had a richer gastropod fauna both in number of species and abundance. The snail fauna consisted of a mixture of stenoecious, calciphile species (Columella ...
Polar Biol (1984) 3 : 4 5 - 53 © Springer-Verlag1984
Species Composition, Abundance, Habitat Requirements and Regional Distribution of Terrestrial Gastropods in Arctic Norway J. Andersen and O. Halvorsen Institute of Biology and Geology, University of Troms¢, N-9001 Trorns0, Norway Received 29 August 1983; accepted 5 January 1984
Summary. The species composition, abundance and habitat distributions of the terrestrial gastropods at lat. 70 ° N in Finnmark county, northern Norway were studied. Within an area with bedrocks of sandstone there were few snail species and abundance was low. Calciumrich bogs and birch woods with a luxuriant undergrowth had a richer gastropod fauna both in number of species and abundance. The snail fauna consisted of a mixture of stenoecious, calciphile species (Columella columella, Vertigo genesii, V. modesta) and very euryoecious species, e.g., Discus ruderatus, Vitrina pellucida. Cochlicopa lubrica and Nesovitrea hammonis were found only in moist, rather eutropic habitats and seemed to be more stenoecious than further south in their geographical range. There were few snails within the study area (16 species) compared with > 30 species found in the coastal areas of northern Norway (Troms county) at the same latitude. This difference in the faunal composition coincides with regional divisions based on the vegetation, and may indicate a general difference in the biota of oceanic and continental areas of northern Norway. The changes in snail fauna along a coast-inland transect at about lat. 70 ° N are similar to those occurring along a vertical gradient in the inner fjord districts of Western Norway. It is suggested that low temperatures during the coldest part of the year are responsible for this common change in the species composition.
northernmost part of Fennoscandia represented by Finnmark county, Norway. The results of a study of the terrestrial gastropod fauna found in a particular area of Finnmark county are presented. The study area lies between about latitude 69030 ' and 70°15 ' N, is little influenced by man and extends from the fjord region inland towards the Finnish border. In this paper the species composition, abundance and habitat distribution of the snail fauna are described. A further purpose was to make zoogeographical comparisons of the gastropod fauna in this and other areas of Norway. The present survey comprises part of a project d e signed to study the epidemiology of the metastrongyloid nematode Elaphostrongylus rangiferi Mitskevich. This nematode, for which reindeer is the final host, has gastropod species as intermediate hosts. The relationship between the prevalence of infection and abundance of gastropods is discussed by Halvorsen et al. (1980), and experimental infections of gastropods with E.rangiferi have been carried out by Skorping and Halvorsen (1980) and Halvorsen and Skorping (1982). The study area for this study of gastropod distributions coincided with the summer range, migration route and part of the winter range of a reindeer herd, the Munkovarri herd.
Introduction
The location of the study area is shown in Fig. 1A. The summer range of the Munkovarri herd (Fig. 1B) has an area of approximately 265 km 2 and is delimited by the Porsangerfjord to the west and is enclosed by a fence on the remaining sides. For the most part the bed-rocks are sandstones (Gayer and Roberts 1971), but in certain areas layers of schist are also present. At the northern border of the Munkovarri area dolomite is present (Gayer and Roberts 1971). The migration route of the reindeer herd is from Karasjfikk in south to the summer range in north (Fig. 2). "
Several workers have studied the terrestrial gastropod fauna of northern Fennoscandia (Okland 1925; Rensch and Rensch 1932; Valovirta 1967; Wald6n 1966, 1971; Fosshagen et al. 1972; Kerney and Cameron 1979; Andersen 1982) and the broad geographical distributions of the species found in this area are fairly well known. However, details as to local distributions and abundances of the species and their ecological demands are less well known, and this applies especially to the
Study Area
46
S
1A
Porsangerfjord
t
'( i I t r- I iI
J
lo@
,
7I
6 0
1B 0 I
i
i
3 km I
[
Fig. 1. A The geographical situation of the area investigated. S: summer range, M: migration route. B The summer range of the Munkovarri herd limited by the fjord and a fence with the position of the localities investigated. Squares: localities where quantitative samples were taken; hatched areas: areas examined qualitatively. The habitats investigated in each locality are described in Table 1
