The occurrence of Nematoda in coastal sea ice on Svalbard (European Arctic) determined with the 18S small subunit rRNA gene

Abstract

Understanding the diversity and functioning of Arctic sea ice ecosystems is vital to evaluate and predict the impact of current and future climate change. In the microscopic communities inhabiting the brine channels inside sea ice, nematodes often dominate numerically and act as bacterivores and herbivores. Despite nematodes great abundances and known ecological roles, molecular tools have not been applied to investigate their species diversity in sea ice. In an attempt to begin establishing a molecular baseline for species diversity of sea ice nematodes, we Sanger sequenced 74 specimens from four locations around Svalbard (European Arctic), using the 18S rRNA barcode. Currently available nucleotide reference databases are both underpopulated with representative marine nematode taxa and contain a substantial number of misidentified organisms. Together, these limitations inhibited the ability to identify marine specimens collected in this study with certainty. Nevertheless, our molecular data indicate the presence of two genera in sea ice on Svalbard—Theristus and Halomonhystera. While it is possible that the latter represents a novel ice nematode species, future studies, including morphometric analysis, are needed to verify our molecular findings. We leverage the assignment of molecular information to robustly identify nematodes and provide the first insight into the diversity of sea ice nematodes in the European Arctic. We advocate for an intensified cooperation between molecular and morphological taxonomists to expedite the establishment of baseline surveys that are required to predict biological consequences of the diminishing sea ice habitat in the future.

Temporal and spatial variability of sympagic metazoans in a high-Arctic fjord, Svalbard

“…Samples were analyzed either alive or after fixation in 96 % ethanol or 4 % formaldehyde (Table 1, Supplementary material 1). Both ethanol and formalin were used to have samples available for DNA extraction (see Pitusi et al, 2021), as well as purely for community count and composition. A Leica stereomicroscope (Leica M16, 0.71 -11.5 x, Wetzler, Germany) was used to identify and count sympagic meiofauna.…”

“…No identification keys for eggs were available and thus photographs were taken, and their width and color was noted. A sub-sample of eggs was identified molecularly (see Pitusi et al, 2021). Although eggs do not represent distinct taxa, in this study, we considered them as a unique part of the community and included them in the abundance count.…”

First trait-based characterization of Arctic ice meiofauna taxa

“…The literature survey was composed of both relatively early observations of Arctic sea ice fauna (Carey and Montagna 1982;Chengalath 1985) and more recent comprehensive lists (Riemann and Sime-Ngando 1997;Friedrich and De Smet 2000;Arndt and Swadling 2006;Pitusi 2021). Halectinosoma finmarchicum, appearing most recently in Arndt and Swadling (2006), had been reclassified as H. elongatum in Clément and Moore (2000).…”

“…Most Nematoda are either only sympagic or sympagic-benthic (Fig. 2g) (Tchesunov and Riemann 1995;Tchesunov and Portnova 2005;Portnova et al 2019;Pitusi 2021), All Acoela are only known from the ice (Fig. 2g).…”

“…However, few studies describing full tolerance ranges existed, and most species-level information was instead inferred from the temperature and salinity at which an organism was sampled (e.g., from Friedrich and De Smet 2000;Marquardt et al 2011). Most data were recorded at genus or family level and this lower taxonomic resolution, coupled with the fact that many sympagic species share genera and family (Friedrich and De Smet 2000;Bluhm et al 2017;Pitusi 2021), naturally caused the data to tend toward uniformity among taxa. Additionally, brackish water tolerance was better documented than brine tolerance, and the fact that almost all studied species could tolerate 0-25 to some degree introduces a bias toward lower salinities in the data.…”