A short-term investigation of diel vertical migrations of the calycophoran Siphonophora in the open south Adriatic Sea (July 2003)

Morning, midday, evening and night repetitive sampling was used to demonstrate calycophoran diel vertical migration (DVM) at a fixed station in the oligotrophic southern Adriatic Sea at 8 depth intervals. Of 20 calycophoran species collected, most of them inhabited layers of specific temperature and light intensity, and migrated during the night. The deep species Kephyes ovata is primarily non-migratory. Typical nocturnal movements to the surface were recorded for Lensia conoidea and Sphaeronectes koellikeri. Lensia subtilis and Eudoxoides spiralis migrated toward the surface in the evening but sank deeper at night. Lensia meteori and Lensia fowleri reached upper layers at midday. The DVM of Sphaeronectes irregularis was irregular and independent of diel light patterns. Though low in numbers, some calycophorans were found above the thermocline at night. For mesopelagic species, however, higher summer surface temperatures proved an effective barrier to migration above 100 m. Thus, certain species could be represented as key species of planktonic cnidarian assemblages found within a certain depth range. Though not homogenous, and while some undertake nocturnal migrations in both directions, all are interrelated by preferences of bathymetric distribution and specific DVM behavior.Original Abstract: Istrazivanje dnevne vertikalne migracije (DVM) kalikofora obavljeno je na jednoj postaji u oligotrofnom juznom Jadranu neprekidnim uzimanjem uzoraka unutar 8 dubinskih slojeva tijekom jutra, sredine dana, popodneva i noci. Od 20 zabiljezenih vrsta kalikofora, glavnina obitava unutar slojeva karakteristicne temperature i dnevnog intenziteta svjetlosti, a migriraju nocu. Duboka vrsta Kephyes ovata nije migratorna. Tipicne nocne migracije prema gornjim slojevima su zabiljezene za vrste Lensia conoidea i Sphaeronectes koellikeri. Sifonofore Lensia subtilis i Eudoxoides spiralis migriraju prema povrsini u vecernjim satima, a nocu tonu dublje, dok su Lensia meteori i Lensia fowleri nadene u visim slojevima tijekom sredine dana. DVM vrste Sphaeronectes irregularis bile su nepravilne i neovisne o dnevnoj promjeni intenziteta svjetlosti. Manji broj vrsta kalikofora naden je tijekom noci iznad sloja termokline, a za mezopelagicne vrste, 100 m dubine bila je gornja migratorna granica. Stoga, kalikofore mogu predstavljati kljucne vrste zajednice planktonskih zarnjaka unutar pojedinih dubinskih raspona. Premda nisu homogene i neke vrste obavljaju migracije u oba smjera, povezan