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Occurrence of nematodes, tardigrades and rotifers on ice-free areas in East Antarctica
ARTICLE IN PRESS Pedobiologia 48 (2004) 395–408
www.elsevier.de/pedobi
Occurrence of nematodes, tardigrades and rotifers on ice-free areas in East Antarctica ¨ma, K. Ingemar Jo ¨rn Sohleniusa,*, Sven Bostro ¨nssonb Bjo a
Department of Invertebrate Zoology, Swedish Museum of Natural History, Box 50007, Stockholm SE-10405, Sweden Department of Theoretical Ecology, Ecology-Building, Lund SE-223 62, Sweden
b
Received 14 October 2003; accepted 3 June 2004
KEYWORDS East Antarctica; Microfauna; Nunataks; Nematoda; Tardigrada; Rotatoria
Summary Nematodes, rotifers and tardigrades were collected on three nunataks (mountain peaks penetrating the ice sheet) in Vestfjella, on six nunataks in Heimefrontfjella and on the Schirmacher Oasis in East Antarctica in the austral summers of 1996/97 and 2001/02. Most samples were taken on the nunatak Basen in Vestfjella where the Swedish station Wasa is located. The microfauna was patchily distributed and the highest densities of animals were found on sites with visible vegetation of mosses, lichens or algae. Thirty-four taxa of nematodes and tardigrades were found. Only seven of these occurred regularly in apparently actively reproducing populations. Other occasional records of nematodes had very few specimens. The highest number of species was found on the nunatak Basen. Rotifers, found in 66% of the samples, were the most frequent animal group. Nematodes occurred in 37% of the samples and tardigrades in 42%. The most frequent nematodes were Plectus and Panagrolaimus, occurring in 26% and 5% of the samples, respectively. Macrobiotus, Hebesuncus and Acutuncus were the most frequent and abundant tardigrades. The pattern of animal distribution can be related to both habitat characteristics and to the geographic position of the nunatak. The communities are little organised and the distribution of the fauna has similarities with an early phase of colonisation. & 2004 Elsevier GmbH. All rights reserved.
*Corresponding author. E-mail address: [email protected] (B. Sohlenius). 0031-4056/$ - see front matter & 2004 Elsevier GmbH. All rights reserved. doi:10.1016/j.pedobi.2004.06.001
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Introduction Nematodes, rotifers and tardigrades, here called metazoan microfauna, are patchily distributed over the ground on nunataks (mountain peaks penetrating the ice sheet) and oases (ice-free coastal areas) in continental Antarctica (Miller et al., 1988; Freckman and Virginia, 1990; Steele et al., 1994; Sohlenius et al., 1995, 1996; Petz, 1997; Sinclair, 2001). Because of the very harsh climate, these sites are inhabited by animals living at the extremes of what is possible for animals to survive (Wharton, 2002). Relatively few species have the physiological capacity to live here, and this may be one cause to the low number of species found in active populations. Other limitations to species richness are probably the very isolated position of Antarctica and the very patchy occurrence of suitable habitats on the often widely dispersed nunataks. The greatest abundance of microfauna generally occurs in association with patches of moss, lichens or algae. High abundances of nematodes and rotifers can also be found in the surroundings of colonies of snow-petrels (Pagodroma nivea). The distribution of habitat patches for the microfauna is restricted by the microtopography of the landscape, edaphic factors, microclimatic conditions and occurrence of vegetation. The animals found may be either survivors from an earlier, warmer pre-Pleistocene period in Antarctica or the progeny of more recently arrived propagules originating from other parts of the globe. Some authors believe that most of the multicellular fauna and flora on continental Antarctica are relicts from previous warmer periods (Kappen, 1993; McInnes and Pugh, 1998). Since the habitable patches are often small and isolated both within a nunatak and between different nunataks, the question still remains whether and to what extent dispersal between and within nunataks occurs. The probability of colonisation of a particular new habitat patch is certainly very low and the occurrence of habitat patches without animals can thus be expected. The dynamics of suitable microhabitats are largely unknown but there are changes in size and distribution of tufts of mosses and lichens (Pannewitz et al., 2003). The probability of arrival of propagules is then dependent on both the distance from and the size of the source populations (Walton, 1990). The dynamics of a population after colonisation of various habitats are also important for the survival of a species in an area (Hanski, 1999). Thus the abilities of dispersal and colonisation are probably of crucial importance for the persistence of these animals on nunataks. Some small animals can be dispersed in a dried
B. Sohlenius et al.
state over long distances by wind (Orr and Newton, 1971; Baujard and Martiny, 1994; Miller et al., 2001; Moorhead et al., 2002). They may also be dispersed by birds or attached to plant material moved around during storms. Nematodes can also be dispersed by running water (Villenave et al., 2003). The recent activity of people involved in Antarctic expeditions may be an additional means of dispersal of microscopic animals. The aim of this paper is to report the occurrence and abundance of nematodes, rotifers and tardigrades and compare the results with those from previous Swedish Antarctic Expeditions to Dronning Maud Land in order to get a better picture of the pattern of distribution of this fauna. The field study and the sampling during 1996/97 was undertaken by Cecilia Eriksson and in 2001/02 by K. Ingemar . Jonsson. The data are compared with results from previous collections made in the austral summers of 1991/92 and 1993/94 (Sohlenius et al., 1995, 1996).
Materials and methods Study sites In all, 273 samples were taken on the nunataks Basen, Fossilryggen, Plogen, Haldorsentoppen, Mora. nryggen, Vardeklettane, Steinnabben, Okkenhaugrusta and Baileyranten, and in the Schirmacher Oasis. For simplicity, all sites are here called nunataks, although the Schirmacher Oasis is not a nunatak in a strict sense. The locations of some of the nunataks are given in Fig. 1. Some nunataks in the area are poorly explored and information about geological conditions, etc. is lacking. Schirmacher oasis The Schirmacher Oasis (701460 S/111480 E) is remote from the other studied nunataks (900 km NE of Basen), closer to the coast and at a low altitude (7– 120 m above sea level). The area is rather classified as an oasis than as a nunatak. It has a milder climate and is larger (19.5 3.4 km) than the nunataks. The vegetation of moss is in some places rather extensive. Twenty-one samples (15 with moss) were taken in 2001/02 close to the Russian station ‘Novolazarevskaya’. Vestfjella; Basen (Wasa) Basen (731020 S/131240 W, altitude 250–580 m, size 5 3 km) with the Swedish station ‘Wasa’, is 110 km from the shelf-ice border. It has a relatively isolated position. The closest nunataks are Plogen
ARTICLE IN PRESS Microfauna in East Antarctica
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Figure 1. Distribution of areas sampled in Dronning Maud Land, East Antarctica in 1996/97 and 2001/02.
and Fossilryggen. The bedrock is basalt. Macrovegetation (lichens, mosses, algae) occurs in restricted areas, especially close to snow- and ice-melting zones. Twenty-five samples were taken in 1996/97 and 145 (43 with moss) in 2001/02.
Vestfjella; Fossilryggen Fossilryggen (731230 S/131020 W, altitude 600–730, size 2.5 0.5 km) is situated 42 km SSE of Basen. The closest nunatak is Plogen, situated 24 km NW of Fossilryggen. The bedrock is shale, sometimes with individual small concretions of limestone. Only lichens are found. Twelve samples were taken in 1996/97 and 30 in 2001/02.
Vestfjella; Plogen Plogen (731130 S/131500 W, altitude 900–910 m, size 11 0.5 km) is situated 20 km SW of Basen. The western ridge has a length of about 5 km and the eastern ridge a length of about 6 km. Lichens and mosses are found. Nine samples (three with moss) were taken in 2001/02.
Heimefrontfjella; Haldorsentoppen (Svea) Haldorsentoppen (741340 S/111130 W, altitude 1245 m) with the Swedish station ‘Svea’, is situated about 172 km S of Basen. It has a bedrock consisting of slightly metamorphosed red granite and augen gneiss. Lichens and mosses are found. Nine samples
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Mannefallknausane; Baileyranten (741370 S/141390 W, altitude 1141 m, area 0.40 km2) is situated 155 km SSV of Basen and 88 km W of Haldorsentoppen. Lichens are found. One sample was taken in 1996/97.
(one with moss) were taken in 1996/97 and seven (three with moss) in 2001/02. . Heimefrontfjella; Moranryggen Mora. nryggen (741340 S/111130 W) is a small nunatak lying adjacent and parallel to Haldorsentoppen. Lichens are found. Three samples were taken in 1996/97.
Vegetation, soil and climatic conditions Samples were classified into: (a) samples dominated by inorganic material and its texture (gravel with particle size 42.0 mm or sand with particle size 0.05–2.0 mm), (b) mixed inorganic material (mixture of clay and other soil fractions) and (c) samples with organic material and macro-vegetation, i.e. moss, lichens, blue-green algae (Nostoc commune) or green algae (Prasiola crispa). The moss generally grows in relatively small cushions with a diameter of only a few cm. The number of each kind of samples is indicated in Table 1 along with their water content and temperatures at sampling in 2001/02. Temperatures inside substrates were measured to the nearest 0.11C by using a digital thermometer.
Heimefrontfjella; Steinnabben Steinnabben (741330 S/111150 W, altitude 1200– 1300 m, size 500 200 m) has a bedrock consisting of probably augen gneiss. Lichens and mosses are found. Four samples (one with moss) were taken in 1996/97 and two in 2001/02. Heimefrontfjella; Okkenhaugrusta (741430 S/111200 W). Lichens are found. Three samples were taken in 1996/97. Heimefrontfjella; Vardeklettane (751S/131W) Lichens are found. Two samples were taken in 1996/97.
