Macrobenthic assemblages from the methane seeps in six South Georgia troughs collected in 2017

In 2017, the RV METEOR M134 expedition investigated macrobenthic assemblages associated with methane seeps on the South Georgia continental shelf. Six shelf troughs with active methane seepage were sampled to assess species richness, abundance, and environmental conditions. Data were collected from eleven shelf stations, with species richness ranging from 19 to 51 species and abundances from 3,303 to 30,326 individuals per square meter. A total of 103 species were identified, with arthropods (primarily crustaceans) and annelids comprising most of the species richness. Environmental data include methane and sulfate flux, hydrogen sulfide concentrations, and sediment geochemistry. Seep assemblage data is combined with data from non-seep benthic communities from other expeditions.The dataset provides: 1 South Georgia methane seep station locations and environmental data. 2 Macrobenthic species absolute and normalized abundances at seep sites. 3 A combination of seep assemblages with non-seep benthic communities from other expeditions. Funding: The fieldwork for this study, was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme 'Antarctic Research with comparative investigations in Arctic ice areas' (project-id 40464014) and within the DFG-Research Center/Cluster of Excellence EXC 309 'The Ocean in the Earth System' (project-id 49926684). The expedition, titled 'Emissions of free gas around South Georgia: distribution, quantification, and sources for methane ebullition sites in sub-Antarctic waters,' was supported by MARUM - Center for Marine Environmental Sciences, Research Faculty University of Bremen, and the University of Bremen. Additional support came from the Helmholtz Association (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven). The cruise was funded by the German Research Foundation (DFG) and the Federal Ministry of Education and Research (BMBF). Katrin Linse is part of the British Antarctic Survey Polar Science for Planet Earth Programme (NC Science), funded by the Natural Environment Research Council (NERC). Studies around South Georgia were conducted under permit RAP 129/2016 (M134) issued by the Foreign and Commonwealth Office, UK. Macrobenthic faunal sorting was supported by the Natural Environment Research Council through a DEI Internship for Madeline PBC Anderson (via the NERC Diversity, Equity and Inclusion engagement funding) and an IAPETUS2 PhD studentship held by Madeline PBC Anderson (grant reference NE/S007431/1).

Oceanographic data were collected using RV METEOR's 24 x 10 L Niskin bottle rosette with a Seabird CTD equipped with conductivity, temperature, pressure, and an SBE 43 dissolved oxygen sensor. The near seafloor water data were used to report bottom temperature, salinity, and oxygen. Seafloor sediment cores and macrobenthic assemblages were obtained with a multicorer (MUC) (OKTOPUS GmbH), comprising eight 10 cm diameter and four 6 cm diameter cores per deployment. On arrival on deck, cores were photographed to document sediment height, layering, and colour before being distributed for geochemical, sediment, and biological analyses. Water depth of sediment recovery ranged from 136 m (Cumberland East Bay station CB 07) to 369 m (Church Trough station CT 05). MUC cores allocated for macrobiology (a total of 38) were sliced into 0-2 cm and 2-5 cm horizons using a core extruder, sieved through a 500 micrometer mesh, and preserved in 96 percent ethanol. Specimens were initially sorted to higher taxonomic levels onboard using a Meiji stereomicroscope, then further sorted to morphospecies on land under a Zeiss Stemi SV6 stereomicroscope. Photographs were taken using ScopeTek ScopePhoto 3.1.475, and taxonomic identifications were verified by experts using literature (Arntz and Rauschert, 2015). Due to identification challenges, nematodes were grouped into a single taxon, and indeterminate specimens were marked as 'indet.'. Only individuals with heads were counted to prevent duplication. Abundance data were scaled to m squared for quantitative analyses. Patterns in species richness, abundance, and diversity were assessed by pooling cores per MUC deployment to obtain an assemblage per core. Abundance data were summed at the phylum level and scaled for comparisons between stations. Species richness was verified with a species accumulation curve to ensure observed richness was not an artifact of sampling effort. Data have been combined with other species/polychaete Southern Ocean non-seep datasets (see references).

NA in Environmental_parameters.csv data - data were not collected Indet - the abbreviation 'indet.' was used to denote an indeterminate specimen. Species were identified to highest taxonomic level possible, and quality checking occurred for consistency in identification. Specialists were contacted to assist in identification for specific taxa.

1. RV METEOR's 24 x 10 L Niskin bottle rosette - Equipped with a Seabird CTD (Conductivity, Temperature, Depth) sensor. Sensors: Conductivity Temperature Pressure SBE 43 dissolved oxygen sensor 2. Multicorer (MUC) (OKTOPUS GmbH) - Used for seafloor sediment and macrobenthic assemblage collection. Core sizes: Eight 10 cm diameter cores Four 6 cm diameter cores 3. Stereomicroscopes: Meiji stereomicroscope - Used onboard for initial macrofaunal sorting. Zeiss Stemi SV6 stereomicroscope - Used in the laboratory for further taxonomic sorting. 4. Core Extruder: Used for sediment slicing at 0-2 cm and 2-5 cm horizons. 5. 500 micrometer sieve - Used for sieving sediment samples on deck.