Polar Biology

, Volume 28, Issue 6, pp 439–448

The geographic distribution of metazoan microfauna on East Antarctic nunataks

Authors

    • Department of Invertebrate ZoologySwedish Museum of Natural History
  • Sven Boström
    • Department of Invertebrate ZoologySwedish Museum of Natural History
Original Paper

DOI: 10.1007/s00300-004-0708-z

Cite this article as:
Sohlenius, B. & Boström, S. Polar Biol (2005) 28: 439. doi:10.1007/s00300-004-0708-z

Abstract

The abundance and distribution of nematodes, rotifers and tardigrades in samples from nunataks in continental Antarctica were investigated during four Antarctic expeditions in the austral summers of 1991/92, 1993/94, 1996/97 and 2001/02. Altogether 368 samples were collected from 14 nunataks and one oasis in East Antarctica. Nematodes were found in 35%, rotifers in 67% and tardigrades in 40% of all samples. Fifty-four microfaunal taxa were identified. Of these, 27 were nematodes, 8 tardigrades and 19 rotifers. The size and geographic location of the nunatak and oasis influenced the abundance and taxonomic composition of the microfauna. The highest abundance and diversity of nematodes were found on large nunataks close to the coast. Nematodes were not found on small inland nunataks. Very high population densities of tardigrades and rotifers were found on two small and isolated nunataks. No microfauna was found on the two southernmost nunataks (Okkenhaugrusta and Vardeklettane), or on the smallest one (Utsikta). The Sørensen’s Quotient of Similarity was generally low, especially between faunas on nunataks in different mountain ridges. The results indicate rather limited rates of dispersal and colonization between nunataks.

Introduction

In continental Antarctica, the snow- and ice-free areas constitute about 2% of the entire area (Walton 1990; Block 1994). These exposed areas are to a large extent made up of coastal regions (so-called oases), inland nunataks (mountain peaks penetrating the ice sheet), coastal and inland dry valleys. The snow and ice-free areas are widely dispersed, have surface areas of different size and ecologically can be considered habitable islands surrounded by large areas of uninhabitable environment (ice-fields). On the nunataks, scattered populations of mites, springtails and microscopic metazoans occur (Sømme 1986; Ryan et al. 1989; Sohlenius et al. 1995, 1996; Marshall and Pugh 1996; Thor 1996; Petz 1997). The microscopic metazoans belong to the hydrophilic microfauna, which is composed of nematodes, rotifers and tardigrades, here referred to as ‘microfauna’. They depend on water or water films for an active life. The microfaunal species found in continental Antarctica have an ability to survive desiccation and may survive dry periods in a cryptobiotic state (Powers et al. 1998; Treonis et al. 2000; Wharton 2002). In this state, they are very resistant to temperature extremes (Sømme and Meier 1995). It is also thought that microscopic animals can be dispersed over long distances in a dry cryptobiotic state (Fenchel 1993). Besides low temperature, shortage of free water is considered a main factor restricting life on nunataks (Ryan et al. 1989; Kennedy 1993). Other factors of great importance for dispersal and growth of plants and animals on the nunataks are birds and their waste products (Ryan and Watkins 1989).

The climatic conditions are increasingly severe towards the geographic South Pole. This climatic gradient may also influence the richness of animal species. For example, Smith (1992) found a decreasing number of testate rhizopod protozoan species towards the South Pole. Previous studies indicated that different species of microscopic animals occur on different nunataks or groups of nunataks (Sohlenius et al. 1996). This was interpreted as an indication of a high degree of geographic isolation (Sohlenius et al. 2004).

The dispersal ability of different types of organisms found on Antarctica has been much discussed (Virginia and Wall 1999; Wall and Virginia 1999). Tardigrades and nematodes are considered to have a cosmopolitan distribution (Fenchel 1993). This view has, however, been questioned for tardigrades since it was determined that some ‘cosmopolitan’ tardigrade species in reality are made up by several species, each with a distinct geographical distribution (Pilato and Binda 2001). McInnes and Pugh (1998) are of the opinion that tardigrades found on Antarctic nunataks have a low ability of long distance dispersal, which is opposed to the view held by Miller and Heatwole (1995). Similarly, DNA analyses of the nematode Scottnema lindsayae from various locations in the Dry Valleys indicate that nematode populations also may have a low dispersal ability (Virginia and Wall 1999; Courtright et al. 2000). Records of nematode species common to other parts of the globe may still indicate a global dispersal of nematodes among localities with appropriate conditions (Sohlenius et al. 2004).

