Vertical Migration and Habitat Preference of Planktonic Ostracods (Crustacea) in the Deep Adriatic Sea

The main objective of our study was to determine for the first time the daily vertical migration (DVM) of 15 planktonic ostracod taxa in the southern Adriatic Sea. We analysed the influence of environmental factors on the Weighted Mean Depth (WMD) of these species, considering differences between males, females and juveniles. Planktonic ostracods were collected during a research cruise in July 2003 at a depth of 1200 m. A total of 152 vertical hauls, divided into 19 sample series, were conducted from the surface to the seafloor at standard oceanographic depths at four times of day. The results showed that the species Archiconchoecia striata, Porroecia spinirostris and Conchoecia magna exhibited significant DVM and migrated daily between the surface and deeper waters. In contrast, the species Porroecia porrecta porrecta, Mikroconchoecia curta, Proceroecia procera, Proceroecia microprocera, Discoconchoecia elegans, Paraconchoecia spinifera and Metaconchoecia rotundata showed less movement. Species with subtle DVM were Porroecia porrecta adriatica, Mikroconchoecia echinulata, Proceroecia macroprocera, Paramollicia rhynchena and Loricoecia loricata, reflecting their adaptation to environmental factors such as hydrographic and biological conditions. Our analysis of WMD revealed noteworthy differences in the vertical distribution of ostracods, focussing on their diurnal migration patterns and depth preferences.