Table 1. Characteristics of samples with different textures and vegetation types taken from all nunataks 2001/02 Gravel
Sand
Mixed inorg
Lichens
Moss
Prasiolaþorg
Nostoc
All samples
57
29
30
17
64
15
2
214
(a) Water content (% water by weight) Mean 5.6 7.6 Max. 58.0 21.4 Min. 0.1 0.1
5.3 21.7 0.1
2.5 12.0 0.2
16.7 90.9 0.2
6.8 11.5 1.9
3.1 3.1 3.1
8.7 90.9 0.1
(b) Temperature (1C) Mean Max. Min.
4.5 16.7 0.8
9.0 13.7 3.9
8.7 13.6 2.5
8.1 9.7 6.6
F F F
7.1 16.7 0.8
94 29 65 47
92 78 78 59
87 67 87 20
100 50 100 100
88 44 72 48
(d) Abundance of microfauna (mean number/g dry weight on occurrence) Nematodes 0.2 0.8 4.0 35 94 Rotifers 5.1 1.9 204 94 30 Tardigrades 0.5 2.1 0.3 2.1 76
1230 868 16
1.2 16 4.9
182 119 29
Max. number/g dry weight Nematodes 0.5 Rotifers 88 Tardigrades 7.5
5063 2719 31
1.2 30 9.1
5063 4251 2395
Number of samples
6.8 15.6 0.2
6.7 14.8 0.5
(c) Frequency of occurrence (% of all samples) Any animal 88 79 83 Nematodes 14 35 37 Rotifers 70 62 70 Tardigrades 54 41 27
3.3 12 14
35 4251 0.6
153 959 13
1369 279 2395
Figures show water content (a), temperature (b), frequency (c) and abundance (d) of microfauna.
ARTICLE IN PRESS Microfauna in East Antarctica
Sampling, extraction and counting The 59 samples collected in 1996/97 were kept deep-frozen (201C) until extraction in Stockholm several months later. The 214 samples taken in 2001/02 were extracted at the field station Wasa or dried and later extracted in Stockholm. For extraction a wet funnel method was used (Sohlenius, 1979). The volume of material for each extraction was about 3–5 cm3. After extraction, the animals were killed by heat and fixed in TAF (formalin-triethanolamine solution). The total number of animals extracted was counted under a dissecting microscope. The number of animals/ gram dry weight (gdw) extracted material was calculated. Since the number of animals/gdw in samples with organic material (especially moss) differed greatly from that in samples with mineral material, the number of specimens/extraction gives a more comparable indication of abundance. In 1996/97, the samples were taken mostly in places without macro-vegetation. In 2001/02, a higher proportion of the samples was taken in places with organic material or macro-vegetation. Because of this and the differences in handling before extraction, the sampling series are not fully comparable. Detailed analyses of the effects of substrates are thus only made for the 2001/02 samples. For identification, animals were transferred to glycerol according to Seinhorst’s (1959) method. Nematodes and tardigrades were identified to genus or species.
Results Fauna composition at various sites Animals were found in samples from all nunataks except Okkenhaugrusta, Vardeklettane and Baileyranten. On most nunataks rotifers was the most frequent group followed by tardigrades and nematodes (Table 2b). The presence of various nematode and tardigrade taxa on the nunataks differed (Table 3). Thus active populations of nematodes belonging to Chiloplacoides and Eudorylaimus were found only on Schirmacher Oasis. Plectus (probably P. acuminatus) was found on Schirmacher Oasis, Basen, Plogen and occasionally on Fossilryggen and Haldorsentoppen. Panagrolaimus (probably P. magnivulvatus) was found in large numbers on Basen, Haldorsentoppen and Steinnabben in samples taken in the vicinity of bird colonies.
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In both seasons there were quite a lot of occasional records of several nematode species (Table 3). In Table 2a, they are grouped in the category ‘other Nematoda tot’. The genera and species listed in Table 2 are those found regularly in higher numbers and thus considered to represent actively reproducing populations. Among tardigrades, one Macrobiotus species (probably M. blocki) was found on Schirmacher Oasis, Haldorsentoppen and Mora. nryggen. Another Macrobiotus species (probably M. krynauwi) was found on Basen, Fossilryggen and Plogen. In earlier publications (Sohlenius et al., 1995, 1996) M. krynauwi was tentatively named M. furciger. Diphascon chilenense langhovdensis was found in both seasons on Haldorsentoppen but nowhere else. In previous investigations this species was also found on Fossilryggen (Sohlenius et al., 1995, 1996). Hebesuncus (probably H. ryani) was found only on the nunataks in Vestfjella. During both seasons Acutuncus antarcticus ( ¼ Hypsibius antarcticus), was found in the same areas on Basen. In 1996/97, there was an occasional record from Fossilryggen. On Schirmacher Oasis several specimens of A. antarcticus were found in moss.
Frequency and abundance in samples of different textures and vegetation types The distribution of microfauna in samples from different kinds of soils and vegetation types was analysed for the 214 samples extracted in 2001/02. Depending on substrate, 79–100% of these samples contained animals (Table 1c). The frequency of samples with microfauna was generally somewhat lower in inorganic than in organic material. Overall rotifers were found in 155 samples (72% of the samples). They were found in almost equal frequency in inorganic and organic material. Nematodes were found in 94 samples (44%). They occurred much more frequently in samples from moss, Prasiola, organic material and Nostoc than in samples with essentially inorganic material. Tardigrades were found in 102 samples (48%). The frequency of tardigrades was low in plots with Prasiola and in samples with mixed inorganic material. The highest frequency of tardigrades occurred in moss and in gravel. The proportion of samples containing different genera of nematodes and tardigrades varied greatly between substrates. Thus Plectus occurred in high frequency in moss (72% of the samples), but was also present in a low proportion of the samples without macro-vegetation (Fig. 2a). The highest
400
Table 2. Abundance (a), frequency (b) and species richness (c) of microfauna from investigated nunataks Nunatak
All sampling sites
Schir-macher Basen
Year
1996/97
2001/02
2001/02
Fossilryggen
Plogen
Haldorsen toppen
1996/97 2001/02 1996/97 2001/02 2001/02 1996/97
Steinnabben
Mora. n-ryggen
2001/02
1996/97 2001/02 1996/97
F 928 82 F 0.4
F F F F 0.2
F 0.1 0.1 F 0.1
F F 7.4 F F
F 10 0.3 F 2.1
F 1392 F F 0.5
F F F F F
F 244 F F F
F F F F F
Tardigrada Macrobiotus blocki Macrobiotus krynauwi Diphascon chilenense Hebesuncus ryani Acutuncus antarcticus
6.6 1.7 3.7 17 0.2
3.0 60 11 3.9 6.1
12 F F F 53
F 3.4 F F 0.3
F 65 F 3.3 1.6
F 0.7 F 17.3 0.1
F 0.5 F 2.6 F
F 9.1 F 7.9 F
0.7 F 3.7 F F
F F 11 F F
F F F F F
F F F F F
1.0 F F F F
Nematoda Rotatoria Tardigrada
1.9 9.8 5.0
181 119 30
17 25 26
0.1 1.5 1.3
161 118 40
0.2 2.7 9.9
0.1 1.7 1.2
7.4 11 9.8
6.3 15 2.7
1114 680 11
F 100 F
244 53 F
F 8.7 1.0
(b) Occurrence in percent of all samples Nematodes 12 44 Rotifers 44 72 Tardigrades 25 47
62 43 33
8 36 16
47 81 47
25 58 50
17 47 50
22 56 78
22 78 33
71 86 43
F 25 F
50 100 F
F 67 67
(c) Species richness Number of observed taxa 15
8
4
22
10
9
5
12
4
1
2
2
29
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(a) Abundance (number of animals/g dry weight on occurrence) Nematoda Chiloplacoides F 8.7 8.7 F Panagrolaimus 10 947 F F Plectus 0.2 71 31 F Eudorylaimus F 7.3 7.3 F Other Nematoda tot 0.5 2.1 5.7 F
B. Sohlenius et al.
Plogen
Haldorsen toppen
Steinnabben
Mora. n-ryggen
2001/02
1996/97
2001/02
2001/02
1996/97
2001/02
1996/97
2001/02
1996/97
25
145
12
30
9
9
7
4
2
3
F F F F F F F F F 1 2 F F F F 12 F F 1 F F F 5 F F F F F
F F F F F F F F F F F F F F F F F 2 F F F F F F F F F F
3 F 2 2 3 F 2 F 3 3 F 1 7 F F 54 F F F F 5 1 F 1 3 1 1 3
F 1 F F F 1 F F F F F F F 1 1 1 F 2 F F F F F F F F F F
F 3 F F F F F F F F F 1 1 F F 1 F F F 1 F F F F 1 F F F
F F F F F F F F F F F F F F F 2 F F F F F F F F F F F F
F 1 F F F 1 F 1 F F F F 5 1 1 1 1 1 F F F F F F F F F F
F 1 F F F F F F F F F F 4 F F F F F F F F F F F F F F F
F F F F F F F F F F F F F F F F F F F F F F F F F F F
F F F F F F F F F F F F 1 F F F F F F F F F F F F F F F
F F F F F F F F F F F F F F F F F F F F F F F F F F F F
5 F F F 2 F
F 3 F F 1 F
F 34 F 17 21 4
F 5 F 3 1 F
F 4 F 5 F F
F 4 F 4 F 1
1 F 2 F F F
F F 3 F F F
F F F F F F
F F F F F F
2 F F F F F
All sampling sites
Schir-macher
Basen
Year
1996/97
2001/02
2001/02
1996/97
No. of samples
59
214
21
NEMATODA Filenchus Tylenchida indet. Tylenchorhynchus Apratylenchoides Paratylenchus Aphelenchoides Rhabditida indet. Bunonema Acrobeloides Cephalobidae indet. Chiloplacoides Eucephalobus Panagrolaimus Teratocephalus Metateratocephalus Plectus Prismatolaimus Eumonhystera Geomonhystera Tripyla Mesodorylaimus Epidorylaimus Eudorylaimus Microdorylaimus Aporcelaimellus Aporcelaimus Dorylaimida indet. Nematoda indet.
