Terrestrial microarthropods of Victoria Land and Queen Maud Mountains, Antarctica: Implications of climate change

Abstract

We review aspects of climate change likely to impact upon the Collembola and mites (microarthropods) of Victoria Land and the Queen Maud Mountains (VLQMM) in the Ross Sea Region of Antarctica. Five important aspects of biological and biological–environmental interactions are identified as key for understanding the impact of climate change on VLQMM microarthropods: (1) Water availability and utilization; (2) mean temperature (which will affect development and population processes) and extreme temperatures (which affect persistence); (3) ultraviolet radiation, although we note that the periods of peak UV irradiance and microarthropod activity do not coincide; (4) dispersal within and between habitats; and (5) potential establishment of invasive species from within and without Antarctica. The current evidence for effects of climate change on VLQMM microarthropods is equivocal, and we advocate targeted experimental and monitoring studies. Finally, we highlight several areas of high priority for future research, particularly on the mite fauna for which detailed information is currently lacking. These are: (1) functional ecology (including thermal biology, feeding and nutrition and water relations); (2) distribution, dispersal and colonization processes and (3) population and community ecology.

Introduction

Less than 2% of the 14 million km² of the Antarctic continent is presently ice-free, and Antarctic terrestrial habitats provide exemplary extreme environments (Block, 1994; Miller and Mabin, 1998; Wharton, 2002; Roberts et al., 2003). However, the climate cooling that resulted in the glaciation of Antarctica did not occur until the South Tasman Rise cleared the Oates Land coast of East Antarctica (∼32 MYA) and the Drake Passage opened to deep-water circulation (∼28 MYA) (Lawver and Gahagan, 2003). Even so, Nothofagus-herb-moss tundra vegetation replaced the Gondwanan forest and persisted in the region until the late Miocene (∼12–5 MYA) or Pliocene (∼5–2 MYA) (Ashworth and Preece, 2003). Pliocene extinction of the last remaining higher insects (Ashworth and Kuschel, 2003; Ashworth and Thompson, 2003) and freshwater macrofauna (e.g. Ashworth and Preece, 2003) has left a depauperate terrestrial fauna, at least some of which are Gondwanan relicts that have diversified since the completion of glaciation in the late Miocene (∼21–11 MYA) (Wise, 1967; Marshall and Pugh, 1996; McInnes and Pugh, 1998, Stevens et al., in press).

The extant terrestrial fauna of Antarctica is characterised by low species richness, patchy distribution and an overwhelming dominance of mites (Acari) and springtails (Collembola) (Block, 1994) at the macroscopic level, as well as the microscopic protozoans, tardigrades, rotifers and nematodes (Gressitt, 1965; Block, 1992). Although widely separated taxonomically, mites and springtails are similar in size and often co-occupy functional groups, and are therefore often considered together as microarthropods (e.g. Cannon and Block, 1988; Worland and Convey, 2001), a convention we follow here. Microarthropods are restricted to ice-free areas, although not always found in close association with macroscopic vegetation (Sinclair, 2001), and even when macroscopic vegetation is present, microarthropods are sparsely distributed with a growing season reduced to weeks or months by the long polar night and extremely low winter temperatures (Janetschek, 1967a; Robinson et al., 2003). Microarthropods are known to be sensitive to a wide variety of environmental conditions, including pollutants, temperature and moisture (Hopkin, 1997; Kohler et al., 1999; Stark and Banks, 2003), and as such have been proposed as sensitive environmental bioindicators (see McGeoch, 1998, for a discussion of the nature of bioindicators). Because Antarctic terrestrial microarthropods are perceived to be at the limits of their biological capacities to tolerate the environment, any change in the abiotic conditions is expected to result in substantial (and detectable) consequences for the fauna (Kennedy, 1995a; Convey, 2001; Clarke et al., 2005), and microarthropods have thus been suggested as a means of detecting and monitoring climate change in Antarctica (e.g. Weller, 1992; Block and Harrisson, 1995; Kennedy, 1995a; Convey and Arnold, 2000).

Microarthropods in Antarctica are patchily distributed at several scales (for example at scales from cm to km, see Fanciulli et al., 2001; Frati et al., 2001; Sinclair, 2001; Sinclair and Sjursen, 2001b; Sinclair, 2002; Stevens and Hogg, 2002, Stevens and Hogg, 2003), and this is clearly evident along the Trans-Antarctic Mountains of the Ross Sea Region (Fig. 1). Kennedy (1999) proposes that the continent-wide distribution of arthropods in Antarctica can be readily modelled using dual filters. The first, a dispersal filter, determines whether or not a species is present at a location; the second, a survival filter, determines whether or not a species will survive in that habitat. At smaller scales, Antarctic microarthropods are subject to the same controls as organisms elsewhere—temperature, habitat, food, moisture—that impose abiotic limits on biological processes. However, biotic interactions, like predation, parasitism, and competition, are often assumed to be greatly reduced (Convey, 2001). Nevertheless, the extent to which biotic interactions impact on community assemblages in Antarctica has not been explored.

Although temperature is the most obvious abiotic influence on Antarctic microarthropods (Convey, 2000), the major limiting factor at both small and large scales is probably the availability of liquid water (Janetschek, 1967a; Kennedy, 1993), which determines both the survival and growth of the arthropods themselves and the primary productivity underlying their presence.

Dating back to the expeditions led by James Clark Ross in the 19th Century, the western coast of the Ross Sea has the richest history of human exploration on the continent (Waterhouse, 2001). This has translated into a solid base of research on the terrestrial microarthropods of the region, with Collembola described from Cape Adare (Carpenter, 1902) and Granite Harbour (Carpenter, 1908) during the Heroic era of exploration. A sizeable effort by US-funded researchers during the 1950s and 1960s (Gressitt, 1967a) provides basic knowledge of taxonomy and broad-scale distribution that remains robust to this day. Here, we assess the likely effects of climate change on the microarthropods of Victoria Land, the Queen Maud Mountains, and offshore islands (abbreviated henceforth as VLQMM) (see Fig. 1), with a view to identifying the biological impacts of climatic change on the terrestrial microarthropod fauna of this region. We do not propose to assess the evidence for (or the direction of) climatic change here, as current models are generated at a scale too coarse to be relevant to millimetre-long arthropods (e.g. Van den Broeke and Van Lipzig, 2002), and indeed, the actual nature of the change itself is uncertain (IPCC, 2001a; Doran et al., 2002; Bertler et al., 2004). We will assume that climatic changes are at a scale relevant to microarthropods and may take the form of changes in (1) temperature; (2) precipitation (available water), evaporation or snow accumulation; and (3) UV radiation, as well as interactions between all three.