Pan-Arctic distribution of the hydrozoan Sympagohydra tuuli? First record in sea ice from Svalbard (European Arctic)

Arctic sea ice is rapidly declining in presence, thickness and extent. The consequences that this has for the overall biodiversity in Arctic marine ecosystems are poorly addressed. Especially the so-called sympagic meiofauna, the many tiny organisms living in sea ice, is rarely identified to species level. Here we present the first record of the hydrozoan Sympagohydra tuuli living in sea ice in the Svalbard fjords (European Arctic). Previously, this tiny ice-cnidarian has only been reported from sea ice of Barrow (Alaska), the Canadian Arctic and the central Arctic Ocean. In April 2015, two small hydrozoans were recorded in the landfast sea ice in Van Mijenfjorden (West Spitsbergen). Both of them were preserved in ethanol and one specimen was successfully identified with Sanger sequencing. DNA barcoding confirmed it to be the Protohydridae S. tuuli. Little is known about S. tuuli lifecycle, but its occurrence within the sea ice of seasonal ice-covered fjords in Western Svalbard with no sea-ice connection to the Arctic Ocean strengthens the theory about a sympago-benthic life strategy. We propose that S. tuuli has a pan-Arctic distribution and only spends parts of its life cycle in sea ice.