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

Davor LUČIĆ1*, Adam BENOVIĆ1, Mirna BATISTIĆ1, Mira MOROVIĆ2, Ivona ONOFRI1, Juan-Carlos MOLINERO3, Tjaša KOGOVŠEK4, Barbara GANGAI1and Marijana MILOSLAVIĆ1

1 Institute for Marine and Coastal Research,
University of Dubrovnik, Dubrovnik,
D. Jude12, 20000 Dubrovnik, Croatia
2 Institute of Oceanography and Fisheries,
P.O. Box 500, 21000 Split, Croatia
3Leibniz Institute of Marine Sciences,
IFM-GEOMAR, 24105 Kiel, Germany
4Marine Biological Station, National Institute of Biology,
6330 Piran, Slovenia
*Corresponding author, e-mail: davor.lucic@unidu.hr

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 tempera-ture 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 pat-terns. 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 cni-darian 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.

Key words: Cnidaria, PAR, jelly plankton, vertical distribution, Mediterranean Sea

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