Thalassiosira species (Bacillariophyceae, Thalassiosirales) in the North Sea at Helgoland (German Bight) and Sylt (North Frisian Wadden Sea) – a first approach to assessing diversity

Thalassiosira species are an important component of phytoplankton populations in pelagic waters around the islands of Helgoland and Sylt in the German North Sea. This taxonomic study revealed the presence of at least 27 species, 21 at Helgoland and 21 at Sylt. Fifteen species had not been recorded previously for Helgoland (T. aestivalis, T. angulata, T. concaviuscula, T. curviseriata, T. delicatula, T. diporocyclus, T. hendeyi, T. kuschirensis, T. minima, T. minuscula, T. oceanica, T. pacifica, T. proschkinae, T. tealata, T. tenera) and 16 for Sylt (T. aestivalis, T. angulata, T. concaviuscula, T. constricta, T. curviseriata, T. delicatula, T. guillardii, T. hendeyi, T. lundiana, T. mediterranea, T. minima, T. pacifica, T. partheneia, T. punctigera, T. tealata, T. tenera). We provide brief descriptions with illustrations and document the seasonal occurrence of these species at the two stations. We also discuss investigation methods used for different levels of species recognition, namely Utermohl counts, ...