Malakologický bulletin, December 14, 2006 http://www.mal‐bull.blogspot.com/ USE OF TERRESTRIAL MOLLUSCS FOR BIOINDICATION OF THE IMPACT OF THE GABČÍKOVO HYDRAULIC STRUCTURES (THE DANUBE RIVER, SLOVAKIA) TOMÁŠ ČEJKA Institute of Zoology of the Slovak Academy of Sciences, Dúbravská cesta 9, SK‐84506 Bratislava, Slovak Republic; e‐mail: [email protected] The aim of this paper is (1) describe main methods using within the biomonitoring programme of the Gabčíkovo hydraulic structures along the Danube River, SW Slovakia; (2) present main results of the monitored long‐term structural changes in alluvial molluscan fauna over the past ten years; (3) describe changes to surface and ground water dynamics on communities of terrestrial molluscs and (4) compare structure of molluscan faunas before the Danube damming and ten years on. Bioindication abilities of terrestrial molluscs • With long‐term monitoring of the changes in The advantages of molluscs as a model group the natural environment, the changes in the can be characterized as follows: mollusc community structure reflect rather • Molluscs belong, within the scope of Central long‐term trends than short‐term fluctuations in Europe, to well investigated animal groups environmental parameters. For this reason, they from the viewpoint of community structure, are an ideal group for biomonitoring or sur‐ distribution and habitat requirements, veillance, • The species form well‐defined communities • In river sediments rich in calcium, the mol‐ and have strong ecological relationships to spe‐ lusc conchs easily fossilize and form thanato‐ cific habitats and reliably react (although more coenoses in situ and, in this way, make it possi‐ slowly) to changes in soil moisture and the ab‐ ble to study the development of natural envi‐ sence or presence of floods. In the Slovak part of ronment at sites where they occur from a very the iuxta‐Danubian area, the occurrence of 58 long‐term perspective. species of terrestrial molluscs has been con‐ firmed, including species indicating relatively Calibration of indication properties natural habitats, changes in soil moisture and It is known that animals, hence also molluscs, different degrees of habitat degradation, can often have relatively different ecological re‐ • Most Central European land snails are small quirements in different zoogeographical units. (several millimetres) and little mobile animals Thus, knowledge of habitat requirements of the with a strong dependence on habitat, unlike iuxta‐Danubian (close, at, beside the Danube) some insect groups and spiders. Small species molluscs cannot be automatically applied for penetrate into the adjacent habitats very slowly, example to conditions of the Borská nížina 1 lowland and not at all to more remote parts of Principles for selection of investigation plots and Europe under the influence, for example, of the problems of data interpretation Atlantic climate. For this reason, results of Within the scope of the monitoring plots set by monitoring from geographically and climati‐ the monitoring coordinator, the structurally cally distant areas are not fully comparable. most homogeneous parts are to be selected, in Prior to a monitoring investigation, a calibrating which specific investigation plots are then es‐ indication investigation must be carried out in tablished. Investigation plots of 50×50 m are each area where the local ecological require‐ suitable. The investigation plots should be situ‐ ments of individual species are not known in ated as far from the stand margin as possible to detail in order to determine (calibrate) them by eliminate the edge effects. It is important to en‐ means of the methods given below. sure that the monitoring plots remain unaf‐ fected by silvicultural interventions (e. g. thin‐ ning or even timber exploitation) during the A brief description of methods and interpreta‐ whole period of monitoring. Otherwise, we tion of results would be monitor the influence of silvicultural, Field and laboratory work but not the influence of changes to hydrological When evaluating changes in the natural envi‐ conditions. ronment by means of molluscan communities, Problems with sampling arise on those plots the quantitative and semi‐quantitative methods that are flooded by surface water several times a are used. The most applied method is the vol‐ year. After a flood most molluscs are washed ume method, with which a standardised vol‐ away from the plot or the local patchy structure ume (mostly 5 litres) of litter and soil upper lay‐ of communities is mixed by water turbulence. ers are taken from several places in a homoge‐ For this reason the samples obtained 5‐8 weeks nous plot, approximately up to a depth of 3‐5 after the flood are hardly interpretable from the