Svalbard, the Norwegian archipelago in the Arctic Ocean
Situated north of mainland Europe, it is about midway between continental Norway and the North Pole.
The Arctic is a region experiencing rapid environmental change. Temperatures are rising and are projected to continue to do so. Precipitation patterns will alter. Sea-ice cover is in retreat. The region is a sink for pollutants originating from lower latitudes. Human activities in the High Arctic are on the increase. All of these combine to threaten the characteristic Arctic environments of the far north. One key component of the terrestrial system that will be affected by such changes is the soil invertebrate fauna. It is clear that the invertebrate community plays a fundamental role in many ecosystem processes including nutrient cycling, energy flow, decomposition, pollination, herbivory, and parasitism all of which contribute to the characteristic High Arctic ecology. Moreover, the relatively simple polar (Arctic and Antarctic) ecosystems are thought to be particularly valuable for studies addressing basic questions of ecosystem function, providing examples across a wide range of levels of assemblage structure. For example, biodiversity of terrestrial ecosystems may provide a robustness and stability to the characteristically large annual variation in the climate of the Arctic and, hence, also provide a resilience to environmental change. Yet, the relationship between species diversity and ecosystem function often remains unclear, despite considerable debate around the importance, or otherwise, of ‘functional redundancy’ in maintaining stability in ecosystems. Nonetheless, while invertebrates represent the majority of eukaryotic biodiversity, little is known about their distributions, populations or associated trends. This is particularly true for Arctic regions. However, despite this possibly inherent resilience to great natural environmental variability, these High Arctic systems may be particularly vulnerable to human disturbance, predominantly due to lengthy recovery and regeneration times. With a complex terrestrial High Arctic ecology and the intense international attention (scientific, political and industrial), Svalbard can make an important case study for Arctic invertebrate communities.
Scientific activities in Svalbard commenced in the middle of the nineteenth century. Amongst the first biological investigations were those of Boheman (1865) and Holmgren (1869). But biological projects really only commenced after the turn of the century. Publications pertaining to the invertebrate fauna of the archipelago increased rapidly through the 1920s and 30s but declined during the period 1940-45 with the intervention of the Second World War. After the restoration of peace, science activities recommenced including the development of the international research village in the former Norwegian mining settlement of Ny-Ålesund. The settlement attracted increased international attention and has developed into the Kongsfjord International Research Base (KIRB). At the time of writing, 13 nations have research stations located in Ny-Ålesund. The establishment of KIRB led to a rapid increase in the number of publications from 1990 in a wide range of subjects including upper atmosphere, ecotoxicology, pollutant studies, meteorology, marine and terrestrial ecology including invertebrate studies.
In 1957 the Polish station in Hornsund, southern Spitsbergen, was established and is now operated year round by the Institute of Geophysics, Polish Academy of Sciences. Research at the station focusses on physical geography but there have been terrestrial invertebrate studies. In Barentsburg there are research stations operated by several Russian institutions including the Kola Scientific Centre of Russian Academy of Sciences. While botanical projects are conducted, there appear to be few terrestrial invertebrate studies. There are also smaller field based projects at diverse locations around Svalbard, for example the recent establishment of Czech and Polish stations in Petuniabukta close to Isfjord, Spitsbergen. In 1993, the University Centre in Svalbard (UNIS) located in Longyearbyen was opened. This provided new research opportunities at this High Arctic location. With an international airport in Longyearbyen, the archipelago offers perhaps unparalleled ease of access to High Arctic latitudes and comprehensive logistical support.
Svalbard is located close to the confluence of ocean currents and air masses of differing thermal characteristics. This results in Svalbard being one of the most climatically sensitive regions in the world. Low pressure systems in the vicinity of Iceland and high pressure systems over Greenland determine the synoptic airflow to Svalbard. In the winter this pattern is displaced further south resulting in cold air masses extending to Svalbard while in the summer, warmer air from more southerly latitudes is directed to Svalbard. Furthermore, considerable heat is transported north from more southerly latitudes by the West Spitsbergen Current, a branch of the North Atlantic Drift. The result is that the climate of the islands is mild for the latitude. The annual mean air temperature is –6.7°C but four months have positive mean air temperatures, from +0.3°C in September to 5.9°C in July.
Svalbard is experiencing some of the greatest changes in temperatures in the Arctic. Located at the southern limit of the Barents Sea winter sea-ice, the winter and summer temperatures are heavily influenced by the presence or absence of this sea ice. In particular lack of sea ice in the winter resulting in warmer winter and spring air temperatures. Recent decreases in the extent of this sea ice have therefore exacerbated local increases in global mean air temperature. Warm air masses may also arrive during winter resulting in abnormally mild periods. In the winter 2011-2012 temperatures were on average some 10°C above long term normal. Precipitation was also remarkably great in this winter. Ny-Ålesund received 98mm of rain in one 24 hour period, 28% of the average annual precipitation. While this particular winter was unusually extreme, it demonstrates the wide variation in winter conditions that are characteristic of this region.
