Creepy-Crawlies of the Arctic deep sea: Metazoan meiobenthic communities across latitudinal and bathymetric gradients in the western Arctic Ocean

Knowledge on meiofauna in the Arctic Ocean is lacking despite their importance for ecosystem functioning. The Synoptic Arctic Survey aimed to fill such knowledge gaps and thus included meiofaunal sampling. A bathymetric transect (from shelf to central basins) was sampled in the western Arctic Ocean during the HLY2202 expedition. Four sampled transect stations were investigated to answer three key questions: (1) How does the meiofaunal community change along the transect? (2) Which sedimentary parameters drive the meiofaunal community compositions? (3) Has the meiofaunal community at the North Pole changed since 1996, and if so, how? The uppermost three centimeters of sediment were analyzed for metazoan meiofaunal composition (including meiofaunal abundance and nematode biomass) in relation to food proxies (i.e. bacterial abundance and biomass, organic carbon, phospholipids, chlorophyll a, phaeophytin) and sediment porosity. Meiofaunal density and taxa count decreased with increasing water and sediment depth, as did nematode body sizes. This supported the concept of deep-sea miniaturization. Thicker nematodes dominated near-surface sediments, while slimmer individuals dominated deeper layers, a pattern related to sediment porosity. Sediment pigments (i.e. chlorophyll) and bacteria were confirmed as important food sources, and sediment porosity was corroborated as an important driver of meiofaunal communities. Virtually no differences were found in abundance of higher meiofauna taxa at the North Pole between 1996 and 2022, potentially due to relative stability provided by the still permanent ice-cover. Examining the meiofaunal composition at genus level will allow analysis of potential changes in diversity and ecosystem functions in relation to environmental changes. • Central Arctic meiofaunal density and biomass decreased with increasing water depth and sediment depth. • Food proxies (chlorophyll a and bacterial abundance) were key drivers for meiofaunal community composition. • Virtually no differences were found in the meiofaunal abundance of higher taxa at the North Pole between 1996 and 2022.