F 2 F F F 2 F 1 F F F F 1 2 2 2 1 5 F F F F F F F F F F
3 4 2 2 3 F 2 F 3 4 2 2 14 F F 69 F F 1 1 5 1 5 1 4 1 1 3
TARDIGRADA Macrobiotus blocki Macrobiotus krynauwi Diphascon chilenense Hebesuncus ryani Acutuncus antarcticus Tardigrada indet.
3 8 2 3 2 F
5 42 3 26 23 5
401
Taxa in bold are assumed to represent actively reproducing populations.
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Fossilryggen
Nunatak
Microfauna in East Antarctica
Table 3. Number of samples in which different taxa of nematodes and tardigrades occurred
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Macrobiotus
Plectus 80
(a)
40
(a)
30
%
%
60 40
20 10
20
0 Gr
Sa
Mi in
Li
Mo
Pr+o
Nos
All
Pr+o
Nos
All
0 Gr
Sa
Mi in
Li
Mo
Pr+o
Nos
All
Hebesuncus
Panagrolaimus
15
(b) %
50 40
%
(b)
20
30
10 5
20
0
10
Gr
Sa
Mi in
Li
Mo
0 Sa
Mi in
Li
Mo
Pr+o
Nos
All
Other nematodes
75
(c)
%
50 25
.
Al ls am pl es
N os to c
rg as
io
la
+o
M os s Pr
Li ch en s
in or g.
Sa nd
M ix ed
G ra ve l
Figure 2. Relative frequency of 2001/02 samples with three categories of nematodes in substrates of different kinds. Gr ¼ Gravel; Sa ¼ sand; Mi in ¼ Mixed inorganic material; Li ¼ lichens; Mo ¼ moss; Prþo ¼ Prasiolaþorþorganic material; Nos ¼ Nostoc; All ¼ All samples.
frequency of Panagrolaimus (47% of the samples) was found in Prasiola and in organic material in the vicinity of bird colonies (Fig. 2b). The species of nematodes found occasionally (other nematodes) were most frequent in samples with mixed inorganic material (Fig. 2c). Among the tardigrades, the relative frequencies of samples with Macrobiotus and Hebesuncus covaried (Figs. 3a and b). These tardigrades were most frequent in samples with sand, lichens and moss. A. antarcticus had a different pattern of variation with the highest frequency of occurrence in samples from wet places or from a pond with blue-green algae (Nostoc) (Fig. 3c). It also occurred abundantly in an area with gravel on Basen and in some moss samples from Schirmacher Oasis. D. chilenense langhovdensis was found in moss and Prasiola (31.3 specimens/ gdw) on Haldorsentoppen. When the occurrence and abundance of different groups and taxa in the samples were compared only one significant correlation was found. There was a correlation between numbers of rotifers and Panagrolaimus (r ¼ þ0:52; po0:05; N ¼ 14). While
es pl am ls
Al
os
to
c
rg la io
N
+o
s
s en ch
or
os
as
0
Li
in ed
M
ix
G
ra
10
nd
ve
l
g.
.
0
20
Sa
%
30
M
40
Acutuncus
(c)
100
Pr
Gr
Figure 3. Relative frequency of 2001/02 samples with tardigrades in substrates of different kinds. Abbreviations as in Fig. 2.
no significant negative correlations were found, there was a tendency of a negative correlation between numbers of Plectus and Macrobiotus, and between numbers of Plectus and rotifers. The mean abundance of microfauna groups in different substrates indicates that nematodes reached their highest abundance in Prasiola and in organic material in the vicinity of bird colonies (Table 1d). In contrast, tardigrades reached their highest abundance in moss. The highest abundance of rotifers was found in mixed inorganic material. The abundance and relative contribution of different taxa varied among substrates (Fig. 4). The proportion of rotifers was the largest in inorganic samples, lichens and Nostoc. In samples with moss and Prasiola, nematodes contributed the largest proportion. Tardigrades had their highest relative abundances in sand, moss and Nostoc.
Numbers of species and abundance in single samples The number of taxa and abundance in each sample was investigated for the 188 samples yielding animals. Sixty-nine samples contained one and 65 samples contained two taxa. A single sample
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Figure 4. Relative composition of metazoan microfauna in various substrates.
contained six taxa, which was the highest number found. Four samples contained five taxa; 11 contained four taxa and 39 contained three taxa. The highest number of extracted animals/sample was found in samples containing 2–3 taxa. In four of the 64 samples from moss, no animals were found. Rotifers, nematodes and tardigrades were found in 50, 49 and 38 of the moss samples, respectively. Twenty-four moss samples contained three taxa (Fig. 5) and in these samples the highest number of animals were found. The samples that contained four taxa did not reach as high abundances as those with three taxa (Fig. 5). Among nematodes Plectus dominated, whereas Panagrolaimus was found only in one moss sample from Basen and one from Haldorsentoppen. Among tardigrades, Macrobiotus was found in all moss samples with four or five taxa and often in a relatively high proportion. Macrobiotus never occurred as a single taxon in a moss sample. This genus was found in 24 (38%) of the moss samples with a mean abundance of 111 specimens/gdw on occurrence. Hebsuncus was found in 10 of the moss samples from Basen and Plogen with a mean abundance of 6.2 specimens/gdw. Acutuncus was also found in 10 moss samples with a mean abundance of 13 specimens/gdw. Diphascon was found in two moss samples from Haldorsentoppen with a mean abundance of 0.9 specimens/gdw.
In 24 moss samples with Macrobiotus the mean abundance7s.e. of Plectus was 52718 specimens/ gdw and in 25 samples without Macrobiotus the mean abundance7s.e. of Plectus was 129764 specimens/gdw. This difference is not significant. The mean abundanceþs.e. of rotifers in samples together with Macrobiotus was similar (27712) as in samples without Macrobiotus (2779 specimens/ gdw). In most samples taken in the vicinity of bird colonies, Panagrolaimus and rotifers occurred in high numbers (Fig. 6). Very few specimens of Plectus and tardigrades were found in these samples. Rather few animals were found in most of the 116 samples with inorganic material (Fig. 7). Forty-eight of these samples contained only one taxon and 15 were devoid of animals. The abundance and fauna composition in the samples varied greatly. In a few samples the number of animals were much higher than in the others. This was especially the case with rotifers, which occurred in a very high abundance in one of the samples with three taxa and in one of the samples with two taxa (Fig. 7).
Discussion The general pattern of distribution of the microfauna agrees with earlier studies (Sohlenius et al., 1995, 1996; Petz, 1997). As reported by Petz
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Figure 5. Composition of microfauna in samples from moss. Each bar shows number of animals extracted from one sample. The bars are arranged with decreasing total abundance in each group with the same numbers of taxa. The groups are arranged with decreasing numbers of taxa (no. of taxa). The x-axis gives numbers of taxa in each group.
Figure 6. Composition of microfauna in samples with organic material taken in the vicinity of birds’ colonies. For explanations see Fig. 5.
(1997), rotifers occurred more frequently in the samples than did tardigrades or nematodes. The densities of animals in inorganic soil and moss were
lower than those found by Petz, but in ornithogenic soil the number of nematodes and tardigrades was higher.
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Figure 7. Composition of microfauna in samples with inorganic material. For explanations see Fig. 5.
There were great differences in abundance of animals recorded in 1996/97 in comparison with 2001/02, especially on Basen. However, the results from the two seasons are not fully comparable since the samples were taken by different persons and handled in different ways. Despite this, the occurrence of different species of tardigrades on specific nunataks agrees with the results from samplings from previous expeditions (Sohlenius et al., 1995, 1996). The tardigrades Macrobiotus krynauwi and Hebesuncus ryani were originally described from the nunatak Vesleskarvet in an area some 370 km from the nunatak Basen sampled in our investigations (Dastych and Harris, 1994, 1995). The nematodes Eudorylaimus nudicaudatus and Chiloplacoides antarcticus were described from the nunatak group Robertskollen by Heyns (1993, 1994). The importance of macro-vegetation, especially moss, for nematodes and tardigrades was apparent. Especially for Plectus a connection with moss was clear. The moss habitat also favoured the tardigrades Macrobiotus and Hebesuncus. The microclimatic conditions prevailing in the moss rather than the moss itself are of importance. The climate inside the moss isolates the microfauna from very rapid microclimatic changes. The water content was often high in the moss samples (Table 1a), and moisture is probably of decisive importance for
moss growth. Much of the moisture originates from nearby patches of thawing snow and ice. The mean temperature was higher in the samples with macrovegetation than in samples without vegetation. The temperature range at sampling was also much higher in inorganic samples than in samples with macro-vegetation. It was remarkable that the highest numbers of rotifers and nematodes occurred in organic material in the vicinity of bird colonies, especially in the growth of Prasiola. High numbers of Panagrolaimus in ornithogenic soils have been observed previously (Sohlenius, 1988; Sinclair, 2001). The most obvious reason for these high numbers is that this substrate is very energy-rich and has a high content of nitrogen and other nutrients, and certainly a high bacterial activity (Ryan and Watkins, 1989). A high abundance of Panagrolaimus and rotifers associated with penguin rookeries was found by Porazinska et al. (2002b). These authors found a positive correlation between number of Panagrolaimus and substrate carbon and ammonium content. The positive correlation between rotifers and Panagrolaimus in the samples with ornithogentic material suggests that both these taxa are stimulated by the high bacterial production. The low proportion of tardigrades in the ornithogenic soils agrees with observations made by Porazinska et al. (2002b). This could indicate that tardigrades do not
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thrive very well in nutrient-rich substrates with a high bacterial activity. In these environments a high content of ammonium and other harmful substances may depress many groups of soil animals. A species, which seemed to be favoured by bird colonies, was the mite Nanorchestes antarcticus (Ryan and Watkins, 1989). Despite the simple classification according to soil textures, there were indications that texture influenced the distribution of the microfauna. For example nematodes lumped together as ‘other Nematoda’ were especially abundant in the clayish samples classified as ‘mixed inorganic’. Among tardigrades. Macrobiotus and Hebesuncus occurred most frequently in sandy samples (Figs. 3a and b). Acutuncus was rather frequent in some places with coarse gravel on the nunatak Basen. The factors influencing these microfaunal distributions may be indirect. The influence of water content and microscopic algae, etc. may be significant. The direct relationship between relative humidity and the abundance of metazoan microfauna in Antarctic terrestrial environments was demonstrated by Kennedy (1993) and the importance of moisture for nematode distribution in Antarctica was noted by Porazinska et al. (2002a). The biotic interactions between various animal species should be revealed in these simple communities (Block, 1994). The food webs are simple. Both dominant nematode genera, Plectus and Panagrolaimus, have frequently been cultured on bacteria (Yeates et al., 1993). However, in some of our specimens greenish material in the intestines indicates that they may feed on microalgae. The feeding habits of tardigrades are less well established. In some specimens of Macrobiotus greenish material in the intestines may indicate herbivory but according to Dastych and Harris (1995) M. krynauwi is probably detrivorous. No information has been found on the feeding habits of M. blocki. Several species of the genus Macrobiotus are documented as predators on nematodes and rotifers (Hallas and Yeates, 1972; Altiero and Rebecchi, 2001). The observation of a tendency of lower number of nematodes (Plectus) in moss samples containing tardigrades (Macrobiotus) could therefore possibly be an effect of predation. However, no influence by Macrobiotus on number of rotifers was seen. Competition for food could be expected to occur in places where very high population densities of microfauna are found. However, populations could be high because of abundant food and a low competition. The high variability in nematode and tardigrade densities and the lack of these organisms in a high
