engleski

Annual distribution of marine cladocerans in the coastal area of the Southern Adriatic (Croatia)

Cladocerans rapidly react on enviromental changes make this group possible indicator of environment changes. From March 1989 to May 1990 samples were taken at a five neritic stations in southern Adriatic at 5 and 2 meter intervals from the surface to the bottom with a 125 ľm mesh using the "ADRIATIC" sampler type of 250 l volume. At the offshore station P-100 material was collected during 44 cruises from May 1996 to May 1997. Samples were taken in a three depth layers with 200 ľm Nansen net. The observed changes of cladocerans populations densities, seasonal species succession and vertical distribution were interpreted to assess the proportion of environment influences. At the oligotrophic stations P-100 and the Lokrum Channel, and in the naturally eutrophicated Mali Ston Bay we noted a regular seasonal successions of species. The most numerous cladocera at these stations was Penilia avirostris. The maximum number of 9360 ind.m-3 in the Mali Ston Bay at 8 m depth accords with results of cladocerans population densities in the stable coastal areas. At a moderately anthropogenic eutrophicated Gruž Bay and Ombla River estuary a very high number of juvenile specimens of Podon polyphemoides in the surface layers and the juvenile P. intermedius at the bottom layers were noted. The values of 100 332 ind.m-3 at 5 m depth and 103 032 ind.m-3 near the bottom in the Ombla River estuary surpassed the maximum numbers of cladocerans in other coastal regions. Thus high numbers of cladocerans may be indicators of highly eutrophicated environment.

cladocerans; distribution; coastal regions; environment influences

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