Understanding the global distribution of biodiversity is critical for studying the evolution, ecology and dynamics of ecosystems and to address how global scale changes in climate, invasive species, and land use will affect ecosystems, ecosystem services, and subsequently, people. Antarctic terrestrial ecosystems might seem less sensitive to global change because this polar desert has low species diversity distributed across a limited area of biologically active ice-free land, comprising less than 0.32% of the continent’s 14 million km² (Chown and Convey 2007). However, terrestrial ecosystems of Antarctica are not immune to global changes (Adams et al. 2009; Chown et al. 2012b). Small changes in polar climate are amplified through biophysical feedbacks leading to biologically significant alterations in soil habitats and their communities (Doran et al. 2002; Nielsen et al. 2011a). The low species diversity of Antarctic soils makes them uniquely suited for studying the relationships between soil biodiversity and ecosystem functioning, and identifying how global changes may affect species level changes in biodiversity, community composition and distribution (Barrett et al. 2008; Simmons et al. 2009). Measures to conserve, manage and sustain ecosystem functioning in Antarctic and Earth’s other low diversity terrestrial environments will rely on knowledge of species diversity, distributions, and their role in ecosystem processes (Adams et al. 2006; Barrett et al. 2008; Wall 2004).

Aboveground, the diversity and biogeography of terrestrial flora (mosses, lichens and liverworts) has been recently assessed and used to further refine the geographic floral regions of Antarctica (Peat et al. 2007). It is well known that the warmer maritime and subantarctic ecosystems have higher precipitation, organic soils, a more diverse and abundant vegetation (Bölter et al. 2002; Maslen 1979; Nielsen et al. 2011b; Peat et al. 2007) and greater soil faunal diversity (including earthworms and beetles) than continental Antarctica (Block and Christensen 1985; Chown and Van Drimmelen 1992). For example, the northern maritime Antarctic has 100-115 moss and c. 350 lichen species compared to continental Antarctica’s 20–30 moss and c. 90 lichen species (Peat et al. 2007). Throughout Victoria Land vascular plants are absent and fauna are reduced to only a few soil groups and are represented by a patchy spatial distribution of protozoans, nematodes, rotifers, tardigrades, springtails (Collembola), and mites (Acarina) (Adams et al. 2006; Bamforth et al. 2005; Frati et al. 1997; Moorhead et al. 1999; Stevens and Hogg 2002; Virginia and Wall 1999).

Nematoda are a major component of soil food webs in all terrestrial ecosystems including the exposed lands of Antarctica, though their spatial distribution and abundance are highly heterogeneous. In more productive ecosystems, they typically have much higher diversity (Wall Freckman and Virginia 1998) than the Antarctic (Boag and Yeates 1998; Bunt 1954; Maslen 1981). For example, 431 nematode species were recorded from a Cameroon tropical forest ecosystem, with a maximum of 89 species found in 200 individuals enumerated in a soil core (Bloemers et al. 1997). In contrast, the diversity of nematodes in all of Antarctica, including the continental, maritime, and Sub- Antarctic is 54 nematode species, of which only c. 22 species, all endemic, occur on the ice-free terrestrial areas of the continent (Andrássy 1998; Andrássy 2008).

In Antarctica, soil nematodes have been studied primarily in localized and easily accessible areas largely centered around research bases and concentrated on the Antarctic peninsula and islands of the maritime Antarctic and further south in ice-free areas. As a consequence there is relatively little known of their regional biogeography or of the habitats that are suitable for functioning communities. Additionally, there are many remote inland ice-free areas which have yet to be sampled (Convey 1996; Wall 2005), adding to questions on how widespread species are, and whether species rich communities and habitats exist in the more extreme climate zones of the continent.