B. Sohlenius et al.
percentage of samples collected from Antarctic localities where they are known to occur, agree with previous observations (Miller et al., 1988; Freckman and Virginia, 1990; Sohlenius et al., 1995, 1996). In both moss and inorganic samples, the variable frequencies and abundances of taxa indicate that the microfauna may be regarded as loosely associated populations rather than as wellorganised communities. This shows similarities with an early stage of a primary succession and it was not possible to predict microfauna composition in a certain sample. Some of the tardigrades are known only from Antarctica. Their distribution within the investigated area indicates that there is a limited dispersal between nunataks, which in turn indicates that they may have remained isolated on the various nunataks for very long periods. A detailed analysis of morphological variability may throw further light on the question as to how isolated the populations are on the various nunataks. Occurrence within the nunataks in different microhabitats indicates, however, an apparent dispersal between microsites within a particular nunatak. The results are, however, not sufficiently clear to rule out a more global, long distance source. The present results support the idea that the tardigrades are survivors from the pre-Pleistocene period (McInnes and Pugh, 1998). Among the nematodes, the Plectus populations could be expected to have a similar power of dispersal as certain tardigrades such as Macrobiotus. A further analysis of morphological variability of the Plectus populations from various nunataks would reveal this. The nematode Panagrolaimus living in association with bird colonies might be dispersed by birds. However, Marshall and Pugh (1996) stated that birdmediated transportation of Panagrolaimus has never been demonstrated. Panagrolaimus is known to be resistant to harsh environmental conditions (Wharton, 2002) and has been recorded in material of birds’ nests in such remote places as the island of . Surtsey (Bostrom, 1988). The findings of nematodes belonging to genera and species common in temperate soils around the world is enigmatic, especially since the food resource some of them generally use (roots of higher plants) does not occur on the nunataks. Their occurrence in the samples might be due to contamination during handling and extraction in the laboratory, although in this investigation special care was taken to avoid contamination. The nematodes of the genera indicated in Table 3 were sometimes found in more than one sample. Similar kinds of observations have been made
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previously. Thus, plant feeding nematodes belonging to the genera Helicotylenchus and Rotylenchus have been reported from continental Antarctica by Yeates (1979) and Van den Berg and Harris (1996). Our records of Apratylenchoides, Tylenchorhynchus and Paratylenchus are new for continental Antarctica and will be presented in a separate paper (Ryss pers. comm.). We found one juvenile of Geomonhystera on Schirmacher Oasis. Several specimens of Geomonhystera villosa were reported from the McMurdo Sound Region of continental Antarctica by Timm (1971) and Wharton and Brown (1989), but these populations together with other material have recently been described by Andra! ssy (1998) as Geomonhystera antarcticola. Several of the nematode records in the present investigation are rather occasional, often with a single specimen in one sample. This indicates that these animals are not likely to be members of actively growing populations, but rather occasional long-distance dispersers, with no or only a low possibility of reproducing in this habitat. Some of the specimens found appeared to be in a poor or starving condition, which further indicates that they may have been occasionally introduced into the area without being able to reproduce. Due to the cold and often very dry conditions it could be expected that accidental dispersers may persist for very long periods. Another explanation to the presence of unexpected nematode species could be that they may have been introduced as contaminations on boots and other equipment by the activities of the Antarctic expeditions. This is indicated by the fact that these nematodes were found in places on Basen where people walk around and this was particularly evident in samples taken around the station Wasa.
Conclusions The occurrence of apparently habitable places without microfauna and the very variable abundances indicated a low probability of successful invasion of such isolated outcrops of rock plus vegetation in the polar ice sheet. This is probably due to a combination of long distances from potential source populations and the very isolated position of habitable patches. The area appears to be similar to an early phase of colonisation. The dynamics of habitable places and their microfauna populations are probably rather slow because of the cold climatic conditions.
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Acknowledgements We are grateful to the Swedish Polar Research Secretariat for providing transport and facilities for . K. Ingemar Jonsson, who conducted the field sampling in Antarctica in 2001/02 and for Cecilia Eriksson, who made the sampling in 1996/97. Kent Larsson is thanked for providing the map and Ingegerd Sohlenius for technical assistance. Valuable comments on the manuscript were given by an anonymous referee.
References Altiero, T., Rebecchi, L., 2001. Rearing tardigrades: results and problems. Zool. Anz. 240, 217–221. Andra! ssy, I., 1998. Nematodes in the sixth continent. J. Nem. Morph. Syst. 1, 107–186. Baujard, P., Martiny, B., 1994. Transport of nematodes by wind in the peanut cropping area of Senegal, West Africa. Fundam. Appl. Nematol. 17, 543–550. Block, W., 1994. Terrestrial ecosystems: Antarctica. Polar Biol. 14, 293–300. . Bostrom, S., 1988. Descriptions and morphological variability of three populations of Panagrolaimus Fuchs, 1930 (Nematoda: Panagrolaimidae). Nematologica 34, 144–155. Dastych, H., Harris, J.M., 1994. A new species of the genus Hebesuncus from the Antarctic nunataks. Dronning Maud Land (Tardigrada). Ent. Mitt. Zool. Mus. Hamb. 11, 139–145. Dastych, H., Harris, J.M., 1995. A new species of the genus Macrobiotus from inland nunataks in western Dronning Maud Land, continental Antarctica (Tardigrada). Ent. Mitt. Zool. Mus. Hamb. 11, 175–182. Freckman, D.W., Virginia, R.A., 1990. Nematode ecology of the McMurdo Dry Valley ecosystems. Antarct. J. US 25, 229–230. Hallas, T.E., Yeates, G.W., 1972. Tardigrada of the soil and litter of a Danish beech forest. Pedobiologia 12, 287–304. Hanski, I., 1999. Metapopulation Ecology. Oxford University Press, New York, 313pp. Heyns, J., 1993. Eudorylaimus nudicaudatus sp.n. from Antarctica (Nematoda: Dorylaimoidea). S. Afr. J. Antarct. Res. 23, 33–36. Heyns, J., 1994. Chiloplacoides antarcticus n.gen., n.sp. from western Dronning Maud Land, Antarctica (Nematoda: Cephalobidae). Fundam. Appl. Nematol. 17, 333–338. Kappen, L., 1993. Lichens in the Antarctic region. In: Friedmann, E.I. (Ed.), Antarctic Microbiology. WileyLiss Inc., New York, pp. 433–490. Kennedy, A.D., 1993. Water as a limiting factor in the Antarctic terrestrial environment: a biogeographical synthesis. Arct. Alp. Res. 25, 308–315. Marshall, D.J., Pugh, P.J.A., 1996. Origin of the inland Acari of continental Antarctica, with particular
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reference to Dronning Maud Land. Zool. J. Linn. Soc. 118, 101–118. McInnes, S.J., Pugh, P.J.A., 1998. Biogeography of limnoterrestrial Tardigrada, with special reference to the Antarctic fauna. J. Biogeogr. 25, 31–36. Miller, J.D., Horne, P., Heatwole, H., Miller, W.R., Bridges, L., 1988. A survey of the terrestrial Tardigrada of the Vestfold Hills, Antarctica. Hydrobiologia 165, 197–208. Miller, W.R., Horning, D.S., Heatwole, H.F., 2001. Tardigrades of the Australian Antarctic: Macquarie Island, Sub-Antarctica. Zool. Anz. 240, 475–491. Moorhead, D.L., Wall, D.H., Virginia, R.A., Parsons, A.N., 2002. Distribution and life-cycle of Scottnema lindsayae (Nematoda) in Antarctic soils: a modeling analysis of temperature responses. Polar Biol. 25, 118–125. Orr, C.C., Newton, O.H., 1971. Distribution of nematodes by wind. Plant Dis. Rep. 55, 61–63. Pannewitz, S., Green, T.G.A., Scheidegger, C., Schlensog, M., Schroeter, B., 2003. Activity pattern of the moss Hennediella heimii (Hedw.) Zand. in the Dry Valleys, South Victoria Land, Antarctica during the mid-austral summer. Polar Biol. 26, 545–551. Petz, W., 1997. Ecology of the active soil microfauna (Protozoa, Metazoa) of Wilkes Land, East Antarctica. Polar Biol. 18, 33–44. Porazinska, D.L., Wall, D.H., Virginia, R.A., 2002a. Population age structure of nematodes in the Antarctic Dry Valleys: perspectives on time, space, and habitat suitability. Arctic Antarct. Alpine Res. 34, 159–168. Porazinska, D.L., Wall, D.H., Virginia, R.A., 2002b. Invertebrates in ornithogenic soils on Ross Island, Antarctica. Polar Biol. 25, 569–574. Ryan, P.G., Watkins, B.P., 1989. The influence of physical factors and ornithogenic products on plant and arthropod abundance at an inland nunatak group in Antarctica. Polar Biol. 10, 151–160. Seinhorst, J.W., 1959. A rapid method for the transfer of nematodes from fixative to anhydrous glycerin. Nematologica 4, 67–69. Sinclair, B.J., 2001. On the distribution of terrestrial invertebrates at Cape Bird. Ross Island, Antarctica. Polar Biol. 24, 394–400. Sohlenius, B., 1979. A carbon budget for nematodes. rotifers and tardigrades in a Swedish coniferous forest soil. Holarct. Ecol. 2, 30–40.
