Trajectory of increased iceberg kill-off in West Antarctica's shallows.

Compared with low latitude coasts, many polar latitudes are still little impacted by intense and direct anthropogenic stressors. Climate forcing is now bringing rapid physical change to nearshore polar realms. In the shallow coastal waters adjacent to the United Kingdom's Rothera Research Station in the West Antarctic Peninsula (WAP), 225 seabed markers at 5-25 m depth have been surveyed and replaced every year from 2002-2023 (75 markers at each of 5, 10 and 25 m). This is one of the longest continuously running marine disturbance experiments in the world, in one of Earth's fastest changing environments. Different categories of sea ice are recorded (including when the sea surface freezes into fast ice) at Rothera since the 1980s, and losses of marine ice in both polar regions are one of the striking responses to a warming planet1. Five to ten years of seabed marker hit rate data (marker broken or moved) showed that reduced sea ice cover is correlated with disturbance and mortality on the seabed2,3.

Benthic functionality under climate-induced environment changes offshore on the Antarctic Peninsula continental shelf.

Marine ecosystems in Antarctica are thought to be highly vulnerable to aspects of dynamic global climate change, such as warming. In deep-water ecosystems, there has been little physico-chemical change in seawater there for millions of years. Thus, some benthic organisms are likely to include strong potential indicators of environmental changes and give early warnings of ecosystem vulnerability. In 2017 we sampled deep-water benthic assemblages across a continental shelf trough in outer Marguerite Bay, West Antarctic Peninsula (WAP). This region is one of the hotspots of climate-related physical change on Earth in terms of seasonal sea ice loss. Video and images of the seabed were captured at 5 stations, each with 20 replicates. From these, we identified substratum types and biota to functional groups to assess variability in benthic composition and diversity. We also collected coincident environmental information on depth, temperature, salinity, oxygen and chlorophyll-a (using a CTD). Climax sessile suspension feeders were the most spatially dominant group, comprising 539 individuals (39% of total abundance) that included Porifera, Brachiopoda and erect Bryozoa. ST5, the shallowest station was functionally contrasting with other stations. This functional difference was also influenced by hard substrata of ST5, which is typically preferred by climax sessile suspension feeders. Depth (or an associated driver) and hard substrates were the most apparent key factor which functionally characterised the communities, shown by the abundance of climax sessile suspension feeders. Our study showed that non-invasive, low taxonomic skill requirement, functional group approach is not only valuable in providing functional perspective on environment status, but such groupings also proved to be sensitive to environmental variability.

Spatial competition in a global disturbance minimum; the seabed under an Antarctic ice shelf.

The marine habitat beneath Antarctica's ice shelves spans ∼1.6 million km2, and life in this vast and extreme environment is among Earth's least accessible, least disturbed and least known, yet likely to be impacted by climate-forced warming and environmental change. Although competition among biota is a fundamental structuring force of ecological communities, hence ecosystem functions and services, nothing was known of competition for resources under ice shelves, until this study. Boreholes drilled through a âˆ¼ 200 m thick ice shelf enabled collections of novel sub-ice-shelf seabed sediment which contained fragments of biogenic substrata rich in encrusting (lithophilic) macrobenthos, principally bryozoans - a globally-ubiquitous phylum sensitive to environmental change. Analysis of sub-glacial biogenic substrata, by stereo microscopy, provided first evidence of spatial contest competition, enabling generation of a new range of competition measures for the sub-ice-shelf benthic space. Measures were compared with those of global open-water datasets traversing polar, temperate and tropical latitudes (and encompassing both hemispheres). Spatial competition in sub-ice-shelf samples was found to be higher in intensity and severity than all other global means. The likelihood of sub-ice-shelf competition being intraspecific was three times lower than for open-sea polar continental shelf areas, and competition complexity, in terms of the number of different types of competitor pairings, was two-fold higher. As posited for an enduring disturbance minimum, a specific bryozoan clade was especially competitively dominant in sub-ice-shelf samples compared with both contemporary and fossil assemblage records. Overall, spatial competition under an Antarctic ice shelf, as characterised by bryozoan interactions, was strikingly different from that of open-sea polar continental shelf sites, and more closely resembled tropical and temperate latitudes. This study represents the first analysis of sub-ice-shelf macrobenthic spatial competition and provides a new ecological baseline for exploring, monitoring and comparing ecosystem response to environmental change in a warming world.

