Wiggling in the deep – Diversity of Arctic deep-sea nematodes at the long-term ecological research observatory HAUSGARTEN

Nematodes are the most abundant multicellular organisms on this planet and yet our knowledge of them is still very limited. They occur as parasites or free-living in virtually every environment, ranging from terrestrial soils, to sediments in fresh-, brackish-, and marine waters, down to the deepest trenches in the oceans. Free-living nematodes constitute a major part of the so called meiofauna, a group of different animal phyla with a size between 32 µm and 500 µm, which inhabits the interstitial space between the sand grains. In deep-sea sediments, more than 95% of all meiofauna organisms are free-living nematodes, with abundances ranging from 1mio. to 12mio. individuals per square meter. They express different feeding types, ranging from selective microbial feeders to predators and play a big role in nutrient recycling. But in one way or the other are all feeding-types reliant on food input from the water column above, whose composition is changing with changing environmental conditions in surface waters. Therefore, studying nematode diversity can be a way of monitoring surface/deep-sea relations and also effects of climate change in the deep ocean. The annual meiofauna sampling in the long-term ecological research deep-sea observatory HAUSGARTEN, which has been established by the Alfred-Wegener-Institute in the marginal ice zone of the Fram Strait more than 20 years ago, provides the world’s longest time series on deep-sea meiofauna, allowing for a comprehensive investigation of the deep-sea nematode community with abundance- and functional-based biodiversity analyses over spatial and temporal scales