Hornsundbanken methane seep epimegabenthos Arunima Sen The University Centre in Svalbard (UNIS) Associate Professor

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Corentin Caudan Sorbonne University student Nil Rodés The University Centre in Svalbard (UNIS) engineer Wei Li Hong Stockholm University Associate Professor Sophie ten Hietbrink Stockholm University student Beata Szymczycha Institute of Oceanology Polish Academy of Sciences (IOPAN) Associate Professor Magdalena Diak Institute of Oceanology Polish Academy of Sciences (IOPAN) Researcher Fredrik Broms North Norwegian Humpback Whale Catalogue (NNHWC) Researcher Jochen Knies Norwegian Geological Survey (NGU), iC3: Centre for ice, Cryosphere, Carbon and Climate Researcher Arunima Sen The University Centre in Svalbard (UNIS) Associate Professor

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arunimas@unis.no author 2026-05-12 eng This dataset consists of all the epimegabenthic fauna marked and enumerated from two seafloor georeferenced image mosaics from the shelf off Svalbard's Hornsund fjord (Hornsundbanken). Videos of the seafloor were obtained with the the remotely operated vehicle (ROV) Ægir from the research vessel Kronprins Haakon, maintaining an altitude of between 1 and 1.5 m. Images were extracted every 3 seconds via the free software ffmpeg and using the images and their associated navigation data, georeferenced mosaics were generated with Agisoft's Metashape software. The two mosaics cover areas of 282 m2 and 164 m2 (446 m2 combined). The mosaics were inputted into Arc Desktop and using the Editor tool, all fauna were identified, marked and enumerated. All individuals were marked to obtain numbers for each taxon. Colonial or encrusting animals were outlined to obtain areal coverage. Identifications were made to the lowest possible level which was species in many cases, but only phylum in some cases. The faunal data from these mosaics were used in the publication by Sen et al. Fauna of shallow water Arctic seep not driven by water masses currently under review. Occurrence GBIF Dataset Type Vocabulary: http://rs.gbif.org/vocabulary/gbif/dataset_type_2015-07-10.xml This work is licensed under a Creative Commons Attribution (CC-BY 4.0) License. Creative Commons Attribution 4.0 International https://spdx.org/licenses/CC-BY-4.0.html CC-BY-4.0 Continental shelf off the Hornsund fjord of Svalbard, known as Hornsundbanken 14.159 14.1683 76.7928 76.791 2023-03-06 2023-03-06 N/A phylum Chordata phylum Mollusca phylum Arthropoda phylum Porifera phylum Nemertea phylum Cnidaria phylum Annelida phylum Echinodermata notPlanned Arunima Sen The University Centre in Svalbard (UNIS) Associate Professor

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Video imaging of the seafloor was conducted via the downward facing HD camera on the ROV. Overlap was maintained between adjacent video lines. Images were extracted from the video every three seconds and in combination with the corresponding navigation data for the images, a single, composite, georeferenced image (mosaic) was created via Agisoft's Metashape software. Two mosaics were generated. The mosaics were inputted into ArcMap Desktop and all visible features and fauna were marked and enumerated. Two locations within an area of active methane seepage on the seafloor on the continental shelf off the Hornsund fjord of Svalbard (Hornsundbanken). Numerous gas flares (gas bubbles escaping from the seafloor) have been detected acoustically on the shelf off the Hornsund fjord of Svalbard (known as Hornsundbanken). Using the remotely operated vehicle (ROV) Ægir from the research vessel Kronprins Haakon, video of the seafloor was recorded, maintaining an altitude of about 1-1.5 m. The HD video camera of the ROV was facing directly downwards (perpendicular to the seafloor) for the imaging process. Video acquisition was performed in a lawn-mower pattern, ensuring at least 25% overlap between adjacent lines. Images were extracted from the video every 2 seconds using the free software, ffmpeg. Navigation coordinates for each image were obtained from the ROV's track. These images were stitched together to create a single, composite georeferenced image (mosaic) of the seafloor. For this, structure-from-motion photogrammetry processing was conducted using Agisoft Metashape (version 2.0.2, build number 16334). Two digital models were constructed, covering a total area of 446 m². The georeferenced mosaics were imported into ArcMap Desktop version 10.8.2 and all visible fauna were marked with the Editor tool. Individual organisms were marked as points (point feature class). Colonial or encrusting organisms were outlined to get areal coverages (polygon feature classes). Identification was done to lowest taxonomic level as possible, which was species in some cases, but often reliable identification was limited to higher levels such as genus or family and in certain cases, only phylum level. Arunima Sen https://orcid.org/0000-0001-7847-2137 author Epimegabenthic fauna marked in a GIS (Geographic Information System) from two georeferenced mosaics constructed from still images obtained from ROV (remotely operated vechicle) video. Arctic SGD (Submarine groundwater discharge) project (The Norwegian Financial Mechanism 2014-2021, project number 019/34/H/ ST10/00645 and 2019/34/H/ST10/00504). 2026-05-04T13:53:54.535+00:00 dataset Sen A, Caudan C, Rodés N, Hong W L, ten Hietbrink S, Szymczycha B, Diak M, Broms F, Knies J (2026). Epimegabenthos based on seafloor georeferenced mosaics of the Hornsundbanken methane seep area. Version 1.1. The University Centre in Svalbard. Occurrence dataset. https://ipt.gbif.no/resource?r=epimegabenthos_hornsundbanken_seep&v=1.1 https://ipt.gbif.no/resource?id=epimegabenthos_hornsundbanken_seep/v1.1.xml