Patricia Martos

Fish abundance and distribution patterns related to environmental factors in a choked temperate coastal lagoon (Argentina)

O objetivo deste estudo foi avaliar a influencia de fatores ambientais sobre a distribuicao e abundância de peixes na lagoa costeira Mar Chiquita. Estacoes sazonais de amostragem de peixes foram distribuidas ao longo da lagoa e agrupadas em tres zonas de uma zona de aguas Mixo-oligohalino com elevado aporte de agua doce para uma zona de aguas Mixo-eurihaline com alta influencia da agua do mar. Uma zona de aguas Mixo-mesohalino caracteriza a parte do meio da lagoa. Os resultados mostraram que a composicao dos peixes foi dominada por especies marinhos estuarinos dependentes (ED) em todas as tres zonas e em todas as estacoes: Odontesthes argentinensis, Brevoortia aurea, Mugil liza e Micropogonias furnieri foram as especies mais representativas. A categoria seguinte mais importante foi peixes de agua doce (FW), com Platanichthys platana e Jenynsia multidentata sendo as especies mais representativas. De acordo com o melhor modelo selecionado pelo ajuste de modelos lineares generalizados, a abundância de ED aumentou de acordo com a temperatura da agua durante o verao e outono, em todas as tres zonas. A maior abundância foi registrada na zona de aguas mixo-eurihalinas. Por outro lado, a abundância de FW aumentou com o aumento da pluviosidade e tambem quando os ventos de direcao leste sopraram. Em conclusao, a utilizacao diferencial do habitat pelas especies que ocorrem na lagoa costeira Mar Chiquita foi observada. Poucas especies ED dominaram a composicao de especies de peixes, enquanto FW fizeram uso da lagoa quando as condicoes de alta pluviosidade foram observados.

Diel vertical distribution of the larvacean Oikopleura dioica in a North Patagonian tidal frontal system (42°–45°S) of the SW Atlantic Ocean

Abstract In frontal systems, larvaceans generally comprise a significant fraction of the mesozooplankton. Given the low mobility of these organisms, their vertical distribution is directly influenced by the physical conditions of the water column. The main goal of this study was to investigate the day and night vertical distribution of the larvaceans Oikopleura dioica in the different sectors of the Península Valdés tidal front (42°–45°S; SW Atlantic Ocean), focusing on possible causes such as oceanographic conditions (well-mixed, frontal and stratified), feeding activities, reproductive behaviour and predation risks. Day and night samples were collected with a MultiNet of 67 µm and 300 µm mesh size, from two depth layers. Conductivity-temperature-depth (CTD) profiles were also recorded. In the well-mixed waters, the size structure of O. dioica was similar in the upper and lower layers both in the day and night samples, probably due to the continuous vertical movement caused by the turbulent mixing of waters. In the frontal and stratified areas, mature animals were found in the upper layers during the night, possibly due to their aggregation in surface waters for synchronized spawning. In these areas, a high percentage of well-fed larvaceans was also found. Principal component analysis showed that, at night, the abundance of potential predators such as chaetognaths, ctenophores and anchovy larvae was correlated with the parameter of stability of the water column (Simpson parameter), and that these were more abundant in the upper layers of the stratified area containing larvaceans. Our results suggest that the degree of stratification of the water column was the main factor affecting the vertical distribution of O. dioica.