and moraine deposits. The species found were Aplidium radiatum, Synoicum adareanum, Distaplia cylindrica, Sycozoa gaimardi, Sycozoa sigillinoides, Tylobranchion speciosum, Corella eumyota, Ascidia challengeri, Cnemidocarpa verrucosa, Styela wandeli, Dicarpa insinuosa, Pyura bouvetensis, Pyura discoveryi, Pyura obesa, Pyura setosa, Molgula enodis and Molgula pedunculata. Highest diversity and patchy distribution was found in less stringent environments, where epibiosis is a commmon phenomenon on stolidobranch ascidians. Differences in stalk development were found in the most abundant species Molgula pedunculata and Cnemidocarpa verrucosa. Ice action may be the main factor that determines the absence of ascidians above 15 m in all the stations sampled.

2005. What determines the likelihood of species discovery in marine holozooplankton: is size, range or depth important? Á/ Oikos 109: 567 Á/576.The relationship between date of first description and size, geographic range and depth of occurrence is investigated for 18 orders of marine holozooplankton (comprising over 4000 species). Results of multiple regression analyses suggest that all attributes are linked, which reflects the complex interplay between them. Partial correlation coefficients suggest that geographic range is the most important predictor of description date, and shows an inverse relationship. By contrast, size is generally a poor indicator of description date, which probably mirrors the size-independent way in which specimens are collected, though there is clearly a positive relationship between both size and depth (for metabolic/trophic reasons), and size and geographic range. There is also a positive relationship between geographic range and depth that probably reflects the near constant nature of the deep-water environment and the wide-ranging currents to be found there. Although we did not explicitly incorporate either abundance or location into models predicting the date of first description, neither should be ignored.

Two populations of Salpa thompsoni, collected from the Weddell–Scotia confluence area at the end of two summers (1994 and 1995) with contrasting densities, are compared. The present study was aimed at corroborating whether fluctuations in abundance could be related to some life history parameters considered as indicators of growth rate in salp populations, such as the body size of solitary reproductive individuals, number of buds per block or chain in the stolon, and the offspring to parent ratio. No differences were observed in the sizes reached by aggregate individuals, or in the size at which oocyte maturity was attained (moment at which the development of the embryo can be detected). There were no differences in the size reached by the embryos during their residence inside the mother's blastozooid. In 1995, the percentage of non-fecundated blastozooids (which included even the largest individuals) was higher than in 1994. The mean size of the solitary individuals was significantly higher in 1994 than in 1995. The number of buds per block was also significantly higher in most of the stages, confirming that this is the mechanism used by these organisms to produce swarms. This species eventually attains high population densities under favorable environmental conditions such as poor sea-ice cover in winter. Under optimal conditions, the number of potential descendants produced by a single solitary individual would exceed 800.

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The reproductive biology of the common Antarctic ascidian Cnemidocarpa verrucosa (Lesson) (Tunicata, Ascidiacea) was studied in a shallow-water population at Potter Cove, South Shetland Islands. Samples were taken monthly by SCUBA diving over a 15 mo period during 1996 and 1997. The reproductive cycle was examined by histological analysis of the gonads and gonad index measurements. Mean oocyte diameter peaked in June and showed a sharp decrease in August. A similar pattern was exhibited by gonad indices, which suggests a strong seasonality in reproduction. Gametogenesis was continuous year-round, although vitellogenesis, mature oocytes and mature spermatocytes were mainly observed during the austral winter. It is interesting that reproduction of this suspension feeder seems to be decoupled from the pulses of primary production characteristics of Antarctic systems and was not related to the slight, but present, temperature changes. It was striking since these 2 factors are usually among the most important in determining reproductive cycles, especially in suspension feeders. This suggests either that winter time is not so stressful, in energetic terms, at least in the Potter Cove ecosystem, or that this ascidian species is able to store energy in some organs during favorable periods to later fuel reproduction. This later idea is supported by the higher gonad production observed in 1997 compared to 1996, which coincided with higher levels of chl a that year.

The stomach contents of 532 adult specimens of the Argentine anchovy, Engraulis anchoita, caught in coastal waters of the Argentine Sea from 1994 to 1996, were analyzed. Larger amounts of food were found in the stomachs of anchovies collected in the northern surveys (35-40°S), with the highest values attained in 1994. Main diet items were copepods, appendicularians, cladocerans, fish eggs, and pteropods. Anchovies caught in the southern surveys (40-45°S) ingested less food, whereby the main items were copepods and appendicularians. Plankton samples collected simultaneously with the fishing trawls were also analyzed. Except for Fritillaria borealis, which occurred only in plankton samples, the same appendicularian species (Oikopleura dioica and O. fusiformis) were found in both stomach contents and in plankton samples. The Ivlev selectivity index calculated for O. dioica and O. fusiformis and for the different maturity stages of both species were in all cases 0, supporting the hypothesis of a non-selective feeding.

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