Physiological indicators of fitness present a measure of an organism's response to a changing environment. An analysis of how these organisms allocate and store their energy resources provides an understanding of how they cope with such environmental changes. Each individual has to balance the investment necessary to acquire a certain resource with the energy gained by it. This trade-off can be monitored by measuring several physiological indicators of fitness such as energy storage components, metabolic state or RNA/DNA ratio. Because environmental adaptations and ecological strategies of survival are best examined within the natural environment, our research has to rely on the physiological indicators that are easily accessible in the field. The physiological indicators presented here are significant for an individual's fitness and in turn lead to reliable values in field-collected samples. Based on our own expertise and on a literature survey, the physiological relevance of the presented indicators is explained. Furthermore, some consideration to the analytical methods used to obtain the physiological indicators is given, and possible errors introduced at the sampling site and during the laboratory procedures are discussed. This work demonstrates that the integration of ecological and physiological expertise facilitates the identification of future ecological problems much earlier than separate approaches of both disciplines alone.

1. We conducted an experimental study of predation by benthivorous fish on a natural community of stream invertebrates using a reach-scale approach. Over a 2-year period (experimental phase), the benthic invertebrate community of a stretch containing two species of benthivorous fish was compared with a fishless stretch. Thereafter, all fish were removed and benthic community structure was analysed again to account for natural differences between the two stretches (reference phase). 2. Benthivorous fish at the moderate densities investigated did not affect total benthic biomass or density, but did alter species composition. In addition, the fish effect differed between pool and riffle habitats, with larger effects in the pools indicating a habitatspecific predation effect. In the reference phase, when all fish were removed from the stream, the difference between the two stretches was reduced. 3. The benthivorous fish reduced the densities of four taxa (Pisidium sp., Dugesia gonocephala, Gammarus pulex, Limoniidae), representing 29% of total biomass. It is possible that density reductions of other species were masked by prey migration despite the relatively large spatial scale. Indeed, higher drift activity in the upstream fishless stretch could have increased the density of Baetis rhodani in the fish stretch, as indicated by the results of a drift model. 4. Our results provide insights into stream food web ecology because fish predation showed effects even in a natural system where habitat complexity was high, environmental factors were highly variable and many predator and prey species interacted and because benthivorous fish were the focus, whereas the majority of previous predation experiments in streams have used drift-feeding trout.

Taking into account the continuous increase in freshwater introductions, and to support the recent European legislation on invasive alien species, the identification of priority pathways and gateways of introductions is of utmost importance to develop adequate control strategies. The aim of this paper was to analyse the main pathways and gateways of introductions of freshwater alien species in Europe. Based on a thorough review of the scientific and grey literature, information on pathways, country and year of initial introduction of all freshwater alien species in Europe, was retrieved. The spatial and temporal patterns and trends of biological invasions in freshwater ecosystems in Europe, in relation to different pathways, were assessed. Our results pinpoint the major importance of aquaculture, pet/aquarium trade and stocking activities as pathways of introduction of freshwater alien species in Europe. For species native to some European countries, shipping and inland canals were the most important pathways, highly responsible for the entry of many harmful species. Germany, the United Kingdom and Italy were the main entry gateways of freshwater alien species in Europe. We found a geographical pattern related to some pathways of introduction in Europe: introductions through inland canals were concentrated in Central/North-eastern Europe, while introductions through pet/terrarium/aquarium trade were mainly observed in Central/Western Europe. While Chordata species entered Europe mainly through the three major above mentioned pathways, many harmful Arthropoda and Mollusca entered through shipping and inland canals. The information gathered in this study clearly indicates the entry routes that should be prioritised by Member States, for which stronger control and management actions should be implemented and prevention efforts concentrated under the scope of the related new EU Regulation.

Freshwater ecosystems are polluted with various environmental chemicals. For example, pesticides enter the aquatic environment via spray drift or surface runoff from catchment areas used for industrialised agriculture. In the present study, we investigated the response of the grazer−aufwuchs interaction when exposed to the herbicide terbutryn in a microcosm experiment. Terbutryn induced a trophic cascade with negative effects on grazers by inhibiting growth of primary producers. We determined a no-observed-effect concentration (measured as particulate organic carbon, NOEC POC ) of 0.21 µg l −1 for aufwuchs biomass and a lowest-observed-effect concentration (LOEC POC ) of 2.01 µg l −1. Furthermore, a shift in the aufwuchs community was detected in all terbutryn treatments nearly 4 wk after exposure, and this shift persisted until the end of the experiment in the treatment with the highest terbutryn concentration. In addition, reduced energy stores (triglycerides, TG) of the grazer Rhithrogena semicolorata (Heptageniidae: Ephemeroptera) were found (NOEC TG = 0.03 µg l ), which was interpreted as an indication of moderate starvation during the experiment. While starvation did not result in reduced larval growth as might have been expected, the ob served reduction of TG content in larvae (24%) is consistent with results from a separate experiment in which starvation alone induced a 15% reduction of TG content as well as reduced emergence, reduced size at emergence, and reduced egg production.

Please cite this article as: Worischka, S., Schmidt, S.I., Hellmann, C., Winkelmann, C.,Selective predation by benthivorous fish on stream macroinvertebratesndashthe role of prey traits and prey abundance, Limnologica (2015), http://dx.