Analysis of multitrophic plankton assemblages in the Lagoon of Venice

The paper illustrates the spatial and temporal succession of multitrophic plankton assemblages in the Lagoon of Venice and relates them to biogeochemical properties. Five communities were identified by recognizing patterns of co-occurrence of phyto-, protozoo- and metazooplankton organisms through a classification procedure combining self-organizing maps and cluster analysis. The complexity of time and space co-variation of 47 plankton taxa was thus compressed to the variation of only one qualitative variable. Biogeochemical observations provided information for an ecological description of the environment in which different biocenoses develop. Our results provide an objectively derived typology of plankton assemblages and an ideal representation of their typical succession in time and space. This can be used to better understand the dynamics of the plankton community, and as a reference term for the identification and evaluation of anomalous situations, as required by implementation of the EU Water Framework Directive. Our results indicated the importance of seasonality in ruling succession among different biocenoses. River inflows, exchanges with the sea, remineralization processes and benthic–pelagic coupling were all important factors in shaping plankton communities and defining their spatial extension. Autotrophy prevailed in late winter to spring in inner areas of the lagoon, whereas heterotrophy prevailed in late summer to early winter and generally in areas close to the inlets. Diatoms, including resuspended benthic species, dominated autotrophic compartments, and copepods Acartia spp. were the most abundant mesoplankton organisms. Our results also point out the prominent role of protozooplankton in the trophodynamic of the Lagoon of Venice.