| Resumo: |
The Península Valdés tidal front was studied in its rol in the control of the spatial distribution, abundance, assemblages, diversity and life histories of the zooplankton community using samples from two oceanographic surveys. Although the front showed in general high zooplankton abundances, highest values, mainly due to the presence of immature stages of copepods, were recorded in the transitional and stratified zones coinciding with highest values of chlorophyll a. The zooplankton groups showed a distinctive spatial distribution across the front. The results showed that this front did not exert any control on zooplankton composition and diversity, but did on the abundance. In the homogeneous zone the harpacticoid copepods were more abundant, followed by barnacle nauplii and decapod larvae. The transition zone was largely dominated copepod nauplii and high abundances of cyclopoid, calanoid and harpacticoid copepods. Other taxa such as appendicularians, cladocerans, cumacea and mysids also showed higher abundances in this zone. In the stratified zone copepodites I-III, calanoid copepods, euphausiids, jellyfish, ctenophores and hyperiid amphipods were more abundant. The hydrographic characteristics of the front would be controlling the zooplankton community. Nictimeral migrations were observed in almost all zooplankton groups mainly in the stratified zone. The high phytoplankton and zooplankton concentrations suggest a predominance of control "bottom up" in this frontal system.
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