Methodology:

Sites from 10 km to 100 km apart were selected throughout the Barents Sea incorporating a wide range of conditions from the southernmost shelf edge to the northernmost shelf break. Within each of these sites we further selected three or more locations kilometres apart to provide nested samples. Sampling took place in the summer of 2017 during the scientific cruise JR16006. A vertical, calibrated, high-resolution camera tripod (Shelf Underwater Camera system (SUCS)) with twin 2000 lumen dimmable lights and an ultra-short baseline positioning beacon was used to take images of the seafloor. To minimize distortion and error, the camera was always perpendicular to the seabed (as opposed to being vertical in the water column), with a mid-focal length (F11) and flat glass port, such that error within the field of view was ± less than 1 mm. Finally an Agassiz trawl was used to collect zoobenthos from each site, by means of three replicate 5 min trawls. Using the SUCS, we captured 586 high-resolution (12 MB) images, each of which was 406x341 mm; these were then analysed for the density of each of 14 functional groups. These functional groups were pioneer sessile suspension feeders, climax sessile suspension feeders, sedentary suspension feeders, mobile suspension feeders, deposit-feeding crawlers, deposit-feeding vermiform, deposit-shelled infauna, grazers, soft-bodied sessile predators, calcareous sessile predators, soft-bodied mobile predators, calcareous mobile predators, arthropod predators and flexible (mixed strategy), as used in Antarctic and sub-Antarctic datasets. Functional groups were assigned on the basis of the literature applied to identified morphotypes in images and closer inspection of trawl specimens (matched to similar morphotypes in images). Antarctic data (collected in the same way) have verified that functional groups work as effective surrogates (which therefore lose little information in comparison) for species identity-level data. Trawled sample specimens were separated into morphotypes and functional groups from which morphometrics were measured. Each morphotype was then dried at 60°C for 24 h and weighed. The individual morphotypes were then ashed at 475°C for 12-24 h and reweighed. Approximate carbon content was calculated as 50% of organic mass plus 12% of ash (skeleton) mass (approximate proportion of carbon in carbonate by molecular mass).

Data collection:

Shelf Underwater Camera system (SUCS) was used to collect seafloor imagery.

Agassiz trawl was used to collect zoobenthos from each site, by means of three replicate 5 min trawls.

Images where scored using different photographic packages such as BIIGLE. Specimens where preserved in ethanol.

Data quality:

20 replicates on average and three sites nested per location. High resolution imagery allowing for ID of 1mm fauna.