Competitive hierarchies in bryozoan assemblages mitigate network instability by keeping short and long feedback loops weak.

Competitive hierarchies in diverse ecological communities have long been thought to lead to instability and prevent coexistence. However, system stability has never been tested, and the relation between hierarchy and instability has never been explained in complex competition networks parameterised with data from direct observation. Here we test model stability of 30 multispecies bryozoan assemblages, using estimates of energy loss from observed interference competition to parameterise both the inter- and intraspecific interactions in the competition networks. We find that all competition networks are unstable. However, instability is mitigated considerably by asymmetries in the energy loss rates brought about by hierarchies of strong and weak competitors. This asymmetric organisation results in asymmetries in the interaction strengths, which reduces instability by keeping the weight of short (positive) and longer (positive and negative) feedback loops low. Our results support the idea that interference competition leads to instability and exclusion but demonstrate that this is not because of, but despite, competitive hierarchy.

Quantifying microplastics in fjords along the Western Antarctic Peninsula.

Microplastics are ubiquitous around the world. Microplastics have been documented around the Southern Ocean, in coastal sediments and in Antarctic marine organisms, however microplastics data for Antarctic waters remain scarce. Microplastics concentrations were characterized from fjord habitats on the Western Antarctic Peninsula where most glaciers are rapidly retreating. Water samples were collected from 2017 to 2020 from surface and benthos, vacuum-filtered, quantified to determine the classification of microplastic, color, and size. Micro-FTIR spectrophotometry was utilized to confirm chemical composition. Comparisons over time and location were made for average microplastic per liter. Despite the new emergent youth and remoteness of these habitats, it was determined that all fjord habitats had microplastics present each year sampled and increased from 2017 to 2020 in each fjord. Despite physical 'barriers' such as the Antarctic Circumpolar Current (and particularly its strongest jet, the Polar Front), microplastics are clearly present and increasing in even recent habitats.

Filling the data gaps: Transferring models from data-rich to data-poor deep-sea areas to support spatial management.

Spatial management of the deep sea is challenging due to limited available data on the distribution of species and habitats to support decision making. In the well-studied North Atlantic, predictive models of species distribution and habitat suitability have been used to fill data gaps and support sustainable management. In the South Atlantic and other poorly studied regions, this is not possible due to a massive lack of data. In this study, we investigated whether models constructed in data-rich areas can be used to inform data-poor regions (with otherwise similar environmental conditions). We used a novel model transfer approach to identify to what extent a habitat suitability model for Desmophyllum pertusum reef, built in a data-rich basin (North Atlantic), could be transferred usefully to a data-poor basin (South Atlantic). The transferred model was built using the Maximum Entropy algorithm and constructed with 227 presence and 3064 pseudo-absence points, and 200 m resolution environmental grids. Performance in the transferred region was validated using an independent dataset of D. pertusum presences and absences, with assessments made using both threshold-dependent and -independent metrics. We found that a model for D. pertusum reef fitted to North Atlantic data transferred reasonably well to the South Atlantic basin, with an area under the curve of 0.70. Suitable habitat for D. pertusum reef was predicted on 20 of the assessed 27 features including seamounts. Nationally managed Marine Protected Areas provide significant protection for D. pertusum reef habitat in the region, affording full protection from bottom trawling to 14 of the 20 suitable features. In areas beyond national jurisdiction (ABNJ), we found four seamounts that provided suitable habitat for D. pertusum reef to be at least partially protected from bottom trawling, whilst two did not fall within fisheries closures. There are factors to consider when developing models for transfer including data resolution and predictor type. Nevertheless, the promising results of this application demonstrate that model transfer approaches stand to provide significant contributions to spatial planning processes through provision of new, best available data. This is particularly true for ABNJ and areas that have previously undergone little scientific exploration such as the global south.

