OFOS photographic survey transects characteristics, megabenthic communities characteristics, seafloor algae coverage and environmental conditions during POLARSTERN cruise PS80 (ARK-XXVII/3, IceArc)

A photographic survey was carried out during the expedition ARK-XXVII/3 to the Nansen and Amundsen basins. The seafloor was photographed using a towed Ocean Floor Observation System (OFOS). Nine transects were performed: four in the Nansen Basin between 83-84°N and 18-110°E at depths 3571-4066 m, and five in the Amundsen Basin between 83-89°N and 56-131°E at depths 4041-4384 m. All images were analysed and stored using the image analysis program and database BIIGLE (www.BIIGLE.de). The laser points were used for calculation of the seafloor surface area on images. Visible megafauna was counted and identified to the lowest possible taxonomic level. The number of different taxa on each image was converted to individuals per m² (density). Total megafauna density (±standard deviation) was calculated for each transect. The mean taxa biomass per m² and the total megafauna biomass per m² were roughly estimated for each transect. The mean biomass (preserved wet weight) was calculated based on the wet weight of preserved individuals sampled by trawls. For taxa with insufficient trawl data the biomass was estimated using the biomass data of congeneric taxa or taxa with similar body shape; in some cases such taxa were excluded from analyses. The coverage of seafloor by algae aggregations and their remains was calculated based on sixty images at each transect using ImageJ software. Images for this analysis were chosen with equal spatial intervals depending on the total number of images within a transect. Several environmental parameters were measured at the ice stations.

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