Effects of shoreline alteration and habitat heterogeneity on macroinvertebrate community composition across European lakes

Highlights

• The effect of morphological alterations to lake littoral zones was investigated.

• Macroinvertebrate communities differed among shore types and habitats.

• Morphological alteration had a negative effect on macroinvertebrate biodiversity.

• Regional indicator taxa were identified for different shore types and habitats.

• We validated the use of macroinvertebrates to assess morphological alterations.

Abstract

Human lake shore alterations often result in a substantial decrease of littoral and riparian habitat diversity and physical complexity, but the intensity at which shore alterations affect biodiversity may differ among European geographical regions. We tested if the response of littoral macroinvertebrate communities to human shoreline alterations is consistent among geographical regions. We compared community composition and diversity of human altered with those of unmodified littoral zones from 51 lakes across seven European countries in four geographical regions based on pooled composite as well as habitat-specific macroinvertebrate samples. Taxon richness and community composition differed among shore types and different habitats in all geographic regions, with morphological alteration having an overall negative effect on macroinvertebrate taxon richness. In addition, habitat heterogeneity also had a strong effect on littoral communities, with highest taxon richness found in the structurally complex macrophyte habitats in all regions. Average proportional densities of Diptera and Oligochaeta taxa generally increased in morphologically altered shores in all geographical regions, while Bivalvia, Crustacea, Ephemeroptera, Gastropoda and Trichoptera showed comparatively lower numbers in many anthropogenically altered sites. Furthermore, taxon richness was positively correlated with habitat diversity. We were able to relate changes in littoral communities to anthropogenic shoreline alterations, and linked the effect to the loss of habitats and habitat complexity. The results of our study demonstrate that littoral macroinvertebrates respond consistently negative to the influence of morphological alterations across European geographical regions in terms of biodiversity. While macroinvertebrates have previously been identified to be useful descriptors of morphological change in single countries/regions, we can now validate that they can be used to assess the ecological status of lakes in terms of morphological alterations across European regions. Our results can be used to further improve ealready existing WFD-compliant multimetric indices, for example by including taxa groups, which show a strong reaction to shoreline alterations. This could be supported by the inclusion of a suit of indicator taxa reflecting the loss of complex habitats such as macrophytes in the lake littoral.

Introduction

Lake littoral zones, as interfaces between aquatic and terrestrial ecosystems, are characterised by high natural diversity and productivity (Strayer and Findlay, 2010). Their physical complexity and heterogeneity typically support highly diverse plant and animal communities, including benthic macroinvertebrates, which form a major component of lake ecosystem functioning (Vadeboncoeur et al., 2002, Wetzel, 2001). This natural diversity, however, is increasingly threatened by a variety of anthropogenic pressures on lakeshore zones including human settlement, associated industry or recreational activities (Miler et al., 2013, Porst et al., 2015, Solimini et al., 2006). Alterations to lakeshores include the stabilization of littoral zones by rip-rap or retaining walls, for the protection of banksides, and the creation of bathing or angling sites (Solimini et al., 2006, Solimini and Sandin, 2012).

Human induced morphological alterations to lake shores constitute one of the most severe threats to lakes and their ecological integrity worldwide (Donohue et al., 2009, Elias and Meyer, 2003, European Environment Agency, 2012, Schmieder, 2004). Shoreline alterations are closely associated with loss of natural habitats such as substantial removal of shoreline vegetation and littoral macrophyte stands, particularly reed belts (Brauns et al., 2007, Elias and Meyer, 2003, Radomski and Goeman, 2001). Clear cutting of riparian areas reduces the amount of coarse woody debris (CWD) and tree roots that provide habitat for a range of organisms, and are generally absent in littoral zones at highly modified shorelines (Christensen et al., 1996, Czarnecka, 2016). Changes to the lake littoral zone such as habitat degradation as a consequence of shoreline alteration consequently alter macroinvertebrate communities (Bänziger, 1995, Porst et al., 2012) by reducing littoral macroinvertebrate diversity and modifying macroinvertebrate community structures (Brauns et al., 2007, Porst et al., 2012, Porst et al., 2016).

How to quantify the impacts of morphological pressures on biodiversity and community composition across European lakes has been the focus of recent studies within the framework of the EU-project WISER (Water bodies in Europe – Integrative Systems to Assess Ecological Status and Recovery; www.wiser.eu) (e.g. Porst et al., 2013, 2016). McGoff et al. (2013a) tested the potential of metrics derived from an existing lake assessment system, the Lake Habitat Survey (LHS) (Rowan et al., 2006), for the assessment of European lakes and concluded that the LHS is not useful for consistently relating habitat quality and pressure to littoral macroinvertebrate metrics in European lakes. The recently developed multimetric indices LIMCO and LIMHA (Littoral Macroinvertebrate Index based on Composite and Habitat samples, respectively) (Miler et al., 2013, Miler et al., 2015) represent a new stressor-specific assessment tool. However, during the development, it was detected that the strength of the indices varied across European regions, requiring regional optimization so as to account for variations in the effects of morphological pressures on macroinvertebrate communities across European lakes. While these regional differences can partly be attributed to large-scale historical and climatic factors influencing macroinvertebrate diversity across geographical regions (Heino, 2009), differences in intensities of certain stressors such as morphological shoreline degradation, are also likely to influence these regional patterns. In Central and Southern Europe, erosion control structures such as retaining walls are a common morphological alteration of littoral zone of e.g. German riverine lakes (Brauns et al., 2007). However, in Northern Europe (e.g. Ireland, Sweden) lake shores have comparatively less sturdy alteration structures, such as loose boulders or rubble (Jurca et al., 2012, McGoff and Sandin, 2012, White and Irvine, 2003). Recent studies on the impact of anthropogenic shoreline alterations on lake ecological status have focused merely on regional levels (Bänziger, 1995, Brauns et al., 2007, Pilotto et al., 2015, Porst et al., 2012) and monitoring programs compliant with the requirements of the European Water Framework Directive (WFD) (EC, 2000) have been developed for individual EU member states (Böhmer et al., 2014, Urbanič, 2014). Therefore, national methods as well as the recently developed assessment methods LIMCO and LIMHA (Miler et al., 2013, Miler et al., 2015) have yet to be refined further across national borders, as they still contain different assessment metrics for each geographical region or country (Miler et al., 2013). For the identification of harmonised stressor-specific metrics, which account for geological, climatic and environmental differences characterising large-scale (bio-)geographical regions (Poikane et al., 2014), comparative studies testing the response of littoral macroinvertebrates to anthropogenic shoreline alterations across European regions are needed.

We investigated the effects of human shoreline alteration on littoral benthic macroinvertebrate communities across four regions in Europe. We compared communities from two types of shoreline alterations (retaining walls/rip-raps/boulders and recreational beaches/riparian clearcutting) with natural (unmodified) lakeshores to test if:

• the response of littoral macroinvertebrate diversity and community composition to shoreline alterations and associated habitat loss, is consistent among geographical regions,

• if indicator taxa for different alteration types and littoral habitats vary among geographical regions.