Ice retreat in West Antarctica and Antarctic Peninsula has led to important changes in seafloor communities and gains in benthic blue carbon. In most of the Antarctic, however, sea ice increased between the 1970s and 2014, but its effects on the benthos remain largely unexplored. Here, we provide a 1988–2014 record of macro- and megafauna from the north-eastern Weddell Sea shelf, where benthic biomass decreased by two thirds and composition shifted from suspension feeders to deposit feeders. Concomitant increases in sea-ice cover suggest a reduced flux of primary production to the benthos. As benthic communities are major repositories for Antarctic biodiversity and play an important role in biogeochemical cycling, the observed changes have far-reaching consequences for the Antarctic ecosystem and its feedback to the climate system. The findings underscore the importance of long-term ecological monitoring in a region vulnerable to warming and ice-shelf collapse.

Corer sampling and seabed imaging are two quantitative approaches used to investigate benthic fauna. Despite the complementary nature of these methods, very few studies have been done using both in parallel. Here, we compare benthic composition and abundance data derived from the quantitative faunistic analysis of both multibox corer samples (MBC) and seabed images (SBI) taken concomitantly at 16 stations in the Filchner–Ronne region of the southern Weddell Sea (Southern Ocean) during R/V Polarstern cruise PS82 (ANT-XXIX/9) in 2013/14. A total of 43 benthic taxa were found, 34 in MBC and 29 in SBI samples. Mean benthic abundance derived from MBC was 20 times higher than the SBI abundance (1708 vs. 71 ind m⁻²)—best explained by SBI being a method focusing on the epifauna alone, whereas MBC also captures the more abundant infauna. Differences in taxa caught by both gears demonstrated that MBC alone were not sufficient for a comprehensive representation of the entire benthic fauna. The among-station similarity patterns derived from both methods correlated significantly; a different combination of taxa best explained the specific distribution patterns. Overall, our results demonstrate similar and comparable spatial distribution patterns in the benthic communities by both methods. We therefore highly recommend the use of both, MBC and SBI in combination.

Ecological restoration includes specific technical phases over the course of an ecosystem recovery process. In the marine environment and for oyster reef restoration, the installation and implementation of pilot reefs close the gap between feasibility studies with small‐scale experiments and designated upscaling for marine conservation measures. Against this background, this study presents the design, planning and installation of the first pilot oyster reef in offshore sublittoral regions of the North Sea. The work was conducted as part of marine protected area management in the Natura 2000 site Borkum Reef Ground in the German Bight, in the area of historical offshore oyster grounds. It includes logistical considerations, material selection, methodology for reef base construction and deployment of European flat oysters Ostrea edulis as spat‐on‐shell, young and adult single seed oysters, and spat‐on‐reef, as well as the development of an efficient monitoring approach for reef‐associated biodiversity. Native Oyster Restoration Alliance monitoring methodologies, such as underwater visual census and seabed images were selected, tested and successfully adapted for the pilot oyster reef and study site. The evaluation and optimization of offshore sublittoral oyster reef monitoring are presented here, and biodiversity metrics are put into perspective with data from recent and historical studies. Results show a few mobile fauna species (e.g., fish and decapods) as first colonizers after reef construction. One year later, biodiversity increased due to a larger number of invertebrate and fish species. However, the pilot oyster reef community still represents an early recolonization stage, with lower biodiversity than historical records. This study presents a proof of concept for the design, planning and construction of an offshore oyster reef and indicates stages in the recovery process. Strategies to optimize and to complement reef‐monitoring in challenging environments are discussed, emphasizing additional molecular and functional analyses for future assessments.