Climatic change and its ecological implications at a subantarctic island

Abstract

Marion Island (47°S, 38°E) has one of the most oceanic climates on earth, with consistently low air temperatures, high precipitation, constantly high humidity, and low incident radiation. Since 1968 mean surface air temperature has increased significantly, by 0.025° C year. This was strongly associated with corresponding changes in sea surface temperature but only weakly, or not at all, with variations in radiation and precipitation. We suggest that changing sealevel (atmospheric and oceanic) circulation patterns in the region underlie all of these changes. Sub-Antarctic terrestrial ecosystems are characterized by being species-poor and having a simple trophic structure. Marion Island is no exception and a scenario is presented of the implications of climatic change for the structure and functioning of its ecosystem. Primary production on the island is high and consequently the vegetation has a large annual requirement for nutrients. There are no macroherbivores and even the insects play only a small role as herbivores, so most of the energy and nutrients incorporated in primary production go through a detritus, rather than grazing, cycle. Ameliorating temperatures and increasing CO levels are expected to increase productivity and nutrient demand even further. However, most of the plant communities occur on soils which have especially low available levels of nutrients and nutrient mineralization from organic reserves is the main bottleneck in nutrient cycling and primary production. Increasing temperatures will not significantly enhance microbially-mediated mineralization rates since soil microbiological processes on the island are strongly limited by waterlogging, rather than by temperature. The island supports large numbers of soil macro-arthropods, which are responsible for most of the nutrient release from peat and litter. The activities of these animals are strongly temperature dependent and increasing temperature will result in enhanced nutrient availability, allowing the potential for increased primary production due to elevated temperature and CO levels to be realized. However, housemice occur on the island and have an important influence on the ecosystem, mainly by feeding on soil invertebrates. The mouse population is strongly temperature-limited and appears to be increasing, possibly as a result of ameliorating temperatures. We suggest that an increasing mouse population, through enhanced predation pressure on soil invertebrates, will decrease overall rates of nutrient cycling and cause imbalances between primary production and decomposition. This, along with more direct effects of mice (e.g. granivory) has important implications for vegetation succession and ecosystem structure and functioning on the island. Some of these are already apparent from comparisons with nearby Prince Edward Island where mice do not occur. Other implications of climatic change for the island are presented which emphasize the very marked influences that invasive organisms have on ecosystem structure and functioning. We sugges...

Biological invasions in the Antarctic: extent, impacts and implications

“…Analogous trends are seen at some sub-and continental Antarctic sites (e.g. Smith & Steenkamp, 1990 ;Gordon & Timmis, 1992 ;Frenot et al, 1997 ;Tweedie & Bergstrom, 2000 ;Smith, 2002). By contrast, one report of regional cooling in the Dry Valleys region of Victoria Land (Doran et al, 2002; but see also Turner et al, 2002) has linked local cooling with decreased primary productivity and invertebrate populations.…”

“…Again, these changes may be linked with ENSO. Decreased precipitation has been reported at sub-Antarctic Marion and Kerguelen Islands since the early 1950s (Smith & Steenkamp, 1990;Frenot et al, 1997 ;Smith, 2002 ;Chapuis et al, 2004) and, more recently, from maritime Antarctic Signy Island (Noon et al, 2001). In the maritime Antarctic, there is also an increasing likelihood that summer precipitation will fall as rain rather than snow, and hence be immediately available to terrestrial ecosystems.…”

Changes in Heard Island glaciers, king penguins and fur seals since 1947

“…Poa annual have appeared, apparently as a result of animal disturbance and warmer temperatures (Scott 1989(Scott ,1990. Similar effects on vegetation have been observed at Kerguelen, where recently deglaciated areas have been colonised by the introduced grass Poa annuaas well as by the native grass P. kerguelensis (Frenot et al 1997), and at Marion Island, where warmer temperatures are causing complex changes in nutrient cycles (Smith & Steenkamp 1990).…”

“…At Marion Island, Smith & Steenkamp (1990) reported a strong correlation between air and sea-surface temperatures, which between 1968 and 1985 had increased by 1.6° and 1.2°C, respectively, and attributed these changes to changing atmospheric and oceanic circulation patterns in the region. Likewise, at South Georgia, Gordon & Timmis (1992), analysing synoptic records of atmospheric pressure, attributed rising air temperatures and glacier recession since about 1950 to regional changes in atmospheric circulation.…”

Interactions between a cushion plant (Azorella selago) and surface sediment transport on sub-Antarctic Marion Island

“…Rising temperatures and decreasing rainfall on Marion Island (Smith, 2002;Le Roux and McGeoch, 2008a) could lead to decreasing occurrences of needle ice and related sorting around cushions. On the other hand, predicted decreasing cloud cover (Smith and Steenkamp, 1990) and snow insulation could result in an increase in the number of freeze-thaw days and the spatial variability thereof (Boelhouwers, 2007) and increasing importance of needle-ice related sorting patterns. Therefore, the future implications of climate change for directional grain size sorting patterns and consequent sediment properties are not yet fully understood.…”