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Composition and temporal dynamics of sand-dwelling dinoflagellate communities from three Mediterranean beaches

Albert Reñé*, Mona Hoppenrath, Guillaume Reboul, David Moreira, Purificación López-García

*Corresponding author:

ABSTRACT: Compared to plankton, benthic communities are thought to be heterogeneous among sites and more stable along time. However, benthic protists in general, and sand-dwelling dinoflagellates in particular, have been scarcely studied and their diversity remains mostly unknown. To test those claims, we studied the diversity, structure and temporal dynamics of benthic dinoflagellate communities in sandy sediments obtained from three NW Mediterranean Sea coastal locations during temperate spring and warm summer months. After separating protist cells from the substrate using the seawater-ice method, high-throughput amplicon sequencing of the V4 18S rRNA gene region followed by the analysis of amplicon sequence variants (ASVs) showed a similar richness, alpha-diversity and community composition of sand-dwelling dinoflagellates in the three locations. Dinoflagellates affiliating to the Thoracosphaeraceae or Gymnodiniales sensu stricto were highly represented. By contrast, other well-known dinoflagellate taxa, such as Gonyaulacaceae or Dinophysales, were poorly represented or absent. Dinoflagellate communities showed significant differences between the two studied seasons, mainly driven by water temperature. Samples from temperate months showed higher diversity and were more dissimilar, while samples from warmer months showed lower diversity and higher similarity. Some species were always present in the community, others only appeared sporadically, and some others showed clear differences between seasons. Our results suggest that large-scale changes (pointing to seasonality) prevail over spatial heterogeneity to shape the community composition. The three studied locations showed a similar dinoflagellate community composed by sand-dwelling taxa, with many representatives of undescribed species, highlighting the need to further study the diversity of the benthic compartment.