Benthic Isopoda of the Aegir Ridge (Norwegian Sea) collected during the IceAGE3 (SO276 MerMet17-06) expedition in summer 2020

Benthic isopods from this data set were collected during the IceAGE 3 expedition (SO276) on board RV Sonne in July 2020 with an epibenthic sledge (EBS). A total of seven EBS samples were taken in two areas of the Aegir ridge (Norwegian basin) at depths between 681 m to 3,702 m. The benthic samples taken are the first from the deep seabed within the Aegir ridge and therefore represent an important data set for assessing the diversity of the deep Nordic seas and their relationship to water mass distribution and depth. Isopoda collected by the EBS contained 1,978 specimens divided into eleven families, 25 genera and at least 42 species. Munnopsidae were by far the most dominant family contributing 59.1% to total isopod specimens, followed by the Munnidae (18.3) and Katianiridae (17.8). The remaining families were present with less than 5% of total Isopoda.
"Project information
Sampling took place in the course of the IceAGE3 expedition (Depth transects and connectivity along gradients in the North Atlantic and Nordic Seas in the frame of the IceAGE project (Icelandic marine Animals: Genetics and Ecology), Cruise No. SO276 (MerMet17-06), 22.06.2020 - 26.07.2020, Emden (Germany) - Emden (Germany)).
Study area
The Aegir Ridge is an extinct axis of expansion in the Nordic seas west of the Norwegian Basin, which is associated with the continental break up between Norway and Greenland about 55 Ma ago (Talwani and Eldholm, 1977). According to Harris et al. (2014) the Aegir ridge consists of a rift valley and a spreading ridge part. The North Sea, including the Aegir Ridge, is affected by several different water masses. Warm saline water from the North Atlantic flows into the Norwegian Basin and cools to form dense and deep currents to the south. The southern part of the Aegir ridge is mainly dominated by the Iceland Faroer Slope Jet (IFSJ) that supplies local deep water masses with cold and dense water and flows east along the northern slope of the Greenland-Iceland ridge (Semper et al. 2011).
Sampling
Isopoda were obtained by means of an EBS that consisted of only one epibenthic sampling unit, which corresponds to the epi-net samplers of related EBS types (Rothlisberg - Percy 1977, Brandt - Barthel 1995, Brenke 2005). In addition, an autonomous working camera (GoPro 4 Black Edition) and an Aandera Seaguard RCM DW CTD were attached to the EBS in order to further characterize the environmental parameters (pressure, temperature, salinity, turbidity and current / current direction) and habitats on the sea floor.
A total of seven EBS were deployed in the Aegir ridge area with a depth of 681 m to 3.702 m. Three stations were taken from the bottom of the ridge (stations 26, 39 and 47) and four stations from outside the ridge (16, 30, 55, and 61). The towing distance was calculated according to equation (4) in Brenke (2005). More precisely, the EBS was lowered over the starboard side of the RV Sonne at a rope speed of 0.5 m / s while the ship held the position. The winch stopped about 100 m above the ground for 1 to 2 minutes. Then the ship began to sail at 1 kn, while the cable was paid out at a speed of 0.5 m / s. Additional cable (between 200 and 500 m) was laid depending on water depth. The winch then stopped for 10 minutes to allow video footage to be recorded. After 10 minutes, the winch began to recover the gear at a speed of 0.3 m / s. As soon as the EBS left the ground, the winch speed was increased to 0.7 m / s. In order to monitor the position of the EBS in the water columns and on the ground, in addition to rope tension, a Posidonia transponder system was used, which indicates the time of the landing of the gear on the seabed and the subsequent clearing the ground.

Sample processing
As soon as the EBS arrived on deck, the end of the cod was taken out and immediately placed in the cold room (+ 4 ° C). The sample processing largely followed protocols for a cold chain that enable later molecular analyzes (Riehl et al. 2014); Samples visible to the naked eye were taken from the bulk sample, documented photographically and fixed separately (RNA later and undenatured 96% ethanol) or frozen for genetic, genomic or biochemical analyzes. The remaining sample was carefully eluted in pre-chilled filtered seawater, then passed through a 300µm. Sieved m-sieve, fixed in pre-cooled (-20 ° C) 96% denatured ethanol and stored at -20 ° C for at least 48 hours. The sorting of the samples began on board and was continued in the Senckenberg laboratory (DZMB, Hamburg) and, due to pandemic restrictions, was completed in the home office. All specimens are currently stored at the German Center of Marine Biodiversity Research (DZMB) in Hamburg and are available on request.

Taxonomy
Isopod samples were assigned first to the family level on board and then to the generic and species level in the home laboratory. Parasitic isopod taxa (including gnathiids and cryptoniscid larvae) were not further identified to species level due to taxonomic difficulties in reliably identifying them. All other isopod specimens were identified and assigned to known species according to the relevant literature. All names were then compared to WoRMS (World Register of Marine Species; www.marinespecies.org). When identification was ambitious, the species were named according to the recommendations of the Open Nomenclature (Sigovini et al. 2016). Isopod specimens that were too damaged to be recognizable and assigned to the species level were marked as ""sp. Indet"". 
References
Brandt, A., - Barthel, D. (1995). An improved supra-and epibenthic sledge for catching Peracarida (Crustacea, Malacostraca). Ophelia, 43(1), 15-23.
Brenke, N. (2005). An epibenthic sledge for operations on marine soft bottom and bedrock. Marine Technology Society Journal, 39(2), 10-21.
Harris, P. T., Macmillan-Lawler, M., Rupp, J., - Baker, E. K. (2014). Geomorphology of the oceans. Marine Geology, 352, 4-24.
Riehl, T., Brenke, N., Brix, S., Driskell, A., Kaiser, S., - Brandt, A. (2014). Field and laboratory methods for DNA studies on deep-sea isopod crustaceans. Polish Polar Research, 203-224. 
Rothlisberg, P., - Pearcy, W. G. (1977). An epibenthic sampler used to study the ontogeny of vertical migration of Pandalus dordani (Decapoda caridea).
Semper, S., Pickart, R. S., Våge, K., Larsen, K. M. H., Hátún, H., - Hansen, B. (2020). The Iceland-Faroe Slope Jet: a conduit for dense water toward the Faroe Bank Channel overflow. Nature communications, 11(1), 1-10.
Sigovini, M., Keppel, E., - Tagliapietra, D. (2016). Open Nomenclature in the biodiversity era. Methods in Ecology and Evolution, 7(10), 1217-1225.
Talwani, M., - Eldholm, O. (1977). Evolution of the Norwegian-Greenland sea. Geological Society of America Bulletin, 88(7), 969-999."