in Antarctica

Ecology, 86(2), 2005, pp. 519–527
q 2005 by the Ecological Society of America
EXCEPTIONAL TARDIGRADE-DOMINATED ECOSYSTEMS IN
ELLSWORTH LAND, ANTARCTICA
PETER CONVEY1
AND
SANDRA J. MCINNES
British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
Abstract. We describe a terrestrial faunal community including only Tardigrada and
Rotifera, present on inland nunataks of Ellsworth Land, Antarctica ( ;758–778 S, 708–738
W). The fauna is exceptional in its simplicity, including five tardigrade species (three new
to science) and at least two rotifer species, which comprise two consumer trophic levels.
Nematode worms, the most important element of the simplest faunal communities previously
reported worldwide (from the Ross Sea Dry Valley region of continental Antarctica), and
microarthropods, otherwise represented in all known Antarctic terrestrial communities, are
absent. The tardigrade community composition shows affinity with the continental Antarctic
fauna, with which it shares three species. The remaining two species are unique to Ellsworth
Land and may suggest a prolonged existence as a distinct biogeographical unit.
Key words: Antarctica; Ellsworth Land; evolution; geographical isolation; nunatak; rotifer;
simple food web; tardigrade; terrestrial ecosystem.
INTRODUCTION
Antarctic terrestrial ecosystems are simple, with faunas consisting almost entirely of soil invertebrates, including microarthropods, nematodes, tardigrades, rotifers, and protozoans, and floras comprising bryophytes, lichens, algae, and cyanobacteria (Block 1984,
Smith 1984, Convey 2001). Despite this simplicity and
low biodiversity, clear biogeographical patterns have
long been recognized in the terrestrial biota of Antarctica, and three biogeographical zones are conventionally applied (Smith 1984, Longton 1988), defined
by consistent differences in climate and biology. These
are (1) the sub-Antarctic, a ring of isolated oceanic
islands surrounding the continent at relatively high latitude in the Southern Ocean, (2) the maritime Antarctic,
consisting of the western coast of the Antarctic Peninsula to ;728 S and associated island archipelagos
(the South Shetland, South Orkney, and South Sandwich Islands, and Bouvetøya), and (3) the continental
Antarctic, which includes the bulk of the Antarctic continent and the eastern coast of the Antarctic Peninsula.
It is important to note that the latter two divisions do
not equate to the geological separation of the continent
into East (continental) and West (peninsular) Antarctic.
The faunas of the maritime and continental Antarctic
zones show virtually complete separation at species
level, forming a feature analogous to the Wallace Line
of southeast Asia. Thus, no free-living terrestrial Acari
(Pugh 1993) and only a single Collembola species
(Greenslade 1995) are shared between the two zones.
This pattern is repeated in the Nematoda, where not
only do published data again indicate no overlap beManuscript received 19 April 2004; revised 15 July 2004;
accepted 30 July 2004. Corresponding Editor: P. J. Bohlen.
1 E-mail: [email protected]
tween zones at species level, but all species currently
known from the continent and Antarctic Peninsula are
thought to be endemic to Antarctica (Andrássy 1998).
The boundary between the maritime and continental
Antarctic biogeographical zones on the western Antarctic Peninsula is currently placed at the latitude of
southern Alexander Island (;72–738 S). This placement is justified on the grounds that both faunal and
floral studies of the relatively rich and extensive icefree areas of southeast Alexander Island demonstrate
close affinities with those known from the maritime
Antarctic rather than from the continental Antarctic,
although with reduced diversity and the inclusion of a
distinct endemic element (Maslen 1982, Smith 1988,
Convey and Smith 1997). However, other than a very
small number of botanical samples collected opportunistically by geological field parties since the 1960s,
no detailed biological studies have been attempted in
the region south of Alexander Island (i.e., in the portion
of West Antarctica including southern Palmer Land and
Ellsworth Land) or in the adjacent sector of the continental Antarctic, including the Ellsworth Mountains
(this area is also known as the Ronne Sector; Fig. 1).
