Temporal patterns of the calanoid copepod community in Veliko Jezero, an isolated marine lake (South Adriatic Sea): links to a larger-scale climate changes

Abstract

We complied and analysed a long-term calanoid community data set (1952–2009) with respect to environmental variations in nearly closed seawater lake Veliko Jezero (South Adriatic Sea). Changes in hydrographic properties were influenced by deepening and broadening the channel between Veliko Jezero and the sea in the early 1960s, which was in particular reflected by increasing salinity. Calanoid abundance displayed high intra- and inter-annual fluctuations but lacked any regular and recurrent pattern. Calanoids in the lake comprised 22 coastal and estuarine species, with five of them present over the entire study period (Calanus helgolandicus (Claus, 1863), Paracalanus parvus (Claus, 1863), Centropages kroyeri Giesbrecht, 1893, Isias clavipes Boeck, Acartia (Acartiura) clausi Giesbrecht, 1889). Four sample groups were identified by cluster analysis, with the highest degree of dissimilarity between samples from the 1950s and those from the 1990s and onwards. Observed changes – low densities in early 1980s; a shift in the dominant species; reduction and, finally, disappearance of Pseudocalanus elongatus (Boeck); increases in Paracalanus parvus and Diaixis pygmaea (Scott T., 1894) – can be associated with synchronous changes across trophic levels that have occurred in other European seas. The results presented here underline the importance of long-term studies of semi-closed marine lakes and lagoons, as these are particularly sensitive to global climatic changes.