Most of the Ross Sea has been designated a marine protected area (MPA), proposed ‘to protect ecosystem structure and function’. To assess effectiveness, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) selected Adélie (Pygoscelis adeliae) and emperor (Aptenodytes forsteri) penguins, Weddell seals (Leptonychotes weddellii) and Antarctic toothfish (Dissostichus mawsoni) as ecosystem change ‘indicator species’. Stable for decades, penguin and seal populations increased during 1998–2018 to surpass historical levels, indicating that change in ecosystem structure and function is underway. We review historical impacts to population trends, decadal datasets of ocean climate and fishing pressure on toothfish. Statistical modelling for Adélie penguins and Weddell seals indicates that variability in climate factors and cumulative extraction of adult toothfish may explain these trends. These mesopredators, and adult toothfish, all prey heavily on Antarctic silverfish (Pleuragramma antarcticum). Toothfish removal may be altering intraguild predation dynamics, leading to competitive release of silverfish and contributing to penguin and seal population changes. Despite decades of ocean/weather change, increases in indicator species numbers around Ross Island only began once the toothfish fishery commenced. The rational-use, ecosystem-based viewpoint promoted by CCAMLR regarding toothfish management needs re-evaluation, including in the context of the Ross Sea Region MPA.

In recent years, some scientists have called for research into and potential development of ‘solar geoengineering’ technologies as an option to counter global warming. Solar geoengineering refers to a set of speculative techniques to reflect some incoming sunlight back into space, for example, by continuously spraying reflective sulphur aerosols into the stratosphere over several generations. Because of the significant ecological, social, and political risks posed by such technologies, many scholars and civil society organizations have urged governments to take action to prohibit the development and deployment of solar geoengineering techniques. In this article we take such calls for a prohibitory or a non-use regime on solar geoengineering as a starting point to examine existing international law and governance precedents that could guide the development of such a regime. The precedents we examine include international prohibitory and restrictive regimes that impose bans or restrictions on chemical weapons, biological weapons, weather modification technologies, anti-personnel landmines, substances that deplete the ozone layer, trade in hazardous wastes, deep seabed mining, and mining in Antarctica. We also assess emerging norms and soft law in anticipatory governance of novel technologies, such as human cloning and gene editing. While there is no blueprint for a solar geoengineering non-use regime in international law, our analysis points to numerous specific elements on which governments could draw to constrain or impose an outright prohibition on the development of technologies for solar geoengineering, should they opt to do so.

Tropical coastal ecosystems are in decline worldwide due to an increasing suite of human activities, which threaten the biodiversity and human wellbeing that these ecosystems support. One of the major drivers of decline is poor water quality from land-based activities. This review summarises the evidence of impacts to coastal ecosystems, particularly coral reefs, from sediments, nutrients, chemicals and pathogens entering coastal zones through surface and groundwater. We also assess how these pollutants affect the health of coastal human populations through: (1) enhanced transmission of infectious diseases; (2) reduced food availability and nutritional deficit from decline of fisheries associated with degraded habitat; and (3) food poisoning from consumption of contaminated seafood. We use this information to identify opportunities for holistic approaches to integrated watershed management (IWM) that target overlapping drivers of ill-health in downstream coastal ecosystems and people. We demonstrate that appropriate management requires taking a multi-sector, systems approach that accounts for socio-ecological feedbacks, with collaboration required across environmental, agricultural, public health, and water, sanitation and hygiene sectors, as well as across the land–sea interface. Finally, we provide recommendations of key actions for IWM that can help achieve multiple sustainable development goals for both nature and people on coasts.

In McMurdo Sound, Antarctica, fine-scale bathymetry is poorly defined, and benthic communities at water depths over 30 m have not been well described. We describe the benthic communities on two previously unknown bathymetric highs, sampled in 2012 and 2014, using scuba divers, a remotely operated vehicle, and a specially designed time-lapse camera system (SeeStar). One site (Mystery Peak) was capped by a dense thicket of the sponge Homaxinella balfourensis, a temporally variable community that likely formed in response to iceberg disturbance. Below the H. balfourensis cap (at 40 m) and at the second site (Tongue Peak, 70 m), the communities conformed to a known ecological pattern driven by food availability from benthic diatoms. Overall, mixed hydroids and bryozoans were the dominant organisms, and at greater depths the sponge Rosella podagrosa also became abundant. Over time, there were only minor changes in these communities on isolated bathymetric highs. Ice is a physical factor that interacts with depth and influences benthic communities through disturbance by icebergs and anchor ice, and through food supply by sea ice coverage. The SeeStar time-lapse camera system performed exceptionally and opens up opportunities for new winter observations in the Antarctic.