Potential macroalgal expansion and blue carbon gains with northern Antarctic Peninsula glacial retreat.

The West Antarctic Peninsula (WAP) is a hotspot of physical climate change, especially glacial retreat, particularly in its northern South Shetland Islands (SSI) region. Along coastlines, this process is opening up new ice-free areas, for colonization by a high biodiversity of flora and fauna. At Potter Cove, in the SSI (Isla 25 de Mayo/King George Island), Antarctica, colonization by macroalgae was studied in two newly ice-free areas, a low glacier influence area (LGI), and a high glacier influence area (HGI) differing in the presence of sediment run-off and light penetration, which are driven by levels of glacial influence. We installed artificial substrates (tiles) at 5 m depth to analyze benthic algal colonization and succession for four years (2010-2014). Photosynthetic active radiation (PAR, 400-700 nm), temperature, salinity, and turbidity were monitored at both sites in spring and summer. The turbidity and the light attenuation (Kd) were significantly lower at LGI than at HGI. All tiles were colonized by benthic algae, differing in species identity and successional patterns between areas, and with a significantly higher richness at LGI than HGI in the last year of the experiment. We scaled up a quadrat survey on the natural substrate to estimate benthic algal colonization in newly deglaciated areas across Potter Cove. Warming in recent decades has exposed much new habitat, with macroalgae making up an important part of colonist communities 'chasing' such glacier retreat. Our estimation of algal colonization in newly ice-free areas shows an expansion of ∼0.005-0.012 km2 with a carbon standing stock of ∼0.2-0.4 C tons, per year. Life moving into new space in such emerging fjords has the potential to be key for new carbon sinks and export. In sustained climate change scenarios, we expect that the processes of colonization and expansion of benthic assemblages will continue and generate significant transformations in Antarctic coastal ecosystems by increasing primary production, providing new structures, food and refuge to fauna, and capturing and storing more carbon.

Antarctic Seabed Assemblages in an Ice-Shelf-Adjacent Polynya, Western Weddell Sea.

Ice shelves cover ~1.6 million km2 of the Antarctic continental shelf and are sensitive indicators of climate change. With ice-shelf retreat, aphotic marine environments transform into new open-water spaces of photo-induced primary production and associated organic matter export to the benthos. Predicting how Antarctic seafloor assemblages may develop following ice-shelf loss requires knowledge of assemblages bordering the ice-shelf margins, which are relatively undocumented. This study investigated seafloor assemblages, by taxa and functional groups, in a coastal polynya adjacent to the Larsen C Ice Shelf front, western Weddell Sea. The study area is rarely accessed, at the frontline of climate change, and located within a CCAMLR-proposed international marine protected area. Four sites, ~1 to 16 km from the ice-shelf front, were explored for megabenthic assemblages, and potential environmental drivers of assemblage structures were assessed. Faunal density increased with distance from the ice shelf, with epifaunal deposit-feeders a surrogate for overall density trends. Faunal richness did not exhibit a significant pattern with distance from the ice shelf and was most variable at sites closest to the ice-shelf front. Faunal assemblages significantly differed in composition among sites, and those nearest to the ice shelf were the most dissimilar; however, ice-shelf proximity did not emerge as a significant driver of assemblage structure. Overall, the study found a biologically-diverse and complex seafloor environment close to an ice-shelf front and provides ecological baselines for monitoring benthic ecosystem responses to environmental change, supporting marine management.

Benthic Biodiversity, Carbon Storage and the Potential for Increasing Negative Feedbacks on Climate Change in Shallow Waters of the Antarctic Peninsula.