At a large scale, terrestrial biodiversity decreases
along an environmental gradient between the sub-Antarctic islands and continental Antarctica (Convey 2001,
Clarke 2003). With progression along this gradient, the
larger and more visible groups of biota become less
well represented or are lost, until in the most extreme
cold desert habitats, life may become restricted to microbial endolithic communities, such as those found in
the surface layers of porous sandstone rocks (Friedmann 1982) and partially transparent gypsum crusts
(Hughes and Lawley 2003). Before this stage is
reached, soil faunal communities are increasingly restricted to the meiofaunal groups of Nematoda, Tar-
519
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PETER CONVEY AND SANDRA J. MCINNES
Ecology, Vol. 86, No. 2
FIG. 1. Map of Antarctica, indicating (a) the Antarctic Peninsula, (b) the mountain ranges sampled in Ellsworth Land,
and (c) the different sectors of continental Antarctica referred to in the text.
digrada, and Rotifera (Spaull 1973, Maslen 1979, Andrássy 1998). The simplest soil faunal communities yet
described are found in parts of the Dry Valley region
of Victoria Land (continental Antarctica), containing
only 1–3 species of Nematoda and at most two consumer trophic levels, along with tardigrades, rotifers,
and protozoan groups (Freckman and Virginia 1997,
1998). However, even in the Dry Valleys, more complex floral (bryophyte) and faunal (microarthropod)
communities are also present in restricted areas near
glaciers, melt streams, and the edges of frozen lakes.
The aim of the current study was to complete a survey of the terrestrial fauna of mountain groups in Ellsworth Land, between ;758 and 778 S, thereby placing
more accurately the boundary between continental and
maritime Antarctic biogeographical zones. In the ab-
sence of previous studies, our expectation was that the
fauna would include microarthropods, nematodes, tardigrades, and rotifers, all of which are represented in
virtually all faunas studied in detail in both the maritime and continental zones. Here, we present the findings of this survey, highlighting the community composition and biogeographical affinities of the faunal
taxa found, and placing these in the wider context of
Antarctic biogeography and the geological history of
Ellsworth Land.
METHODS
Survey extent
Detailed biological field surveys of sites in Ellsworth
Land were completed by P. Convey between 29 De-
February 2005
TARDIGRADE-DOMINATED ANTARCTIC ECOSYSTEMS
521
TABLE 1. A summary of sampling details from terrestrial biological survey and additional geological collections in Ellsworth
Land in 2000–2001 and 2002–2003 austral summers, and in Palmer Land in 2002–2003.
GPS coordinates of
sampling sites
Location
Palmer Land (2002–2003)‡
Avery Plateau
668399
668499
698109
698149
Wakefield Mountains
Ellsworth Land (2000–2001)
Sky-Hi Nunataks, ‘‘Mt Mende’’
Merrick Mountains‡
Behrendt Mountains (N)
Behrendt Mountains (S)
Quilty Nunataks
Hauberg Mountains
Haag Nunataks
S,
S,
S,
S,
0648209
0648069
0648259
0648489
W
W
W
W
74850.59 S, 71838.09 W
758039–758109 S, 72 039–728099 W
75816.89 S, 072833.09 W
75826.09 S, 072835.69 W
75826.09 S, 072837.59 W
75824.89 S, 072841.39 W
75843.99 S, 071844.39 W
75843.89 S, 071845.09 W
75849.39 S, 069815.39 W
75849.69 S, 069822.09 W
75851.19 S, 069820.99 W
77802.39 S, 078816.39 W
77802.19 S, 078814.19 W
Altitude
(m)
Samples extracted
(number and source)†
1900
2100
1350
1800
2L, 1S
1L
4L, 4M
2L
1500
1L, 1S
3S
2L, 3S
1F, 5L, 4S
5L, 4M, 2S
4F
2L, 4M, 3S
1L, 3M, 2S
8S
2L, 7S
3L, 4S
3L
5L, 1S
1160
750
860
1100
1177
Ellsworth Land (2002–2003)‡
various
6F, 10L, 24S
† Key to abbreviations: F 5 fungal/cyanobacterial mat; L 5 lichen; M 5 moss; S 5 soil/rock particles. Most samples
included soil in addition to named component, and moss samples also included lichen material.
