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Species composition and ecological preferences of the most important periphytic diatom taxa were studied in lentic ecosystems in the salt marshes of Emporda wetlands (NE Spain). Correspondence analysis with the diatom communities suggested that water confinement/flooding gradient and productivity of the system were the principal factors affecting diatom distribution in the salt marshes of Emporda wetlands. Hierarchical analysis clusters allowed 5 diatom assemblages be distinguished, each one characteristic of different degrees of confinement and productivity. Bacillaria paradoxa appeared as the most characteristic species in low confinement and high productivity conditions. Navicula perminuta and N. salinarum were representative of flooding and low productivity conditions. During maximum confinement and low productivity situations Cocconeis placentula dominated the diatom community. When maximum confinement was attained in the waterbodies with higher productivity, this dominance was shared with Nitzschia archibaldii. The 39 species considered proved to be tolerant to salinity and nutrients (nitrogen, phosphorus and organic matter) variability. This seems to be a prerequisite for survival in salt marshes where the very dynamic nature of the system results in a large variability of the physical and chemical water composition.

A study of the diversity and succession of phytoplankton in the Lagos Lagoon was carried out for two years 1988-1989. Species richness (d) and Shannon and Weaver Index (H) decreased inland while the relationship between equitability (J) and total number of individuals (N) was inverse. There was greater similarity between stations in the wet season and among stations close to one another. Coscinodiscus, Aulacoseira, Bacillaria, Odontella, Gomphosphaeria, Paralia, Desmidium, Microcystis, Hyalodiscus and Amphora were possibly the most prevalent phytoplankton genera in the lagoon at different periods.