The importance of cold-water blue carbon as biological carbon pumps that sequester carbon into ocean sediments is now being realised. Most polar blue carbon research to date has focussed on deep water, yet the highest productivity is in the shallows. This study measured the functional biodiversity and carbon standing stock accumulated by shallow-water (<25 m) benthic assemblages on both hard and soft substrata on the Antarctic Peninsula (WAP, 67° S). Soft substrata benthic assemblages (391 ± 499 t C km-2) contained 60% less carbon than hard substrata benthic assemblages (648 ± 909). In situ observations of substrata by SCUBA divers provided estimates of 59% hard (4700 km) and 12% soft (960 km) substrata on seasonally ice-free shores of the Antarctic Peninsula, giving an estimate of 253,000 t C at 20 m depth, with a sequestration potential of ~4500 t C year-1. Currently, 54% of the shoreline is permanently ice covered and so climate-mediated ice loss along the Peninsula is predicted to more than double this carbon sink. The steep fjordic shorelines make these assemblages a globally important pathway to sequestration, acting as one of the few negative (mitigating) feedbacks to climate change. The proposed WAP marine protected area could safeguard this ecosystem service, helping to tackle the climate and biodiversity crises.

Actions to halt biodiversity loss generally benefit the climate.

The two most urgent and interlinked environmental challenges humanity faces are climate change and biodiversity loss. We are entering a pivotal decade for both the international biodiversity and climate change agendas with the sharpening of ambitious strategies and targets by the Convention on Biological Diversity and the United Nations Framework Convention on Climate Change. Within their respective Conventions, the biodiversity and climate interlinked challenges have largely been addressed separately. There is evidence that conservation actions that halt, slow or reverse biodiversity loss can simultaneously slow anthropogenic mediated climate change significantly. This review highlights conservation actions which have the largest potential for mitigation of climate change. We note that conservation actions have mainly synergistic benefits and few antagonistic trade-offs with climate change mitigation. Specifically, we identify direct co-benefits in 14 out of the 21 action targets of the draft post-2020 global biodiversity framework of the Convention on Biological Diversity, notwithstanding the many indirect links that can also support both biodiversity conservation and climate change mitigation. These relationships are context and scale-dependent; therefore, we showcase examples of local biodiversity conservation actions that can be incentivized, guided and prioritized by global objectives and targets. The close interlinkages between biodiversity, climate change mitigation, other nature's contributions to people and good quality of life are seldom as integrated as they should be in management and policy. This review aims to re-emphasize the vital relationships between biodiversity conservation actions and climate change mitigation in a timely manner, in support to major Conferences of Parties that are about to negotiate strategic frameworks and international goals for the decades to come.

Biogeochemical consequences of a changing Arctic shelf seafloor ecosystem.

Unprecedented and dramatic transformations are occurring in the Arctic in response to climate change, but academic, public, and political discourse has disproportionately focussed on the most visible and direct aspects of change, including sea ice melt, permafrost thaw, the fate of charismatic megafauna, and the expansion of fisheries. Such narratives disregard the importance of less visible and indirect processes and, in particular, miss the substantive contribution of the shelf seafloor in regulating nutrients and sequestering carbon. Here, we summarise the biogeochemical functioning of the Arctic shelf seafloor before considering how climate change and regional adjustments to human activities may alter its biogeochemical and ecological dynamics, including ecosystem function, carbon burial, or nutrient recycling. We highlight the importance of the Arctic benthic system in mitigating climatic and anthropogenic change and, with a focus on the Barents Sea, offer some observations and our perspectives on future management and policy.

Quantification of blue carbon pathways contributing to negative feedback on climate change following glacier retreat in West Antarctic fjords.

Global warming is causing significant losses of marine ice around the polar regions. In Antarctica, the retreat of tidewater glaciers is opening up novel, low-energy habitats (fjords) that have the potential to provide a negative feedback loop to climate change. These fjords are being colonized by organisms on and within the sediment and act as a sink for particulate matter. So far, blue carbon potential in Antarctic habitats has mainly been estimated using epifaunal megazoobenthos (although some studies have also considered macrozoobenthos). We investigated two further pathways of carbon storage and potential sequestration by measuring the concentration of carbon of infaunal macrozoobenthos and total organic carbon (TOC) deposited in the sediment. We took samples along a temporal gradient since time of last glacier ice cover (1-1000 years) at three fjords along the West Antarctic Peninsula. We tested the hypothesis that seabed carbon standing stock would be mainly driven by time since last glacier covered. However, results showed this to be much more complex. Infauna were highly variable over this temporal gradient and showed similar total mass of carbon standing stock per m2 as literature estimates of Antarctic epifauna. TOC mass in the sediment, however, was an order of magnitude greater than stocks of infaunal and epifaunal carbon and increased with time since last ice cover. Thus, blue carbon stocks and recent gains around Antarctica are likely much higher than previously estimated as is their negative feedback on climate change.