‡ Samples from these locations were collected by unconnected geological field parties.
cember 2000 and 20 January 2001, and included the
Hauberg Mountains, Quilty Nunataks, Behrendt Mountains, and Sky Hi Nunataks (Table 1, Fig. 1). The more
isolated location of Haag Nunataks was visited on 2–
TABLE 2. Taxonomic details of lichen and moss species
identified from Ellsworth Land; herbarium specimens were
prepared after the completion of extractions, mostly consisting of mixed species assemblages, and it was not possible to link extracted meiofauna with specific moss/lichen
species.
Species
Mosses
Ceratodon purpureus
Coscinodon lawianus
Crustose lichens
Acarospora gwynnii
Buellia frigida
B. grisea
B. pallida
Caloplaca citrina
Candelariella flava
Carbonea vorticosa
Lecanora flotowiana
L. physciella
L. polytropa
L. sverdrupiana
Lecidea cancriformis
Pleopsidium chlorophanum
Rhizoplaca melanophthalma
Foliose lichens
Pseudephebe minuscula
Usnea sphacelata
Taxonomy
(Hedw.) Brid.
(Willis) Ochyra
Dodge & Rudolph
Darb.
Dodge & Baker
Dodge & Baker
(Hoffm.) Th. Fr.
(Dodge & Baker)
Castello & Nimis
(Flk.) Hertel s.lat.
Spreng.
(Darb.) Hertel
(Hoffm.) Rabenh.
Ovst.
Dodge & Baker
(Wahlenb.) Zopf
(Ram.) Leuck. & Poelt
(Nyl. ex Arnold)
Brodo & Hawksw.
R. Br.
3 February 2001. A separate geological field party traveling in the same region over the same period collected
five additional samples from Cape Zumberg (eastern
extremity of the Hauberg Mountains) and the Merrick
Mountains. In total, these sites generated 83 samples
that were subjected to Baermann (wet) extractions and
46 samples subjected to Tullgren (dry) extractions. Between December 2002 and January 2003 a further 40
samples were obtained from Ellsworth Land, and two
locations in eastern Palmer Land were sampled (four
samples from the Avery Plateau, 10 samples from the
Wakefield Mountains), all by geological field parties.
Material from these latter sites could not be processed
to extract fauna for a much longer period (up to 2 mo)
after collection than those obtained during 2000–2001,
and thus the data obtained are not strictly comparable.
All these sites are, effectively, groups of nunataks penetrating through a 500–1500 m deep ice sheet, and
separated from their neighbors by 20–150 km.
Samples obtained
These mountain groups offer a limited range of potential habitats for soil meiofauna. Areas of frost-sorted
patterned ground, typical of many localities in the Antarctic, are not present. Rather, simple mineral soils
were found to be concentrated in small pockets or frost
boils between boulders or among rock scree, or in rock
crevices or ledges. Some of these soils were visibly
colonized by cyanobacteria and/or fungal hyphae, or
encrusting lichens. Epilithic crustose and foliose lichens were also sampled, as were the very occasional
patches of moss encountered (Tables 1, 2). What was
522
PETER CONVEY AND SANDRA J. MCINNES
available at each sampling location determined the
quantity of material sampled. Where possible, 50–100
g of soil were collected from each, although it was
often possible to collect only 5–10 g of moss-encrusted
or lichen-encrusted soil.
Air temperatures throughout the periods of fieldwork
were generally in the range 2208 to 258C, rising briefly
to about 128C during the visit to Quilty Nunataks.
However, at most sites the soil surface was sufficiently
warmed by solar radiation to thaw to a depth of 2–5
cm, and soils were visibly moist, receiving water either
from melt water trickling between rocks, or direct
snowmelt. Samples were obtained by using a knife to
transfer material into sealable plastic bags. Collected
material was stored in the dark, and maintained at ambient temperature in the field. At the end of the survey
period samples were returned by air to the British Antarctic Survey’s Rothera Research Station, where they
were stored in a cooled incubator at 158C until extraction (1–3 wk after collection).
