Include or exclude? A review on the role and suitability of aquatic invertebrate neozoa as indicators in biological assessment with special respect to fresh and brackish European waters

Abstract

This paper reviews published knowledge on how to deal with invasive species during biological quality assessments in European river systems for water management and assessments of ecological quality required, for example, by the European Water Frame Work Directive. The papers studied included international papers and some standards for water assessment. An overview of the current state of neozoa research showed that many different topics are treated, comprising biogeography and fauna records, species replacements and effectiveness of colonisation, life cycles, competition between native and invasive species, habitat quality and pathways of migration. Additionally, some papers have been published recently on the integration of neozoa in index-based assessment systems. Although the decline or increase of alien species populations and the corresponding impacts on indigenous populations were frequently observed, the mechanisms behind the invasions often remain hypothetical. In the reviewed papers, issues such as possible reasons for coexistence, tolerances, quality of habitat or water, life history traits and introduction of diseases were rarely covered. Few neozoa are sufficiently investigated to be categorised as indicators. After discussing the advantages and disadvantages of inclusion or exclusion, inclusion of invaders in assessments of both biodiversity (all species) and human impact (only species classified in their specific tolerance) is suggested. Further research is required to (1) update and assign ecological profiles of the non-indigenous species currently and (2) assess the effects of new invaders on native communities.

Management challenges related to long‐term ecological impacts, complex stressor interactions, and different assessment approaches in the Danube River Basin

“…Besides, early species invasions in the Middle Danube cannot not be directly linked to the early constructions of HPPs in the upper reach. It seems likely that other factors related to anthropogenic alterations are relevant, further complicating management interventions (Orendt et al, ).…”

“…Restoration and rehabilitation measures may enhance habitat diversity and enable a coexistence of native and nonnative species. However, the extirpation of alien species seems unmanageable in the long term (Orendt, Schmitt, Liefferinge, Wolfram, & Deckere, 2009).…”

Biological Introductions to the Systems

“…There is growing recognition of a need to include, in one way or another, NIS into overall an environmental status assessment (e.g., Cardoso and Free, 2008;Orendt et al, 2009). However, the nature of bioinvasion impacts varies in broad extent (see Section 8.06.7.1); therefore, the detection of a signal to noise ratio (sensu Elliott, 2003) should be based on ranking of overall bioinvasion effect rather than on attempts to quantify multiple impacts of various IAS.…”

Parasite-mediated intraguild predation as one of the drivers of co-existence and exclusion among invasive and native amphipods (Crustacea)

“…However, some resident freshwater assemblages have been shown capable of integrating invaders, leading to patterns of coexistence (Skadsheim, 1984;Dick, 1996;MacNeil et al, 2001aMacNeil et al, , 2009Orendt et al, 2010). Understanding the factors that promote coexistence of native and invasive species is thus a research priority if we are to predict the community impacts of future invaders.…”