Potenciales presas zooplanctónicas (Copepoda y Appendicularia) para Engraulis anchoita en relación con las distribuciones de larvas tempranas y de desove en la región frontal patagónica (océano Atlántico sudoccidental)

We investigated the spatial distribution of the abundance, biomass and size of zooplankton (nauplii, calanoids, cyclopoids and appendicularians) in relation to the distribution of first-feeding larvae and eggs of Engraulis anchoita across the frontal system of Peninsula Valdés. Twelve samples of zooplankton and ichthyoplankton were taken with small Bongo (67 μm) and Pairovet (200 μm) nets during the spring of 2004 along two transects. The total abundance of zooplankton and the chlorophyll a concentration were higher in homogeneous waters, while total biomasses were higher in stratified waters. Temperature was negatively correlated with biological variables and was the main factor affecting the zooplankton distribution. In both transects, abundance peaks of first-feeding larvae were detected at coastal stations along with the smallest fraction of zooplankton ( < 500 μm), while the largest fraction was dominant at the external stations, coinciding with the highest egg abundance. The physical structure of this front generates different levels of food availability for first-feeding larvae. Calanoids (southern transect) and cyclopoids (northern transect) are predominant followed by nauplii and appendicularians. The biomass of zooplankton preys contributes to the carbon transfer to the upper trophic levels and is probably important for the survival and growth of anchovy larvae in this frontal system.Se investigó la distribución espacial de la abundancia, biomasa y las tallas del zooplancton (nauplii, calanoideos, ciclopoideos y apendicularias) en relación con la distribución de las larvas en estadio de primera alimentación y los huevos de Engraulis anchoita en el sistema frontal de Península Valdés. Se tomaron 12 muestras de zooplancton e ictioplancton durante la primavera de 2004 a lo largo de dos transectos, mediante una red Minibongo (67 μm) y una Pairovet (200 μm) respectivamente. La abundancia total del zooplancton y la concentración de clorofila fue mayor en aguas homogéneas, mientras que la biomasa fue mayor en aguas estratificadas. La temperatura se correlacionó negativamente con las variables biológicas siendo ésta el principal factor que afectó la distribución del zooplancton. En las estaciones costeras de ambos transectos, se encontró la mayor abundancia de larvas en coincidencia con la fracción más pequeña de zooplancton ( < 500 μm), mientras que la fracción más grande fue dominante en las estaciones externas, en coincidencia con la mayor abundancia de huevos. La estructura física de este frente genera diferente disponibilidad de alimento para las larvas siendo los calanoideos (transecto sur) y los ciclopoideos (transecto norte) predominantes, seguidos por nauplii y apendicularias. La biomasa de dicho alimento zooplanctónico podría contribuir a la transferencia de carbono a los niveles tróficos superiores y esto sería importante para la supervivencia y crecimiento de la anchoita en este sistema frontal

An evaluation of the systematics of the genus Thalia (Thaliacea, Salpidae) based on new material from the EASTROPAC and MORO expeditions

Until 1973, when Van Soest revised Thalia Blumenbach, 1798, this genus comprised only two species: Thalia democratica (Forsskål, 1775) and Thalia longicauda (Quoy & Gaimard, 1824). The former showed great variability, which led Van Soest to distinguish five species: T. rhomboides, T. cicar, T. democratica, T. orientalis, and T. sibogae. Some authors have ignored this revision considering the observed differences of infraspecific level. In the present work new material is studied analysing variables not previously considered, such as the development of blastogenic stolons in the solitary zooids and the location of the tunnel opening through which the bud blocks are liberated. These characters previously permitted a separation of closely related species in the genus Ihlea. The results show that stolon features, even though they permit a separation of solitary zooids of Thalia longicauda, do not discriminate all species of the “T. democratica group” since they are only useful in distinguishing T. democratica from T. sibogae. Other variables, mainly qualitative, do permit differentiation. The sympatric distribution of these taxa supports Van Soest’s hypothesis as well