A total of 123 samples (Table 1) were extracted using
a modified Baermann funnel technique. Each sample
was wrapped in a single layer of tissue paper and placed
on a piece of stainless steel gauze in a funnel. Water
was added to the funnel to immerse the sample, which
was then left at room temperature (;158C) for 24 h.
During this period, active meiofauna collected at the
base of the funnel, and were then run off in ;5 mL of
water into a glass vial. The extracted animals were
killed by heating briefly to 508C and preserved in 4%
formaldehyde, following Hooper (1986). Tullgren extractions were carried out on 42 samples obtained from
Ellsworth Land during 2000–2001 and four samples
from Palmer Land (Wakefield Mountains) in 2002–
2003, in order to obtain any microarthropods present.
Soil moisture content was not measured, although all
soils collected were visibly damp. For those substrates
incorporating moss, lichen or visible cyanobacteria or
fungi, subsamples were air dried and have been deposited in the British Antarctic Survey’s Herbarium,
and listed in the associated databases (see Peat 1998).
Preliminary inspection of the extractions revealed
that the only fauna present were tardigrades and rotifers. Preserved material was returned to the United
Kingdom for detailed examination, which confirmed
the absence of other faunal groups. Tardigrades were
removed and post fixed in GAW (Glycerol–Acetic
acid–Water; see McInnes et al. 2001), before being
passed through a glycerol series and mounted in de
Faure’s medium. After drying, slides were ringed with
Glyceel (Gurrs, BDH Chemicals, Poole, UK). In cases
where initial examination of slide-mounted specimens
indicated a need for further detail (e.g., inspection of
eggs) additional material was obtained from the appropriate herbarium samples. Subsamples of these were
soaked in distilled water, homogenized, and the meiofauna extracted using a flotation technique (Nelson
and McInnes 2002) analogous to the sugar-gradient
Ecology, Vol. 86, No. 2
centrifugation technique of Freckman and Virginia
(1993). Although targeted at obtaining tardigrades, this
protocol is also appropriate for obtaining all active and
inactive meiofauna, including any nematode material,
present in dried samples. Eight samples including lichen and moss vegetation were extracted in this way.
Slide-mounted specimens were examined under oil immersion (1003) phase contrast and differential interference contrast (DIC) microscopy.
RESULTS
Tardigrades were found to be present in 33 of the 83
Baermann extractions (40%) and rotifers in 40 of the
83 (48%) from the 2000–2001 collections from Ellsworth Land. The presence of the two groups was associated, with 35% of extractions containing both, 15%
only one group, and 50% neither group (relative to an
expectation of a random distribution of the two groups;
x2, 2 df 5 48.5, P , 0.001), suggesting that both groups
have similar requirements and were present wherever
the sampled habitat was suitable. Tardigrades were
present in a much smaller proportion (three out of 40)
of Baermann extractions from the geological collections made in 2002–2003, with the difference most
likely due to either the small number of vegetated substrates obtained or the extended 2–3 mo period of postcollection storage in the field experienced by the latter
collections.
Nematodes and microarthropods were absent from
the extracted samples. Although negative results are
not conclusive, these extraction techniques are routinely applied successfully to similar substrata in our
and other studies elsewhere in the Antarctic. The absence of these groups in extractions very strongly supports their being absent or, at most, comprising only a
very minor faunal component in Ellsworth Land terrestrial communities.
The smaller number of eastern Palmer Land samples
available (n 5 14) do not permit firm conclusions to
be drawn, although it is notable that one of the four
Tullgren extractions resulted in six juvenile specimens
of a single prostigmatid mite species (Nanorchestes sp.,
Wakefield Mountains), and four of the 14 Baermann
extractions included tardigrades (both Avery Plateau
and Wakefield Mountains).