14030 ' ost Oslo
According to data given by Norges Geologiske UndersCkelse (Karasjok. Berggrunnskart 1:250000) the bedrocks along the migration route are mostly amphibolite, hornblende schist and gabbro. Over large areas the bedrocks are covered by sandy moraine. According to data given by Bruun (1967) and the Norwegian Institute of Meteorology (Norsk meteorologisk ~rbok 1 9 6 0 - 7 5 ) the climate of the area is of continental type. The mean precipitation during the years 1 9 6 0 - 7 5 , was 463 m m at Brennelv meteorological station. The mean January temperature was - 7 . 6 ° C and mean temperature in July was 13.5 °C. The station at Brennelv is situated close to the summer range of the reindeer herd, but the summer range is at a higher elevation and the annual precipitation is thought to be higher and the summer temperature lower than at Brennelv. There is a gradient f r o m a moderately continental climate at Porsangerfj ord to a very continental climate in the area around Karasjfikk. In Karasjfikk the mean temperature in July is 13.9 °C and - 14.8 °C in January. The mean annual precipitation is 338 ram. Fig. 2. The area which the migration route goes through with the position of the localities investigated (quantitative and qualitative samples) along the route. The habitats investigated in each locality are described in Table l
Material and Methods The investigations in the Munkovarri area were carried out in the years 1974 - 78, and those on the reindeer migration route were conducted in 1977. Areas of 5 × 5 m 2 were selected within which 50 × 50 cm2 sam-
47 pling squares were chosen at random. All vegetation, litter and the uppermost h u m u s layer from the sampling squares were thoroughly sifted using Reitter sieves (ca. 5.5 m m mesh size). No more than 1 1 of material was sifted at any one time and the sifting of a sample square took about 5 - 10 rain. The material retained by the sieve was examined in the field and both slugs and snails were collected from this material. The material collected below the sieve meshes was stored frozen in polythene bags for examination in the laboratory at a later date. In the laboratory this material was thawed and dried and then examined under 10 × magnification. Investigations were carried out in order to check the limitations of the method. In four representative habitats (dry aspea forest; mesic birch forest; luxuriant, moist Salix forest; calcareous fens) 55 samples were taken and both the material retained by the sieve and that collected below the meshes were examined in the laboratory. A yield of 1098 gastropod shells was obtained. The proportions of shells recovered were 80070 in the fen, 8607o in the Salix forest and 97070 in the birch and aspen forest. Litter was also collected from outside the 5 ×5 m 2 sampling squares. This material was sorted immediately after collection and all gastropods and empty shells were preserved in 70°7o alcohol. Gastropods were also collected by hand, involving the turning of stones and fallen tree trunks and the peeling of bark from trees etc. These collection methods were practised in most of the habitat types investigated. The calculation of the median values given in Table 5 was performed as follows: a. The proportion of shells recovered varied with the habitat (see above), b. During non-quantitative sampling of gastropods in July 1977 it was found that the fraction of living snails varied between 52 and 6807o of the total. Vitrinapellucida (Mtiller) was excluded from the calculations because most of the shells found were empty. The total n u m b e r of snails in a given litter sample were assessed by multiplying the actual n u m b e r of shells recovered by a correction factor based on the sampling losses for the appropriate habitat. This total represented the total n u m b e r of shells (living snails + empty shells). The density of living snails in the litter was calculated using the values gathered during the non-quantitative sampling i.e., 5 2 - 68070 of these collections were living snails, the remainder being empty shells. Snails usually show a contagious distribution and the medians of the values for the different habitats were compared by Mann-Whitney U-tests. The p H value of the litter layer was measured using a Methron pHmeter E488, and the chemical analyses of the various soil types were made by Statens Landbrukskjemiske kontrollstasjon Holt. The nomenclature of vascular plants follows Lid (1974), of mosses Lye (1974) and of lichens H o v d a et al. (1975). The plant communities are classified using the terminology given by Marker (1973).