On the continental shelf of the Antarctic the major disturbance to benthic ecosystems is from iceberg scouring; however, this is based on observations from the Peninsula region. We combine observation and experimentation in the McMurdo Sound region of the Ross Sea to determine if community recovery patterns there are similar to those in better-studied Antarctic regions, and if local immigration is an important factor in recovery dynamics. We found that regardless of habitat differences in depth, substrate, and oceanographic setting, iceberg disturbance strongly impacted benthic communities in McMurdo Sound. Notably, in shallow water (<30 m) where anchor ice is an annual disturbance, both the benthic communities and recovery processes were more variable than at deeper locations. A manipulative experiment performed in a shallow area indicated that recruitment might be more important than immigration to infaunal community recovery. We conclude that whilst disturbance frequency influences dominant epifauna, recovery from iceberg disturbance is a slow ecological progression that is dependent on the extremely inconsistent recruitment processes of the high Antarctic benthic ecosystem.

Evidence indicates that Antarctic minke whales (AMWs) in the Ross Sea affect the foraging behaviour, especially diet, of sympatric Adélie penguins (ADPEs) by, we hypothesize, influencing the availability of prey they have in common, mainly crystal krill. To further investigate this interaction, we undertook a study in McMurdo Sound during 2012–2013 and 2014–2015 using telemetry and biologging of whales and penguins, shore-based observations and quantification of the preyscape. The 3D distribution and density of prey were assessed using a remotely operated vehicle deployed along and to the interior of the fast-ice edge where AMWs and ADPEs focused their foraging. Acoustic surveys of prey and foraging behaviour of predators indicate that prey remained abundant under the fast ice, becoming successively available to air-breathing predators only as the fast ice retreated. Over both seasons, the ADPE diet included less krill and more Antarctic silverfish once AMWs became abundant, but the penguins' foraging behaviour (i.e. time spent foraging, dive depth, distance from colony) did not change. In addition, over time, krill abundance decreased in the upper water column near the ice edge, consistent with the hypothesis (and previously gathered information) that AMW and ADPE foraging contributed to an alteration of prey availability.

Habitats under ice shelves are minimally explored, primarily because of technological limitations. These areas are separated from photosynthetic primary productivity by thick ice and distance to open water. Nevertheless, a diverse macrofaunal benthic community was discovered at 188 m depth, 80 km back from the edge of the McMurdo Ice Shelf. The general habitat was fine sediment with occasional dropstones, and dominant taxa were polychaetes and brittle stars, with alcyonacean soft corals and anemones on hard substrates. Gelatinous animals were abundant near the seafloor, and possibly part of a food web that supports the benthic community.

Fast ice plays important physical and ecological roles: as a barrier to wind, waves and radiation, as both barrier and safe resting place for air-breathing animals, and as substrate for microbial communities. While sea ice has been monitored for decades using satellite imagery, high-resolution imagery sufficient to distinguish fast ice from mobile pack ice extends only back to c. 2000. Fast ice trends may differ from previously identified changes in regional sea ice distributions. To investigate effects of climate and human activities on fast ice dynamics in McMurdo Sound, Ross Sea, the sea and fast ice seasonal events (1978–2015), ice thicknesses and temperatures (1986–2014), wind velocities (1973–2015) and dates that an icebreaker annually opens a channel to McMurdo Station (1956–2015) are reported. A significant relationship exists between sea ice concentration and fast ice extent in the Sound. While fast/sea ice retreat dates have not changed, fast/sea ice reaches a minimum later and begins to advance earlier, in partial agreement with changes in Ross Sea regional pack ice dynamics. Fast ice minimum extent within McMurdo Sound is significantly correlated with icebreaker arrival date as well as wind velocity. The potential impacts of changes in fast ice climatology on the local marine ecosystem are discussed.

Large floods bringing significant sediments into the coastal oceans have not been observed in Antarctica. We report evidence of a large flood event depositing over 50 cm of sediment onto the nearshore benthic habitat at Salmon Bay, Antarctica, between 1990 and 2010. Besides direct observations of the sedimentation, the evidence involves a debris flow covering old tyre tracks from the early 1960s, as well as evidence of a considerable amount of sediment transported onto the Salmon Creek delta. We believe that the flood was sourced from the Salmon Glacier and possibly the smaller Blackwelder Glacier. Such floods will be more common in the future and it is important to better understand their ecological impacts with good monitoring programmes.