Tardigrade numbers extracted ranged from single individuals up to 30–40 specimens from samples of
;50–100 g mass. Low numbers of specimens usually
represented single taxa, but where several specimens
were obtained, two or three taxa were normally present,
including the predatory Milnesium cfr. tardigradum.
With large differences in sample size and composition,
a quantitative comparison between samples of the numbers extracted is not justified, although qualitatively,
the most productive habitats were associated with vegetation (moss, encrusting lichens, and microbial mats).
Due to the nature of the substrata, even those with
vegetation included large quantities of soil.
February 2005
TARDIGRADE-DOMINATED ANTARCTIC ECOSYSTEMS
The only other fauna present in any of the extractions
were bdelloid rotifers, present in 40 of the 2000–2001
Ellsworth Land samples. The extraction and preservation methods used precluded their identification to
species. The majority belong to the genus Adineta, with
the remainder belonging to Philodina (H. G. Dartnall,
personal communication).
Five tardigrade species were present in the Ellsworth
Land samples, including three thought to be new to
science (one, Milnesium cfr. tardigradum, also known
from the continental Antarctic). The four species present in the small number of eastern Palmer Land samples also included two new species, with the remainder
again previously recorded from the continental Antarctic. Table 3 lists all tardigrade species currently
known from the continental and maritime Antarctic
biogeographical zones, and the sub-Antarctic island of
South Georgia, with data for the Antarctic Peninsula
region being further subdivided into those from Ellsworth Land, Palmer Land, Graham Land (definitions
as given by Pugh 1993), and the associated South Shetland and South Orkney archipelagos. The previously
published distributional data in Table 3 show that, at
species level, only a minority of Antarctic tardigrades
are shared between both continental and maritime
zones (six species shared, of 18 confirmed from the
continental and 24 known from the maritime zones).
DISCUSSION
The tardigrades of the maritime Antarctic appear relatively well known (e.g., Murray 1906, Richters 1908,
Jennings 1976, Dastych 1984, Usher and Dastych 1987,
Ottesen and Meir 1990, McInnes 1995, 1996, McInnes
and Pugh 1999), although the majority of work relates
to Signy Island (South Orkney Islands) and King George
Island (South Shetland Islands). Studies within continental Antarctica are more limited and are, additionally,
largely restricted to the coastal regions and locations
near research stations (e.g., Maud sector [Dastych and
Harris 1994, Sohlenius et al. 1995, 1996, Dastych and
Drummond 1996]; Enderby sector [Miller et al. 1994];
Wilkes sector [Miller et al. 1996]; Scott sector [Binda
and Pilato 1994, 2000]). There are no previous records
available from either the Byrd or Ronne sectors of continental Antarctica. The current study, therefore, provides both the first records from the Ronne sector, and
records from more isolated inland sites than have previously been studied.
The ice-free sites surveyed in Ellsworth Land and
additional limited samples obtained from eastern Palmer Land indicate a relatively diverse tardigrade community for such an isolated region (Table 3). This fauna
is linked with that of the continental Antarctic, sharing
two species (Diphascon sanae and Hebesuncus ryani)
with this region only. A third species (Milnesium cfr.
tardigradum) has a pan-Antarctic distribution, but morphological comparisons suggest there may be distinct
‘‘forms’’ or speciation occurring at the different sites
523
within the continental, maritime, and sub-Antarctic, including those found in the Ellsworth Land samples.
This adds to the third group of species that are ‘‘endemic’’ to this region (i.e., the two new species, Echiniscus sp. and Ramazzottius sp., not previously known
elsewhere in the Antarctic). While the meiofaunal diversity is very low, limited to tardigrades and bdelloid
rotifers, two trophic levels are represented, primary
consumers by the rotifers and most of the tardigrade
taxa, and predators by Milnesium cfr. tardigradum.
