Distribution of Hydromedusae Population and Aglaura hemistoma Peron and Lesueur, 1810 (Cnidaria, Hydrozoa) in the surface layers (0-10 m) of Izmir Bay (Aegean Sea)

Sufficient information regarding the distribution of Hydromedusae communities in the waters of Turkey and the Aegean Sea is not available. Aglaura hemistoma (Cnidaria, Hydrozoa) is investigated for the first time in Izmir Bay (Turkey). Study material was collected in April by vertical samplings from 10 m depth to the surface at stations distributed from the innermost section to the mouth of the bay. Hydromedusae communities displayed a low abundance (max 50 ind./m super(3)) in the area and represented a very small proportions (maximum 0.69%) of the total zooplankton population. They are observed to be more abundant in waters close to the shore except for the very polluted inner section of the bay. The abundance of A. hemistoma and its proportion in the hydromedusae population increased significantly at the mouth of the bay which is deeper. However, a remarkable decrease in abundance is observed in direction to the inner side. This species is almost disappeared around the beginning of the middle bay area, and is not found further inside, shalower and polluted. A. hemistoma is a markedly offshore form. The distributional patterns of this species in Izmir Bay progress depending on the effect of the currents from the Aegean Sea. So the spread of the species in the study area indicate weakening effect of the open sea currents near the middle bay area.