The microfauna on Antarctic nunataks was investigated during four Swedish Antarctic expeditions (SWEDARP 1991/92, 1993/94, 1996/97 and 2001/02). The original results have been published previously (Sohlenius et al. 1995, 1996, 2004). We predicted that species richness will decrease with decreasing size, increasing isolation, increasing latitude and altitude of the nunatak. The aim of the present study is to synthesize material from all expeditions to analyse patterns of microfaunal distribution.

Materials and methods

Site descriptions

Samples of soil, mosses, lichens or algae were collected in 15 areas, viz. one oasis and 14 nunataks (Fig. 1, Table 2). The different nunataks were visited on one or several occasions during the four Swedish Antarctic expeditions undertaken in the austral summers of 1991/92 (samples collected by Göran Thor), 1993/94, 1996/97 (samples collected by Cecilia Eriksson), and 2001/02 (samples collected by K. Ingemar Jönsson). Various numbers of samples were collected on the nunataks. Several of the nunataks visited were rather recently explored. The information about vegetation, size and soil conditions are in many cases limited. Göran Thor, who investigated the macroflora on the nunataks, found one species of moss, 23 species of lichens and one species of macroalgae in the samples extracted for microfauna (G. Thor, personal communication). Details of sample characteristics and local conditions are found in previous publications (Sohlenius et al. 1995, 1996, 2004).
Fig. 1

Map of the nunatak areas sampled in East Antarctica. The various nunataks in the Heimefrontfjella mountain ridge are not indicated separately. They are all situated close to Haldorsentoppen with the Swedish station Svea. The distant Schirmacher Oasis is situated outside this map

Schirmacher Oasis (70°46′S/11°48′E, altitude 7–120 m, size 19.5×3.4 km) is remote from the other nunataks, (situated 900 km NE of Basen), closer to the coast and at a much lower altitude. The area is classified rather as an oasis than as a nunatak, but for simplicity it is here classified as a nunatak. It has a milder climate and is larger than the other investigated nunataks. The vegetation of moss is in some places extensive (Bormann and Binda 1994). Twenty-one samples were collected in 2001/02 close to the Russian station Novolazarevskaya.

Vestfjella; Basen (73°02′S/13°24′W, altitude 250–584 m, size 5×3 km) with the Swedish station ‘Wasa’, is situated 110 km from the ice-shelf border. It has a relatively isolated position. The closest nunataks are Plogen and Fossilryggen. The bedrock is basalt. Moss-cushions occur in restricted areas, especially close to snow- and ice-melting zones. Colonies of snow petrels (Pagodroma nivea) are present. The area was sampled during all four expeditions (1991/92, 93/94, 96/97 and 2001/02) and 15, 55, 25 and 145 samples were collected respectively. Twelve species of lichens, one of moss and one of macroalgae were recorded in the samples.

Vestfjella; Plogen (73°13′S/13°50′W, altitude 564–898 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. Nine samples were collected in 2001/02 and in these, lichens and moss were found.

Vestfjella; Dagvola (73°21.6′S/14°06.1′W, altitude 1130 m, area 0.07 km2) is situated 17 km SW of Plogen. The closest nunatak is Olanuten, situated 3.6 km SW of Dagvola. One sample was collected in 1993/94. Three species of lichens and one of moss were recorded in the sample.

Vestfjella; Fossilryggen (73°23′S/13°02′W, altitude 600–731 m, 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. The nunatak was sampled on all four expeditions, when 4, 7, 12 and 30 samples were collected, respectively. Ten species of lichens were recorded in the samples.

Vestfjella; Olanuten (73°23.2′S/14°09.1′W, altitude 1000 m, area 0.06 km2) is situated 3.6 km SW of Dagvola and 21 km SW of Plogen. One sample was collected in 1993/94. Two species of lichens were recorded in the sample.

Vestfjella; Utsikta (73°33.9′S/14°33.8′W, altitude 970 m, area 0.02 km2) is situated 24 km SW of Olanuten. The closest nunatak is Hildringia, situated 13 km S of Utsikta. One sample was collected in 1993/94. Two species of lichens were recorded in the sample.

Mannefallknausane; Baileyranten (74°37′S/14°39′W, altitude 1141 m, area 0.4 km2) is situated 155 km SSW of Basen and 88 km W of Haldorsentoppen. One sample was collected in 1993/94 and one in 1996/97. Four species of lichens were recorded in the samples.