Results and Discussion
The Snail Fauna o f the Habitats Habitat characteristics is given in Table 1 and 2. The composition of the snail fauna in the various habitats is shown in Tables 3 - 4. The abundance of snails in the summer range is generally low (Table 5). The only habitat with a comparatively rich snail fauna is Alg, i.e., the aspen forest. If dead shells of Vitrina pellucida are included, the habitats A1 c and A4b reveal an appreciably higher abundance of shells (Table 4). Snails were not found above the timber line except in one habitat, a calcium rich fen (habitat B6), but even here abundance was low ( < 1 individual per litre material during J u l y - A u g u s t 1978). Generally, the abundance of snails along the migration route appears to be higher than in the summer range (Table 5). Shells of Vitrina pellucida were very numerous in habitat A l b (Table 3), and this habitat may have a higher abundance of snails than suggested by examination of Table 5. Thus, the calcium-rich fens (habitats A3a, A3b) and the tall herb birch forests (Alb) are the habitats richest in snails. The differences in snail abundances between the habitats and areas are most probably attributable to the differing abilities of the habitats to fulfill the nutritional requirements of the snails. A correlation between the abundance of snails and the calcium content of the litter (soil) has frequently been found (e.g. by Valovirta 1968; W/ireborn 1969; Peake 1978; Wald6n 1981), and such a correlation is also suggested by the present study. Thus, the habitats AI a and A1 d which are very poor in snails, have a low concentration of lime, whereas some of the habitats with a high concentration of calcium (e.g., A1 b, A3a) have a rich snail fauna. The majority of the summer range has acid bedrocks and a very poor, usually podzolized soil. In the summer
Table 1. Habitat descriptions. Mineral analysis of the soil of the habitats is given in Table 2 Habitat
Habitat characteristics
Ala A lb
b,f. Barbilophozio-Pinetum b, f. (Betula pubescens). Lactucion alpinae
A lc
b, f. Myrtillo-Betuletum dryopteridetosum b,f. (Betulapubescens), dense, moist Carex spp, Comarum palustre, Vaccinium spp. Sphagnum sp. Pleurozium schre-
Ald
Additional plant species not typical of the community
Soil type, profile
pH
Represented at localities
Trollius europaeus, Geum rivale, Solidago virgaurea, Chamaenerion angustifolium
podzol mull gradually merging into the mineral layer. Moist
4.4-4.5 5.3 - 5.5
1, 18 13, 17
Rhodobryum roseum, Equisetum silvaticum
4 . 5 - 5.1
Notes
Terrain flat
N W facing slope
podzol
5.4 - 5.6
2
No clear podzolization podzol
4.9-5.1
2, 4
3.3 - 5.1
2,5,13, 14, 15, 17, 18 (continued overleaf)
beri Ale
b,f. Myrtillo-Betuletum
A If
b, f. Myrtillo-Betuletum Rather dry ground
Cornussuecica, Thelypteris phegopteris Empetrum hermaphroditum, Cladonia rangiferina
48 Table 1 (continued) Habitat
Habitat characteristics
Alg
b, f. (Populus tremulae)
Additional plant species not typical of the community
Soil type, profile
pH
Represented at localities
Notes
podzol
4.3-5.4
5, 14, 16
S-SW facing slope
No podzolization
5 . 4 - 5.5
18
No podzolization
6.2
13
Empetrum hermaphroditum, Vaeeinium spp., Pleurozium sehreberi, Hylocomium splendens A2a
b,o. Lactucion alpinae
A2b
b,o. Wet meadow-fen Scirpus sp., Carex sp.,
Festuca ovina, Poa alpiaena, Carex vayinata, Trollius europaeus, Astragalus alpinus, A. frigidus
Pinguicula alpina, Salix reticulata, Trollius europaeus, Parnassia palustris A2c
b,o. Lactucion alpinae
Chamaenerion angustifolium, Equisetum pratense
A3a
b,o. Drier parts of fen
A3b
b, o. Wet fen
Scirpus spp., Carex spp., Tofieldia pusilla, Pinouicula alpina, Andromeda polifolia Carex rostrata, Scirpus sp. Paludella squarrosa, Campylium stellatum, Mnium pseudopunctarum
A3c
b,o. Wet mire Carex sp. Scirpus
13
No podzolization
5.9-6.8
S-facing, steep slope. Large stones, warm, dry habitat
18
18
No podzolization
4.1 - 5 . 6
1, 2, 3, 14, 17
hudsonianus, Eriophorum angustifolium, Andromeda polifolia A4a
No podzolization
b,o. Alongside brooks, small rivers. Filipendula ulmaria,
15, 16
Trollius europaeus, Geranium sylvaticum, Viola palustris, Saussurea alpina A4b
b.