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Sohlenius, B., 1988. Interactions between two species of Panagrolaimus in agar cultures. Nematologica 34, 208–217. . Sohlenius, B., Bostrom, S., Hirschfelder, A., 1995. Nematodes, rotifers and tardigrades from nunataks in Dronning Maud Land, East Antarctica. Polar Biol. 15, 51–56. . Sohlenius, B., Bostrom, S., Hirschfelder, A., 1996. Distribution patterns of microfauna (nematodes. rotifers and tardigrades) on nunataks in Dronning Maud Land, East Antarctica. Polar Biol. 16, 191–200. Steele, W.K., Balfour, D.A., Harris, J.M., Dastych, H., Heyns, J., Eicker, A., 1994. Preliminary biological survey of Vesleskarvet, northern Ahlmannryggen, western Queen Maud Land: Site of South Africa’s new Antarctic base. S. Afr. J. Antarct. Res. 24, 57–65. Timm, R.W., 1971. Antarctic soil and freshwater nematodes from McMurdo Sound region. Proc. Helminthol. Soc. Wash. 38, 42–52. Van den Berg, E., Harris, J.M., 1996. Rotylenchus capensis Van den Berg and Heyns (Tylenchida: Hoplolaimidae) in soils of isolated inland nunataks in western Dronning Maud Land, Antarctica. Afr. Plant Prot. 2, 19–24. " Villenave, C., Cadet, P., Planchon, O., Esteve, M., Lapetite, J.M., 2003. Transport of free-living nematodes by runoff water in a Sudano-Sahelian area. Appl. Soil Ecol. 23, 85–91. Walton, D.W.H., 1990. Colonization of terrestrial habitatsForganisms, opportunities and occurrence. In: Kerry, K.R., Hempel, G. (Eds.), Antarctic Ecosystems. Ecological Change and Conservation. Springer, Berlin, Heidelberg, New York, pp. 51–60. Wharton, D.A., 2002. Life at the Limits. Organisms in Extreme Environments. Cambridge University Press, Cambridge, 307pp. Wharton, D.A., Brown, L.M., 1989. A survey of terrestrial nematodes from the McMurdo Sound region, Antarctica. N. Z. J. Zool. 16, 467–470. Yeates, G.W., 1979. Terrestrial nematodes from the Bunger Hills and Gaussberg, Antarctica. N. Z. J. Zool. 6, 641–643. Yeates, G.W., Bongers, T., DeGoede, R.G.M., Freckman, D.W., Georgieva, S.S., 1993. Feeding habits in soil nematode families and generaFan outline for soil ecologists. J. Nematol. 25, 315–331.
www.elsevier.de/pedobi
Occurrence of nematodes, tardigrades and rotifers on ice-free areas in East Antarctica ¨ma, K. Ingemar Jo ¨rn Sohleniusa,*, Sven Bostro ¨nssonb Bjo a
Department of Invertebrate Zoology, Swedish Museum of Natural History, Box 50007, Stockholm SE-10405, Sweden Department of Theoretical Ecology, Ecology-Building, Lund SE-223 62, Sweden
b
Received 14 October 2003; accepted 3 June 2004
KEYWORDS East Antarctica; Microfauna; Nunataks; Nematoda; Tardigrada; Rotatoria
Summary Nematodes, rotifers and tardigrades were collected on three nunataks (mountain peaks penetrating the ice sheet) in Vestfjella, on six nunataks in Heimefrontfjella and on the Schirmacher Oasis in East Antarctica in the austral summers of 1996/97 and 2001/02. Most samples were taken on the nunatak Basen in Vestfjella where the Swedish station Wasa is located. The microfauna was patchily distributed and the highest densities of animals were found on sites with visible vegetation of mosses, lichens or algae. Thirty-four taxa of nematodes and tardigrades were found. Only seven of these occurred regularly in apparently actively reproducing populations. Other occasional records of nematodes had very few specimens. The highest number of species was found on the nunatak Basen. Rotifers, found in 66% of the samples, were the most frequent animal group. Nematodes occurred in 37% of the samples and tardigrades in 42%. The most frequent nematodes were Plectus and Panagrolaimus, occurring in 26% and 5% of the samples, respectively. Macrobiotus, Hebesuncus and Acutuncus were the most frequent and abundant tardigrades. The pattern of animal distribution can be related to both habitat characteristics and to the geographic position of the nunatak. The communities are little organised and the distribution of the fauna has similarities with an early phase of colonisation. & 2004 Elsevier GmbH. All rights reserved.
*Corresponding author. E-mail address: [email protected] (B. Sohlenius). 0031-4056/$ - see front matter & 2004 Elsevier GmbH. All rights reserved. doi:10.1016/j.pedobi.2004.06.001
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Introduction Nematodes, rotifers and tardigrades, here called metazoan microfauna, are patchily distributed over the ground on nunataks (mountain peaks penetrating the ice sheet) and oases (ice-free coastal areas) in continental Antarctica (Miller et al., 1988; Freckman and Virginia, 1990; Steele et al., 1994; Sohlenius et al., 1995, 1996; Petz, 1997; Sinclair, 2001). Because of the very harsh climate, these sites are inhabited by animals living at the extremes of what is possible for animals to survive (Wharton, 2002). Relatively few species have the physiological capacity to live here, and this may be one cause to the low number of species found in active populations. Other limitations to species richness are probably the very isolated position of Antarctica and the very patchy occurrence of suitable habitats on the often widely dispersed nunataks. The greatest abundance of microfauna generally occurs in association with patches of moss, lichens or algae. High abundances of nematodes and rotifers can also be found in the surroundings of colonies of snow-petrels (Pagodroma nivea). The distribution of habitat patches for the microfauna is restricted by the microtopography of the landscape, edaphic factors, microclimatic conditions and occurrence of vegetation. The animals found may be either survivors from an earlier, warmer pre-Pleistocene period in Antarctica or the progeny of more recently arrived propagules originating from other parts of the globe. Some authors believe that most of the multicellular fauna and flora on continental Antarctica are relicts from previous warmer periods (Kappen, 1993; McInnes and Pugh, 1998). Since the habitable patches are often small and isolated both within a nunatak and between different nunataks, the question still remains whether and to what extent dispersal between and within nunataks occurs. The probability of colonisation of a particular new habitat patch is certainly very low and the occurrence of habitat patches without animals can thus be expected. The dynamics of suitable microhabitats are largely unknown but there are changes in size and distribution of tufts of mosses and lichens (Pannewitz et al., 2003). The probability of arrival of propagules is then dependent on both the distance from and the size of the source populations (Walton, 1990). The dynamics of a population after colonisation of various habitats are also important for the survival of a species in an area (Hanski, 1999). Thus the abilities of dispersal and colonisation are probably of crucial importance for the persistence of these animals on nunataks. Some small animals can be dispersed in a dried
B. Sohlenius et al.
state over long distances by wind (Orr and Newton, 1971; Baujard and Martiny, 1994; Miller et al., 2001; Moorhead et al., 2002). They may also be dispersed by birds or attached to plant material moved around during storms. Nematodes can also be dispersed by running water (Villenave et al., 2003). The recent activity of people involved in Antarctic expeditions may be an additional means of dispersal of microscopic animals. The aim of this paper is to report the occurrence and abundance of nematodes, rotifers and tardigrades and compare the results with those from previous Swedish Antarctic Expeditions to Dronning Maud Land in order to get a better picture of the pattern of distribution of this fauna. The field study and the sampling during 1996/97 was undertaken by Cecilia Eriksson and in 2001/02 by K. Ingemar . Jonsson. The data are compared with results from previous collections made in the austral summers of 1991/92 and 1993/94 (Sohlenius et al., 1995, 1996).
Materials and methods Study sites In all, 273 samples were taken on the nunataks Basen, Fossilryggen, Plogen, Haldorsentoppen, Mora. nryggen, Vardeklettane, Steinnabben, Okkenhaugrusta and Baileyranten, and in the Schirmacher Oasis. For simplicity, all sites are here called nunataks, although the Schirmacher Oasis is not a nunatak in a strict sense. The locations of some of the nunataks are given in Fig. 1. Some nunataks in the area are poorly explored and information about geological conditions, etc. is lacking. Schirmacher oasis The Schirmacher Oasis (701460 S/111480 E) is remote from the other studied nunataks (900 km NE of Basen), closer to the coast and at a low altitude (7– 120 m above sea level). The area is rather classified as an oasis than as a nunatak. It has a milder climate and is larger (19.5 3.4 km) than the nunataks. The vegetation of moss is in some places rather extensive. Twenty-one samples (15 with moss) were taken in 2001/02 close to the Russian station ‘Novolazarevskaya’. Vestfjella; Basen (Wasa) Basen (731020 S/131240 W, altitude 250–580 m, size 5 3 km) with the Swedish station ‘Wasa’, is 110 km from the shelf-ice border. It has a relatively isolated position. The closest nunataks are Plogen
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Figure 1. Distribution of areas sampled in Dronning Maud Land, East Antarctica in 1996/97 and 2001/02.
and Fossilryggen. The bedrock is basalt. Macrovegetation (lichens, mosses, algae) occurs in restricted areas, especially close to snow- and ice-melting zones. Twenty-five samples were taken in 1996/97 and 145 (43 with moss) in 2001/02.
