ABSTRACT: Compared to plankton, benthic communities are thought to be heterogeneous among sites and more stable through 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 3 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 similar richness, alpha-diversity, and community composition among sand-dwelling dinoflagellates at the 3 locations. Dinoflagellates affiliating with the Thoracosphaeraceae or Gymnodiniales sensu stricto were highly represented. In contrast, other well-known dinoflagellate taxa, such as Gonyaulacales or Dinophysales, were poorly represented or absent. Dinoflagellate communities showed significant differences between the 2 studied seasons, mainly driven by water temperature. Samples from temperate months had 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 in shaping community composition. The 3 studied locations had a similar dinoflagellate community composed of sand-dwelling taxa, with many representatives of undescribed species, highlighting the need to further study the diversity of the benthic compartment.

中文翻译：

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来自三个地中海海滩的沙生鞭毛藻群落的组成和时间动态

摘要：与浮游生物相比，底栖生物被认为在地点之间是异质的，并且随着时间的推移更加稳定。然而，很少研究底栖生物，尤其是栖沙的鞭毛虫，其多样性仍然未知。为了检验这些说法，我们研究了温带春季和夏季温暖月份从3个西北地中海沿岸地区获得的含沙沉积物中底栖鞭毛藻群落的多样性，结构和时间动态。使用海水冰方法从基质分离原生质细胞后，对V4 18S rRNA基因区域进行高通量扩增子测序，然后对扩增子序列变异体（ASV）进行分析，显示出相似的富集度，α多样性和沙子间的群落组成在3个位置居住的鞭毛虫。与胸果科或严格的Gymnodiniales sensu stricto有联系的恐龙鞭毛虫被高度代表。相比之下，其他著名的鞭毛类生物，例如or龙或犀牛，则代表性很差或不存在。鞭毛藻群落在两个研究季节之间显示出显着差异，这主要是由水温引起的。温带月份的样本具有较高的多样性，且相异程度更高，而温带月份的样本具有较低的多样性和较高相似度。一些物种始终存在于社区中，其他物种只是偶尔出现，而其他物种则表现出明显的季节差异。我们的结果表明，在塑造社区组成方面，大规模的变化（指向季节性）胜于空间的异质性。