minerogenic and organogenic brooks and for moss carpet and pool habitats, but none for .... black outline. ..... numbers in all habitat types, and aquatic beetles.
Springer 2005
Hydrobiologia (2005) 533: 99–113
Benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics: patterns in abundance and diversity Jari Ilmonen1,* & Lauri Paasivirta2 1
Finnish Environment Institute, P.O.Box 140, FIN-00251 Helsinki, Finland Finnish Institute of Fisheries and Environment, Kalakouluntie 72, FIN-21610 Kirjala, Finland (*Author for correspondence: Tel.: +358-9403000, Fax: +358-940300190, E-mail: jari.ilmonen@ymparisto.fi) 2
Received 27 October 2003; in revised form 9 June 2004; accepted 17 June 2004
Key words: spring habitats, benthic macrocrustaceans and insects, habitat classification, diversity, indicator species analysis, crenobiont species
Abstract We studied variation in benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics in six springs located in a single groundwater area in south-west Finland. We defined five habitat types in the studied springs according to water flow and benthic substrate characteristics: minerogenic brooks, organogenic brooks, helocrenes, floating moss carpets and limnocrene pools. Most studied invertebrate orders, as well as individual taxa, showed differences in relative abundances between the habitat types, but the most common taxa occurred in all springs and habitat types. The studied macroinvertebrates were most abundant in the moss carpet sites and least abundant in the pool sites, but the difference was not statistically significant. We did not observe significant differences in mean taxonomic richness per sample between habitat classes. The observed taxonomic richness in pooled samples of habitat classes was highest in moss carpet habitat and lowest in pool habitat, and the rarefied richness estimate was lowest in pool habitat. Benthic macrocrustacean and insect assemblages varied more between habitat types than between individual springs. In an Nonmetric Multidimensional Scaling ordination analysis, spring brook sites were separated from the moss carpet and pool sites, whereas helocrene sites were widely scattered among sites in other habitat classes. The strongest ecological gradients were related to water flow and the presence of minerogenic substrate, separating lentic and lotic habitats. Abundances of moss and coarse detritus accounted for most of the within-class variation. We identified several indicator species for minerogenic and organogenic brooks and for moss carpet and pool habitats, but none for the helocrenes. We found several occurrences of two crenobiont insect species considered threatened in Finland. We suggest that combined studies on macroinvertebrate and bryophyte assemblages would be a powerful approach in assessing the biodiversity of springs.
Introduction Due to their relatively stable environmental conditions and spatial isolation, springs can provide an important research system for basic as well as applied ecology (Glazier, 1998; Williams & Williams, 1998). Adequate knowledge of the characteristics of the biota in the studied area and habitat is required for applied ecological studies. The
invertebrate fauna of springs and spring brooks has been a subject of numerous studies and reviews in North America (e.g. Williams & Danks, 1991; Ferrington, 1995) and Europe (e.g. Crema et al., 1996; Botosaneanu, 1998). Although the invertebrate fauna of springs has been widely studied in Denmark (e.g. Lindegaard et al., 1975; Lindegaard
100 et al., 1998), until recently the spring fauna has been insufficiently studied in Fennoscandia. In Finland there are hitherto only a few published studies on selected taxonomic groups of aquatic invertebrates in springs (Hirvenoja, 1960a; Hirvenoja, 1960b; Hirvenoja, 1960c; Sa¨rkka¨ et al., 1997; Sa¨rkka¨ et al., 1998; Bagge, 1999; Salmela, 2001; Hirvenoja, 2002), and in Sweden the first comprehensive ecological study on spring macroinvertebrates was published only recently (Hoffsten & Malmqvist, 2000). Adequate knowledge of the biodiversity and habitat structure of different spring types, as well as the habitat preferences of rare and threatened species, is essential for the conservation of springs. Although new records on crenobiont species (species living exclusively in springs), such as Crunoecia irrorata (Curtis) (Trichoptera: Lepidostomatidae) (Saarela, 1999; Rassi et al., 2001), have raised awareness of the need for conservation of springs in Finland, assessment of the conservation value of springs is still based mainly on a subjective assessment of the naturalness of a spring. More information on the relationship between habitat structure, species distributions and overall biodiversity of springs is needed for their more efficient conservation. There have been several approaches to classifying springs with respect to their biota and chemical and physical characteristics (e.g. Glazier & Gooch, 1987; Lindegaard, 1995; Lindegaard et al., 1998; Hoffsten & Malmqvist, 2000; Zollho¨fer et al., 2000). When sets of springs are studied on a regional scale, relatively distinct spring types can often be identified with respect to variation in environmental and faunal characteristics. As well as regional and large scale variability, withinspring habitat heterogeneity is also an important factor in determining the composition of spring macroinvertebrate communities (e.g. Glazier & Gooch, 1987; Lindegaard, 1995; Lindegaard et al., 1998). In particular, emergent mosses provide a wide array of microhabitats with environmental conditions varying horizontally from edges to the inner parts of moss carpets, and also vertically as the conditions change from dry to submersed through a madicolous transition zone (Lindegaard et al., 1975; Thorup & Lindegaard, 1977). These habitats provide an ecotone between terrestrial and aquatic conditions, and are well known as