Vestfjella; Fossilryggen Fossilryggen (731230 S/131020 W, altitude 600–730, size 2.5 0.5 km) is situated 42 km SSE of Basen. The closest nunatak is Plogen, situated 24 km NW of Fossilryggen. The bedrock is shale, sometimes with individual small concretions of limestone. Only lichens are found. Twelve samples were taken in 1996/97 and 30 in 2001/02.
Vestfjella; Plogen Plogen (731130 S/131500 W, altitude 900–910 m, size 11 0.5 km) is situated 20 km SW of Basen. The western ridge has a length of about 5 km and the eastern ridge a length of about 6 km. Lichens and mosses are found. Nine samples (three with moss) were taken in 2001/02.
Heimefrontfjella; Haldorsentoppen (Svea) Haldorsentoppen (741340 S/111130 W, altitude 1245 m) with the Swedish station ‘Svea’, is situated about 172 km S of Basen. It has a bedrock consisting of slightly metamorphosed red granite and augen gneiss. Lichens and mosses are found. Nine samples
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B. Sohlenius et al.
Mannefallknausane; Baileyranten (741370 S/141390 W, altitude 1141 m, area 0.40 km2) is situated 155 km SSV of Basen and 88 km W of Haldorsentoppen. Lichens are found. One sample was taken in 1996/97.
(one with moss) were taken in 1996/97 and seven (three with moss) in 2001/02. . Heimefrontfjella; Moranryggen Mora. nryggen (741340 S/111130 W) is a small nunatak lying adjacent and parallel to Haldorsentoppen. Lichens are found. Three samples were taken in 1996/97.
Vegetation, soil and climatic conditions Samples were classified into: (a) samples dominated by inorganic material and its texture (gravel with particle size 42.0 mm or sand with particle size 0.05–2.0 mm), (b) mixed inorganic material (mixture of clay and other soil fractions) and (c) samples with organic material and macro-vegetation, i.e. moss, lichens, blue-green algae (Nostoc commune) or green algae (Prasiola crispa). The moss generally grows in relatively small cushions with a diameter of only a few cm. The number of each kind of samples is indicated in Table 1 along with their water content and temperatures at sampling in 2001/02. Temperatures inside substrates were measured to the nearest 0.11C by using a digital thermometer.
Heimefrontfjella; Steinnabben Steinnabben (741330 S/111150 W, altitude 1200– 1300 m, size 500 200 m) has a bedrock consisting of probably augen gneiss. Lichens and mosses are found. Four samples (one with moss) were taken in 1996/97 and two in 2001/02. Heimefrontfjella; Okkenhaugrusta (741430 S/111200 W). Lichens are found. Three samples were taken in 1996/97. Heimefrontfjella; Vardeklettane (751S/131W) Lichens are found. Two samples were taken in 1996/97.
Table 1. Characteristics of samples with different textures and vegetation types taken from all nunataks 2001/02 Gravel
Sand
Mixed inorg
Lichens
Moss
Prasiolaþorg
Nostoc
All samples
57
29
30
17
64
15
2
214
(a) Water content (% water by weight) Mean 5.6 7.6 Max. 58.0 21.4 Min. 0.1 0.1
5.3 21.7 0.1
2.5 12.0 0.2
16.7 90.9 0.2
6.8 11.5 1.9
3.1 3.1 3.1
8.7 90.9 0.1
(b) Temperature (1C) Mean Max. Min.
4.5 16.7 0.8
9.0 13.7 3.9
8.7 13.6 2.5
8.1 9.7 6.6
F F F
7.1 16.7 0.8
94 29 65 47
92 78 78 59
87 67 87 20
100 50 100 100
88 44 72 48
(d) Abundance of microfauna (mean number/g dry weight on occurrence) Nematodes 0.2 0.8 4.0 35 94 Rotifers 5.1 1.9 204 94 30 Tardigrades 0.5 2.1 0.3 2.1 76
1230 868 16
1.2 16 4.9
182 119 29
Max. number/g dry weight Nematodes 0.5 Rotifers 88 Tardigrades 7.5
5063 2719 31
1.2 30 9.1
5063 4251 2395
Number of samples
6.8 15.6 0.2
6.7 14.8 0.5
(c) Frequency of occurrence (% of all samples) Any animal 88 79 83 Nematodes 14 35 37 Rotifers 70 62 70 Tardigrades 54 41 27
3.3 12 14
35 4251 0.6
153 959 13
1369 279 2395
Figures show water content (a), temperature (b), frequency (c) and abundance (d) of microfauna.
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Sampling, extraction and counting The 59 samples collected in 1996/97 were kept deep-frozen (201C) until extraction in Stockholm several months later. The 214 samples taken in 2001/02 were extracted at the field station Wasa or dried and later extracted in Stockholm. For extraction a wet funnel method was used (Sohlenius, 1979). The volume of material for each extraction was about 3–5 cm3. After extraction, the animals were killed by heat and fixed in TAF (formalin-triethanolamine solution). The total number of animals extracted was counted under a dissecting microscope. The number of animals/ gram dry weight (gdw) extracted material was calculated. Since the number of animals/gdw in samples with organic material (especially moss) differed greatly from that in samples with mineral material, the number of specimens/extraction gives a more comparable indication of abundance. In 1996/97, the samples were taken mostly in places without macro-vegetation. In 2001/02, a higher proportion of the samples was taken in places with organic material or macro-vegetation. Because of this and the differences in handling before extraction, the sampling series are not fully comparable. Detailed analyses of the effects of substrates are thus only made for the 2001/02 samples. For identification, animals were transferred to glycerol according to Seinhorst’s (1959) method. Nematodes and tardigrades were identified to genus or species.
Results Fauna composition at various sites Animals were found in samples from all nunataks except Okkenhaugrusta, Vardeklettane and Baileyranten. On most nunataks rotifers was the most frequent group followed by tardigrades and nematodes (Table 2b). The presence of various nematode and tardigrade taxa on the nunataks differed (Table 3). Thus active populations of nematodes belonging to Chiloplacoides and Eudorylaimus were found only on Schirmacher Oasis. Plectus (probably P. acuminatus) was found on Schirmacher Oasis, Basen, Plogen and occasionally on Fossilryggen and Haldorsentoppen. Panagrolaimus (probably P. magnivulvatus) was found in large numbers on Basen, Haldorsentoppen and Steinnabben in samples taken in the vicinity of bird colonies.
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In both seasons there were quite a lot of occasional records of several nematode species (Table 3). In Table 2a, they are grouped in the category ‘other Nematoda tot’. The genera and species listed in Table 2 are those found regularly in higher numbers and thus considered to represent actively reproducing populations. Among tardigrades, one Macrobiotus species (probably M. blocki) was found on Schirmacher Oasis, Haldorsentoppen and Mora. nryggen. Another Macrobiotus species (probably M. krynauwi) was found on Basen, Fossilryggen and Plogen. In earlier publications (Sohlenius et al., 1995, 1996) M. krynauwi was tentatively named M. furciger. Diphascon chilenense langhovdensis was found in both seasons on Haldorsentoppen but nowhere else. In previous investigations this species was also found on Fossilryggen (Sohlenius et al., 1995, 1996). Hebesuncus (probably H. ryani) was found only on the nunataks in Vestfjella. During both seasons Acutuncus antarcticus ( ¼ Hypsibius antarcticus), was found in the same areas on Basen. In 1996/97, there was an occasional record from Fossilryggen. On Schirmacher Oasis several specimens of A. antarcticus were found in moss.
Frequency and abundance in samples of different textures and vegetation types The distribution of microfauna in samples from different kinds of soils and vegetation types was analysed for the 214 samples extracted in 2001/02. Depending on substrate, 79–100% of these samples contained animals (Table 1c). The frequency of samples with microfauna was generally somewhat lower in inorganic than in organic material. Overall rotifers were found in 155 samples (72% of the samples). They were found in almost equal frequency in inorganic and organic material. Nematodes were found in 94 samples (44%). They occurred much more frequently in samples from moss, Prasiola, organic material and Nostoc than in samples with essentially inorganic material. Tardigrades were found in 102 samples (48%). The frequency of tardigrades was low in plots with Prasiola and in samples with mixed inorganic material. The highest frequency of tardigrades occurred in moss and in gravel. The proportion of samples containing different genera of nematodes and tardigrades varied greatly between substrates. Thus Plectus occurred in high frequency in moss (72% of the samples), but was also present in a low proportion of the samples without macro-vegetation (Fig. 2a). The highest
400
Table 2. Abundance (a), frequency (b) and species richness (c) of microfauna from investigated nunataks Nunatak
All sampling sites
Schir-macher Basen
Year
1996/97
2001/02
2001/02
Fossilryggen
Plogen
Haldorsen toppen
1996/97 2001/02 1996/97 2001/02 2001/02 1996/97
Steinnabben
Mora. n-ryggen
2001/02
1996/97 2001/02 1996/97
F 928 82 F 0.4
F F F F 0.2
F 0.1 0.1 F 0.1
F F 7.4 F F
F 10 0.3 F 2.1
F 1392 F F 0.5
F F F F F
F 244 F F F
F F F F F
Tardigrada Macrobiotus blocki Macrobiotus krynauwi Diphascon chilenense Hebesuncus ryani Acutuncus antarcticus
6.6 1.7 3.7 17 0.2
3.0 60 11 3.9 6.1
12 F F F 53
F 3.4 F F 0.3
F 65 F 3.3 1.6
F 0.7 F 17.3 0.1
F 0.5 F 2.6 F
F 9.1 F 7.9 F
0.7 F 3.7 F F
F F 11 F F
F F F F F
F F F F F
1.0 F F F F
Nematoda Rotatoria Tardigrada
1.9 9.8 5.0
181 119 30
17 25 26
0.1 1.5 1.3
161 118 40
0.2 2.7 9.9
0.1 1.7 1.2
7.4 11 9.8
6.3 15 2.7
1114 680 11
F 100 F
244 53 F
F 8.7 1.0
(b) Occurrence in percent of all samples Nematodes 12 44 Rotifers 44 72 Tardigrades 25 47
62 43 33
8 36 16
47 81 47
25 58 50
17 47 50
22 56 78
22 78 33
71 86 43
F 25 F
50 100 F
F 67 67
(c) Species richness Number of observed taxa 15
8
4
22
10
9
5
12
4
1
2
2
29
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(a) Abundance (number of animals/g dry weight on occurrence) Nematoda Chiloplacoides F 8.7 8.7 F Panagrolaimus 10 947 F F Plectus 0.2 71 31 F Eudorylaimus F 7.3 7.3 F Other Nematoda tot 0.5 2.1 5.7 F