Regional to continental-scale descriptions of the Antarctic nematofauna have pointed to a paucity of distributional records for much of the continent (Andrássy 1998; Velasco-Castrillón and Stevens 2014). Amongst all regions of Antarctica, Victoria Land is arguably the most intensively studied (Adams et al. 2006). Victoria Land is “ that part of Antarctica which fronts on the western side of the Ross Sea, extending southward from about 70°30'S to 78°00'S, and westward from the Ross Sea to the edge of the polar plateau” (USGS 2003). Here, we synthesize information on the nematode biodiversity, geographic distribution and soil and sediment habitats of the terrestrial nematodes in Victoria Land, Antarctica. Much of this information comes from a series of studies to assess nematode diversity and distribution begun in austral summer 1989–1990 by Wall (formerly Freckman) and Virginia and extending to the present as part of the McMurdo Dry Valley Long Term Ecological Research program funded by the US National Science Foundation (www.mcmlter.org). We report on findings of these studies through 2004 which captures most of the biodiversity information gathered by this research group, whereas more recent research has focused on nematode species response to climate change and soil resource manipulations (Ayres et al. 2010; Doran et al. 2002; Simmons et al. 2009). For purposes of our synthesis, we define two areas, Northern Victoria Land - the area from about 70°30'S to about 76°S, encompassing Terra Nova Bay, Edmonson Point and Cape Hallett (Figure 1); and Southern Victoria Land - the area from about 76°S to about 78°S including all of the McMurdo Dry Valleys and nearby coastal regions (Adams et al. 2006) (Figure 2).

The McMurdo Dry Valleys (76°5'to 78°5'S, 160°0' to 164°0'E) are located along the TransAntarctic Mountains in Southern Victoria Land and comprise about 4, 800 km² of ice-free land and have different geo/ecological legacies and climatic conditions (Lyons et al. 2000; Moorhead et al. 1999). They are the oldest, driest and coldest deserts on earth (Beyer et al. 1999; Campbell et al. 1998; Fountain et al. 1999). Annual precipitation is less than 10 cm water equivalent, most of which sublimates before it melts (Doran et al. 2002; Fountain et al. 1999). Mean annual air temperature is –20°C (Fountain et al. 1999) and surface soil temperature ranges from -59 °C in winter to 26 °C for short periods during summer (Doran et al. 2002). No vertebrate animals or vascular plants are present and mosses and lichens are rare and mostly confined to ephemeral meltponds, streams and lake moats (Cameron et al. 1970; Horowitz et al. 1972; Kappen 1993). Across the region soils are poorly developed, coarse textured (95 to 99% sand by weight) (Bockheim 1997), low in organic carbon (<1%) (Burkins et al. 2000), saline, and have low biological activity compared to warmer ecosystems (Ball et al. 2009; Barrett et al. 2006a; Parsons et al. 2004). Nematodes are the dominant soil invertebrate, but many soils (~35%) lack extractable soil invertebrates and approximately 50% of McMurdo Dry Valleys soils that contain invertebrates have only one invertebrate species (Freckman and Virginia 1997; Wall Freckman and Virginia 1998).

The distributions of the Dry Valley metazoan species are associated with specific sites and correlate to soil habitat differences in organic matter content, moisture and salinity, and microclimate differences encountered over environmental gradients of coastal to interior sites, latitude, and soil chronosequences and differences in glacial tills (Barrett et al. 2006a).

Coastal areas of Victoria Land are a moister environment than the Dry Valleys and are habitat for birds and marine mammals (e.g. skua gulls, penguins, and seals). Penguin rookeries are associated with ornithogenic soils with significant inputs of carbon and nitrogen transferred from the marine environment to the soil (Bargagli et al. 1997). Ornithogenic soils are the only soils south of the Antarctic Circle containing high concentrations (14–21%) of organic matter (Campbell and Claridge 1966; Heine and Speir 1989). However, even with high C and N availability these soils often have lower nematode diversity than soils of the Dry Valleys, probably owing to very high concentrations of salts and soil compaction and cementing (Porazinska et al. 2002a; Sinclair 2001).

Each of the unique soil ecosystems of Victoria Land imposes considerable physiological constraints on nematode life history traits, requiring adaptive responses to freeze/thaw cycling, osmotic and desiccation stress, and a short growing season (Convey 1996). Nematode responses include cryoprotective dehydration via anhydrobiosis (Adhikari et al. 2009; Adhikari and Adams 2011; Crowe et al. 1992), as well as tolerance to inter and intracellular freezing (Adhikari et al. 2010; Wharton 2003, 2010) and multiyear lifecycles (de Tomasel et al. 2013; Overhoff et al. 1993; Yeates et al. 2009). In addition to stress survival, anhydrobiosis also facilitates long-distance aeolian dispersal (Barrett et al. 2006a), an important mechanism implicated in explanations of their geographic distributions and population genetic structure (Adams et al. 2006; Courtright et al. 2000). All of the nematodes of Victoria Land are inferred to be microbivores with the exception of Eudorylaimus, which is omnivorous (Yeates et al. 1993) (but see Wall 2007).

