Freshwater Snail Communities and Lake Classification. an Example
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Limnologica 31 (2001) 129-138 LIMNOLOGICA http ://www.urbanfischer.de/j ournals/limno © by Urban & Fischer Verlag Hus6 Biological Station, Department of Biology, Abo Akademi University, Emkarby Aland, Finland Freshwater Snail Communities and Lake Classification. 0 An Example from the Aland Islands, Southwestern Finland RALF CARLSSON With 4 Figures and 6 Tables Key words: Freshwater snails, calcium, hardness, lake types, Aland Islands Abstract The freshwater snail fauna in 51 lakes on the A1and Islands was in- and vascular plants (CEDERCPmUTZ 1934, 1937, 1947), fol- vestigated. By means of cluster analysis it appears that lakes may be lowing the ideas of SAMUELSSON (1925) and ALMQVIST divided into four groups on the basis of snail species composition. (1929). CEDERCREUTZ classified lakes into "Weissmoor"- The lakes of the four groups show a spatial distribution which is re- lakes (dystrophic lakes), Lobelia-lakes (oligotrophic lakes) lated to topographical differences, terrestrial vegetation and land use. and Potamogeton-lakes (eutrophic lakes). The Potamogeton- Snails may be divided on the basis of water hardness into hard water species and calcium indifferent species or into demanding and mod- lakes were further subdivided into Chara-lakes (relatively est/indifferent species when clustering is based on presence/absence. shallow lakes, usually recently isolated from the sea), An- abaena-lakes (relatively deep and large lakes with open sur- faces), "Algengyttja"-lakes (shallow lakes, deteriorating be- Introduction cause of sedimentation, and therefore they often partly or completely dry up during summer) and "Braunmoor"-lakes MACAN (1977) summarised the work of BOYCOTT (1936) on (shallow lakes, overgrowing from the shores). "Zwischen"- British freshwater snails in the following way: "The optimum lakes (mixed lakes), do not fit well into any category but conditions in a habitat are much the same for all the species, show traits from two or more of them. with few exceptions. Good conditions are a large volume of Landscape ecology is an emerging discipline and the eco- moderately warm calcareous water, free from inorganic matter logical organisation of lake districts has recently paid much in suspension and from organic pollution, flowing not too attention (e.g. KRATZ et al. 2000; LEWIS & MA~NUSON 2000). rapidly over a shallow bottom, with a moderate but not exces- In a study of species-area relationships CARLSSON (2001a) sive growth of plants". Do different types of lakes offer differ- found that water hardness and aquatic vegetation were the two ent environments to which some species are adapted and some most import factors determining the number of snail species are not? Do particular snail communities develop in the differ- in lakes on the *land Islands, while lake area was of minor ent lake types or are the snail species distributed at random? (and not even statistically significant) importance. This lead Many earlier investigations have dealt with these problems to the belief that there was a general pattern with a higher (e.g. CALOW 1973; A~o et al. 1981; LODGE 1985; Pip 1986a, species richness in some lakes than in others and that this pat- 1986b, 1987, 1988; CosTm 1994). In this paper, the division of tern is perceivable in the landscape. This paper may be seen as lakes into lake types is based on the assumption that the pres- a continuation of the above mentioned paper. ence of a particular snail species reflects the environmental needs of that species, or its ecological niche. The Aland land uplift area with its many lakes (CEDERCREUTZ 1934, 1937; Study area LINDHOLM 1991) offers an excellent opportunity to study lakes of different age and thus different water chemistry properties. The Aland Islands are located in southwestern Finland, The Finnish botanist CARL CEDERCREUTZ classified lakes approximately at Lat. 60 ° N, Long. 20 ° E, about halfway on the Aland Islands on the basis of their planktonic algae between Sweden and the Finnish mainland (Fig. 1). Between 0075-9511/01/31/02-129 $15.00/0 129 Fig. 1. The Aland Islands with lines separat- ing different types of lakes. Dashed lines in- dicate uncertain limits. The 51 investigated lakes in black, other visited lakes, more ex- tensively surveyed, in