The absence of other faunal groups is exceptional,
even in Antarctic terrestrial ecosystems. While microarthropods are generally absent from the most extreme locations studied in the continental Antarctic
(e.g., Freckman and Virginia 1997), even within such
areas they are present at specific sites where water is
available and simple vegetation present (Wise and
Gressitt 1965, Freckman and Virginia 1998, Marshall
and Coetzee 2000, Stevens and Hogg 2003). Studies
of the fauna of nunataks at comparable latitudes in
Dronning Maud Land (73–758 S; Sohlenius et al. 1995,
1996) found nematodes (seven taxa in total) to be present in under 40% of soil and vegetation samples examined, with tardigrades and rotifers being more abundant and diverse. Other studies in Dronning Maud Land
have documented the presence of microarthropod communities (Sømme 1980, Ryan and Watkins 1989, Marshall and Convey 1999), and mites are found on nunataks to at least 858329 S in the Scott Sector (Wise and
Gressitt 1965).
Some continental microarthropod species inhabiting
nunataks are thought to be relicts whose presence may
predate the breakup of the Gondwanan supercontinent
(Greenslade 1995, Marshall and Pugh 1996, Marshall
and Coetzee 2000). Analogous microarthropods are
also expected to be present at higher altitude inland
sites along the spine of the Antarctic Peninsula, although other than the record of juvenile Nanorchestes
sp. reported here, no studies or even baseline surveys
of the terrestrial biota of these sites exist. Although the
occurrence of some continental microarthropods is
linked with nutrient enrichment near bird colonies,
these links are generally indirect (through association
with increased vegetation cover) or unclear (Ryan and
Watkins 1989). Thus, although no birds or evidence of
breeding areas were observed during our survey, the
lack of microarthropods remains surprising in the context of analogous habitats studied in continental Antarctica.
The absence of nematodes in the collected fauna is
even more striking, as this group is otherwise considered to be ubiquitous on Earth (Freckman and Virginia
1997). While the Baermann extraction used in the current study relies on individuals being active, the failure
to find nematodes is supported by (1) a separate study
of eukaryotic molecular biological diversity present in
soils at some of the same sampling sites (Lawley et al.
2004), which, among others, identified tardigrade, but
PETER CONVEY AND SANDRA J. MCINNES
524
Ecology, Vol. 86, No. 2
TABLE 3. Tardigrade species recorded in the published literature as being present (P) in East/continental and West Antarctica,
and the sub-Antarctic island of South Georgia.
West
Antarctica
Taxon
Mopsechiniscus imberbis (Richters, 1907)
Oreella mollis J. Murray, 1910
Echiniscus jenningsi; Dastych (1984)
Echiniscus macronyx Richters, 1907
Echiniscus pseudowendti; Dastych (1984)
Echiniscus punctus; McInnes (1995)
Echiniscus sp.
Echiniscus sp.
Testechiniscus meridionalis; Murray (1906)
Pseudechiniscus cfr suillus
Macrobiotus blocki; Dastych (1984)
Macrobiotus furciger; Murray (1906)
Macrobiotus krynauwi Dastych and Harris, 1995
Macrobiotus cfr hufelandi
Macrobiotus cfr livia
Minibiotus stuckenbergi Dastych, Ryan and
Watkins, 1990
Dactylobiotus cfr ambiguus
Calohypsibius cfr ornatus
Hexapodibius boothi Dastych and McInnes, 1994
Acutuncus antarcticus (Richters, 1904)
Hypsibius cfr convergens
Hypsibius cfr dujardini
Hypsibius pallidus Thulin, 1911
Isohypsibius asper; Murray (1906)
Isohypsibius improvisus; Dastych (1984)
Isohypsibius laevis; McInnes (1995)
Isohypsibius papillifer (J. Murray, 1905)
Isohypsibius prosostomus Thulin, 1928
Diphascon (Diphascon) langhovdensis (Sudzuki,
1964)
Diphascon (Diphascon) dastychi Pilato and
Binda, 1999
Diphascon (Diphascon) mirabilis; Dastych (1984)
Diphascon (Diphascon) polare Pilato and Binda,
1999
Diphascon (Diphascon) pingue (Marcus, 1936)
Diphascon (Diphascon) victoriae Pilato and
Binda, 1999
Diphascon (Diphascon?) puniceum (Jennings,
1971)
Diphascon sanae Dastych, Ryan and Watkins,
1990
Diphascon (Adropion) greveni Dastych, 1984
Diphascon (Adropion) maucci Dastych and
McInnes, 1996
Hebesuncus ryani Dastych and Harris, 1994
Hebesuncus schusteri (Dastych, 1984)
Ramazzottius cfr oberhaeuseri
Ramazzottius sp. A
Ramajendas frigidus Pilato and Binda, 1990
Ramajendas renaudi (Ramazzotti, 1972)
Milnesium tardigradum Doyère, 1840
Milnesium cfr tardigradum
East
Ellsworth Palmer
Antarctica Land
Land
South Shetland,
Graham South Orkney
Land
Islands
P
P
P
The subAntarctic
South
Georgia
P
P
P
P
P
P§
P§
P
P
P
P
†
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
‡
P
P
P
P
P
P
P
Note: Ellsworth Land and Palmer Land data are those obtained in the current study.