No podzolization
Elevated, but moist parts of river banks, shaded (Betula pubescens, Salix sp.).
5.1
substratum watersaturated
2, 3
Deschampsia caespitosa, Polygonum viviparum, Alehemilla alpina
B2
a,o. Phyllodoco-Vaccinion Dry heath a,o. Phyllodoco-Vaccinion
B3
a,o. Meadow. Trollius
B1
europaeus, Sibbaldia procumbens, Geranium sylvaticure, Eriophorum angustifolium, Nardus stricta Bogs. Sphagnum sp. Betula nana
B4
a, o.
B5
a,o. Fens with open water. Carex sp. a,o. Dry fens without open water. Carex sp., Equisetum
B6
Betula nana
palustris, Pinyuicula alpina, Tofieldia pusilla, Salix herbacea a: above timber line; b: below timber line; f: forest; o: open areas, without trees
No podzolization No podzolization No podzolization
8, 9, 13, 17 3.6-5.0
8 9
3.1-5.0
8,13
4.0-6.0
10, 11
6.0
11
silty-muddy substratum
49
range the habitats with the richest snail fauna (Alc, A1 g, A4b) have certain peculiarities. A4b is situated on a river bank and A l c contains marine deposits which are rich in calcium (Table 1). Habitat A l g , the aspen wood, is situated within an area of podzolized soils. However, aspen has the ability to concentrate calcium and therefore, m a y support a snail fauna even though the general conditions within the area m a y appear to be too poor (Valovirta 1968). As the habitats A l c , A4b and A l g constitute a very small part of the total area of the summer range (p < 1 °70) it is concluded that the density of snails in most of the summer range is very low or nil. The bedrocks in the migration route contain calcium compounds. However, even within the migration route much of the terrain is covered by tills yielding poor soils. The poor quality of the soils m a y be the reason that snails are usually absent above the timber line. Several
Table 2. Mineral analysis of the litter layer in the habitats investigated
Habitat
locality
P(-HC1) mg/100 g
K(-HNO3) mg/100 g
Ca(O)%
N%
Ala Alb Alc Ald Ale Alf Alg A2a A2b A3a A3c B3 B4
18 13 4 2 4 2 5 18 18 18 2 8 8
37 75-108 88 66 109 43-75 36 61 - 68 53 31 109 40-48 15
100 123-313 253 215 438 118-453 108 90 - 130 110 70 438 60-120 36
0.60 2.79-3.54 1.40 0.75 0.53 0.44-1.00 1.59 2.3 - 3.40 4.38 2.00 0.53 0.50-0.70 0.06
0.76
1.82-2.37
Table 3. The total number of shells of the different snail species found by quantitative sampling (0.5 x 0 . 5 m 2 squares) in the various habitats investigated in the summer range and the migration route in 1977
Species
Habitats A
B
la
Vitrinapellucida
lb
m
s
+
+
lc
ld
le
If
m
m
s
s
s
s
5
82
1
1
+
1
lg m
s
m
5
6
2a
2b
2c
3a
3b
3c
m
m
m
m
m
s
2
4a
4b
1
m
s
m
+
+
+
41
+
19
+
10 28
+
+
38
+
7
m
s
2
3
4
s
s
m
s
5
6
s
s
(Mialler)
Vertigo alpestris
3
Alder
Nesovitrea petronella
2
1 56
2
5 42
1
+
3
10
5
13
(Pfeiffer)
Punctum pygmaeum (Draparnaud)
Euconulusfulvus
+
+
23
32
24
6
1
+
+
+
10
+
12
43
+
(MUller)
Nesovitrea hammonis
1
7
16
8
(StrCm)
Zoogenetes harpa (Say) + Discus ruderatus +
+
3
5
+
+
1
3
+
+ +
+
+
+
28 1
+ 13
12 4
14 98
+ +
199
+
1 4
+
(Ferrussac)
Vertigo ronnebyensis
1
+
+
(Westerlund)
Vertigo 9enesii
8O
13
5
(Gredler)
Columella columella
55
(Martens)
Vertigo lilljeborgi
28
18
1 6
5 1 1
+
+
2
(Westerlund)
Vertigo modesta (Say) Vertigo sp. Cochlicopa lubrica
8
1 18 +
+
+ 5
(Mialler)
Arion subfuscus
+
+
+
