Epipelic diatom spatial and temporal distribution and relationship with the main environmental parameters in coastal waters

The benthic diatom abundance and taxonomic composition were investigated in the Venice lagoon to integrate the knowledge on the trophic food web of shallow coastal areas. Samples of surface sediment layer (ca. 1 cm) were collected and stored until inverted light microscope determination. One-year comparison was carried out in six sites with a monthly frequency. In summer 2003, sediment cores were also collected at 165 stations distributed throughout the whole lagoon. Abundance varied between 0.26 and 5.65 × 106 cells ml−1, whereas the Shannon diversity index ranged between 0.93 and 4.36 H′ depending on seasonal and spatial variability. The seasonal variations were not correlated with water temperature, although it varied between 6 and 29 °C, but with nutrient concentrations, sediment re-suspension and grain size. The spatial fluctuations mostly were influenced by water turbidity. Amphora, Cocconeis, Navicula, Nitzschia and Thalassiosira were the most common genera. Thalassiosira sp. constituted an interesting case as it was quite abundant near the mainland and was correlated with nutrient concentrations. The community structure was investigated by applying univariate and multivariate statistical analysis such as cumulative dominance curves, cluster analysis and canonical correspondence analysis.