Effects of invasive benthic macroinvertebrates on assessment methods of the EU Water Frame Work Directive

Abstract

The assessment of the ecological status of aquatic ecosystems for the implementation of the European Water Framework Directive is based on different methods, many of which include the study of macroinvertebrate organisms. We examined whether and how invasive species affect the calculation of metrics used for fresh water assessment utilizing data from different substrate types in the streams of Central Germany. In these streams, the proportion of macroinvertebrate invasives increased from a very low fraction of the community up to 75% of species, or 96% of individuals, within 15 years. The values of the German Saprobic Index (GSI, reflecting the degree of organic load) did not differ significantly between different substrate types or within the examined stream reaches. However, saprobic valences of the species recorded did differ between substrates and between localities. This obvious contradiction is caused by an abundance of exotic species all having a medium GSI index between 2.2 and 2.3. Moreover, the minimum total number of organisms required for this method cannot be reached for a large majority of the sites dominated by invasives making it impossible to use the GSI. Regarding distribution of zonation types, the proportion of metarhithral species is low, and it is even lower on hard substrates than it is on soft substrates. This contradicts the general assumption that dwellers preferring metarhithral reaches (=lower-trout region) will show an affinity for habitats with higher oxygen concentrations and stronger flow velocities, both appearing more on hard than on soft substrates. This latter contradiction results from the classification of the most abundant invasive species Potamopyrgus antipodarum, Dikerogammarus villosus, and Chelicorophium curvispinum in the AQEM taxa reference list. The metrics 'locomotion type' and 'feeding type' were also affected by the presence of invasive species. Possible options for overcoming these assessment problems are discussed.

Potential effects of the invasive ‘killer shrimp’ (Dikerogammarus villosus) on macroinvertebrate assemblages and biomonitoring indices

“…For instance, our mesocosm study shows that D. villosus is far more predatory towards other taxa than the resident amphipod species it may be replacing, such as G. pulex (MacNeil & Platvoet, 2005) or G. duebeni (Dick & Platvoet, 2000), supporting the conjecture that increased predation results in the decline of residents. From German river field surveys, Arndt et al (2009) found that D. villosus presence could undermine the usefulness of the GSI, and now our study shows that D. villosus has the potential to undermine the reliability of an additive biotic index such as the BMWP score. For instance, the aggressive and predatory activities of D. villosus could cause a decline in resident predators such as Ecnomidae (Trichoptera), as they are outcompeted for shared prey species.…”

“…The accuracy of other indices commonly used in Central Europe, such as the Belgian Biotic Index (BBI - Gabriels, Goethals & De Pauw, 2005) and the German Saprobic Index (GSI - Arndt et al, 2009), has also been shown to be compromised by the presence of abundant invaders, such as the Asian clams Corbicula spp. There remains a lack of consensus on inclusion ⁄ exclusion or assigned score ⁄ tolerance values with respect to invaders and biotic indices (Gabriels et al, 2005;Arndt et al, 2009). There remains a lack of consensus on inclusion ⁄ exclusion or assigned score ⁄ tolerance values with respect to invaders and biotic indices (Gabriels et al, 2005;Arndt et al, 2009).…”

Macroinvertebrate metrics and their integration for assessing the ecological status and biocontamination of Lithuanian lakes

“…Various metrics of ecological status, such as the BMWP score, the ASPT, species richness, EPT taxa number, Shannon-Wiener diversity or German saprobic index, have been shown to be affected by the presence of invasive species or at least related to it (Arbačiauskas et al, , 2011Gumuliauskaitė and Arbačiauskas, 2008;Arndt et al, 2009;MacNeil et al, 2010). Our lake macroinvertebrate data did not reveal any significant impact of biocontamination on the LLMI or its core metrics.…”

Alien molluscs affect the composition and diversity of native macroinvertebrates in a sandy flat of Lake Neuchâtel, Switzerland

“…Interestingly, duck do not feed on C. fluminea, which has thicker valves than D. polymorpha and lives buried in the upper layer of sand . Several studies suggest that alien species generally have a negative impact on native communities (Strayer, 1999(Strayer, , 2010Rahel, 2002;Arndt et al, 2009). However, Botts et al (1996) demonstrated in a field experiment that Dreissena species can change the physical structure of sandy habitats which in turn may lead to increased densities of native species.…”