+
(Draparnaud) n N
3 10
10 10
6 6
3 5
1 5
1 5
6 6
5 5
6 6
10 10
10 10
9 9
6 6
5 6
0 10
0 10
s: summer range; m: migration route; N: number of quantitative samples of 0.5 x 0.5 m2; n: number of quantitative samples in which shells were found; + : present in non-quantitative samples (based on collections for the whole period 1 9 7 4 - 1 9 7 8 )
50
species of snails are found above the timber line in other parts of Scandinavia (Solh~y 1969; Wald6n 1971, Solh~y 1976). In these areas, the bedrocks and deposits are ric in calcium. The richest snail fauna is found at sites where the ground water level is high and minerals are available to the plants. An appreciable part of the migration route passes through such sites, e.g., lake shores, mires, moist meadows etc. and therefore, areas within the migration route have a comparatively richer snail fauna than areas within the summer range.
Habitat Characteristics of the Species The various snail species were probably not collected with the same degree of efficiency. Small shells may have been overlooked more frequently than larger ones. Thus, the abundances of Puncture pygmaeum (Draparnaud) and the juveniles of the other small species may have been underestimated (see also Wald6n 1981). Nevertheless, the values given in Tables 3 - 4 indicate the species
which were relatively the most abundant within the various habitats. The following synopsis of the habitat characteristics of the species is based upon the information from the present study and the literature.
Cochlicopa lubrica (Mtdleri was present in Ca-rich, moist meadows and fens (A2b, A3b) and at the edge of a brook with luxuriant vegetation. In other parts of northern Norway the species occurs both in very wet and in dry habitats (Andersen 1982). It has not been found in typically oligotrophic habitats in northern Norway. In northern Sweden this species is regarded as rather euryoecious (Wald6n 1971) and according to Kerney and Cameron (1979) it is a catholic species. Within the study area, as elsewhere (SolhCy 1969; Wald6n 1966, 1971; Valovirta 1967; Kerney and Cameron 1979), Columella columella (Martens) and Vertigo genesii (Gredler) are limited to calcareous habitats. Vertigo genesii was very abundant and was the dominant species in a wet meadow (A2b), whereas Columella
Table 4. T h e total n u m b e r o f shells o f snail species f o u n d in the various habitats investigated in the s u m m e r range during 1975 and 1976 Species
Habitat Alc
Vitrina pellucida Eucon ulus f u l v us
89
Discus ruderatus
11
Nesovitrea petronella Vertigo ronnebyensis Punetum pygrnaeum Zoogenetes harpa Vertigo lilljeborgi Arion subfuscus
10 5
N
28
Ald
19
Ale
Alf
Alg
A4b
10
1
256
59
3
1
158
8
141
2
56 53
2
1
2
2
1
11
5
A3c
B3 - B 4
3 136 3
2 16
32
16
2
1
28
26
31
48
N : N u m b e r o f samples o f 0.5 x 0 . 5 m 2
T a b l e 5. T h e estimated range o f the m e d i a n s and results o f statistical analysis ( M a n n W h i t n e y U-tests) o f the a b u n d a n c e o f living land gastropods (exc. Vitrina pellucida) in the habitats investigated in July 1977 M i g r a t i o n route
S u m m e r range
A
A
la
lb
If
lg
2a
2b
3a
3b
4a
lc
if
lg
ld
~0.3
10.5-13.2
5.3-8.0
1.3-3.0
3.0-4.6
7.2-9.5
20.5-27.5
11.8-15.0
0.8
~
