Annual cycle of protozoan communities in an estuarine epibenthic sublittoral area

A protozoan community living in sandy marine sediments in a shallow sublittoral environment was studied in terms of diversity, density and biomass. Different abiotic parameters (granulometry, pH, temperature, dissolved oxygen, redox potential, salinity and conductivity) were recorded, as well as factors relating to nutrients (phosphate, nitrate, nitrite and organic matter). Bacterial biomass was also analyzed. The protozoan species were grouped as follows: ciliates, pigmented flagellates (AFLA), heterotrophic flagellates (HFLA), pigmented dinoflagellates (ADIN), heterotrophic dinoflagellates (HDIN) and sarcodines. Despite the fact that with regard to the relative frequencies of protozoan species, there were statistical differences between the sampling points, no significant differences existed when the protozoan groups were considered throughout the year. In addition, there were no differences with respect to surveys previously carried out in the same and neighbouring areas, and using the protozoan groups mentioned, which shows their stability. The trophic relations between these protozoan groups have been deduced from the data and the statistical results. The annual cycle appeared divided into four stages: herbivorous web (February–April), microbial loop (May–July), microbial web (August–October) and multivorous web (November–January).