The effects of Po River induced eutrophication on the distribution and conimunity structure of ciliated protozoan and micrometazoan populations in the northern Adriatic Sea

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Abstract
The ciliated protozoans and micrometazoans in the northern Adriatic were repeatedly sampled and analyzed during summer and winter periods, with emphasis on quantifying the changes in abundance, and community structure, associated with a trophic gradient created by the discharge of the Po River. The community was characterized by major groups, organism abundance and volume, and size class frequency. The microzooplankton biomass increased 2- to 3-fold toward the western side of the Adriatic off the Po delta, during both ‘mixed’ and ‘stratified’ seasons, with increases in both the ciliated protozoans and micrometazoan components. At eutrophic sites and under ‘stratified’ conditions a marked increase in the relative abundance of ciliated protozoans was observed, with a relative increase in tintinnid contribution to the total ciliated protozoan biomass. Although marked changes in the ciliated protozoan biomass occurred, little change in their size class structure occurred except as influenced by inflowing waters from the central Adriatic.