Dinoflagellate diversity in the Barents Sea: a comparative identification analysis

An important group in the protist community in marine habitats are dinoflagellates. In this study the diversity of dinoflagellates in a transect of seven pelagic sea stations in the Northern Barents Sea in August 2018 and August 2019 was assessed. The two sampling periods were characterized with low and high sea-ice extent, respectively. I have studied the diversity and presence of dinoflagellate species in the sample transect using the molecular method DNA metabarcoding, and the morphological methods light microscopy (LM), and scanning electron microscopy (SEM). The results from species identification were used to observe and compare potential differences in the two sampling years. It was shown that the morphological methods were limited in identification success by little amount of material in several of the vertical net haul samples, resulting in some bias when these results were compared with DNA metabarcoding that revealed a high number of OTU (operational taxonomic unit) reads assigned to division Dinoflagellata. Species classification by DNA metabarcoding was shown to be limited by the availability of reference sequences in the curated protist ribosomal database PR2. It yielded a rough overview of the composition of dinoflagellate species in the sampling transect that could be closer examined with more time to study single OTUs. Identification done by LM and SEM revealed the presence of genera in certain stations that was not revealed in metabarcoding, and vice versa. I also found that Lugol’s solution functioned well for the preservation of cell structure for sample analysis in SEM. Climate change is shown to cause more and rapid alterations in the Arctic, and the loss of sea-ice is an important consequence of a warmer climate. Regarding interannual differences in 2018 and 2019, the morphological methods showed some differences in species composition with genus Protoperidinium more often identified in 2018 than other species, and the same for Gymnodiniales species in 2019. This could potentially show a shift in phytoplankton communities in a changing environment, although time-series are necessary to predict the future compositions of dinoflagellate species. As phytoplankton makes up the fundament for the Arctic food chain, studies of changing environmental conditions are valuable for ecological reasons.