We present a synthesis of marine soft sediment macrofaunal communities from the Vestfold Hills, East Antarctica, spanning historical data (1978–1982) and recent surveys from 47 locations (2010–2021). We examined relationships between environmental conditions, such as sediment properties and sea-ice duration, and community structure and biodiversity. Macrofaunal biodiversity was high, with 148 taxa identified in recent surveys. Community composition varied significantly between locations, influenced primarily by sediment grain size. Sediments ranged from mud to coarse sands, with organic content varying from < 1% to 15%, and locations were classified into four sediment categories: muds, very fine sands, fine sands and medium/coarse sands. Significant differences in community structure were found between sediments groups, but the considerable variability within groups suggests additional influences from factors such as sea ice, depth and stochastic processes. Crustaceans, including amphipods, ostracods and tanaids, dominated communities across all locations. Macrofaunal abundance was highest in muds and very fine sands and declined significantly in coarser sediments. Species-level abundance patterns showed high heterogeneity, with some trends linked to sediment grain size. Areas with abundant large sessile epifauna were associated with higher sediment biodiversity. This study highlights the complexity of environmental factors shaping macrofaunal communities in Antarctic coastal ecosystems.

Antarctic ice-free coastal environments, like the Vestfold Hills (East Antarctica), are shaped by a complex interplay of physical processes. This study synthesizes new data and existing research from the Vestfold Hills across marine, terrestrial and cryosphere science, meteorology, geomorphology, coastal oceanography and hydrology to explore interconnected processes ranging from icescape morphology and sediment transport to ocean-floor scouring and ocean-atmosphere interactions. Coastal landforms and habitats result from the interaction of marine dynamics with the aeolian and fluvial transport of glacially derived sediments and geomorphic features. Rocky shorelines dominate the region, and extensive fjords are prominent coastal features, whereas intertidal sediments and beaches are scarce. The marine environment is characterized by slow currents, low-energy waves, annually variable land-fast ice, irregular sedimentation rates and a geomorphologically complex shoreline. Aeolian and fluvial sediment deposition into coastal waters and onto sea ice can significantly impact local ecological and physical processes. Human activity further modifies these dynamics. Ice-free coastal areas such as the Vestfold Hills are predicted to experience substantial environmental shifts due to climate change. Wind speeds, temperature and precipitation are increasing in the Vestfold Hills. Retreating grounded ice sheets are likely to expand this coastal area and increase meltwater and sediment inputs into nearshore marine systems. Concurrently, changes in sea-ice extent, thickness and/or duration may profoundly alter the structure and function of this coastal environment.

The Vestfold Hills are a 400 km2, isolated ice-free oasis in eastern Antarctica featuring large areas with translucent quartz rocks that provide habitat for hypolithic microbial communities underneath. We used high-throughput DNA sequencing of 16S and 18S ribosomal RNA amplicons to characterize bacterial and eukaryotic hypolithic communities across the Vestfold Hills. We found high-level, local heterogeneity in community structure consistent with limited dispersal between hypoliths. Hypolithic communities were dominated by heterotrophic Bacteroidetes (mean bacterial relative read abundance: 56%) as well as Cyanobacteria (35%), with the eukaryote component often dominated by Chlorophyta (43%). Small but significant proportions of the variation in microbial community composition and function were explained by soil salinity (5–7%) and water availability (8–11%), with distinct taxa associated with different salinities and water availabilities. Furthermore, many inferred bacterial metabolic pathways were enriched in hypolithic communities from either dry or high-salinity sites. Vestfold Hills hypolithic habitats are likely to be local refuges for bacterial and eukaryotic diversity. Gradients in soil salinity and water availability across the Vestfold Hills, in addition to the number and diversity of lake types and fjords as potential source populations, may contribute to the observed variation in the extremophile, hypolithic microbial community composition.

A proportion of the southern elephant seal (Mirounga leonina) population that breeds in the Kerguelen Plateau region seasonally migrates between their natal sub-Antarctic islands and moult haul-out locations on the Antarctic coastline. Analyses of survey data collated for one moult location at the Vestfold Hills, East Antarctica, showed that there had been no appreciable change in the timing (phenology) of maximum seal arrivals between 1974 and 2022; however, the maximum number of seals moulting at that site had declined by ~90% over the same time interval. Spatial analyses showed rates of population change were survey area dependent, as seal numbers decreased most rapidly at haul-out areas closest to the permanently occupied Davis Station, suggesting that a relationship exists between seal numbers and human activities. The range of potential factors that contribute to population change for southern elephant seals moulting at the Vestfold Hills includes changes in status at primary source populations, one of which has not been surveyed since the 1990s, and species relocation. Should numbers of southern elephant seals in the Vestfold Hills continue to decrease at the current average rate of change (-7.78 seals/year) the species could vanish from the area by c. 2040.

Species distributions are predicted to change with future climate-associated ecosystem changes such that so-called ‘vagrant’ individuals may become established or re-establish in areas currently thought to be beyond their principle ranges. Survey data were collated for occurrences of pinniped (seal) species at very high latitudes of the Vestfold Hills, East Antarctica. Aside from Weddell seals (Leptonychotes weddellii) and southern elephant seals (Mirounga leonina), which aggregate annually at the Vestfold Hills to breed and/or moult, three other pinniped species were observed with the recession of the fast-ice edge. Leopard seal (Hydrurga leptonyx) occurrences increased with an increase in a seasonally abundant prey resource, and crabeater seals (Lobodon carcinophaga) were seen at a time that coincides with their moult period. Occurrences of sub-adult male Antarctic fur seals (Arctocephalus gazella) increase the known southward range for this species and may reflect population increases at source populations in the Kerguelen Plateau area. Although there were no direct sightings of Ross seals (Ommatophoca rossii), their presence close to the Vestfold Hills was detected by underwater passive acoustic monitoring. Sightings of obligate drift-ice species and sub-Antarctic fur seals may change at the Vestfold Hills with climate-mediated changes in sea-ice conditions.

Areas around western Vestfold Hills, East Antarctica, feature two sedimentary units in outcrops and excavations. Uppermost Dingle Sand is a gravelly, silty sand with boulders, which drapes bedrock ridges and more thickly covers valley floors and continues below modern sea level. Underlying Vestfold Beds are gravelly, muddy sands that are found in deeper valley fills. High-resolution aerial photography, topographic and bathymetric surveys, sediment grain size and field observations indicate that Dingle Sand formed as ablation till during the last deglaciation. Post-depositional modifications of Dingle Sand by decay of ground ice, mass movement, water, wind and marine transgression and regression have altered the texture, structure and fossil content in this region. Vestfold Beds are older, finer-grained tills. Indirect age estimation of Dingle Sand suggests deglaciation-age deposition with younger (Holocene) reworking in places, whereas Vestfold Beds may be as old as the Pliocene. These sediments post-date the early Pliocene Sørsdal Formation found on Marine Plain in southern Vestfold Hills. Identification of Dingle Sand as a separate, primarily glacial deposit helps clarify the glacial history of the Vestfold Hills. Evidence for marine modification of the deposits after deglaciation suggests that other regions might also have glacial deposits interpreted as marine because of post-depositional processes.