Annual cycle of the gelatinous invertebrate zooplankton of the eastern South Adriatic coast (NE Mediterranean)

Abstract

Frequent sampling at a fixed South Adriatic station over 1996 was designed to capture the annual cycle of life-history stages of the dominant gelatinous invertebrate zooplankton, which are very seldom encountered in the world literature. Two groups of dominant species were distinguished by their periods of most intense reproduction, one in late summer–autumn and the other in late summer–autumn and winter. Of 66 species identified, there were 19 hydromedusae, 14 calycophores, 3 ctenophores, 2 heteropods, 12 pteropods, 8 polychaetes and 8 chaetognaths. Compared with historical data, the numerically dominant species of calycophores, pteropods and polychaetes have changed dramatically. The calycophore Muggiaea atlantica, newly observed in the Adriatic, has replaced its formerly dominant congener M. kochi; the pteropod Creseis virgula has supplanted C. acicula, and the previously very rare Pelagobia longicirrata now is the dominant pelagic polychaete. Faunal changes coincide with—and perhaps partly are owed to—newly documented circulation changes in the Eastern Mediterranean, the proximate source of southern Adriatic water. Thus, using an extended description of Adriatic zooplankton, data presented herein provide baseline information that is essential in the evaluation of biological changes in the Adriatic, which have appeared possible as a consequence of larger-scale oceanographic processes on zooplankton community structure.