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1 2015

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Molluscan diversity in stream driftwood: relation to land use and river section

Čiliak M., Čejka T., Šteffek J.

Polish Journal of Ecology

2015

Vol. 63, nr 1

124--134

In stream corridors, driftwood represents mainly a dead vegetation biomass and diverse artificial material relocated along a stream by flooding. Most driftwood can contain empty molluscan shells or a minor proportion of live individuals (i.e. molluscan allocoenoses). Drifted material is important for spreading of fauna and flora. Molluscan allocoenoses can provide valuable information on molluscan fauna of the upstream area. The main objective of the study was to describe changes of the species composition, diversity and similarity in molluscan allocoenoses along the model river ecosystem in relation to land use of partial watersheds. In the years 2010–2011, 23 samples of driftwood were taken at 23 sites along the Hron River (Central Slovakia) from the spring to the mouth. Molluscan allocoenoses were composed of 135 species (95 terrestrial and 40 aquatic). The number of species found at particular sites ranged from 29 to 72 with a mean of 48. We confirmed our hypotheses that similarity in molluscan species composition of driftwood from different sampling sites is related to distance between them, the proportion of woodland species is highest in the upper course of the river with highest forest coverage and, finally, the highest total number of species (gamma diversity) in driftwood is in the most heterogeneous (in terms of land use) middle river section. Whereas alpha and gamma diversity were highest in the middle section, beta diversity was lowest. The molluscan assemblages were most variable within the lower section (the highest beta diversity). The studied river with a length of nearly 280 km appeared to be suitable to allow the changes associated with different land use to be reflected in species composition of molluscs. Changes in molluscan community structure documented by repeated driftwood sampling can reveal the changes in land use within the river watershed. Thus, sampling of driftwood can also be used in landscape ecology research.