Temporal changes of species belonging to Acartia genus (Copepoda: Calanoida) in the northern basin of the Venice lagoon

This paper deals with the results that have been obtained from counting and taxonomy of zooplankton samples collected during a number of projects in the northern basin of the lagoon of Venice, starting from the 1970s up to now. Special attention has been paid to the species belonging to the Acartia genus, which is quite predominant in the lagoon, and whose distribution and life-cycle are considered of particular significance in estuarine and lagoon ecosystems. Up to now, four species were present, showing different dynamics throughout these 30 years. While three of these species indicated a decreasing trend of the population, the latter appeared in an explosive manner in the last few years and reached considerably high peaks. The species are the following: i) A. clausi Giesbrecht, characteristic of coastal waters; ii) A. latisetosa Kriczaguin, mainly found near the lagoon border; iii) A. margalefi Alcaraz, collected for the first time in the lagoon at the beginning of the 1970s; iv) A. tonsa Dana, whose habitat is the same of the latter two species, with a life-cycle supported by large amounts of particulated organic matter. As far as total zooplankton was concerned, abundance appeared to decrease in coastal waters, while the inner area showed an increasing trend in the 1990s, mainly due to the presence of A. tonsa.