† Literature record is uncertain.
‡ The record requires examination of eggs for complete confirmation.
§ Different undescribed Echiniscus species were present in Ellsworth Land and Palmer Land samples.
P
February 2005
TARDIGRADE-DOMINATED ANTARCTIC ECOSYSTEMS
not nematode, sequences; (2) the failure to find nematode material during flotation extraction of herbarium
material; and (3) given that the substrata extracted were
hydrated, any nematodes present would be expected to
be active. As with microarthropods, the distribution of
some continental Antarctic nematodes has been linked
with vertebrate breeding sites (Boström 1995, Sohlenius et al. 1996, Swart and Harris 1996) but this is, again,
insufficient to explain their complete absence in the
current study.
To date, the simplest faunal assemblages known have
been described from the desert soils of the Victoria
Land Dry Valleys (Freckman and Virginia 1997, 1998).
These include up to three species of nematode, one
predatory, in addition to tardigrades, rotifers and protozoans (the latter group was not sampled in the current
study). Thus, the fauna described here represents a further step of simplification. The Dry Valley studies are
not directly comparable with ours, as they describe
desert soils with very low water content, and used an
extraction methodology that is effective in obtaining
inactive (e.g., anhydrobiotic) animals from dry substrates (sugar gradient centrifugation; Freckman and
Virginia 1993). Nevertheless, the overall proportion of
samples containing fauna were similar in the two studies, with 60% of Dry Valley samples containing nematodes (Freckman and Virginia 1997) and 50% of Ellsworth Land samples containing tardigrades or rotifers
in the current study. However, only 14% of Dry Valley
samples contained the latter two groups, and these were
associated with higher soil moisture levels. The absence of fauna in 33% of Dry Valley soil samples was
described as unique by Freckman and Virginia (1997)
and is even more striking (50% of 2000–2001 samples)
in the current study.
The factors underlying the absence of arthropods and
nematodes from Ellsworth Land are unclear. Many species of Antarctic free-living nematodes, like tardigrades and bdelloid rotifers, possess features such as
well-developed cold tolerance and resistant anhydrobiotic stages (Pickup and Rothery 1991, Sømme and
Meier 1995, Wharton 1995, 2002, Sømme 1996), which
are thought to preadapt them for opportunistic longdistance transport and colonization of new habitats, or
for survival in refugia. Prevailing winds in the region
move from the continental Antarctic plateau outwards.
These have the potential to carry continental species
northwards, while only the occasional storm or contrary weather patterns will carry maritime material
southwards, which may explain the presence in Ellsworth Land of tardigrades currently known only from
the continental zone. The dispersal mechanisms used
by Antarctic microarthropods have not been identified
conclusively, particularly for long-distance dispersal or
movement between noncoastal sites, but a number are
plausible (Convey 1996, Pugh 1997, 2003) and must
be effective given that contemporary distribution pat-
525
terns, particularly in Antarctic coastal regions, include
many sites deglaciated over recent decades to centuries.
