Limnetica 38

We analysed the changes in the zooplankton composition in several new and old lagoons in La Pletera, a confined Mediterranean coastal salt marsh located in the Baix Ter wetlands (NE Iberian Peninsula) that was subjected to a restoration project (Life Pletera). We sampled the zooplankton from three new lagoons immediately after their creation (1 and 2 months after), and we compared the zooplankton with those of three existing lagoons, two natural lagoons and one lagoon created fourteen years ago in a previous restoration project. The sampling included seven months before the first hydrological connection to the surface waters, when flooding during a sea storm connected the new lagoons with the existing lagoons for the first time, and seven months after. The results showed that the nutrient and organic matter concentrations were lower in the new lagoons than in the old lagoons, suggesting accumulation processes in these ecosystems, which were probably related to the long periods of confinement that typically follow flooding events in this type of lagoons. However, we did not find significant differences in the zooplankton community between the old and new lagoons. The seasonal variation in the zooplankton communities was strongly affected by the seasonal hydrological flooding – confinement pattern, which did not differ between the old and new lagoons. Calanoid copepods, mainly Eurytemora velox, dominated during winter, while the rotifer Brachionus plicatilis dominated in summer, coinciding with the highest degree of confinement. The environmental variables and the hydric connection explained 31 % of the zooplankton variability. The high connectivity of the system once it flooded aided dispersal, the hatching of the egg banks existing in the restored lagoons and the fast response of the zooplankton species to changes in the environmental conditions (although with some degree of delay) might explain the lack of significant differences between the zooplankton composition in the old and new lagoons.