white. One of the A l- lakes (M6ntrfisk) is in the A3-area, its location is depending on the south-westerly extension of the northern hill area. the central island of Aland and Finland is a vast archipelago Materials and Methods and the Sea of Aland separates the Aland Islands from Swe- den in the west. The bedrock of the main island of Aland is Snails were collected 2-15 times, depending on size and complexity composed of different kinds of acidic rapakivi granites while of the lakes, in 51 lakes by hand picking and with a rod sieve during the archipelago is built up of older bedrock consisting mainly I994-1996. The species have been identified according to HUBEN- of gneisses, migmatites and related kinds of rocks (BERGMAN DICK (1949), MANDAHL-BARTH(1970) and MACAN (1977). The two species Radix ovata (DRAPARNAUD)and R. peregra L. were treated as 1986). Despite the acidic bedrock, many lakes on the Aland one species together with Radix auricularia L. from which they with Islands are rich in calcium due to lime in the moraine, which certainty can be told only by examination of their internal genitalia covers the bedrock (HAusEN 1964). However, in the northern (MACAN 1977). Also Stagnicola palustris (MOLLER) [Syn. Lymnaea part of the province, in the municipalities of Geta, Saltvik and palustris (MIdLLER)] is treated as one species though it is nowadays Sund, there are bare rock outcrops and only a very thin regarded as a complex of several species (JACKIEWICZ ~% VON moraine cover. The hills gradually descend into a more flat PROSCHWITZ 1991; yon PROSCHWITZ, pers. comm.). landscape with till and clay deposits between residual rocky Water samples were taken at a depth of about 20 cm in the littoral hills. The lakes in the northern area are more oligotrophic and zone of each lake during one week in July 1994. Hardness (°dH) was poor in calcium than are the lakes in the lowland areas, which analysed by EDTA titration (Hath test kit), conductivity (~S em-j) also are affected by farming. The landscape is dissected by with a Metrohm 660 conductometer, pH with a Metrohm 691 pH meter and water colour with a Shimadzu UV 160 spectrophotometer. faults running in different directions, making a mosaic of bays Alkalinity was analysed by titration with 0.01 M HC1. and firths alternating with smaller and larger islands. New Areas of lakes and cultivated fields and circumferences of the lakes are still being formed in the area due to land uplift, the lakes were measured from 1:20000 topographical maps. rate of it is currently about 4-5 mm per year (LINDHOLM Statistical analysis was performed with a SYSTATby SPSS, Ver- 1991). sion 5.05 programme package and included Kolmogorov-Smirnov 130 Limnologica 31 (2001) 2 and Lilliefors test for testing of normality and average +_ standard de- Results viations. Cluster analyses on both lake and snail data (Euclidean dis- tance, average linkage) were performed with SYSTAT 9. The cluster analysis of the lakes was based solely on the occurrences of snails. The results from the water sampling are in agreement with ear- The status of a snail species in each lake was designated by the num- lier results from similar investigations (e.g. HELMINEN 1977; ber 1 (present) or 0 (absent). The presence of a snail species in a par- (~)STMAN1988; unpubl, data on Hus6 Biological Station), and ticular lake is assumed to reflect the total ecological niche of that may be regarded as representative (Table 1). Altogether, 18 particular species (AHo et al. 1981). Kruskal-Wallis one way species of snails were encountered in the 51 Aland lakes. As ANOVA was used to find out differences in the characters of the each lake was visited more than once, there is a large probabil- lakes. For comparison, the same clustering technique was also applied ity that most occurring species were encountered. Other inves- on data on Finnish lakes (AHo 1966) to show possible regional dif- tigations (e.g. OI~AND 1990) are based on sampling limited to ferences. For clustering of snails two methods were used; one based half an hour, and then some species may have been missed. on the presence/absence in lakes and one based on average _+ S.D. Some species were present in most lakes while others were values for water hardness of the lakes where the species occurred. found only in a few lakes (Table 2). 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