cm. After washing, drying and subsequent viewpoint of moisture changes. Another prob‐ sieving, the mollusc conchs are sorted from in‐ lem of data interpretation arises in the habitats dividual fractions, identified and counted. The situated at a considerable distance from the proportion of individual species in a sample of flood zone and which remain for a long time the community determines its character (mutual out of the influence of floods, especially in proportion of hygrophilous, shadow‐preferring, habitats situated on elevated places (terrace hygrotolerant or euryecious species). Another, platforms, fluvial levees), where the ground less frequently used method is the qaudrat water table is deep and does not influence the method, which differs just by collecting litter hydropedological regime in the soil upper lay‐ and soil substrate over a specific surface area ers. In such a habitat it is mostly problematic to (e.g. 50×50 cm). In this case the number of mol‐ interpret changes in molluscan communities as luscs is related to the area unit. a direct consequence of water regime changes. Analysis and synthesis of data Influence of changes to surface and ground Counting individuals in samples gives us ab‐ water dynamics on communities of terrestrial solute data, which should firstly be transformed molluscs (converted to a scale determined by experts, transformed logarithmically, etc.), to be pre‐ Molluscs, and their communities, reliably react pared for statistical analysis. In addition, to to changes in soil moisture and the absence or usual descriptive quantitative characteristics presence of floods. like population density, relative abundance (a) Habitats frequently flooded by more or less (dominance) and structural characteristics like destructive (streaming) surface floods are char‐ diversity and equitability, data can be subjected acterised by the exclusive presence of polyhy‐ also to different methods of multivariate analy‐ grophilous species and by a naturally low al‐ sis (cluster analysis, ordination), which helps us pha‐diversity of communities (in average 12 visualise the data structure and makes data in‐ species). The poorest in the number of species terpretation easier. Results obtained in individ‐ are molluscan communities in the initial stages ual years can be continuously compared and the of floodplain forest (in average 6 species) [3, 4]. trends estimated. Only those species that are adapted to flood 2 conditions survive there. They are represented Influence of silviculture on molluscs especially by larger species that are able to es‐ From the 48 species of terrestrial molluscs cape from the rising water level by climbing regularly occurring in the iuxta‐Danubian onto trees (Arianta arbustorum, Cepaea hortensis, floodplain forests, as many as 32 species also Succinea putris, Oxyloma elegans, Trochulus his‐ occur in older poplar lignicultures [1, 3]. Ac‐ pidus, Trochulus striolatus danubialis) or that are cording to existing data, the most constant spe‐ able to survive for a time directly in the water or cies inhabiting the stands of poplar cultivars are in different water‐bearing substrates, especially Monachoides incarnatus, an eurytopic forest spe‐ in deposits of plant material (Zonitoides nitidus, cies, which reaches a dominant to subdominant Pseudotrichia rubiginosa, Carychium minimum, position here, and Fruticicola fruticum having and partly also probably Trochulus striolatus da‐ similar ecological requirements as Monachoides nubialis and Trochulus hispidus). incarnatus, but only managing a subdominant to In recently flooded habitats, which are covered receding position here. Among the constant after an intensive flood by a silt crust, the poly‐ species, the forest mesohygrophilous Aegopinella hygrophilous species Oxyloma elegans, Succinea nitens, forest hygrophilous Arianta arbustorum putris, Zonitoides nitidus and Pseudotrichia rubigi‐ and forest eurytopic Alinda biplicata also should nosa appear as pioneer species. Other strongly be named. Cochlicopa lubrica, Cepaea hortensis hygrophilous species, Carychium minimum, ap‐ and Trochulus striolatus danubialis, having opti‐ pears later, because it is a small species having a mum conditions in moister sites in willow‐ small dispersal power, and the oligotrophic poplar forests, and forest hygrophilous species type of substrate does not satisfy its trophic re‐ Vitrea crystallina, Urticicola umbrosus and Clausi‐ quirements. lia pumila, as well as forest mesohygrophilous (b) In sporadically flooded parts of the flood‐ Cochlodina laminata occur here mostly as sub‐ plain, which are influenced by surface waters dominant species [3]. Richterová [11] found 28 only at high or very high water levels in the species in poplar ligniculture of the within‐dike