Can biological invertebrate traits resolve effects of multiple stressors on running water ecosystems?

Abstract

SUMMARY1. Accurately assessing the effects of multiple human-caused stressors on freshwater (and other) ecosystems is an essential step in the development of efficient decision support tools for environmental managers. Our objective is to review potentials and limitations of the use of biological traits as indicators (BTIs) of multiple stressor effects on running water (i.e. lotic) ecosystems. 2. Pioneers in ecology provided mechanistic explanations for responses of alternative biological traits to a given stressor and for the action of habitat harshness as a trait filter. These ideas were subsequently integrated in theoretical ecological constructs (e.g. Habitat Templet Concept) that form the basis of the BTI approach. 3. To resolve the effects of multiple stressors on running waters requires multiple traits of a biologically diverse group of organisms such as lotic invertebrates. To meet this goal, however, recently created databases on the biological traits of lotic invertebrates must be expanded and unified. 4. Addressing the technical implementation of the BTI approach, we illustrate that anticipated problems with phylogenetic trait syndromes are seemingly less serious in reality and that presence-absence data of genera and few sample replicates are sufficient for accurate trait descriptions of invertebrate communities. 5. Current trends in politics demand that biomonitoring tools be effective at large scales, i.e. large-scale trait patterns of natural communities (i.e. at reference conditions) should be relatively stable. The trait composition of natural invertebrate communities is relatively stable at the scale of Europe and North America because trait filters of natural lotic habitats act similarly across large biogeographical units. 6. The mechanistic actions of stressors on the biological traits of invertebrates should facilitate a priori predictions, but the complexity of potential trait responses makes such predictions sometimes difficult. 7. To illustrate potentials and limitations of BTIs to identify a given stressor acting exclusively (or primarily), we examine the (i) use of functional feeding groups to indicate the action of various stressors and (ii) trait responses to an indirectly acting stressor (discharge variation) and to a more directly acting stressor (near-bottom flow). If the excessive use of specific traits for the indication of too many different stressors is avoided and a given stressor acts directly on traits as a priori predicted, reliable interpretations of trait responses can be achieved. Thus, the BTI approach has the potential to inaugurate a new era in the biomonitoring of lotic (and other) ecosystems.

Biomonitoring of lake sediments using benthic macroinvertebrates

“…While the method has been successfully used to develop effective indices for running waters responding to individual pressures {e.g., eutrophication, morphological alteration, climate change and toxic contamination [77]}, works on invertebrate community traits in lakes have not been published yet.…”

“…The resistance and the resilience characteristics adopted by taxa therefore determine the response of the community to disturbance events. The advantage of using functional traits instead of taxonomic composition of communities is bound to the a priori predictable response of traits to individual stressors [16,54,77]. Each trait is supposed to respond independently to a given pressure and each pressure affects different traits.…”

“…At present, fuzzy coding analysis has been successfully used to match species with individual traits [16,77], but other approaches may be more powerful {e.g., Giller et al [51] suggested the allocation of species into groups based on several relevant traits}.…”

“…The recent trait approach was successfully used to develop mechanistic models based on a solid theoretical basis to predict the response of natural communities, considering both structural and functional aspects [13,77,80,82]. To understand how multiple stressors may affect trait composition, microcosms and mesocosms can be used to find a priori models explaining direct and indirect effects on communities.…”

“…In particular, the loss of non-random species, the additivity of ecosystem functioning between habitats and the impact of local processes should be clarified [50]. Moreover, it is necessary to disentangle the effects of multiple stressors into single impacts with direct effects on community [77]. Figure 3.…”