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Responses of copepoda life-history stages to climatic variability in a southern-European temperate estuary

Abstract:

In this study, we investigated the effects of an extreme climate event (severe drought) on copepod ecology. Monthly sampling events were conducted from 2005 to 2007, at 5 stations, using 63- and 335-μm-mesh nets in Mondego Estuary, Portugal. The Calanoida were represented mainly by Acartia clausi, Temora longicornis, and A. tonsa and the Cyclopoida by Oithona plumifera and Acanthocyclops robustus. Acartia clausi and T. longicornis dominated at the mouth and middle estuary; A. tonsa and A. robustus were associated with the upper estuary while O. plumifera showed the highest densities in the downstream section. Nauplii occurred in higher densities at the mouth. Relationships of copepod assemblages and environmental factors were analyzed using the STATICO method which allowed us to distinguish the combination of factors that most contributed to these relationships. Winter was characterized by high concentrations of nutrients, cold waters, and low salinities, while summer was generally characterized by high values of phosphate, salinity, and temperature. Marine and estuarine species (mainly copepodites) showed high densities in summer. Freshwater species occurred at maximal densities in winter, coincidently with higher river flow. Copepod assemblages showed a clear seasonal pattern that was superimposed on the interannual variability. Moreover, a severe drought was responsible for the dominance of marine species.