Vertical mesozooplankton abundance and distribution in the deep eastern Mediterranean sea southeast of Crete, Greece.

Mesozooplankton from the Levantine Basin, Eastern Mediterranean, were analysed for composition and vertical distribution from the surface to 4000 m, with special emphasis on calanoid copepods. Copepods were dominant, ostracods and chaetognaths ranked next. Zooplankton abundance and biomass were highest in the top 100 m layer. A secondary concentration maximum was between 450 and 750 mM. The exponential decrease of zooplankton with deph was stronger than in the open ocean, but less strong than in the Red Sea. Similarly to the Red Sea, three genera among calanoid copepods, were predominant in the deep sea. As with the Western Mediterranean, but different from the Red sea, populations of mesopelagic and one bathypelagic species were found to occur well below 1250 m to depths of at least 3000 m. Similarly to both seas, long-range vertical migrators were rare, those present mainly belonging to the genus Pleuromamma, and diel migrations were restricted to the upper 600 or 1000 m. Due to the high temperatures in the deep water bodies of the Levantine and Red Seas, the decomposition of sedimentary particles is assumed to be accelerated. This prevents much detritus from reaching the sea floor which may explain the anomalous low abundances of deep-sea zooplankton and benthos. Though the similarities to the Red Sea seem to be strong, the Levantine Sea is likely to hold an intermediate position between the open ocean and the Western Mediterranean on one side and the Red Sea on the other side.