Effects of shoreline modification on lake littoral macroinvertebrate assemblages

Abstract

<p>The general aim of this study was to explore the effects of shoreline modifications on the<br />structure of littoral macroinvertebrate assemblages in lakes, across the gradients of<br />nutrients and alkalinity concentrations. Following this general aim, several aspects of the<br />topic were investigated. The first aim was to establish whether shoreline habitat<br />characteristics influence the composition of littoral macroinvertebrate assemblages. For<br />this purpose, characteristics of shoreline habitats were recorded using the Lake Habitat<br />Survey and associated with the assemblages at each site across six studied lakes. The<br />relevance of specific shoreline features in structuring the macroinvertebrate composition<br />was estimated. The aim was, therefore, to establish the relative influence of shoreline<br />features on the composition of macroinvertebrate assemblages, with special attention to<br />diversity-related characteristics of the shorelines. Results indicated that the community<br />composition of the littoral macroinvertebrates was affected by morphological features of<br />the shoreline zone when the effects of nutrients and alkalinity were taken into account.<br />However, shoreline features were less important in structuring the macroinvertebrate<br />assemblages than the chemical and physical properties of the water column. In addition,<br />pressures related to anthropogenic activities and hydrological pressures were<br />demonstrated to have influence on the composition of the littoral assemblages. Among<br />the habitat features, the macrophyte- and substrate-related diversity features were most<br />important for structuring the macroinvertebrate assemblages across Hab-plots. Aside<br />from the direct effect of the littoral zone features, macorinvertebrate assemblages were<br />influenced by riparian zone land-cover.<br />The second aim was to assess the impact of riparian and littoral morphological<br />modification on littoral macroinvertebrate assemblages using diversity and abundance<br />measures in generalised and simple linear mixed-effects models. Within this goal, the<br />effect of morphological modification was estimated, while accounting for the effect of<br />other environmental variables including the concentrations of nutrients. According to the<br />results of the mixed-effects models, diversity measures of macroinvertebrate assemblages<br />were affected by shoreline modifications, when unmodified and modified littoral<br />shorelines were compared and after the effects of other environmental factors were<br />accounted for. In contrast, abundances of assemblages from modified riparian zone were<br />increased compared with assemblages from unmodified and modified littoral shorelines.</p><p>TP concentrations were demonstrated to negatively affect the taxon richness and<br />Margalef diversity index of littoral macroinvertebrate assemblages, while the abundances<br />were not affected. According to the results of the taxon richness model, the response of<br />the assemblages to anthropogenic pressures (nutrient enrichment and shoreline<br />modifications) varied depending on the type of mesohabitat. Moreover, nutrient<br />enrichment was demonstrated to reduce the differences among the assemblages from<br />distinctive mesohabitats. Surprisingly, there was no interaction between the effects of TP<br />concentrations and shore modifications on either diversity measures or abundances of<br />littoral macroinvertebrates.<br />The third aspect of this study was to elucidate the effects of shoreline modifications using<br />the ecological traits of littoral macroinvertebrate assemblages. This compared the<br />efficiency of two different approaches in assessment of shoreline modifications using<br />littoral macroinvertebrates. The first approach was based on the resemblance matrix of<br />the composition of macroinvertebrate assemblages and the second approach was based on<br />the specific preferences of individual taxa toward mesohabitat types. Since the second<br />approach reflects the response from the autecological information of the species, it was,<br />therefore, expected to provide more insight into the mechanisms of shoreline<br />modification pressure. Correspondingly, Indicator Value analysis and consequently<br />applied mixed-effects model revealed taxa with specific mesohabitat preferences to be<br />affected by the complexity of the littoral zones in oligotrophic and mesotrophic lakes.<br />Based on these results, stenotopic species (habitat specialists) are proposed as the key to<br />understanding the mechanisms of the impact of morphological alterations along littoral<br />zones of lakes without high nutrient enrichment. Finally, it could be suggested that<br />metrics based on autecological information of macroinvertebrate taxa have potentially<br />higher sensitivity for identifying the impact of altered shoreline morphology than<br />community structure and individual indicator taxa.</p>