Microzooplankton in the open waters of the northern Adriatic Sea from 1990 to 1993: the importance of copepod nauplii densities

Zooplankton was sampled during 39 cruises, from 1990 to 1993, at four fixed stations in the open northern Adriatic. Hydrographic factors were important in determining the abundance of the smallest and largest components of the northern Adriatic food chain during this period. Nauplii—especially those of the smallest size fractions—were the major mediators of material transfer between primary producers and higher trophic levels. There was a significant difference in the vertical distribution of nauplii size fractions between the eastern and western parts of the northern Adriatic, but not in their population density. According to multiple correlation analyses, the abundance of naupliar size fractions in the western area correlated strongly with temperature and with certain biological factors. This study confirms the important influence of the Po River and of mid-Adriatic waters on the planktonic ecosystem of the northern Adriatic. Electronic Publication     

Bathymetric distribution of medusae in the open waters of the middle and south Adriatic Sea during spring 2002

Twenty-eight species of hydromedusae and one scyphomedusa werecollected from the middle and south Adriatic in Spring 2002.Haliscera bigelowi was recorded for the first time in the AdriaticSea and Dicodonium adriaticum for the southern Adriatic. Thecosmopolitan species Rhopalonema velatum, Aglaura hemistomaand Persa incolorata averaged 88% of total medusan abundance.The Mediterranean species Rhabdoon singulare and Solmissus albescenswere numerous at the deeper stations. These species were foundeither in the southern or in middle Adriatic, and their abundanceis greater than in other regions of the Mediterranean Sea. Speciesdiversity and abundance generally were highest in the upper200 m and decreased with depth. Diel vertical migration patternsincluded some species that nocturnally sought shallower or deeperlayers, and some species migrated in both directions. A fewspecies did not show any vertical migration. Although lightlikely triggers vertical movements, data suggest that foragingstrategies also influence the vertical migration of medusae.