Colonization of newly forming Arctic sea ice by meiofauna: a case study for the future Arctic?

Global warming has led to a strong deterioration of the Arctic sea ice cover. Ice thickness, age and coverage have been strongly declining in recent years. Brine channels that form in sea ice when seawater freezes represent a unique habitat for bacteria, algae, proto- and small metazoans. We hypothesized that the loss of multi-year ice and the more prevalent formation of first-year ice even in central regions of the Arctic will lead to changes in the Arctic sea ice meiofauna community composition. We therefore analysed the sea ice meiofauna community composition of three different ice types sampled in summer and autumn 2007. Young, thin ice of few cm thickness was typified by taxa of pelagic origin or with good swimming abilities (ciliates, pelagic foraminifera, rotifers and platyhelminthes). Harpacticoid copepods and nematodes with poor swimming abilities were prevalent in older, thicker (>0.5 m) first- and multi-year ice. Brash ice—which was likely a mix of older broken ice, slush and pancake ice—was characterized by a high abundance of platyhelminthes and rotifers. An experimental analysis of colonization efficiencies of artificial thin ice also revealed that species with poor swimming ability are less successful to colonize newly forming thin ice. We conclude that observed and predicted changes in the ice formation regime will likely result in changes in the composition of Arctic sea ice communities. We predict negative effects particularly for species with low dispersal capacities like harpacticoid copepods and endemic nematodes, as these are less successful in colonizing newly forming thin ice