The microbenthic community, mainly the microalgal part, was studied to assess the role of inorganic and organic nutrients, as well as the importance of this algal community for other processes in the sediment. The sediment was collected from two types of micro-tidal shallow-water sediment: a sandy beach (moderately wind exposed); and a bay with fine-grained sediment (sheltered) on the Swedish west coast, the northern Skagerrak. The sandy sediment was dominated by autotrophic biomass, mainly pennate diatoms, all year round and the balance between autotrophic and heterotrophic (bacteria, ciliates and meiofauna) biomass did not change with water depth (< 4m). A substantial microbial activity occurred even during winter. Vital planktonic diatoms contributed to the benthic microalgal biomass in spring. Algae appeared to be a more important food source than bacteria for meiofauna. A thin sand-agar substratum was found to to be a useful tool in short-term experiments to facilitate the study of nutrient uptake and response of microphytobenthos to environmental changes.

An experiment with changed Si:N:P ratios suggest that a raised N:Si ratio, as a result of eutrophication, will change the composition of the microphytobenthos towards a community dominated by algae other than diatoms, e.g. flagellates, cyanobacteria and filamentous green algae.

Microautoradiography was used to assess the proportion of autotrophic cells and biomass capable of taking up dissolved free amino acids (DFAA), supplied as a tritium-labelled mixture to a natural microbenthic community in a sandy sediment. The microalgae took up DFAA all year around. Uptake was most frequent among diatoms, on average 23-30% of the cells showing uptake.

An experiment on the effect of juvenile CRANGON CRANGON suggests that epibenthic predators have only a small trophic impact on microalgae and bacteria, although a slight stimulus was noted, most probably via reduced meiofaunal grazing and nutrient excretion by CRANGON. The behaviour of the large diatom GYROSIGMA BALTICUM was observed in intact microbial mats from silty sediment.