Quantitative Invertebrate megabenthic data from the Nansen Legacy project collected in 2018 cruise JC2-1 with bottom Campelen trawl from R/V Kronprins Haakon

Mega-benthos was sampled from the seabed by the Nansen Legacy joint cruise 1-2, on R/V Kronprins Haakon, 6-23 August 2018 (Cruise 2018707). A Campelen 1800 bottom trawl was used after rigged with rock-hopper ground gear and towed on double warps. The mesh size was 80 mm (stretched) in the front and 16–22 mm in the cod end. The horizontal opening was 11.7 m, and the vertical opening 4 –5 m. The trawl configuration and bottom contact was monitored remotely by SCANMAR trawl sensors. The standard procedure is to tow 15 min after the trawl had contacted the bottom with towing speed of 3 knots, equivalent to a towing distance of 0.75 nautical miles (1.4 km) during a 15 min tow. The trawl settings allow the capture and retention of small-sized fish and the largest benthos (benthic megafauna) from the seabed. In addition, the trawl may also be contaminated by organisms entering the trawl when it is lowered or heaved. The sample was sorted, and each benthos taxon was counted and weighted (i.e., biomass is wet mass) and identified to closest possible taxa onboard the ship. The count of individuals per species/taxa in the trawl (Tot abun) and the wet-weight of the individuals per species/taxa in the trawl (Tot weight (kg)) was recorded. A total of 100 taxa (14 phyla, 28 taxonomic groups), were recorded with 30-46 taxa at each of the five stations. A total of 193 kg mega-benthos was collected with 15 to 88 kg wet weight per station. A total of 40.661 individuals were collected with 2.219 to 18.086 individuals per station. The hauls were standardized to a fixed sampling effort of one nautical mile: abundance per species/taxon as number of individuals per nautical mile and biomass per species/taxon as kg wet weight per nautical mile.