2020 RRS Discovery Cruise DY108‐109, 6 Sept - 2 Oct 2019. CLASS – Climate‐linked Atlantic System Science Darwin Mounds Marine Protected Area habitat monitoring, BioCAM ‐ first equipment trials. BLT‐ Recipes: pilot study

DY108/109 was a combined expedition, integrating a series of scientific and technological objectives related to three different projects. The main study area was the Darwin Mounds Marine Protected Area, an area of small cold‐water coral mounds in the Northern Rockall Trough, discovered by NOC scientists in 1998 and protected from bottom contact fisheries (mainly bottom trawling) since 2003. As part of the NERC CLASS programme (Climate‐Linked Atlantic Sector Science), the aim was to assess the status of the coral mounds, in order to identify and quantify any long‐term changes to this deep‐sea habitat. The mounds were surveyed with the Autosub6000 AUV (sidescan sonar), the HyBIS video platform and a series of targeted boxcores, repeating a first round of monitoring efforts undertaken in 2011 (expedition JC060). In addition, two settlement experiments deployed in 2011 were recovered on board. The second aim of the cruise was to demonstrate and test the latest innovation in survey technology as a potential new method for monitoring this type of seafloor habitat. The new BioCam system, a combined stereo camera and double laser line scanner integrated in the Autosub6000, was developed under the NERC Oceanids Marine Sensor Capital programme. BioCam enabled millimetre‐resolution 3D colour reconstructions of the seabed over areas that are an order of magnitude larger than typically covered with conventional visual methods (~30ha/day). This type of technology will revolutionise marine habitat monitoring in the future, both in terms of area covered and level of information obtained. In addition to these habitat mapping and monitoring activities in the Darwin Mound area, DY108/109 also supported two oceanographic studies of the Rockall Trough. For the NERC‐funded project BLT‐Recipes, two 24h CTD stations were occupied on the Irish margin, as pilot study to support further work in 2020 and 2021. For the oceanographic part of the CLASS programme, a number of single CTD casts were taken along the “Ellett Line”, while the turn‐around of a lander with upward‐looking ADCP was attempted. Unfortunately, investigation with the HyBIS platform confirmed that the lander was severely damaged and could not be recovered. Despite some time lost to weather and unfortunate equipment malfunctioning, the expedition was a success, with 10 HyBIS dives completed (76h seabed video), two sidescan sonar surveys repeated, 20 successful boxcores taken, sieved an analysed on board, one mooring deployed and 48 CTD casts completed. Most of all, the BioCam system performed excellently, staightaway from its first deployment, and acquired two dense grid survey datasets covering ~60ha in total