B. Sohlenius et al.
Plogen
Haldorsen toppen
Steinnabben
Mora. n-ryggen
2001/02
1996/97
2001/02
2001/02
1996/97
2001/02
1996/97
2001/02
1996/97
25
145
12
30
9
9
7
4
2
3
F F F F F F F F F 1 2 F F F F 12 F F 1 F F F 5 F F F F F
F F F F F F F F F F F F F F F F F 2 F F F F F F F F F F
3 F 2 2 3 F 2 F 3 3 F 1 7 F F 54 F F F F 5 1 F 1 3 1 1 3
F 1 F F F 1 F F F F F F F 1 1 1 F 2 F F F F F F F F F F
F 3 F F F F F F F F F 1 1 F F 1 F F F 1 F F F F 1 F F F
F F F F F F F F F F F F F F F 2 F F F F F F F F F F F F
F 1 F F F 1 F 1 F F F F 5 1 1 1 1 1 F F F F F F F F F F
F 1 F F F F F F F F F F 4 F F F F F F F F F F F F F F F
F F F F F F F F F F F F F F F F F F F F F F F F F F F
F F F F F F F F F F F F 1 F F F F F F F F F F F F F F F
F F F F F F F F F F F F F F F F F F F F F F F F F F F F
5 F F F 2 F
F 3 F F 1 F
F 34 F 17 21 4
F 5 F 3 1 F
F 4 F 5 F F
F 4 F 4 F 1
1 F 2 F F F
F F 3 F F F
F F F F F F
F F F F F F
2 F F F F F
All sampling sites
Schir-macher
Basen
Year
1996/97
2001/02
2001/02
1996/97
No. of samples
59
214
21
NEMATODA Filenchus Tylenchida indet. Tylenchorhynchus Apratylenchoides Paratylenchus Aphelenchoides Rhabditida indet. Bunonema Acrobeloides Cephalobidae indet. Chiloplacoides Eucephalobus Panagrolaimus Teratocephalus Metateratocephalus Plectus Prismatolaimus Eumonhystera Geomonhystera Tripyla Mesodorylaimus Epidorylaimus Eudorylaimus Microdorylaimus Aporcelaimellus Aporcelaimus Dorylaimida indet. Nematoda indet.
F 2 F F F 2 F 1 F F F F 1 2 2 2 1 5 F F F F F F F F F F
3 4 2 2 3 F 2 F 3 4 2 2 14 F F 69 F F 1 1 5 1 5 1 4 1 1 3
TARDIGRADA Macrobiotus blocki Macrobiotus krynauwi Diphascon chilenense Hebesuncus ryani Acutuncus antarcticus Tardigrada indet.
3 8 2 3 2 F
5 42 3 26 23 5
401
Taxa in bold are assumed to represent actively reproducing populations.
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Fossilryggen
Nunatak
Microfauna in East Antarctica
Table 3. Number of samples in which different taxa of nematodes and tardigrades occurred
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B. Sohlenius et al.
Macrobiotus
Plectus 80
(a)
40
(a)
30
%
%
60 40
20 10
20
0 Gr
Sa
Mi in
Li
Mo
Pr+o
Nos
All
Pr+o
Nos
All
0 Gr
Sa
Mi in
Li
Mo
Pr+o
Nos
All
Hebesuncus
Panagrolaimus
15
(b) %
50 40
%
(b)
20
30
10 5
20
0
10
Gr
Sa
Mi in
Li
Mo
0 Sa
Mi in
Li
Mo
Pr+o
Nos
All
Other nematodes
75
(c)
%
50 25
.
Al ls am pl es
N os to c
rg as
io
la
+o
M os s Pr
Li ch en s
in or g.
Sa nd
M ix ed
G ra ve l
Figure 2. Relative frequency of 2001/02 samples with three categories of nematodes in substrates of different kinds. Gr ¼ Gravel; Sa ¼ sand; Mi in ¼ Mixed inorganic material; Li ¼ lichens; Mo ¼ moss; Prþo ¼ Prasiolaþorþorganic material; Nos ¼ Nostoc; All ¼ All samples.
frequency of Panagrolaimus (47% of the samples) was found in Prasiola and in organic material in the vicinity of bird colonies (Fig. 2b). The species of nematodes found occasionally (other nematodes) were most frequent in samples with mixed inorganic material (Fig. 2c). Among the tardigrades, the relative frequencies of samples with Macrobiotus and Hebesuncus covaried (Figs. 3a and b). These tardigrades were most frequent in samples with sand, lichens and moss. A. antarcticus had a different pattern of variation with the highest frequency of occurrence in samples from wet places or from a pond with blue-green algae (Nostoc) (Fig. 3c). It also occurred abundantly in an area with gravel on Basen and in some moss samples from Schirmacher Oasis. D. chilenense langhovdensis was found in moss and Prasiola (31.3 specimens/ gdw) on Haldorsentoppen. When the occurrence and abundance of different groups and taxa in the samples were compared only one significant correlation was found. There was a correlation between numbers of rotifers and Panagrolaimus (r ¼ þ0:52; po0:05; N ¼ 14). While
es pl am ls
Al
os
to
c
rg la io
N
+o
s
s en ch
or
os
as
0
Li
in ed
M
ix
G
ra
10
nd
ve
l
g.
.
0
20
Sa
%
30
M
40
Acutuncus
(c)
100
Pr
Gr
Figure 3. Relative frequency of 2001/02 samples with tardigrades in substrates of different kinds. Abbreviations as in Fig. 2.
no significant negative correlations were found, there was a tendency of a negative correlation between numbers of Plectus and Macrobiotus, and between numbers of Plectus and rotifers. The mean abundance of microfauna groups in different substrates indicates that nematodes reached their highest abundance in Prasiola and in organic material in the vicinity of bird colonies (Table 1d). In contrast, tardigrades reached their highest abundance in moss. The highest abundance of rotifers was found in mixed inorganic material. The abundance and relative contribution of different taxa varied among substrates (Fig. 4). The proportion of rotifers was the largest in inorganic samples, lichens and Nostoc. In samples with moss and Prasiola, nematodes contributed the largest proportion. Tardigrades had their highest relative abundances in sand, moss and Nostoc.
Numbers of species and abundance in single samples The number of taxa and abundance in each sample was investigated for the 188 samples yielding animals. Sixty-nine samples contained one and 65 samples contained two taxa. A single sample
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403
Figure 4. Relative composition of metazoan microfauna in various substrates.
contained six taxa, which was the highest number found. Four samples contained five taxa; 11 contained four taxa and 39 contained three taxa. The highest number of extracted animals/sample was found in samples containing 2–3 taxa. In four of the 64 samples from moss, no animals were found. Rotifers, nematodes and tardigrades were found in 50, 49 and 38 of the moss samples, respectively. Twenty-four moss samples contained three taxa (Fig. 5) and in these samples the highest number of animals were found. The samples that contained four taxa did not reach as high abundances as those with three taxa (Fig. 5). Among nematodes Plectus dominated, whereas Panagrolaimus was found only in one moss sample from Basen and one from Haldorsentoppen. Among tardigrades, Macrobiotus was found in all moss samples with four or five taxa and often in a relatively high proportion. Macrobiotus never occurred as a single taxon in a moss sample. This genus was found in 24 (38%) of the moss samples with a mean abundance of 111 specimens/gdw on occurrence. Hebsuncus was found in 10 of the moss samples from Basen and Plogen with a mean abundance of 6.2 specimens/gdw. Acutuncus was also found in 10 moss samples with a mean abundance of 13 specimens/gdw. Diphascon was found in two moss samples from Haldorsentoppen with a mean abundance of 0.9 specimens/gdw.
In 24 moss samples with Macrobiotus the mean abundance7s.e. of Plectus was 52718 specimens/ gdw and in 25 samples without Macrobiotus the mean abundance7s.e. of Plectus was 129764 specimens/gdw. This difference is not significant. The mean abundanceþs.e. of rotifers in samples together with Macrobiotus was similar (27712) as in samples without Macrobiotus (2779 specimens/ gdw). In most samples taken in the vicinity of bird colonies, Panagrolaimus and rotifers occurred in high numbers (Fig. 6). Very few specimens of Plectus and tardigrades were found in these samples. Rather few animals were found in most of the 116 samples with inorganic material (Fig. 7). Forty-eight of these samples contained only one taxon and 15 were devoid of animals. The abundance and fauna composition in the samples varied greatly. In a few samples the number of animals were much higher than in the others. This was especially the case with rotifers, which occurred in a very high abundance in one of the samples with three taxa and in one of the samples with two taxa (Fig. 7).
