Morpho-molecular characterization of sand-dwelling dinoflagellate communities from the German Wadden Sea and insights into their spatiotemporal distribution

Benthic protist communities, including sand-dwelling dinoflagellates, are still poorly characterized worldwide and there is a lack of knowledge on their diversity and spatiotemporal dynamics. In this study, sediments were obtained from several coastal locations of the German Wadden Sea during the summer months of 2017 and 2018 to determine the diversity and spatiotemporal distribution of sand-dwelling dinoflagellates. The analyses consisted of light microscopy and the metabarcoding of small subunit (SSU) rRNA gene V4 region amplicons. Additionally, SSU rRNA sequences were newly obtained for 15 observed taxa included in a reference database and were used to taxonomically assign the obtained amplicon sequence variants (ASVs). The combination of morphological and molecular approaches allowed a deep characterization of dinoflagellate communities. Seventy-three morphospecies were detected by microscopy, while metabarcoding ASVs (amplicon sequence variants) were assigned to 116 species, resulting in a more comprehensive biodiversity inventory than achieved with either method alone. Pfiesteriaceae, Togula compacta and Thecadinium yashimaense predominated in the different sampling locations. Communities from Wilhelmshaven diverged from the others, consistent with its muddier sediment. A high level of resemblance was determined for the communities from each location, regardless of the sampling month and year, indicating a high summertime stability of benthic communities. Further efforts will be needed to characterize benthic protist diversity, as a first step in obtaining a complete picture of the habitat characteristics and physico-chemical conditions that influence benthic community composition. Metabarcoding and microscopy observations provide complementary results.Much of the diversity of sand-dwelling dinoflagellates is uncharacterized.Benthic dinoflagellate communities were stable at each location in summer.