Data underlying the publication: Lack of Hematodinium microscopic detection in crustaceans at the northern and southern ends of the Wadden Sea and an update of its distribution in Europe

<em>Hematodinium</em> is a parasitic dinoflagellate with a wide distribution along the European coastline. We investigated whether <em>Hematodinium</em> occurs in the Wadden Sea, a large tidal flat system spanning the Netherlands, Germany and Denmark, where to date no records exist. In total, we investigated eight different species from six sites at the southern (Texel, Netherlands) and northern ends (Sylt, Germany) of the system. Based on microscopic hemolymph screening, we did not detect <em>Hematodinium</em> in any of the 1252 investigated individuals. An extensive additional literature review revealed 1489 <em>Hematodinium</em> records in Europe from 14 crustacean species, most locally occurring at high prevalence. This makes our finding of lack of <em>Hematodinium</em> infections surprising and suggests that environmental factors such as a lower salinity may limit the distribution of <em>Hematodimium</em> at the investigated locations at both ends of the Wadden Sea. However, whether the entire Wadden Sea represents a distributional gap for <em>Hematodinium</em> remains to be investigated.

血卵涡鞭虫（Hematodinium）是一类广泛分布于欧洲沿海海域的寄生性双鞭毛虫。本研究旨在探究横跨荷兰、德国与丹麦的大型潮间带系统瓦登海（Wadden Sea）中是否存在血卵涡鞭虫——截至目前，该区域尚无该寄生虫的相关记录。研究人员在瓦登海南部（荷兰特塞尔岛）与北部（德国叙尔特岛）的6个采样位点，共对8个不同物种的个体开展了检测。通过镜检血细胞淋巴液的方式筛查后，在总计1252份受试个体样本中均未检出血卵涡鞭虫。本研究开展的详尽补充文献调研显示，欧洲地区共记录有14种甲壳动物感染血卵涡鞭虫的案例共计1489条，其中多数记录的局部感染率较高。该结果与本次未检出感染的结论形成鲜明反差，提示盐度偏低等环境因素可能限制了血卵涡鞭虫在瓦登海南北两处采样位点的分布范围。然而，整个瓦登海是否均属于血卵涡鞭虫的分布空白区，仍有待后续研究进一步验证。