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A breeding colony of notothenioid icefish (Neopagetopsis ionah , Nybelin 1947) of globally unprecedented extent has been discovered in the southern Weddell Sea, Antarctica. The colony was estimated to cover at least ∼240 km2 of the eastern flank of the Filchner Trough, comprised of fish nests at a density of 0.26 nests per square meter, representing an estimated total of ∼60 million active nests and associated fish biomass of >60,000 tonnes. The majority of nests were each occupied by 1 adult fish guarding 1,735 eggs (±433 SD). Bottom water temperatures measured across the nesting colony 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 the active nesting area. Historical and concurrently collected seal movement data indicate that this concentrated fish biomass may be utilized by predators such as Weddell seals (Leptonychotes weddellii, Lesson 1826). Numerous degraded fish carcasses within and near the nesting colony suggest that, in death as well as life, these fish provide input for local food webs and influence local biogeochemical processing. To our knowledge, the area surveyed harbors the most spatially expansive continuous fish breeding colony discovered to date globally at any depth, as well as an exceptionally high Antarctic seafloor biomass. This discovery provides support for the establishment of a regional marine protected area in the Southern Ocean under the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) umbrella. [Display omitted] [Display omitted] • A vast icefish breeding colony has been discovered in the southern Weddell Sea • Extremely high benthic biomass provides food for predators and scavengers • Oceanographic conditions influence brooding habitat suitability for icefish • Unique ecosystem supports establishment of a marine protected area (MPA) In this report, Purser et al. describe the largest yet discovered fish breeding colony ecosystem. Found in the Weddell Sea, Antarctica and covering at least 240 km2 of seafloor, Neopagetopsis ionah icefish brood eggs in ∼60-cm-diameter nests at a density of 0.26 nests m−2. [ABSTRACT FROM AUTHOR]

In 2016, the research ice-breaker Polarstern surveyed the submerged peaks of the permanently ice-covered Langseth Ridge, a tectonic feature comprising the Karasik seamount and two deeper seamount peaks, abutting the Gakkel ultra-slow spreading ridge (87°N 62°E to 85.5°N 57.4°E) 1. A towed marine camera sled and a hybrid remotely operated vehicle revealed these peaks to be covered by a dense demosponge community, at first glance reminiscent of North Atlantic Geodia grounds (sensu 2). Sponges were observed on top of a thick layer of spicule mat (Figure 1 and Video S1), intermixed with underlying layers of empty siboglinid tubes and bivalve shells, a substrate covering almost the entire seafloor. We observed trails of densely interwoven spicules connected directly to the underside or lower flanks of sponge individuals (Figure 1), suggesting these trails are traces of motile sponges. This is the first time abundant sponge trails have been observed in situ and attributed to sponge mobility. Given the low primary production in this permanently ice-covered region, these trails may relate to feeding behavior and/or a strategy for dispersal of juveniles. Such trails may remain visible for long periods given the regionally low sedimentation rates. In 2016 the icebreaker RV Polarstern investigated the ice-covered Langseth Ridge seamounts at 86.5°N with towed cameras and robots. Here, Morganti et al. describe the discovery of one of the densest sponge communities known to date in a highly oligotrophic region. [ABSTRACT FROM AUTHOR]