Heimefrontfjella; Steinnabben (74°33′S/11°15′W, altitude 1200–1300 m, size 500×250 m) has a bedrock consisting most likely of augen gneiss. There are colonies of snow petrels. Three samples were collected in 1991/92, four in 1996/97 and two in 2001/02. Three species of lichens, one of moss and one of macroalgae were recorded in the samples.

Heimefrontfjella; Haldorsentoppen (74°34′S/11°13′W, altitude 1245 m, area 0.8 km2) 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. There are colonies of snow petrels. Four samples were collected in 1991/92, nine in 1996/97 and seven in 2001/02. Eight species of lichens and one of moss were recorded in the samples.

Heimefrontfjella; Moränryggen (74°34′S/11°13′W, altitude 1500 m, area 0.8 km2) is a small nunatak lying adjacent and parallel to Haldorsentoppen. Three samples were collected in 1996/97. One species of lichen was recorded in the samples.

Heimefrontfjella; Engenhovet (74°34′S/11°01′W, altitude 1757 m, area 0.7 km2). The bedrock is most likely augen gneiss. One sample was collected in 1991/92. One species of lichen was recorded in the sample.

Heimefrontfjella; Wrighthamaren (74°36′S/11°02′W, altitude 2223 m, area 0.1 km2) has a bedrock of augen gneiss. Two samples were collected in 1991/92. Four species of lichens and one of moss were recorded in the samples.

Heimefrontfjella; Okkenhaugrusta (74°43′S/11°20′W, altitude 1290 m). Three samples were collected in 1996/97. Five species of lichens were recorded in the samples.

Heimefrontfjella; Vardeklettane(75°S/13°W, altitude 1590 m). Two samples were collected in 1996/97. Two species of lichens were recorded in the samples.

Methods of analysis

The frequency of occurrence and abundance of microfauna and number of taxa were compared among nunataks in relation to the distance to other nunataks, size of the nunatak, its latitudinal position and altitude. To compare the similarity of the fauna from different nunataks, the Sørensen’s Quotient of Similarity, Q/S=2j×100/(a+b), was used (Wallwork 1970); j is the number of species common to both samples, a is the number of species in one site, and b is the number of species in the other. To detect co-variations, linear correlation analysis was used.

Sampling, extraction and counting

For extraction, a wet funnel method was used (Sohlenius 1979). The volume of material (soil, mosses, lichens or algae) for each extraction was about 3–5 cm3. The microfauna was killed by heat and fixed in TAF (formalin-triethanolamine solution). The total number of nematodes, tardigrades and rotifers per extraction was counted under a dissecting microscope. For species identification, the microfauna was transferred to glycerine according to Seinhorst’s (1959) method. The number of microfauna per gram dry weight (gdw) extracted material was calculated. Specimens of nematodes and tardigrades were identified to genus or species. The species composition of rotifers was examined by Angelica Hirschfelder in samples from six of the nunataks (Sohlenius et al. 1995, 1996).

Slides of tardigrades and nematodes are stored at the Swedish Museum of Natural History.

Results

The frequency and abundance of microfauna per gram dry weight extracted material (soil, moss, lichens or algae) on occurrence and the number of taxa of the three microfaunal groups are shown in Tables 1 and 2. Rotifers, the most frequent group, were found in 67% of all samples (on 12 nunataks). Tardigrades were found in 40% of all samples (on 11 nunataks) and nematodes in 35% of all samples (on 6 nunataks). Plectus, the most frequent taxon, occurred in 24% of all samples, followed by M. krynauwi, which occurred in 20% of all samples. Panagrolaimus had the highest mean abundance, 392 specimens/gdw on occurrence, followed by Plectus with 63 specimens/gdw on occurrence.
Table 1

Frequency and abundance of microfauna in 368 samples of soil, mosses, lichens or algae from 15 nunataks in East Antarctica

 

