We present an update of the ‘key points’ from the Antarctic Climate Change and the Environment (ACCE) report that was published by the Scientific Committee on Antarctic Research (SCAR) in 2009. We summarise subsequent advances in knowledge concerning how the climates of the Antarctic and Southern Ocean have changed in the past, how they might change in the future, and examine the associated impacts on the marine and terrestrial biota. We also incorporate relevant material presented by SCAR to the Antarctic Treaty Consultative Meetings, and make use of emerging results that will form part of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report.

A partly new classification of shelf inhabiting Antarctic macro-zoobenthic communities is proposed in this review. The main components are two core communities. One is dominated by sessile suspension feeders supported by food entrained in strong near-bottom currents. Variants of this community include assemblages without sponges, those that prefer sponge spicule mats as substratum and predator-driven systems. The second core community is dominated by the infauna and mobile epifauna and controlled by vertical phytodetritus flux and soft sediments. This community is obviously restricted to areas with low current velocity, particularly in areas that are sheltered due to a heterogeneous coastal and sea floor topography. In addition, in physically controlled shallow water a small number of representatives of all these ecological guilds can become very abundant. Between both core communities a broad range of mixed assemblages exists that can be explained by a gradient in environmental conditions and trophic amensalism. A concept is also proposed for the ecological functioning of systems with extremely low abundances within ecological guilds, such as those that occur under and close to ice shelves, which cannot satisfactorily be explained by trophic limitation. These extremely low abundances may result from a shift during ontogenesis from a state with predominantly mismatched environmental conditions and ecological demands of young recruits, to a state where a match occurs.

Three species of shrimps (Notocrangon antarcticus, Chorismus antarcticus, Nematocarcinus lanceopes) were investigated in the south-eastern Weddell Sea using of underwater photography. Maximum densities of c. 100 specimens per 100 m2 were found for N. antarcticus on the continental shelf (200–600 m) and for N. lanceopes on the slope (800–1200 m). Small-scale dispersion patterns and size-frequency distributions were analyzed within dense concentrations. These direct observations indicate that the behaviour of the three species is adapted to different habitats with Chorismus distribution correlated with that of sponges and Notocrangon with base sediment.

About 1500 photographs from three different areas along the eastern Weddell Sea shelf and slope were analysed with respect to their sponge fauna. On the basis of material collected in concurrent bottom trawls, 34 sponge taxa were identified. Cluster and multidimensional scaling analysis showed the sponges to belong to different associations. Spatial extension of the associations is judged to be between several hundred meters and about 2 km. A deeper association (390–1125 m) on predominantly muddy substrates along a transect at Halley Bay is characterized by four opportunistic demosponge species; a second association on harder substrate in shallower depths (99–225m) off Kapp Norvegia is more diverse, with hexactinellids as one dominant component. A third cluster, comprising both Halley Bay and Kapp Norvegia stations (458–626 m), is dominated by four species which constitute a subcluster within the Kapp Norvegia sponge association. Densities vary strongly within clusters and in between geographically close stations. The species associations are related to different substrates, not to depth. Within single stations most species are patchily distributed. Both association structure and species distribution within single stations can be explained on the basis of the biology of the single sponge species.

Seventy-three sponge species were caught at 23 stations on the continental shelf of the Lazarev and Weddell Sea (Atlantic sector of the Southern Ocean). Tedania tantula was the most often found species amongst the 63 demosponge species caught and among the five hexactinellid species Rossella racovitzae was most common. The stations were classified according to their species inventory, and so the individual stations of the resulting four groups were rather uniformly dispersed over the entire investigation area. The species composition of adjacent stations varied considerably. There was no discernible relationship between the biological set of data and any combination of the available environmental characteristics of the stations. The sponge fauna of the, so far very poorly investigated, Lazarev Sea did not differ considerably from that of the adjacent Weddell Sea. The only species to be recorded for the first time on the Antarctic continental shelf were Homaxinella flagelliformis and Hyrtios arenosa. Small scale environmental events such as iceberg scouring, or biological characteristics such as extremely slow growth and budding reproduction are thought to generate the patchy distribution pattern.

On the high Antarctic shelf, 374 different epibiotic relationships of the megafauna were photographically registered and statistically analysed. These comprised 47 different epibiotic and 96 substratum taxa and had obvious differences in abundance and presence in three different benthic assemblages. Six abundant obligatory relationships in which the epibiont occurred almost exclusively on one type of substratum had highly specialized epibionts. For an additional eight relationships, a statistical test revealed that the epibionts preferred specific living and elevated mineral substrata. Most of these relationships are interpreted as commensalism (sensu Odum) in which the suspension feeding epibiont profits from the elevated position. Here it has better access to food compared with life on the sediment. The evolution of a rich and mainly sessile epifauna on parts of the high Antarctic shelves and the successful development of epibiotic behaviour in other species are suggested as a major reason for the high species richness in the benthic fauna. The results provide evidence that the Antarctic megabenthos is more biologically accommodated than physically controlled.

We analysed growth of the arborescent Antarctic cheilostome bryozoan Cellaria incula by stable carbon and oxygen isotope analysis. The growth of one complete branch of C. incula takes one year, i.e. owing to the bifurcate colony structure two new branches grow from each branch of the previous generation. The maximum age of a C. incula colony is likely to be more than 14 years. Annual production-to-biomass ratio is 0.67, the highest value hitherto measured for any benthic invertebrate south of 62°S. Comparatively fast growth and high productivity identify C. incula as a pioneer species which is able to quickly occupy spatial niches produced by iceberg scouring on the Antarctic shelf.

Community analyses of the macrobenthos living on the Weddell Sea shelf revealed a distinct horizontal patchiness. Within some systematic groups a specific faunistic classification could clearly be defined, e.g. for asterozoans and holothurians. Whilst for fish, only a general zoogeographical pattern was discernible, there were some recognisable relationships to different microhabitats. The extreme differences in the distribution of sponges observed seems to reflect their highly variable biological characteristics. Studies using underwater imaging methods for benthic research have provided strong evidence for the ecological significance of two factors. The first, iceberg scouring, leads to a variety of simultaneous stages of recolonization, which result in an increase in beta-diversity. As a consequence, it is unlikely that regionally a stage approaching a theoretical climax will ever be attained. Secondly, the structural diversity of living substrata provides the basis for an additional variety of epibiotic species. Only weak or non-detectable correlations have been found between benthic assemblages and physical parameters, such as water depth, sediment type, bathymetric features and the abundance of deposited phytodetritus. This indicates a benthic system which is relatively uncoupled from processes in the water column. The combination of stable environmental conditions and disturbances taking place over long periods of time, which are partly a special feature of Antarctica's glacial history, shaped the diversity and faunal composition of the macrobenthos. Consequently, neither Houston's “intermediate-disturbance-hypothesis” nor Sander's “stability-time-hypothesis” can be rejected for this part of the Antarctic ecosystem.

Based on data from the Weddell Sea in the Atlantic sector of the Southern Ocean, the total number of macrozoobenthic species was estimated for the entire Antarctic shelf using species-accumulation methods, jack-knife estimators, and Incidence-based Coverage Estimators of species richness. Ranging between 11 000 and 17 000 expected species, Antarctica seems to have an intermediate species richness when compared to other selected tropical, temperate or Arctic habitats.