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Towed camera sleds are regularly used as imaging platforms in the exploration of deep-sea seafloor ecosystems. A drawback of the majority of towed camera sleds is that the information received on benthic communities and habitats is limited to the field of view of the cameras mounted on the sled, and is typically restricted to images of the seafloor from directly underneath the device. In order to increase our understanding of benthic ecosystems and to identify benthic communities, their structure, biodiversity and ecosystems functioning over extended regions, combining image and acoustic data can be a useful approach to achieve this. One such system is the Ocean Floor Observation and Bathymetry System (OFOBS), developed by the Alfred-Wegener-Institute, used recently to discover and quantify the sponge grounds of the high Arctic and the world’s largest nesting fish colony in Antarctica. In the Weddell Sea, the Antarctic Ocean, a vast breeding ground with millions of fish nests of the Antarctic Icefish was discovered with the OFOBS. The bathymetric, acoustic data collected by the system was used to infer the extended distribution of round fish nest depressions in the seafloor for swathes of 50 m on each side of the device during each deployment tow. In the Arctic, the OFOBS system has been used to assess the state and distribution of deep-sea trawl marks across the Svalbard shelf and the distribution of geological and biological assemblages across the Fram Strait. In this presentation, we demonstrate how variations in slope and surface structure influence the inhabiting benthic community in the Antarctic as well as the Arctic Ocean, as inferred by the data collected by this combined camera and acoustic towed system.

During the RV Polarstern expedition to the southern Weddell Sea, in Feb 2021, a breeding colony of notothenioid icefish (Neopagetopsis ionah, Nybelin 1947) of globally unprecedented extent has been discovered. The colony, at time of survey, covered at least ~240 square kilometres of the eastern flank of the Filchner Trough and was comprised of fish nests at a density of 0.26 nests per square metre, representing an estimated minimum total of ~60 million active nests, and an associated fish biomass of > 60,000 tonnes. The majority of nests were each occupied by 1 adult fish guarding 1735 eggs (±433 SD). Bottom water temperatures adjacent to the nests were up to 2 °C warmer than the surrounding bottom waters, indicating a spatial correlation between the modified Warm Deep Water (mWDW) upflow onto the Weddell Shelf and active nesting.