IMIS

This study presents a first general analysis of the zooplankton assemblages from the Uruguayan coastal/estuarine ecosystems. The database considered comprised information from seven sites representing three different types of environment: coastal Río de la Plata (Punta Brava and Playa del Buceo in Montevideo, and Bahía Maldonado in Maldonado), coastal plain estuary (Arroyo Solís Grande), and coastal lagoons (José Ignacio, Garzón and Rocha lagoons). The taxonomic richness of the zooplankton was analyzed in relation to salinity ranges and explored the association between the abundance of most representative groups in the holoplankton (Acartia tonsa) and the meroplankton (Amphibalanus improvisus nauplii) with temperature and salinity. Taxonomic richness was low, amounting to 38 taxa for all sites considered and evidenced the typical features of estuarine zooplankton assemblages, i.e. strong dominance by one or few taxa present in high densities. Taxonomic richness along the salinity gradient suggested the classical pattern found in estuaries, with a maximum number of taxa over the highest salinity range and minimum at highly diluted waters. Salinity did not have significant effects on the distribution of the dominant organisms A. tonsa and A. improvisus nauplii. In turn, abundance of A. improvisus nauplii was significantly associated with temperature. The results suggest that salinity plays an important role in structuring zooplankton assemblages at the Uruguayan coast. Dominant species show high eurihaline conditions that allow them to thrive in these environments largely unaffected by the salinity conditions within the ranges found in the present study.