Diversity and biogeography of planktonic diatoms in Svalbard fjords: The role of dispersal and Arctic endemism in phytoplankton community structuring

Abstract

Understanding the processes that shape the community structure of Arctic phytoplankton is crucial for predicting responses of Arctic ecosystems to the ongoing ocean warming. In particular, little is known about the importance of phytoplankton dispersal by the North Atlantic Current and the prevalence and maintenance of Arctic endemism. We investigated the diversity and biogeography of diatoms from five Svalbard fjords and the Hausgarten observatory (Fram Strait) by combining diatom cultivation and 18S rRNA gene metabarcoding. In total, 50 diatom strains were isolated from the area during the HE492 cruise in August 2017. The strains were identified taxonomically using molecular and morphological approaches, and their biogeographic distribution was mapped using the local metabarcoding dataset and a global compilation of published metabarcoding datasets. Biogeographic analysis was also conducted for the locally most abundant diatom metabarcoding amplicon sequence variants. The biogeographic analyses demonstrated that Arctic diatoms exhibit three general biogeographic distribution types: Arctic, Arctic-temperate, and cosmopolitan. At Hausgarten and in outer Isfjorden on the west coast of Svalbard, the communities were dominated by genotypes with Arctic-temperate and cosmopolitan distribution. Diatom communities in nearby Van Mijenfjorden, inner Isfjorden and Kongsfjorden were dominated by genotypes with Arctic-temperate distribution, and cosmopolitan species were less abundant. The genotypes endemic to the Arctic had lower abundance on the west coast of Svalbard. The two northernmost fjords (Woodfjorden and Wijdefjorden) had a higher abundance of genotypes endemic to the Arctic. Our results demonstrate that the diatom communities in the Svalbard area consist of genotypes endemic to the Arctic, and genotypes with broader biogeographic distribution, all of which are further structured by local environmental gradients. Finer biogeographic patterns observed within Arctic-temperate and cosmopolitan genotypes suggest that certain genotypes can be used as indicators of increasing influence of Atlantic waters on the phytoplankton community structure in the Svalbard area.

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“…Previous DNA‐metabarcoding studies in the microscopy realm have considered large taxonomic groups rather than particular species and have an emphasis on the spatial (Boenigk et al., 2018; Gollnisch, 2022; Rimet et al., 2018; Šupraha et al., 2022) rather than the temporal occurrence of protists (Bruhn et al., 2021; Mordret et al., 2023; Siano et al., 2021; Sildever et al., In press). Water temperature is considered one of the most important environmental variables filtering the presence of protists in a given habitat (Rose & Caron, 2007; Weisse et al., 2016).…”

Winners and Losers of Atlantification: The Degree of Ocean Warming Affects the Structure of Arctic Microbial Communities

“…The data of both categories were assembled through an unstructured literature search via WoRMS [ 57 ] based on previous categorizations by Hörstmann et al [ 58 ] and Schneider et al [ 59 ]. The classification of thermal niches into Arctic, Arctic-temperate and cosmopolitan was performed as described by Šupraha et al [ 60 ]. Whenever categories were unclear, species were marked as uncategorized.…”

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“…With cultures, we can obtain both the morphology and long sequences of many genes, which enables the discovery and description of novel species and phylogenetic placement. Šupraha et al (2022) discovered that many species in the Arctic are morphologically similar to temperate species but are genetically different and may represent novel species or varieties. A search against the 18S rRNA gene database metaPR2 (Vaulot et al, 2022), presently containing 41 metabarcoding data sets from 4000 samples from marine waters, can reveal the geographical distribution where a genotype has been found before in the data sets and under which environmental conditions.…”

“…A search against the 18S rRNA gene database metaPR2 (Vaulot et al, 2022), presently containing 41 metabarcoding data sets from 4000 samples from marine waters, can reveal the geographical distribution where a genotype has been found before in the data sets and under which environmental conditions. By using the metaPR2 database, Šupraha et al (2022) discovered that several diatom genotypes isolated from Arctic Svalbard seem restricted to the Arctic, whereas other diatom genotypes had either an Arctic temperate or cosmopolitan distribution.…”