Found on number of nunataks

Occurrence in number of samples

Occurrence in % of samples

Mean number/gram dry material on occurrence

Mean number/gram dry material in all 368 samples

Maximal number/gram dry material

Nematoda

Panagrolaimus

4

18

4.9

392

19

594

Plectus

5

87

24

63

15

69

Other nematodes

4

34

9.2

1.7

0.2

5.7

Tardigrada

Macrobiotus blocki

4

11

3.0

7.9

0.2

12

Macrobiotus krynauwi

4

72

20

37

7.2

55

Diphascon langhovdense

4

9

2.4

24

0.6

36

Hebesuncus ryani

8

41

11

19

2.1

359

Acutuncus antarcticus

3

31

8.4

5.0

0.4

53

Other tardigrades

6

12

3.0

1.4

0.04

3.6

Nematoda

6

128

35

98

34

594

Rotatoria

12

245

67

74

49

753

Tardigrada

11

148

40

30

12

359

Table 2

Latitude, altitude and size of nunataks in East Antarctica. Number of samples collected, mean numbers of microfauna and number of taxa of microfauna and macroflora (mosses, lichens and algae). The nunataks are arranged according to latitude from north to south. nd Not determined

Nunatak

Latitude (°South)

Maximal altitude (m above sea level)

Size (km2)

Number of samples collected

Mean number of microfauna/gram dry material on occurrence

Number of taxa

Nematoda

Tardigrada

Rotatoria

Nematoda

Tardigrada

Rotatoria

Macroflora

Schirmacher Oasis

70.8

120

66

21

32

26

25

5

2

nd

nd

Vestfjella

           

Basen

73.0

584

15

240

121

37

81

20

5

11

14

Plogen

73.2

898

6

9

7.4

9.8

11

1

2

nd

nd

Dagvola

73.4

1130

0.07

1

0

69

461

0

2

7

4

Fossilryggen

73.4

730

1.3

53

0.1

6.1

13

10

4

7

10

Olanuten

73.4

1000

0.06

1

0

359

753

0

1

3

2

Utsikta

73.6

970

0.02

1

0

0

0

0

0

0

2

Mannefallknausane

           

Baileyranten

74.6

1141

0.4

2

0

10

19

0

2

nd

4

Heimefro ntfjella

           

Steinnabben

74.6

1300

0.1

9

112

0

174

1

0

6

5

Haldorsentoppen

74.6

1245

0.8

20

22

32

62

9

2

3

9

Moränryggen

74.6

1500

0.8

3

0

1

8.7

0

1

nd

1

Engenhovet

74.6

1757

0.7

1

0

13

2

0

4

nd

1

Wrighthamaren

74.6

2223

0.1

2

0

8.5

35

0

4

nd

5

Okkenhaugrusta

74.7

1290

Nd

3

0

0

0

0

0

0

5

Vardeklettane

75.0

1590

Nd

2

0

0

0

0

0

0

2

The abundance and diversity of nematodes tended to decrease with increasing latitude. The greatest abundances of nematodes were found on Basen and Steinnabben (Table 2). Most of the inland nunataks had no nematodes. The great numbers of nematodes on the high peaks Steinnabben and Haldorsentoppen occurred in samples collected in the vicinity of colonies of snow-petrels (Pagodroma nivea). No animals were found on the very small and isolated nunatak Utsikta. With the exception of the two southernmost nunataks, Okkenhaugrusta and Vardeklettane where no animals were found, there were no clear effects of latitude on the diversity of tardigrades and rotifers.

There is, on the whole, a co-variation between altitude and latitude of the nunataks (Table 2). The highest abundances of rotifers and tardigrades were found on some of the smallest nunataks, Dagvola and Olanuten, in the middle positions of the latitude and altitude gradient. The abundance of rotifers tended to increase with decreasing size of the nunataks of an area of 0.7 km2 and smaller. There was generally a significant positive correlation between abundance of rotifers and tardigrades (P<0.01). One exception was Steinnabben, where large populations of rotifers were found, but no tardigrades. Rotifers and tardigrades were also found abundantly on the very high peaks, Engenhovet and Wrighthamaren, and on the rather isolated nunatak Baileyranten (Table 2).

Of the 54 microfaunal taxa identified, 27 were nematodes, 8 tardigrades and 19 rotifers (Table 3). Most nematode taxa and three tardigrade taxa were found only occasionally. These are grouped into the categories ‘other nematodes’ and ‘other tardigrades’ in Tables 1 and 4. The greatest number of microfaunal taxa (36) was found on Basen. Many taxa (21) were also found on Fossilryggen and rather high numbers of nematode taxa were found on Schirmacher Oasis and Haldorsentoppen (5 and 9, respectively). One nematode species each was found on Plogen and Steinnabben. Several species of tardigrades (4) were found on Engenhovet and Fossilryggen. The greatest number of rotifer species (11) was identified on Basen. Several rotifer taxa were also found on the other nunataks studied, e.g. six species on Steinnabben and seven on Dagvola and Fossilryggen.
Table 3

