Spatial and temporal variations in deep-sea meiofauna assemblages in the Marginal Ice Zone of the Arctic Ocean

Abstract In order to understand the response of the deep-sea meiobenthos to a highly varying, ice-edge-related input of phytodetritus, we investigated the abundance and composition of the meiobenthos at the arctic long-term deep-sea station HAUSGARTEN (79°N, 4°E) along a bathymetric transect (1200–5500 m water depth) over 5 consecutive years (from 2000 to 2004) in relation to changes in environmental conditions. Results showed high sediment-bound pigment concentrations (chlorophyll a and degradation products) ranging from 4.5 to 41.6 μg/cm 3 , and coinciding high meiobenthic densities ranging from 149±3 to 3409±525 ind/10 cm 2 . Nematodes dominated the metazoan meiofaunal communities at every depth and time (85–99% of total meiofauna abundance), followed by harpacticoid copepods (0–4.6% of total meiofauna abundance). The expected pattern of gradually decreasing meiobenthic densities with increasing water depth was not confirmed. Instead, the bathymetric transect could be subdivided into a shallow area with equally high nematode and copepod densities from 1000 to 2000 m water depth (means: 2259±157 Nematoda/10 cm 2 , and 50±4 Copepoda/10 cm 2 ), and a deeper area from 3000 to 5500 m water depth with similar low nematode and copepod densities (means: 595±52 Nematoda/10 cm 2 , and 11±2 Copepoda/10 cm 2 ). Depth-related investigations on the meiobenthos at the HAUSGARTEN site showed a significant correlation between meiobenthos densities, microbial exo-enzymatic activity (esterase turnover) and phytodetrital food availability (chlorophyll a and phaeophytines). In time-series investigations, our data showed inter-annual variations in meiofauna abundance. However, no consistent relationship between nematode and copepod densities, and measures for organic matter input were found.