Description: During RV MS Merian expedition MSM75, an international, multidisciplinary team explored the Reykjanes Ridge from June to August 2018. The first area of study, Steinahóll (150–350 m depth), was chosen based on previous seismic data indicating hydrothermal activity. The sampling strategy included ship- and AUV-mounted multibeam surveys, Remotely Operated Vehicle (ROV), Epibenthic Sledge (EBS), and van Veen grab (vV) deployments. Upon returning to Steinahóll during the final days of MSM75, hydrothermal vent sites were discovered using the ROV Phoca (Kiel, GEOMAR). Here we describe and name three new, distinct hydrothermal vent site vulnerable marine ecosystems (VMEs); Hafgufa, Stökkull, Lyngbakr. The hydrothermal vent sites consisted of multiple anhydrite chimneys with large quantities of bacterial mats visible. The largest of the three sites (Hafgufa) was mapped, and reconstructed in 3D. In total 23,310 individual biological specimens were sampled comprising 41 higher taxa. Unique fauna located in the hydrothermally venting areas included two putative new species of harpacticoid copepod (Tisbe sp. nov. and Amphiascus sp. nov.), as well as the sponge Lycopodina cupressiformis (Carter, 1874). Capitellidae Grube, 1862 and Dorvilleidae Chamberlin, 1919 families dominated hydrothermally influenced samples for polychaetes. Around the hydrothermally influenced sites we observed a notable lack of megafauna, with only a few species being present. While we observed hydrothermal associations, the overall species composition is very similar to that seen at other shallow water vent sites in the north of Iceland, such as the Mohns Ridge vent fields, particularly with peracarid crustaceans. We therefore conclude the community overall reflects the usual “background” fauna of Iceland rather than consisting of “vent endemic” communities as is observed in deeper vent systems, with a few opportunistic species capable of utilizing this specialist environment.

Description: Peracarid abundance and composition were studied in the Atlantic Sector of the Southern Ocean and the Weddell Sea at a depth range of 403-2021 m. Samples were collected using an epibenthic sledge (EBS) during expeditions on board the RRS James Clarke Ross in the Filchner Trough (JR275), the South Orkney Islands (JR15005), the Prince Gustav Channel (JR17003a) and on board the RV Polarstern in the Eastern Antarctic Peninsula (PS118). Expeditions took place in February-March 2012, 2016, 2018 and 2019 respectively. Since the trawling distance between stations was not always the same, in order to make data comparable between different stations, numbers of individuals were standardized to 1000 m haul distances. In total 64766 peracarids were found and sorted into five different orders (Amphipoda, Cumacea, Isopoda, Mysidacea and Tanaidacea). Amphipods were the most abundant group representing the 32% of the total abundances. The Filchner Trough had the highest abundance of peracarids, while the South Orkney Islands showed the lowest abundance compared to other areas.