Occurrence of nematodes, tardigrades and rotifers on nunataks in East Antarctica where animals were found. nd Not determined; - = not found; x = found in one season; xx, xxx, xxxx = found in 2, 3, 4 seasons

Nunatak

Schir-

Basen

Plogen

Dagvola

Fossil-

Ola-

Bailey-

Stein-

Haldorsen-

Morän-

Engen-

Wright-

 

Macher

 

 

 

ryggen

nuten

ranten

nabben

toppen

ryggen

hovet

hamaren

No. of expeditions

1

4

1

1

4

1

2

2

3

1

1

1

Nematoda

Filenchus

x

x

Tylenchida indet.

xx

xx

Tylenchorhynchus

x

Apratylenchoides

x

Paratylenchus

x

Aphelenchoides

x

x

x

Rhabditida indet.

xx

Bunonema

x

Acrobeloides

x

Cephalobidae indet.

x

x

Chiloplacoides

x

Eucephalobus

x

x

Panagrolaimus

xxx

x

x

xx

Metateratocephalus

x

x

Teratocephalus

x

x

Eumonhystera

xx

xx

x

Geomonhystera

x

Chiloplectus

x

Plectus

x

xxx

x

x

x

Prismatolaimus

xx

x

Mesodorylaimus

x

Epidorylaimus

x

Eudorylaimus

x

Microdorylaimus

x

Aporcelaimellus

x

x

Dorylaimida indet.

x

Nematoda indet.

x

Tardigrada

Echiniscus

x

x

Macrobiotus blocki

x

xx

x

x

x

M. hufelandi

x

M. krynauwi

xxxx

x

x

xxxx

Diphascon langhovdense

x

xxx

 

x

x

Hebesuncus ryani

xx

x

x

xxx

x

x

x

x

Acutuncus antarcticus

x

xxxx

x

Milnesium tardigradum

x

x

Rotatoria

Adineta barbata

nd

nd

x

nd

nd

nd

nd

A. gracilis

nd

x

nd

x

x

nd

x

nd

nd

nd

A. steineri

nd

x

nd

x

x

nd

x

nd

nd

nd

A. vaga

nd

xx

nd

x

x

nd

nd

nd

nd

Habrotrocha constricta

nd

xx

nd

x

x

nd

nd

nd

nd

H.elusa

nd

x

nd

x

nd

nd

nd

nd

H. tridens

nd

xx

nd

nd

nd

nd

nd

Habrotrocha

nd

x

nd

nd

x

nd

nd

nd

Otostephanos torquatus

nd

x

nd

nd

nd

nd

nd

Macrotrachela ambigua

nd

nd

x

x

nd

nd

nd

nd

Ma. cf. Ligulata

nd

nd

x

nd

nd

nd

nd

Ma. Habita

nd

x

nd

nd

x

x

nd

nd

nd

Ma. Insolita

nd

x

nd

nd

x

nd

nd

nd

Ma. Nixa

nd

nd

x

nd

nd

nd

nd

Ma. Libera

nd

nd

nd

x

nd

nd

nd

Ma. Timida

nd

nd

nd

x

nd

nd

nd

Mniobia symbiotica

nd

nd

nd

x

nd

nd

nd

Mniobia sp. Nov.

nd

nd

x

nd

nd

nd

nd

Mniobia

nd

x

nd

x

xx

nd

nd

nd

nd

Table 4

Distribution and population densities of nematodes and tardigrades on nunataks in East Antarctica. The figures show frequency of occurrence of taxa in samples (%) and population density as number per gram dry material on occurrence (No/gdw)

Nunatak

Panagrolaimus

Plectus

Other nematodes

M. blocki

M. krynauwi

D. langhovdense

H. ryani

A. antarcticus

Other tardigrades

%

No/gdw

%

No/gdw

%

No/gdw

%

No/gdw

%

No/gdw

%

No/gdw

%

No/gdw

%

No/gdw

%

No/gdw

Schirmacher Oasis

38

43

38

5.7

29

12

10

53

Vestfjella

                  

Basen

5

594

29

69

7

0.5

20

55

8

7.8

12

1.7

3

1.1

Plogen

22

7.4

44

9.1

44

7.9

11

0.04

Dagvola

100

3.6

100

65

Fossilryggen

2

0.1

4

0.1

4

0.1

38

0.9

2

0.1

26

11

2

0.1

2

0.1

Olanuten

100

359

Utsikta

Mannefallknausane

                  