How do we best synergize climate mitigation actions to co-benefit biodiversity?

A multitude of actions to protect, sustainably manage and restore natural and modified ecosystems can have co-benefits for both climate mitigation and biodiversity conservation. Reducing greenhouse emissions to limit warming to less than 1.5 or 2°C above preindustrial levels, as outlined in the Paris Agreement, can yield strong co-benefits for land, freshwater and marine biodiversity and reduce amplifying climate feedbacks from ecosystem changes. Not all climate mitigation strategies are equally effective at producing biodiversity co-benefits, some in fact are counterproductive. Moreover, social implications are often overlooked within the climate-biodiversity nexus. Protecting biodiverse and carbon-rich natural environments, ecological restoration of potentially biodiverse and carbon-rich habitats, the deliberate creation of novel habitats, taking into consideration a locally adapted and meaningful (i.e. full consequences considered) mix of these measures, can result in the most robust win-win solutions. These can be further enhanced by avoidance of narrow goals, taking long-term views and minimizing further losses of intact ecosystems. In this review paper, we first discuss various climate mitigation actions that evidence demonstrates can negatively impact biodiversity, resulting in unseen and unintended negative consequences. We then examine climate mitigation actions that co-deliver biodiversity and societal benefits. We give examples of these win-win solutions, categorized as 'protect, restore, manage and create', in different regions of the world that could be expanded, upscaled and used for further innovation.

Climate Mitigation through Biological Conservation: Extensive and Valuable Blue Carbon Natural Capital in Tristan da Cunha's Giant Marine Protected Zone.

Carbon-rich habitats can provide powerful climate mitigation if meaningful protection is put in place. We attempted to quantify this around the Tristan da Cunha archipelago Marine Protected Area. Its shallows (<1000 m depth) are varied and productive. The 5.4 km2 of kelp stores ~60 tonnes of carbon (tC) and may export ~240 tC into surrounding depths. In deep-waters we analysed seabed data collected from three research cruises, including seabed mapping, camera imagery, seabed oceanography and benthic samples from mini-Agassiz trawl. Rich biological assemblages on seamounts significantly differed to the islands and carbon storage had complex drivers. We estimate ~2.3 million tC are stored in benthic biodiversity of waters <1000 m, which includes >0.22 million tC that can be sequestered (the proportion of the carbon captured that is expected to become buried in sediment or locked away in skeletal tissue for at least 100 years). Much of this carbon is captured by cold-water coral reefs as a mixture of inorganic (largely calcium carbonate) and organic compounds. As part of its 2020 Marine Protection Strategy, these deep-water reef systems are now protected by a full bottom-trawling ban throughout Tristan da Cunha and representative no take areas on its seamounts. This small United Kingdom Overseas Territory's reef systems represent approximately 0.8 Mt CO2 equivalent sequestered carbon; valued at >£24 Million GBP (at the UN shadow price of carbon). Annual productivity of this protected standing stock generates an estimated £3 million worth of sequestered carbon a year, making it an unrecognized and potentially major component of the economy of small island nations like Tristan da Cunha. Conservation of near intact habitats are expected to provide strong climate and biodiversity returns, which are exemplified by this MPA.

Richness, growth, and persistence of life under an Antarctic ice shelf.