Nematodes were first collected in Victoria Land by the British ‘Discovery’ expedition of 1901-1903, from Discovery Bay, South Victoria Land and described by Steiner (1916) as Dorylaimus antarcticus (syn. Eudorylaimus antarcticus (Yeates 1970)). The nematodes of Victoria Land then remained largely unstudied for over half a century, until the work of Yeates (1970) and Timm (1971). Between them, these two papers described or redescribed all Victoria Land genera of the time and laid the foundation for future taxonomic work. Yeates (1970) recorded Plectus from southern coastal Victoria Land and synonymized Dorylaimus antarcticus and Antholaimus antarcticus with Eudorylaimus antarcticus. However, subsequent studies have described further Eudorylaimus species from continental Antarctica: Eudorylaimus glacialis (Andrássy 1998), Eudorylaimus nudicaudatus (Heyns 1993) and Eudorylaimus shirasei (Kito et al. 1996), Eudorylaimus quintus (Andrássy 2008) and Eudorylaimus sextus (Andrássy 2008). Due to the taxonomic uncertainty of early accounts (Adams et al. 2006), we will henceforth use Eudorylaimus sp. in reference to all previous reports of distribution. Timm (1971) synonymized Plectus murrayi with Plectus antarcticus (de Man 1904) and studied parts of southern and northern coastal Victoria Land and the McMurdo Dry Valleys. He also re-described three known species: Eudorylaimus antarcticus (Steiner 1916), Monhystera villosa (Bütschli 1873) and Plectus frigophilus (Kirjanova 1958), and described two new species, Scottnema lindsayae and Panagrolaimus davidi. Monhystera villosa was later synonymized with Geomonhystera antarcticola (Andrássy 1998). These early studies focused exclusively on the identification and description of nematode species and not their ecologies.

In the McMurdo Dry Valley Region, most nematological studies have investigated the diversity, ecology and distribution patterns of up to three nematode genera; Eudorylaimus, Plectus, Scottnema (Adams et al. 2006), while the coastal areas of Victoria Land remain less well known (Adams et al. 2006; Bargagli et al. 1997; Barrett et al. 2006a; Porazinska et al. 2002a; Raymond et al. 2013a; Sinclair and Sjursen 2001; this paper; Timm 1971; Vinciguerra 1994). Our effort here is a synthesis of the biogeographic distribution of nematodes in Victoria Land and a consideration of the soil habitats that are associated with nematode distribution, diversity and abundance.

Based on published and unpublished data, we summarized biogeographic information on the species represented within each nematode genus described in Victoria Land. In addition to published papers, we present information obtained from data on soil, and lake and stream sediment samples collected throughout Victoria Land, by the authors and team members during the austral summers between and including 1990 and 2004. Data referred to as “this study (year)” were derived from nematode soil extraction procedures optimized for Antarctic soils and all nematodes were identified to species (Freckman and Virginia 1993). Frozen soils from these samples are archived at the Wall lab in the Department of Biology at Colorado State University, Fort Collins, CO, USA. Formalin-preserved extracted specimens from these soils are archived in the meiofauna collection of the Monte L. Bean Life Science Museum at Brigham Young University, Provo, UT, USA. Non-occurrences are not reported but can be extrapolated from Tables 1–5. A brief summary of published information on the ecology of each genus is also provided (Table 6).

Only five genera of terrestrial nematodes are recorded from Victoria Land Antarctica: Scottnema, Plectus, Eudorylaimus, Panagrolaimus, and Geomonhystera. For some genera species delimitation remains unresolved (Andrássy 1998; Velasco-Castrillón and Stevens 2014).

Nematode diversity in Victoria Land is low compared to the Antarctic Peninsula, but the presence of a few cryptic species is likely (Barrett et al. 2006c; Raymond et al. 2013b). Extensive sampling across broader geographic scales, combined with molecular techniques will likely recover additional species from both locations. With the exception of Panagrolaimus davidii and Geomonhystera spp., all species are widely distributed throughout Victoria Land, from the south coast and the most southern McMurdo Dry Valleys to the northern coastal region. This distribution suggests that their dispersal is ubiquitous and primarily by wind while in anhydrobiois (Nkem et al. 2006b), and it is the suitability of the soil habitat that determines the likelihood of population and community establishment and functioning (Virginia and Wall 1999).

