Barbara Gangai

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.

The importance of vertical habitat gradients on zooplankton distribution in an enclosed marine environment (South Adriatic Sea)

Abstract The spatio-temporal patterns of a zooplankton community structure in a strongly stratified enclosed marine environment were studied over a one-year period. Copepods were by far the most abundant group, accounting for 69–91% of the total zooplankton, with a numerical dominance of the genus Oithona. Cluster analysis revealed four different groups of samples and a comparison was made of the hydrographical and biological properties of the resulting groups. Water temperature was the main force discriminating the zooplankton community. The strongest vertical separation was recorded in summer, while a salinity impact was noted during the autumn after a strong intrusion of open sea water. Most of the dominant zooplankters exhibited a distinct vertical separation over the study period, where thermophilic taxa (Cladocera, Centropages kröyeri, C. typicus, Oikopleura fusiformis, O. longicauda, Euterpina acutifrons) kept to the surface and cryophilic species (Diaixis pygmaea, Mesaiokeras hurei, Calanus helgolandicus, Parasagitta setosa) were concentrated below the thermocline layer (20 m depth) for most of the year. Due to the unique physical, chemical and biological properties of the study site, this research is an important step towards better understanding the distribution of zooplankton during stratified conditions.