sources of great invertebrate diversity, being the preferred habitat of many crenobiont arthropod species (Thorup & Lindegaard, 1977; Fischer, 1993; Lindegaard, 1995; Gerecke & Di Sabatino, 1996). Although Danks & Williams (1991) stressed the importance of detailed examination and description of spring microhabitats, only a few studies have hitherto been performed. The most often used typology includes three categories of spring types based on groundwater flow rate and topography of the groundwater source area: helocrene, rheocrene and limnocrene springs (e.g. Danks & Williams, 1991; Smith, 1991). In helocrenes, groundwater percolates through a layer of detritus or vegetation into a marshy holding area, whereas in rheocrenes emergent groundwater flows rapidly over a gravel or sand substrate. In limnocrenes a stenothermic ground water pool is formed at the point of discharge. Helocrenes often form diverse spring complexes, including all the spring habitat types described above (Lindegaard, 1995). Gerecke & Di Sabatino (1996) used the extended terms rheohelocrene and rheopsammocrene for such spring complexes, which form a mosaic of lentic and lotic habitats and groundwater seepage, with either organogenic or minerogenic material as the groundwater seeping substrate. The objective of our study was to describe spring habitat types in six separate springs located within a single groundwater area in southern Finland. We aimed to identify spring habitat types by their environmental characteristics a priori and to assess how the variability of benthic macrocrustacean and insect assemblages corresponds to this habitat typology, and to use the results to provide guidelines for biodiversity assessment of spring habitats.
Materials and methods Study area The studied springs are located in the southern Finland in the southern boreal ecoregion (ecoregions according to Working group on the need for forest protection in southern Finland and Ostrobothnia, 2000) within a single large groundwater area in the Kiikalannummi glacial delta complex
101 (Fig. 1). The complex is a part of the third Salpausselka¨ ice edge formation where the glacier retreating towards northwest stopped about 10 100–10 000 BP (Glu¨ckert, 1978). The Kiikalannummi formation comprises a series of glaciofluvial marginal delta plains, and a steep proximal ice contact slope with strongly undulating dead-ice terrain and end moraines at the northwest edge. The delta plateau of the more than 10 km long and 2–5 km wide delta complex lies 116–118 m above sea level, at the water level of the Baltic sea during the Yoldia phase (Glu¨ckert, 1978; Tikkanen & Oksanen, 2002). The formation, especially the proximal part of it, is rich in springs and spring fens and is known for its valuable flora, such as the only known population of the angelica Angelica archangelica ssp. archangelica L. in southern Finland (Ha¨met-Ahti et al., 1998). We studied the benthic macrocrustacean and insect fauna of six springs located at the proximal northwest slope of the formation (Fig. 1). These springs are generally surrounded by spruce-dominated mesic heath forest and small bogs of varying naturalness (forest fertility classification
according to Reinikainen et al., 2000). The studied springs varied in size and complexity from small limnocrenes covering an area of only about 10 m2 to spring complexes of several hectares (Table 1). The spring area was defined as the area of open water and evident spring vegetation and emergent groundwater. The spring on the northern edge of Pillisto¨nsuo bog (P) is a small and distinct limnocrene, and in Sorttakorpi bog (S) there is a small helocrene with little open water and a small trickle draining the emergent groundwater in the area. Kultala¨hde (K) is a combination of a diverse rheohelocrene complex (as in Gerecke & Di Sabatino, 1996) with all types of spring habitats and a large limnocrene spring pond with a swiftly flowing spring brook. Lammenla¨hde (L) and Yrttikorpi (Y) are also large and diverse rheohelocrene complexes. In Herakkaanla¨hde (H) the groundwater emerges directly as a swiftly flowing spring brook with a detritus bottom and dense vegetation, and ends up in a large spring-fed pond. Kultala¨hde and a small part of Yrttikorpi are protected as nature conservation areas.
S
Y
H
P L K
Figure 1. Location of the study area and the studied springs. The groundwater area is shaded and major watercourses are shown in black outline.
102 Table 1. Characteristics of the studied springs K
L
P
Y
H
S
Spring area (1–5)
3
3
1
5
3
2
Limnocrene (%)
70
20
90
5
100
0
Helocrene (%)
30
80
10
95
1
100
Rheocrene (%) Naturalness (0–3)
1 3
1 2
0 3
1 2
0 3
0 2
pH
7.7
7.6
8.0
7.8
7.3
6.4
Conductivity (mS m)1)
6.7
5.1
6.5
6.3
4.2
4.8
Alkalinity (mmol l)1)
0.44
0.35
0.48
0.48
0.27
0.27
Water colour (mg Pt l)1)
0.005, ** 0.005 > p > 0.001). The habitat categories are: S = minerogenic brook (n = 3), D = organogenic brook (n = 4), H = helocrene (n = 14), M = moss car-pets (n = 9), and P = pools (n = 4).