Our knowledge of nematode biodiversity, distribution, and function in Victoria Land is based on clusters of studies from a few distinct regions, such as the McMurdo Dry Valleys, and far northern coastal Victoria Land, which are accessible from established research stations. The rest of Victoria Land (including other inland ice-free areas) has been largely inaccessible. Studies throughout the McMurdo Dry Valleys are also patchy with some valleys being studied heavily (e.g. Taylor Valley) whilst others (e.g. Barwick Valley) have barely been investigated. More undescribed nematodes may occur in these less studied regions.

Habitat suitability for each nematode species is determined primarily by variations in soil factors such as quantities and types of organic material, moisture and salinity (Nkem et al. 2006a; Virginia and Wall 1999). Scottnema lindsayae is the most abundant and widespread nematode and has a unique tolerance for a wide range of extreme soil habitats, and it is also the most tolerant to low soil moisture and high salinity of all the nematode species studied. These conditions define the most common soil habitats throughout the cold desert ecosystems of Victoria Land and explain the high abundance and broad distribution of Scottnema lindsayae throughout the region. There are less extensive suitable habitats available in Victoria Land for Plectus spp. and Eudorylaimus antarcticus as their distributions are limited to habitats with higher moisture, greater organic material and lower salinity. Panagrolaimus davidii has a very limited biogeographic distribution, almost entirely restricted to coastal Victoria Land. This species is found in habitats with high primary productivity, of which there are few. Factors defining suitable habitats and the biogeographic distribution of Geomonhystera spp. in Victoria Land are the least understood, largely due to very low abundance and limited occurrence, although they have been recovered from sites across Victoria Land. There appears to be an association with algae but little else is known of their habitat requirements.

We have made considerable progress in understanding the basic relationships between soil properties and the distribution of the key nematode taxa throughout Victoria Land. Suitable habitats can be defined by moisture, salinity, organic matter and nutrient content, and the interactions between these factors. Manipulations of soil moisture and field observations of environmental change during pulse warming events show that nematode community composition can respond on time scales of seasons to decades (Ayres et al. 2010; Doran et al. 2002). The climate of Victoria Land is expected to change with warmer conditions (Adams et al. 2009; Jones et al. 1998; Salby et al. 2011; Solomon et al. 2007; Steig et al. 2009; Thompson and Solomon 2002) leading to increasing soil moisture, redistribution of salts, and potentially higher productivity (Gooseff et al. 2011; Nielsen et al. 2012). These changes may alter the spatial distributions of suitable habitats for individual nematode species and/or alter population size and community diversity (Nielsen et al. 2011b). Studies have shown the important role of nematodes in carbon cycling, suggesting that changes in nematode biogeography will be linked with changes in ecosystem functioning in Antarctic soils (Barrett et al. 2008).

The nematofauna of Victoria Land are capable of long distance dispersal by wind (Nkem et al. 2006b) but the Antarctic continent is effectively isolated from source populations elsewhere in the southern hemisphere (Convey et al. 2008; Convey and Stevens 2007). This leaves anthropogenic dispersal by way of tourists and scientists as the primary mechanism for the movement of alien species to Antarctica (Chown et al. 2012a). From a field sample collected in Wright Valley in the 2011-2012 field season, we recovered an individual living female Cuticularia fermata, a nematode heretofore known only from South Orkney Island (subantarctic island). Whether this specimen was transported to the site on clothing or equipment used by scientists or if there are established, low-density, isolated populations in the area is unknown. It is highly likely that the frequency of nematode introductions to Victoria Land will increase as tourism and scientific research increases (Chown et al. 2012a). There is a growing international consensus that action is needed to reduce the potential introductions of invasive soil species to continental Antarctica and the Peninsula and maritime regions (Chown et al. 2012b). A greater knowledge of nematode biogeography will be essential in understanding how to protect special soil habitats to preserve existing biodiversity and to prevent the introduction of non-native species and the potential harm they cause to the unique soil ecosystems of Antarctica.