Protist communities living in sandy sediments located at the inner end of an estuarine area were studied throughout 1 yr. Eight physico-chemical parameters were measured, as well as nutrients and bacterial biomass. A total of 173 protistan species were found encompassing ciliate, autotrophic
flagellates, heterotrophic flagellates, autotrophic dinoflagellates, heterotrophic dinoflagellates and sarcodines. Total biomass values per sample ranged from 49.1 to 12,785.4 mg C m−3 and were dominated by ciliate biomass. Out of all the species isolated, a group of 33 were
frequently found: 11 ciliates, 13 flagellates, 8 dinoflagellates and 1 sarcodine. Relationships between different biotic groups and between these groups and the physico-chemical factors were analyzed. This allowed a division of the annual cycle into four periods (March–May, June, July–October,
November–February). Each period was characterized by certain protist species, physico-chemical conditions and events within the principal protist groups.
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