Igor Brautović

Annual variability and trophic relations of the mesozooplankton community in the eutrophicated coastal area (Vranjic Basin, eastern Adriatic Sea)

Mesozooplankton was sampled during one year in the eutrophicated Vranjic Basin and the influence of environmental variables on its abundance and distribution was analysed. Parallel microzooplankton samples were collected in order to asses trophic relationships within the zooplankton community. Total mesozooplankton abundances were high, exceeding 2 x 104 ind. m-3 in the warmer part of the year, but the biodiversity was low. The annual variability of this assemblage was mostly influenced by temperature. Copepods were dominant among net plankton groups, while ciliates dominated the protozoan community. The key species of the copepod community were Acartia clausi, Oithona nana and Euterpina acutifrons, occurring simultaneously throughout the year. High abundances of small copepod Oithona nana were determined in both meso- and microzooplankton samples, and comparisons of the catches from 125 μ m net and 5 l Niskin bottles revealed no significant differences between them. Significant correlation determined between Acartia clausi and oligotrich ciliates indicates predator-pray relationship and the importance of the ciliate community in the energy transfer through the trophic web of this area.

Population structure and diel vertical migration of euphausiid larvae in the open southern Adriatic Sea (July 2003)

The composition, bathymetric distribution, and diel vertical migration of larval euphausiids in the oligotrophic southern Adriatic Sea were studied during the summer of 2003. Larvae of 11 species were identified. Of these, Thysanoessa gregaria is reported for the first time from the Adriatic Sea. Information is presented on the distribution and diel migrations of the five dominant species. Nematoscelis megalops furciliae had the widest bathymetric range, extending from surface to the bottom (1200 m); larvae of Stylocheiron maximum were found from 100 to 1200 m. Euphausia krohnii (calyptopes and furciliae), Stylocheiron abbreviatum calyptopes, and Stylocheiron longicorne furciliae ranged over 800 m. S. abbreviatum (furciliae) and S. longicorne (calyptopes) had more restricted bathymetric distributions. Different populations were associated with layers characterized by specific light intensities. Three migration patterns were observed: (i) nocturnal ascent to upper layers (E. krohnii, N. megalops, S. abbreviatum); (ii) scattered population through the water column (S. maximum); (iii) migration to upper layers at midday and night, and descent during the morning and evening (S. longicorne). Different stages of the same species showed different preferences for light intensity.