Discussion The general pattern of distribution of the microfauna agrees with earlier studies (Sohlenius et al., 1995, 1996; Petz, 1997). As reported by Petz
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B. Sohlenius et al.
Figure 5. Composition of microfauna in samples from moss. Each bar shows number of animals extracted from one sample. The bars are arranged with decreasing total abundance in each group with the same numbers of taxa. The groups are arranged with decreasing numbers of taxa (no. of taxa). The x-axis gives numbers of taxa in each group.
Figure 6. Composition of microfauna in samples with organic material taken in the vicinity of birds’ colonies. For explanations see Fig. 5.
(1997), rotifers occurred more frequently in the samples than did tardigrades or nematodes. The densities of animals in inorganic soil and moss were
lower than those found by Petz, but in ornithogenic soil the number of nematodes and tardigrades was higher.
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405
Figure 7. Composition of microfauna in samples with inorganic material. For explanations see Fig. 5.
There were great differences in abundance of animals recorded in 1996/97 in comparison with 2001/02, especially on Basen. However, the results from the two seasons are not fully comparable since the samples were taken by different persons and handled in different ways. Despite this, the occurrence of different species of tardigrades on specific nunataks agrees with the results from samplings from previous expeditions (Sohlenius et al., 1995, 1996). The tardigrades Macrobiotus krynauwi and Hebesuncus ryani were originally described from the nunatak Vesleskarvet in an area some 370 km from the nunatak Basen sampled in our investigations (Dastych and Harris, 1994, 1995). The nematodes Eudorylaimus nudicaudatus and Chiloplacoides antarcticus were described from the nunatak group Robertskollen by Heyns (1993, 1994). The importance of macro-vegetation, especially moss, for nematodes and tardigrades was apparent. Especially for Plectus a connection with moss was clear. The moss habitat also favoured the tardigrades Macrobiotus and Hebesuncus. The microclimatic conditions prevailing in the moss rather than the moss itself are of importance. The climate inside the moss isolates the microfauna from very rapid microclimatic changes. The water content was often high in the moss samples (Table 1a), and moisture is probably of decisive importance for
moss growth. Much of the moisture originates from nearby patches of thawing snow and ice. The mean temperature was higher in the samples with macrovegetation than in samples without vegetation. The temperature range at sampling was also much higher in inorganic samples than in samples with macro-vegetation. It was remarkable that the highest numbers of rotifers and nematodes occurred in organic material in the vicinity of bird colonies, especially in the growth of Prasiola. High numbers of Panagrolaimus in ornithogenic soils have been observed previously (Sohlenius, 1988; Sinclair, 2001). The most obvious reason for these high numbers is that this substrate is very energy-rich and has a high content of nitrogen and other nutrients, and certainly a high bacterial activity (Ryan and Watkins, 1989). A high abundance of Panagrolaimus and rotifers associated with penguin rookeries was found by Porazinska et al. (2002b). These authors found a positive correlation between number of Panagrolaimus and substrate carbon and ammonium content. The positive correlation between rotifers and Panagrolaimus in the samples with ornithogentic material suggests that both these taxa are stimulated by the high bacterial production. The low proportion of tardigrades in the ornithogenic soils agrees with observations made by Porazinska et al. (2002b). This could indicate that tardigrades do not
ARTICLE IN PRESS 406
thrive very well in nutrient-rich substrates with a high bacterial activity. In these environments a high content of ammonium and other harmful substances may depress many groups of soil animals. A species, which seemed to be favoured by bird colonies, was the mite Nanorchestes antarcticus (Ryan and Watkins, 1989). Despite the simple classification according to soil textures, there were indications that texture influenced the distribution of the microfauna. For example nematodes lumped together as ‘other Nematoda’ were especially abundant in the clayish samples classified as ‘mixed inorganic’. Among tardigrades. Macrobiotus and Hebesuncus occurred most frequently in sandy samples (Figs. 3a and b). Acutuncus was rather frequent in some places with coarse gravel on the nunatak Basen. The factors influencing these microfaunal distributions may be indirect. The influence of water content and microscopic algae, etc. may be significant. The direct relationship between relative humidity and the abundance of metazoan microfauna in Antarctic terrestrial environments was demonstrated by Kennedy (1993) and the importance of moisture for nematode distribution in Antarctica was noted by Porazinska et al. (2002a). The biotic interactions between various animal species should be revealed in these simple communities (Block, 1994). The food webs are simple. Both dominant nematode genera, Plectus and Panagrolaimus, have frequently been cultured on bacteria (Yeates et al., 1993). However, in some of our specimens greenish material in the intestines indicates that they may feed on microalgae. The feeding habits of tardigrades are less well established. In some specimens of Macrobiotus greenish material in the intestines may indicate herbivory but according to Dastych and Harris (1995) M. krynauwi is probably detrivorous. No information has been found on the feeding habits of M. blocki. Several species of the genus Macrobiotus are documented as predators on nematodes and rotifers (Hallas and Yeates, 1972; Altiero and Rebecchi, 2001). The observation of a tendency of lower number of nematodes (Plectus) in moss samples containing tardigrades (Macrobiotus) could therefore possibly be an effect of predation. However, no influence by Macrobiotus on number of rotifers was seen. Competition for food could be expected to occur in places where very high population densities of microfauna are found. However, populations could be high because of abundant food and a low competition. The high variability in nematode and tardigrade densities and the lack of these organisms in a high
B. Sohlenius et al.
percentage of samples collected from Antarctic localities where they are known to occur, agree with previous observations (Miller et al., 1988; Freckman and Virginia, 1990; Sohlenius et al., 1995, 1996). In both moss and inorganic samples, the variable frequencies and abundances of taxa indicate that the microfauna may be regarded as loosely associated populations rather than as wellorganised communities. This shows similarities with an early stage of a primary succession and it was not possible to predict microfauna composition in a certain sample. Some of the tardigrades are known only from Antarctica. Their distribution within the investigated area indicates that there is a limited dispersal between nunataks, which in turn indicates that they may have remained isolated on the various nunataks for very long periods. A detailed analysis of morphological variability may throw further light on the question as to how isolated the populations are on the various nunataks. Occurrence within the nunataks in different microhabitats indicates, however, an apparent dispersal between microsites within a particular nunatak. The results are, however, not sufficiently clear to rule out a more global, long distance source. The present results support the idea that the tardigrades are survivors from the pre-Pleistocene period (McInnes and Pugh, 1998). Among the nematodes, the Plectus populations could be expected to have a similar power of dispersal as certain tardigrades such as Macrobiotus. A further analysis of morphological variability of the Plectus populations from various nunataks would reveal this. The nematode Panagrolaimus living in association with bird colonies might be dispersed by birds. However, Marshall and Pugh (1996) stated that birdmediated transportation of Panagrolaimus has never been demonstrated. Panagrolaimus is known to be resistant to harsh environmental conditions (Wharton, 2002) and has been recorded in material of birds’ nests in such remote places as the island of . Surtsey (Bostrom, 1988). The findings of nematodes belonging to genera and species common in temperate soils around the world is enigmatic, especially since the food resource some of them generally use (roots of higher plants) does not occur on the nunataks. Their occurrence in the samples might be due to contamination during handling and extraction in the laboratory, although in this investigation special care was taken to avoid contamination. The nematodes of the genera indicated in Table 3 were sometimes found in more than one sample. Similar kinds of observations have been made
ARTICLE IN PRESS Microfauna in East Antarctica
previously. Thus, plant feeding nematodes belonging to the genera Helicotylenchus and Rotylenchus have been reported from continental Antarctica by Yeates (1979) and Van den Berg and Harris (1996). Our records of Apratylenchoides, Tylenchorhynchus and Paratylenchus are new for continental Antarctica and will be presented in a separate paper (Ryss pers. comm.). We found one juvenile of Geomonhystera on Schirmacher Oasis. Several specimens of Geomonhystera villosa were reported from the McMurdo Sound Region of continental Antarctica by Timm (1971) and Wharton and Brown (1989), but these populations together with other material have recently been described by Andra! ssy (1998) as Geomonhystera antarcticola. Several of the nematode records in the present investigation are rather occasional, often with a single specimen in one sample. This indicates that these animals are not likely to be members of actively growing populations, but rather occasional long-distance dispersers, with no or only a low possibility of reproducing in this habitat. Some of the specimens found appeared to be in a poor or starving condition, which further indicates that they may have been occasionally introduced into the area without being able to reproduce. Due to the cold and often very dry conditions it could be expected that accidental dispersers may persist for very long periods. Another explanation to the presence of unexpected nematode species could be that they may have been introduced as contaminations on boots and other equipment by the activities of the Antarctic expeditions. This is indicated by the fact that these nematodes were found in places on Basen where people walk around and this was particularly evident in samples taken around the station Wasa.
Conclusions The occurrence of apparently habitable places without microfauna and the very variable abundances indicated a low probability of successful invasion of such isolated outcrops of rock plus vegetation in the polar ice sheet. This is probably due to a combination of long distances from potential source populations and the very isolated position of habitable patches. The area appears to be similar to an early phase of colonisation. The dynamics of habitable places and their microfauna populations are probably rather slow because of the cold climatic conditions.
407
Acknowledgements We are grateful to the Swedish Polar Research Secretariat for providing transport and facilities for . K. Ingemar Jonsson, who conducted the field sampling in Antarctica in 2001/02 and for Cecilia Eriksson, who made the sampling in 1996/97. Kent Larsson is thanked for providing the map and Ingegerd Sohlenius for technical assistance. Valuable comments on the manuscript were given by an anonymous referee.
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