engleski

Diel vertical migration of medusae in the open Southern Adriatic Sea over a short time period (July 2003)

The present work reports data for medusan DVM at an open-water station in the oligotrophic South Adriatic Sea sampled at morning, midday, evening and night. Among the 26 species identified in the present study, the most abundant hydromedusa was R. velatum, followed by A. hemistoma, R. singulare, P. incolorata, and S. albescens. The less numerous but frequently occurring species were A. australis, A. rubra, and O. funerarium. Seven medusae exhibited substantial depth range distribution. The highest DVM ranges were noted for the deep-sea species S. albescens, O. funerarium, and A. australis. Rhopalonema velatum, P. incolorata, and R. singulare migrated in both directions at evening and night, whereas Amphinema rubra migrated only to deeper waters. Aglaura hemistoma primarily is non-migratory. The interplay of environmental and trophic factors may explain some of the differences observed in medusan DVM: (i) for most medusae, a thermocline at about 15 m depth was an effective upper barrier ; (ii) different populations associated with layers characterized by species-specific preferences for light intensity tend to stay within layers of relatively constant light intensity ; (iii) the significant correlations in DVM were noted between the common medusae and their typical preys. Our findings contribute additional and important understanding of the role of planktonic cnidarians in the marine environment.

Adriatic; Cnidaria; jelly plankton; Mediterranean Sea; medusae; vertical distribution; weighted mean depth

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