Baileyranten

50

6.2

50

3.5

Heimefrontfjella

                  

Steinnabben

44

113

Haldorsentoppen

20

32

5

0.3

5

2.1

10

2.4

30

36

Moränryggen

33

1.0

Engenhovet

100

2.0

100

1.0

100

8.0

100

2.0

Wrighthamaren

50

5.0

50

2.0

50

8.0

50

3.0

Okkenhaugrusta

Vardeklettane

There was a significant positive correlation between the number of samples and number of nematode taxa. The number of tardigrade taxa was not correlated with the number of samples. The size of the nunatak and the number of taxa recorded tended to be positively correlated, which was particularly evident among the nematodes. For the rotifers, on the other hand, this correlation tended to be negative.

The distribution and population densities of the most abundant taxa of nematodes and tardigrades are indicated in Table 4. All these taxa had specific patterns of distribution on the nunataks. Thus, Panagrolaimus occurred abundantly in samples from the vicinity of bird colonies on the nunataks Basen, Steinnabben and Haldorsentoppen. The other common nematode, Plectus, was sometimes found in high abundances in moss samples on the nunataks Schirmacher Oasis, Basen and Plogen and in small numbers in one sample without moss from Haldorsentoppen.

The most frequent and abundant tardigrade species, Hebesuncus ryani, was found in high abundance on Olanuten (359 specimens/gdw) and on Dagvola (65 specimens /gdw) (Table 4). Hebesuncus ryani was found in all groups of nunataks except Schirmacher Oasis. The distribution patterns of the two Macrobiotus species differed. Thus, M. krynauwi was found on four nunataks in Vestfjella (Basen, Plogen, Dagvola and Fossilryggen), while M. blocki was found on four nunataks in Heimefrontfjella (Haldorsentoppen, Moränryggen, Engenhovet and Wrighthamaren) and on Schirmacher Oasis. Diphascon langhovdense was found frequently and abundantly in Heimefrontfjella on Haldorsentoppen, Engenhovet and Wrighthamaren and occasionally recorded on Fossilryggen. Acutuncus antarcticus was found on Schirmacher Oasis, Basen and occasionally on Fossilryggen. There were some very occasional findings of other tardigrade species. Thus, a few specimens of Echiniscus were found on Basen and Wrighthamaren and one specimen of Macrobiotus hufelandi was found on Basen. A few specimens of Milnesium tardigradum were found in samples from Engenhovet and Baileyranten.

The composition of the microfauna based on the mean number of animals in all samples from each nunatak is indicated in Fig. 2. The relative abundance of nematodes was rather high (40–50%) in samples from the northernmost locations (Schirmacher Oasis and Basen), where Plectus was abundant. Also on Steinnabben the relative abundance of nematodes, in this case Panagrolaimus, was high. On the nunataks in the higher latitudes, the relative abundance of rotifers was generally the highest, up to 95% of the microfauna. The relative abundance of tardigrades did not change with latitude or size of the nunatak, but the composition of tardigrade taxa varied among nunataks.
Fig. 2

Relative proportions of microfauna taxa on nunataks in East Antarctica. Ba Basen, Bai Baileyranten, Da Dagvola, En Engenhovet, Fo Fossilryggen, Ha Haldorsentoppen, Mo Moränryggen, Ok Okkenhaugrusta, Ol Olanuten, Pl Plogen, Sch Schirmacher Oasis, St Steinnabben, Ut Utsikta, Va Vardeklettane, Wr Wrighthamaren

The Sørensen’s Quotient of Similarity (Q/S) in species composition of the microfauna among nunataks was generally very low (Fig. 3). The low number of taxa on some nunataks contributed to this situation. There were some clear similarities and dissimilarities. Thus, the highest similarities of microfauna (67–80%) were found between Dagvola and Plogen; between Dagvola and Olanuten; between Baileyranten and Olanuten; and between Engenhovet and Wrighthamaren. The Q/S was also high between the microfauna on the following nunataks: Basen and Fossilryggen; Fossilryggen and Haldorsentoppen. The similarities were low between the rather species-rich Schirmacher Oasis and all the other nunataks.
Fig. 3

Comparison of the Sørensen’s Quotient of Similarity (Q/S) between the microfauna groups nematodes and tardigrades (a) and rotifers (b) found on different nunataks. Increasing values (up to 100) indicate increasing similarity between faunas on nunataks

Discussion

There is obviously a low similarity in species composition between the nunataks. One reason for this is the very depauperate fauna on some small nunataks, where in the most extreme cases, no or only a single species belonging to the metazoan microfauna was found. A comparison is more relevant among nunataks where many species were found. The low similarities in species composition among nunataks can also be interpreted as a very low dispersal incidence and/or a low probability of establishment of animal propagules (e.g. cryptobiotic microfauna, and eggs of nematodes and tardigrades).

