OFFSHORE DIEL VERTICAL DISTRIBUTION OF MESO/MACRO-HOLO/MERO ZOOPLANKTON IN THE SOUTHERN BLACK SEA

Diel vertical distribution and migration (dvm) of meso and macro zooplankton in the black sea were studied at one constant station using plankton net in april 1995 and macro zooplankton in august 1993. five common copepod species were found during the studies. acartia clausi was distributed in the uppermost layers, pseudocalanus elongatus within layer with temperature < 8 ˚c (the cil), calanus euxinus throughout the oxygenated layer, oithana similis above the cil in summer but in both the cil and the upper mixed layer in spring and autumn, and paracalanus parvus mostly in the upper layers. additionally, eight taxa belonging to non-copepods were evaluated in the present work; namely, appendicularia (oikopleura dioica), cladocera (pleopis polyphemoides, podon leucarti, p. intermedius, evadne spinifera, and e. nordmanni), cirripedia larvae, polychaete larvae, bivalvia larvae, chaetognatha (sagitta setosa), scyphozoa (aurelia aurita), and ctenophora (mnemiopsis leidyi and pleurobrachia pileus). three different groups were observed in regard to their vertical distribution layers: the uppermost layer inhabitants (cladocera, bivalvia and cirriped larvae, aurelia and mnemiopsis) that were distributed in correlation with the chlorophyll-a and fluorescence within a narrow depth range; the second group, appendicularians formed patch in both the upper layer with high chl-a and fluorescence, and the deep water characterized with fine-particle maxima whereas pleurobrachia and sagitta were found within the cil; deep layer dweller (polychaete larvae) migrated within the deep homogenous layer in reverse relation to pleurobrachia migration. mnemiopsis extended over a narrow range of vertical depth by day and night being confined to the upper part of the mixed layer. few individuals were localized below thermocline at night. pleurobrachia was found mostly beneath the thermocline down to the anoxic layer. the vertical distribution of pleurobrachia was manifested by a two-maximum structure at night. upper maximum was less pronounced than the lower maximum during the day time. aurelia was strictly associated to the upper mixed layer and layer above seasonal pycnocline.