a b s t r a c tLand use related habitat degradation in freshwater ecosystems has considerably increased over the past decades, resulting in effects on the aquatic and the riparian communities. Previous studies, mainly in undisturbed systems, have shown that aquatic emergent insects contribute substantially to the diet of riparian predators. To evaluate the effect of land use on aquatic prey subsidies of riparian spiders, we performed a longitudinal study from June to August 2012 along a first order stream (Rhineland-Palatinate, Germany) covering three land use types: forest, meadow and vineyard. We determined the contribution of aquatic and terrestrial resources to the diet of web-weaving (Tetragnathidae spp.) and ground-dwelling (Pardosa sp.) riparian spiders using stable isotope analyses of aquatic emergent insects and terrestrial arthropods. The contribution of aquatic and terrestrial sources differed between Tetragnathidae spp. and Pardosa sp. as well as among land use types. Tetragnathidae spp. consumed 80-100% of aquatic insects in the meadows and 45-65% in the forest and vineyards. Pardosa sp. consumed 5-15% of aquatic insects in the forest, whereas the proportions of aquatic and terrestrial sources were approximately 50% in the meadow and vineyard. Thus, aquatic emergent insects are an important subsidy to riparian spiders and land use is likely to affect the proportion of aquatic sources in the spider diet.

In situ assays provide more realistic exposure scenarios than laboratory assays, which is particularly pertinent for estuaries because exposure conditions are difficult to simulate. Traditionally, sublethal toxicity testing endpoints, such as growth, emergence, and reproduction, imply time-delayed extrapolations from individuals to populations, communities, and ecosystems. Sublethal responses mechanistically linked to ecosystem functions have been largely neglected. Feeding is an unequivocal ecologically meaningful response because its impairment has direct and immediate effects on ecosystems, by hampering key functions such as organic matter decomposition, long before its effects at the individual level have consequences at successively higher levels of biological organization. The ultimate goal of the present study was to widen the range of ecosystem functions for estuarine quality assessments. Specifically, a short-term in situ assay based on the postexposure feeding of the mudsnail Hydrobia ulvae is presented. Methodologies to quantify precisely postexposure egestion as a surrogate of feeding were achieved. A multiple regression model from laboratory experiments was successfully applied to an in situ assay at reference (Mira River) and contaminated Portuguese estuaries (Sado River) for predicting reference results and allowing unraveling confounding factors during exposure (temperature, salinity, sediment grain size). Sensitivity comparisons of postexposure feeding with survival and growth, after Cu exposure, were carried out and used for a first preliminary appraisal of the relative consequences of ecosystem-level immediate effects.