Marcelo Pájaro

Salps: possible vectors of toxic dinoflagellates?

Abstract The mortality of the Argentine mackerel Scomber japonicus during the spring of 1993 was studied by analyzing their stomach contents. All dead specimens contained salps. This study suggests that the salps contained high concentrations of the toxigenic dinoflagellate Alexandrium tamarense , and constituted herbivorous vectors of toxicity, causing the death of the mackerel.

Distribution of Oikopleura dioica (Tunicata, Appendicularia) associated with a coastal frontal system (39°- 41°S) of the SW Atlantic Ocean in the spawning area of Engraulis anchoita anchovy

Entre os tunicados, as pequenas apendicularias planctonicas geralmente compreendem uma fracao significativa do mesozooplâncton nos sistemas frontais. Foi estudada a distribuicao (vertical e espacial) durante o verao de 2011 de Oikopleura dioica, em termos de abundância, biomassa, estimativa da producao de ovos e estrutura da populacao em diferentes setores da frente costeiro de El Rincon, segundo os gradientes de temperatura e salinidade. Picos de abundância de larvas de Engraulis anchoita foram comparados com os padroes de O. dioica. As amostras foram coletadas com redes planctonicas de 67 e 200 µm em duas profundidades, acima e abaixo da termoclina. Tambem foram registrados perfis de dados obtidos com CTD. Durante essa campanha, aguas de alta salinidade foram predominantes na area estuarina. No entanto, foi encontrada uma estratificacao termica, sendo mais acentuado nas estacoes externas da frente, onde as maiores densidades e biomassa de O. dioica foram registradas, coincidindo tambem com as maiores densidades de larvas de E. anchoita. A distribuicao de tamanhos de O. dioica tambem foi associada ao gradiente termico. Os menores tamanhos foram encontrados na regiao mais homogenea da costa, onde a temperatura apresentou cerca de 22oC. Essa frente e um ambiente propicio para a reproducao de O. dioica o que favorece tambem o aumento da sobrevivencia e o crescimento de muitas especies de pequenos peixes pelagicos, tais como E. anchoita.

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.

Ichthyoplankton Associated to the Frontal Regions of the Southwestern Atlantic

The study region covers a wide latitudinal range, from 22°S to 55°S, and a bathymetric scope ranging from the coast to the shelf-break and adjacent region to a depth of ca. 1000 m. Hydrography of the region is extremely complex. Oceanographic structures are diverse, including several estuaries, water masses, wind systems, tidal regimes, and two major oceanic currents. A significant portion of the biological production is related to the existence of several marine fronts, characterized by different forcing, and temporal and spatial scales. Fish species that inhabit the region are diverse, covering a range of life strategies. Among those fishes that produce eggs and/or planktonic larvae, there are estuarine, shelf and oceanic forms, and species characteristic of tropical/subtropical or subantarctic waters. Pelagic species are more important in the northern part, while demersal species dominate the southernmost area. The region looks like an intricate mosaic of opportunities for life cycle closure of distinct species. Marine fronts seem to be the preferred areas to establish spawning and nursery grounds by fishes, and current knowledge allow to identify the elements of Bakun’s triad for several of those fronts.

Ecological Role of Common Appendicularian Species from Shelf Waters Off Argentina

Appendicularians generally comprise a significant fraction of mesozooplanktonic tunicates in marine environments. Their eggs, trunks, and houses are important food supply to large copepods, chaetognaths, ctenophores, and larvae and adults of engraulids. They are semelparous and hermaphrodites (except O. dioica) organisms, with a short and temperature-dependent life cycle. In this chapter, we discuss the seasonal dynamics of appendicularians, comparing life strategies of dominant species at distinct coastal environments of the Southwest Atlantic Ocean. O. dioica, O. fusiformis, Appendicularia sicula, and Fritillaria borealis are common coastal species in the southwestern Atlantic. Total abundance, biomass, and house production of O. dioica and A. sicula were higher during spring and summer. O. dioica and A. sicula bloomed during summer with temperatures between 17 and 20 °C. O. fusiformis appeared occasionally during summer and fall but in very low densities. Fritillaria borealis prefers subantarctic and Antarctic cold (<11 °C) and salty waters. The contribution of appendicularians to the zooplankton secondary production had been underestimated. Here we emphasized the role of appendicularians as extraordinary producers of carbon and macroscopic aggregates in planktonic ecosystems, as it has been shown by several studies at the northern hemisphere and herein for the southern SW Atlantic Ocean.