Where polar ice sheets meet the coast, they can flow into the sea as floating ice shelves. The seabed underneath is in complete darkness, and may be Earth's least known surface habitat. Few taxa there have been fully identified to named species (see Supplemental information) - remarkable for a habitat spanning nearly 1.6 million km2. Glimpses of life there have come from cameras dropped through 10 boreholes, mainly at the three largest Antarctic ice shelves - the Ross (McMurdo), Filchner-Ronne and Amery. Pioneering studies of life under boreholes found distinct morphotypes of perhaps >50 species. Here, we report remarkable growth and persistence over thousands of years of benthic faunal species collected in 2018 from the seabed under the Ekström Ice Shelf (EIS), Weddell Sea.

Can Antarctica's shallow zoobenthos 'bounce back' from iceberg scouring impacts driven by climate change?

All coastal systems experience disturbances and many across the planet are under unprecedented threat from an intensification of a variety of stressors. The West Antarctic Peninsula is a hotspot of physical climate change and has experienced a dramatic loss of sea-ice and glaciers in recent years. Among other things, sea-ice immobilizes icebergs, reducing collisions between icebergs and the seabed, thus decreasing ice-scouring. Ice disturbance drives patchiness in successional stages across seabed assemblages in Antarctica's shallows, making this an ideal system to understand the ecosystem resilience to increasing disturbance with climate change. We monitored a shallow benthic ecosystem before, during and after a 3-year pulse of catastrophic ice-scouring events and show that such systems can return, or bounce back, to previous states within 10 years. Our long-term data series show that recovery can happen more rapidly than expected, when disturbances abate, even in highly sensitive cold, polar environments.

1 °C warming increases spatial competition frequency and complexity in Antarctic marine macrofauna.

Environmental conditions of the Southern Ocean around Antarctica have varied little for >5 million years but are now changing. Here, we investigated how warming affects competition for space. Little considered in the polar regions, this is a critical component of biodiversity response. Change in competition in response to environment forcing might be detectable earlier than individual species presence/absence or performance measures (e.g. growth). Examination of fauna on artificial substrata in Antarctica's shallows at ambient or warmed temperature found that, mid-century predicted 1°C warming (throughout the year or just summer-only), increased the probability of individuals encountering spatial competition, as well as density and complexity of such interactions. 2°C, late century predicted warming, increased variance in the probability and density of competition, but overall, competition did not significantly differ from ambient (control) levels. In summary only 1°C warming increased probability, density and complexity of spatial competition, which seems to be summer-only driven.

Interpopulational differences in the nutritional condition of Aequiyoldia eightsii (Protobranchia: Nuculanidae) from the Western Antarctic Peninsula during austral summer.

The Western Antarctic Peninsula (WAP) is a hotspot for environmental change and has a strong environmental gradient from North to South. Here, for the first time we used adult individuals of the bivalve Aequiyoldia eightsii to evaluate large-scale spatial variation in the biochemical composition (measured as lipid, protein and fatty acids) and energy content, as a proxy for nutritional condition, of three populations along the WAP: O'Higgins Research Station in the north (63.3°S), Yelcho Research Station in mid-WAP (64.9°S) and Rothera Research Station further south (67.6°S). The results reveal significantly higher quantities of lipids (L), proteins (P), energy (E) and total fatty acids (FA) in the northern population (O'Higgins) (L: 8.33 ± 1.32%; P: 22.34 ± 3.16%; E: 171.53 ± 17.70 Joules; FA: 16.33 ± 0.98 mg g) than in the mid-WAP population (Yelcho) (L: 6.23 ± 0.84%; P: 18.63 ± 1.17%; E: 136.67 ± 7.08 Joules; FA: 10.93 ± 0.63 mg g) and southern population (Rothera) (L: 4.60 ± 0.51%; P: 13.11 ± 0.98%; E: 98.37 ± 5.67 Joules; FA: 7.58 ± 0.48 mg g). We hypothesize these differences in the nutritional condition could be related to a number of biological and environmental characteristics. Our results can be interpreted as a consequence of differences in phenology at each location; differences in somatic and gametogenic growth rhythms. Contrasting environmental conditions throughout the WAP such as seawater temperature, quantity and quality of food from both planktonic and sediment sources, likely have an effect on the metabolism and nutritional intake of this species.