When combining all taxa of nematodes and tardigrades, the effect of the distance between the nunataks on Sørensen’s Q/S was quite evident. Thus, there was a low value of Sørensen’s Q/S between the microfauna on Schirmacher Oasis and the other nunataks, which could be attributed to the very long distance (900 km) between this nunatak and the other nunataks. There were also rather low similarities between the microfauna on the more distant nunataks in Heimefrontfjella and those in Vestfjella. The high similarities between the microfauna on Plogen, Dagvola and Olanuten seem logical since they are situated rather close to each other in the Vestfjella area. Between Basen and Fossilryggen, the similarity was also comparatively high (51%). The high similarity between the microfauna on Fossilryggen and Haldorsentoppen (64%) is unexpected because of the long distance between these nunataks (130 km). Moreover, they are situated in different mountain ridges. Human activity might be one cause of the high similarity since people moving from Basen to Haldorsentoppen generally visit Fossilryggen en route and may passively transfer microscopic animals. The influence of people on the dispersal of microscopic Antarctic organisms has been pointed out by Kappen (1993) and Kennedy (1995).

Data for rotifer similarities were only obtained by comparing six nunataks. In spite of this, the variation of Sørensen’s Q/S for the rotifer fauna had similarities to the variation of the quotients for the combined fauna of tardigrades and nematodes. Thus, the largest similarities for both groups of microfauna were found among the nunataks Basen, Fossilryggen, Olanuten and Dagvola. Also, in quite another organism group, the lichens found in our samples, the highest similarities were found between Basen and Fossilryggen, between Dagvola and Olanuten and between Haldorsentoppen and Fossilryggen.

The differences in overall faunal similarity among mountain ridges are to some degree caused by the distribution of tardigrade species. In this group, different species were found in different regions. Macrobiotus krynauwi, originally described from Vesleskarvet (Steele et al. 1994) about 370 km north east of Basen, was found on four closely located nunataks in Vestfjella. The other Macrobiotus species, M. blocki, originally described from Enderby Land (Dastych 1984) was found in a restricted area on four nunataks in Heimefrontfjella. Another population of Macrobiotus similar to, and also classified as, M. blocki was found in the distant Schirmacher Oasis. A closer examination will reveal whether any taxonomic differences among these M. blocki populations can be detected. Acutuncus antarcticus and Diphascon langhovdense also had restricted distributions within the investigated area. In contrast, Hebesunchus ryani had a wide distribution, which may indicate a good ability of dispersal among nunataks. The very high population densities of H. ryani on the small nunataks, Dagvola and Olanuten (Table 4), can be related to its wide distribution and indicate the occurrence of vital source populations, which would increase the ability of spreading propagules over the area as postulated by Walton (1990). The differences in distribution of tardigrade species are probably due to historical circumstances (random dispersal etc.) rather than to differences in habitat requirements.

Due to increasing altitude and decreasing insolation, the climatic conditions will be more severe with increasing latitude (Kennedy 1995). This might be expected to have a detrimental effect on species diversity. This was clearly shown by the nematodes, which did not occur at all on most inland (southern) nunataks. However, no clear effect of latitude could be detected on the distribution of tardigrades and rotifers. The depauperate nematode and protozoan faunas with increasing latitude in Antarctica have been mentioned previously (Block 1984; Smith 1992; Kennedy 1993).

The patterns of latitudinal distribution could indicate differences in sensitivity to low temperatures among groups of the microfauna. The restricted distribution of nematodes indicates that they are more susceptible to low temperatures than tardigrades and rotifers. Also the high abundance of rotifers on more southerly situated high altitude nunataks suggests that this group is more resistant to harsh environmental conditions than nematodes and tardigrades. The effects on the nematodes belonging to Plectus and Panagrolaimus could be indirect since they appear dependent on the distribution of moss and bird colonies, which are influenced by climatic conditions, structure of the nunatak and distance from the coast (Kennedy 1995). These factors influenced nematode distribution very much. The influence of ornithogenic products on life on nunataks has been described by Ryan and Watkins (1989).