The settlements in Svalbard, Longyearbyen, Ny-Ålesund, Svea (all Norwegian), Barentsburg (Russian) and Hornsund (Polish), are all located along the west coast. Most of the settlements were originally established as coal mines. Hence the west coast positions of these towns is due to a combination of the geographic location of the coal deposits and the heavier sea ice conditions on the east coast, resulting from the southerly flowing cold East Spitsbergen current restricting access. Precipitation is geographically extremely variable. The west coast having the greatest precipitation, for example Barentsburg on the west coast receives a mean precipitation of 525mm per year but the interior of the islands is substantially dryer. Longyearbyen, 50km to the east of Barentsburg, recording an average annual value of 210mm. In both cases most of the precipitation falls during the winter as snow.
During the last glacial maximum (LGM) the archipelagoes of the Barents Sea were largely covered by ice and were progressively exposed as the ice began to retreat approximately 10,000 YBP. The relatively short period since deglaciation, combined with the Arctic climate and continuing periglacial soil processes, have strongly influenced habitats and ecosystems. As seen across the Arctic, the environment is characteristically highly heterogenous with, for example, dry stony ridges, periglacial features, areas of late snow lie, heath or wet moss all in close proximity. On a regional basis, northern areas consist largely of polar desert characterized by low precipitation and short snow-free growing seasons. Vascular plant cover is typically scarce, often less than 15%, and greatest along the coastal margins. While soils protected under deeper snow experience winter temperatures no lower than -10°C, the ridge tops, blown free of winter snow, or areas kept clear of snow by wind eddies, may track winter air temperatures closely and approach -40°C on occasion. The soil surface temperature may often attain 20ºC due to the 24 hour midnight sun despite air temperatures rarely attaining double figures. Generally soils are thin, rarely more than a few centimeters thick, and overlie old morainic debris, patterned ground or rock but they may vary considerably in depth and form over short distances. In nutrient enriched areas, for example under bird cliffs, organic soils of over 20 cm depth may also accumulate, illustrating the impact of nutrient flow from the marine environment to the nutrient limited terrestrial habitat. Melting snow and permafrost also provides a constant cold water source throughout the summer often resulting in wet moss areas in direct proximity to dryer polar desert vegetation. In such wet areas, the moss may develop into thick carpets, or turfs, some tens of centimeters deep, efficiently insulating the ground beneath against the warming effect of solar insolation.
Running freshwaters are characterised by the dominance of glacial melt water, typically in the form of large braided river systems with high sediment loads, highly irregular flows and low temperatures even in summer. In Svalbard, river flow may start late June to early July. Ice break-up on the lakes however occurs later, from mid-July until late-August. Temporary thaw ponds, permanent shallow ponds and small lakes are numerous and because of the low water depth (usually less than 2 m) many of these water bodies freeze solid during winter while the shallower ones can dry out during summer.
The environment of Svalbard is hence highly heterogenous, both geographically and temporally. It is established that air temperatures globally are increasing, although precise causes are more contentious. Regions such as Svalbard are also under increasing pollutant load, both allochthonous and local, increased industrialisation, human activity and increased threat of introduction of alien species. This article examines how these changes may affect the terrestrial and freshwater invertebrate ecology of the High Arctic, focussing on the Svalbard ecosystem.
Terrestrial and freshwater invertebrate science in Svalbard
The terrestrial invertebrate fauna of Svalbard may be amongst the most comprehensively catalogued for any region of the Arctic. There are close to 600 articles in international journals considering this fauna and three checklists summarising this literature. The current species list for Svalbard cites some 960 species names excluding the Protoctista. This list is under constant revision due to the large number of synonyms and taxonomic confusion and new species, either to Svalbard or new to science, are constantly being described. But it is clear that, contrary to first appearances, Svalbard has a diverse invertebrate fauna which includes apparent endemics, for example the aphid Acyrthosiphon svalbardicum (Heikinheimo 1968) and the gamasid mite Amblyseius magnanalis (Thor, 1930). Since until the end of the last glacial maximum, Svalbard was covered beneath an ice sheet no invertebrates or plants are thought to have survived the glacial maximum in situ, rather the current fauna and flora is the result of recent immigration processes, although there remains the possibility that in small refugia some plants may have persisted during this period of glaciation.
While a general understanding of the terrestrial and freshwater fauna is increasing fast, the great majority of the studies have been undertaken on the west coast, primarily in the Isfjord region close to Longyearbyen and from KIRB at Ny-Ålesund. Less than ten manuscripts consider the invertebrate fauna of the eastern regions. But, despite the lack of knowledge of the invertebrate fauna of the eastern regions, there are indications of different communities here than those found on the west coast. The reasons for this difference are as yet unclear but may be related to different immigration histories. The east coast being influenced by the East Svalbard Current bringing driftwood from the great Russian rivers. On the west coast it is the West Spitsbergen Current that dominates, bringing warm water northwards from the Atlantic and hence potentially baring a dissimilar fauna from the East Spitsbergen Current. An improved knowledge of the fauna of the eastern regions is urgently required.