Julian Gutt

Antarctic climate change and the environment

Abstract The Antarctic climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system. We review these variations from the perspective of the geological and glaciological records and the recent historical period from which we have instrumental data (∼the last 50 years). We consider their consequences for the biosphere, and show how the latest numerical models project changes into the future, taking into account human actions in the form of the release of greenhouse gases and chlorofluorocarbons into the atmosphere. In doing so, we provide an essential Southern Hemisphere companion to the Arctic Climate Impact Assessment.

On the direct impact of ice on marine benthic communities, a review

Abstract. Ice has a significant impact on the polar and sub-polar benthos, but relationships between corresponding physical and biological processes are not yet sufficiently understood. Sea ice contributes to a vertical zonation in shallow waters, which also experience other important disturbances. Due to the length of the non-glaciated coastline, sea ice is of greater relevance in the north than in the south. Scouring by icebergs and ridged sea ice causes an increased diversity when different recolonisation stages coexist. Frequently scoured areas do not recover, especially in the Antarctic, due to slow growth rates of the fauna. Iceberg grounding in the Arctic is mainly restricted to the western Eurasian and northeastern American shelf, including Greenland. Around Antarctica, scouring is more evenly distributed. Glacier termini prevent sessile animals from settling in their proximity where only few motile species occur.

Antarctic climate change and the environment: an update

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

Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota

Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This article reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed.

Structure and biodiversity of megabenthos in the Weddell and Lazarev Seas (Antarctica): ecological role of physical parameters and biological interactions

Abstract A community analysis of the mega-zooepibenthos at water depths between 99 and 1243 m was carried out for the Weddell and Lazarev Seas (47°W 77°S–12°E 70°S). A total of 144,531 specimens were counted and 313 taxa were identified from 3,768 photographs at 55 stations, which represented approximately 3,304 m2 of seafloor. The stations were classified into six groups according to their inventory of taxa although they represented rather a gradient from a rich and diverse suspension feeder assemblage to a poorer assemblage. In the latter, the proportion of deposit feeders was higher than in the former. A statistical comparison between biological and physical data showed that the faunistic pattern could best be explained by a combination of water depth and a geographical gradient. A positive correlation between the abundance of large sponges and the number of all other taxa was found.

Sponge associations in the eastern Weddell sea

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.

Quantification of iceberg impact and benthic recolonisation patterns in the Weddell Sea (Antarctica)

Abstract. Video transects in the eastern Weddell Sea were used to classify the mega-epibenthos into stages of recolonisation after iceberg impact and unaffected fauna. Three site categories differing in bottom topography and concentration of grounded icebergs were analysed. At small iceberg banks and on a comparatively plain seabed, 52–60% of undisturbed seafloor was found, and below 20% at a large iceberg bank. The impact was calculated as a function of values for recently disturbed areas and an estimated recovery time. The results show that, statistically, the Antarctic benthos never reaches peak maturity and that iceberg scouring is among the five most significant disturbances that any large ecosystem on earth experiences.

Some "driving forces" structuring communities of the sublittoral Antarctic macrobenthos

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 Antarcticas glacial history, shaped the diversity and faunal composition of the macrobenthos. Consequently, neither Houstons “intermediate-disturbance-hypothesis” nor Sanders “stability-time-hypothesis” can be rejected for this part of the Antarctic ecosystem.

Epibiotic relationships in the Antarctic benthos

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.

Antarctic macro-zoobenthic communities: a review and an ecological classification

Abstract 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.