An analogy can be drawn with the fauna described
from cryoconite holes that form in the ablation zones
of glacier surfaces. These are found in both polar regions and on montane glaciers worldwide (although are
not present in the area surveyed in this study), and are
often isolated by several kilometers from neighboring
deglaciated or exposed terrestrial habitats. Tardigrades,
rotifers and, less frequently, nematodes have been reported from these habitats in the Northern Hemisphere
(de Smet and van Rompu 1994, Grøngaard et al. 1999,
Dastych et al. 2003), but to date only various microbial
groups have been noted from the Antarctic (Christner
et al. 2003, Mueller and Pollard 2004). These faunal
groups exhibit appropriate life history attributes, which
may include cryptobiosis, parthenogenetic reproduction, and the ability for dispersal (usually wind blown).
However, while cryoconite communities are simple, the
habitats are spatially close to much more complex potential source communities on neighboring ice-free terrain. A small minority of the species found in cryoconites have been described as obligate residents of
this habitat (allowing for occasional records from the
glacial margin; Dastych et al. 2003), but the presence
of the majority of species is thought to be facultative
or accidental, while the existence of individual holes
and communities is temporary (Wharton et al. 1985,
Dastych et al. 2003). In contrast, the surveyed habitats
in Ellsworth Land are extremely isolated, with no such
source of local colonists, and their existence is much
longer term.
Some recent research suggests that tardigrades have
very slow evolutionary rates, and are not as widespread
or as cosmopolitan as previously thought (McInnes and
Pugh 1998, Pilato and Binda 2001). This is consistent
with the presence of a distinct Ellsworth Land fauna
in the survey data, and suggests a novel hypothesis that
mountain groups in this region contain refugia from
which local recolonization may have occurred as terrestrial habitats became accessible after the last glacial
maximum (LGM). The locations of such refugia are
not known, in part because it is currently not possible
to estimate with certainty the age of exposure of mountain groups included in the survey (Bentley and Anderson 1998). It is also clear (Carrara 1979, 1981) that
many summits in the region show evidence of being
overrun by ice. Bentley and Anderson (1998) suggest
that, during the LGM, ice depth in Palmer and Ellsworth Lands may have been 400 m greater than at
present, while modeling approaches (e.g., Huybrechts
1992, Bentley and Anderson 1998) suggest an even
greater depth. The Ellsworth Mountains, 300 km to the
south of Haag Nunataks, may provide a source of refuges, although these mountains experienced up to 1900
m thickening of ice (Bentley and Anderson 1998).
However, no biological data are available, making sur-
526
PETER CONVEY AND SANDRA J. MCINNES
vey work in this region a priority for further understanding contemporary Antarctic biogeography.
The results of the present faunal survey indicate that
the Ellsworth Land study area, while geologically part
of West Antarctica, has faunistic links with the continental rather than the maritime Antarctic biogeographical zone. However, the presence of a distinct element
in the tardigrade fauna that is unique to Ellsworth Land
complicates this interpretation. The existence of this
unique and simple faunal community may suggest that
a separate zone needs to be recognized, physically intermediate between the two existing zones, in order to
permit biological continuity over a period of time sufficient to allow community isolation and the evolutionary processes to occur. If so, this will also require
a reevaluation of glaciological reconstructions of the
region through the period of the LGM.
ACKNOWLEDGMENTS
The fieldwork described would not have been possible
without the skilled and enthusiastic support of staff at the
British Antarctic Survey’s (BAS) Rothera Research Station,
and we particularly thank the BAS Logistics Section and Air
Unit staff, and field general assistant Tim Blakemore. Morag
Hunter, Steve Hinde, and Anke Wendt are thanked for their
efforts in providing extra collections from the survey area.
Herb Dartnall kindly examined the rotifers obtained. We
thank Lloyd Peck, Andy Clarke, Rolf Maslen, David Wharton, and an anonymous referee for helpful discussions and
very constructive comments, and Peter Fretwell for designing
Fig. 1. The study forms part of the BAS core BIRESA (Biological Responses to Environmental Stress in Antarctica)
Project, and also contributes to the SCAR RiSCC (Regional
Sensitivity to Climate Change in Antarctica) Program.
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