A positive relation between number of species and nunatak size was evident among nematodes. Such a relation was less pronounced among tardigrades and least evident among rotifers. The number of species of lichens, mosses and macroalgae decreased with decreasing size of the nunatak. Thus, in the samples extracted for microfauna, 14 species of macroflora were recorded on the largest nunatak, Basen, and two on the smallest nunatak, Utsikta.

A source of bias is the uneven number of samples extracted for microfauna, varying from 240 samples on Basen to only one on some of the smaller nunataks. The high numbers of rotifers and tardigrades on the small nunataks, Olanuten and Dagvola, are interesting. One reason could be that the degree of predation and competition is lower here than on the larger nunataks.

The long-term histories of the populations are quite important for the understanding of the current patterns of microfaunal distribution. The scattered distribution of taxa on various nunataks may indicate a poor dispersal of propagules and the low quality of soil habitats for populations to become established among nunataks in continental Antarctica. This indicates that many species might be survivors from a warmer pre-glaciation period, which is also indicated by the occurrence of apparently endemic species of nematodes and tardigrades. All microarthropods found on continental Antarctica are classified as endemic species (Block 1984; Sømme 1986). Some species of nematodes and tardigrades have a very restricted distribution, while other species may have even a global distribution, such as Plectus acuminatus and Milnesium tardigradum. A closer morphological or genetic examination would most likely reveal differences between local populations (Pilato and Binda 2001). The two testacean rhizopods recorded from Vestfjella by Smith (1992) are classified as cosmopolitan ubiquitous species. Many of the species of lichens and the two rhizopod species are bipolar or ubiquitous in polar and alpine areas. Similar to microscopic animals, these lichens could be long-distance dispersers. If they are survivors on Antarctic nunataks, they must have remained unchanged for very long periods. Spores may even survive long periods in a frozen state in ice. The similarity between lichens found on Antarctic nunataks and those found in other parts on the globe can be related to their very slow growth rates, which are expected on the nunataks due to the low temperatures (Kappen 1993).

Small organisms can be dispersed by means of winds, birds or human movement. If the wind conditions are important for dispersal, there should be similarities in the patterns of distribution among various kinds of organisms. To check this, the patterns of distribution between microfauna and lichens were compared. The latter are known to be wind dispersed. The wind direction is generally from northeast in the area (Walton 1984). Very high wind speeds (up to 50 m/s) have sometimes been recorded during the winter. As discussed previously, there were some similarities between the results regarding nematodes, rotifers, tardigrades and lichens. The results do not clearly indicate that the organisms are dispersed in a southwesterly direction as would be expected from the prevalent wind conditions. The experimental studies by Telenius (2003) indicate a very low rate of spore dispersal by wind in the area.

It is difficult to know how many microfaunal species actually occurred in the area. As is typical for extreme environments the fauna is very patchily distributed. There are apparently habitable patches where no animals are found (Wall and Virginia 1999). Especially the nematodes are very aggregated and often found in small habitable patches, which makes the probability of detection in the present kind of investigations rather small. Because of the small soil volume samples and the aggregated patterns of distribution, it is probable that there are several nematode taxa which have not been detected so far. The more widely distributed rotifers and tardigrades occurred more frequently in the samples and there was no clear relation between the number of samples collected and the number of taxa found. It appears that some species have a very restricted local distribution also within a specific nunatak.

All the occasional findings are enigmatic and it could be discussed whether these specimens were contaminations during the extractions in Sweden. However, great care was taken to avoid such contamination and in the 2001/02 expedition, the majority of the samples were extracted in Antarctica (Sohlenius et al. 2004). The more widely distributed species forming active populations in the investigated area have probably been detected in this study, but the occasional findings indicate that more species could be detected with an enlarged sampling programme.

Acknowledgements

We are grateful to the Swedish Polar Research Secretariat for providing transport and facilities for K. Ingemar Jönsson, who conducted the field sampling in Antarctica in 2001/02, to Cecilia Eriksson, who made the sampling in 1996/97 and to Göran Thor, who made the sampling in 1991/92. G. Thor also supplied information on vegetation. Kent Larsson is thanked for providing the map. The rotifers were identified by Angelica Hirschfelder. Ingegerd Sohlenius is thanked for technical assistance.

Copyright information

© Springer-Verlag 2005