Traits and stress: keys to identify community effects of low levels of toxicants in test systems

Community effects of low toxicant concentrations are obscured by a multitude of confounding factors. To resolve this issue for community test systems, we propose a trait-based approach to detect toxic effects. An experiment with outdoor stream mesocosms was established 2-years before contamination to allow the development of biotic interactions within the community. Following pulse contamination with the insecticide thiacloprid, communities were monitored for additional 2 years to observe long-term effects. Applying a priori ecotoxicological knowledge species were aggregated into trait-based groups that reflected stressor-specific vulnerability of populations to toxicant exposure. This reduces inter-replicate variation that is not related to toxicant effects and enables to better link exposure and effect. Species with low intrinsic sensitivity showed only transient effects at the highest thiacloprid concentration of 100 μg/l. Sensitive multivoltine species showed transient effects at 3.3 μg/l. Sensitive univoltine species were affected at 0.1 μg/l and did not recover during the year after contamination. Based on these results the new indicator SPEARmesocosm was calculated as the relative abundance of sensitive univoltine taxa. Long-term community effects of thiacloprid were detected at concentrations 1,000 times below those detected by the PRC (Principal Response Curve) approach. We also found that those species, characterised by the most vulnerable trait combination, that were stressed were affected more strongly by thiacloprid than non-stressed species. We conclude that the grouping of species according to toxicant-related traits enables identification and prediction of community response to low levels of toxicants and that additionally the environmental context determines species sensitivity to toxicants

Interspecific competition delays recovery of Daphnia spp. populations from pesticide stress

Xenobiotics alter the balance of competition between species and induce shifts in community composition. However, little is known about how these alterations affect the recovery of sensitive taxa. We exposed zooplankton communities to esfenvalerate (0.03, 0.3, and 3 μg/L) in outdoor microcosms and investigated the long-term effects on populations of Daphnia spp. To cover a broad and realistic range of environmental conditions, we established 96 microcosms with different treatments of shading and periodic harvesting. Populations of Daphnia spp. decreased in abundance for more than 8 weeks after contamination at 0.3 and 3 μg/L esfenvalerate. The period required for recovery at 0.3 and 3 μg/L was more than eight and three times longer, respectively, than the recovery period that was predicted on the basis of the life cycle of Daphnia spp. without considering the environmental context. We found that the recovery of sensitive Daphnia spp. populations depended on the initial pesticide survival and the related increase of less sensitive, competing taxa. We assert that this increase in the abundance of competing species, as well as sub-lethal effects of esfenvalerate, caused the unexpectedly prolonged effects of esfenvalerate on populations of Daphnia spp. We conclude that assessing biotic interactions is essential to understand and hence predict the effects and recovery from toxicant stress in communities

Cross-Eurasian and altitudinal distribution of lotic mayflies – species with wider altitudinal ranges have narrower geographical distribution

The aim of the study was to test the hypothesis that patterns of cross-Eurasian longitudinal distribution of lotic mayflies are determined by species' ecological requirements and the presence of the West Siberian Lowland. In particular, the objective was to test whether this great lowland is an environmental barrier preventing longitudinal dispersal of the rheophilic (i.e., preferring fast-running highland waters), but not the potamophilic (i.e., preferring slow-current lowland waters) mayflies, as its entire territory contains no rapidly-flowing streams suitable for rheophilic species. This hypothesis was tested indirectly by comparison of altitudinal ranges of species characterised by different cross-Eurasian distribution patterns (mainly East Palaearctic and Transpalaearctic species distributed over the Asian part of Palaearctica and entire Palaearctica respectively). The material used for the analyses was collected in the centre of Eurasia, south-western Siberia, Russia. The region covered both lowland and mountain territories. The studied biogeographical groups of mayflies have distinctly different altitudinal distribution: the Transpalaearctic species inhabit lowland watercourses only, while the East Palaearctic species inhabit the entire altitudinal range with most of the species preferring high elevations (on average 700 m a.s.l.). These results confirmed the stated hypothesis and showed that for most of the East Palaearctic (but not Transpalaearctic) species the West Siberian Lowland can be an environmental barrier preventing their westward dispersal and therefore precluding mixing of the East and West Palaearctic rheophilic faunas. However, possible alternative hypotheses cannot be ruled out, as altitudinal ranges of some of these species do not fall out of the elevation range of the West Siberian Lowland. Remarkably, the East Palaearctic species, which by definition have narrower distribution than the Transpalaearctic species, have broader altitudinal ranges than the Transpalaearctic species. This pattern is related to the altitudinal Rapoport effect recently detected for mayfly distribution over the river systems

Seasonal changes in the functional diversity of bacterioplankton in contrasting coastal environments of the NW mediterranean

10 pages, 4 figures, 1 tableTo understand the seasonal and intersite variations in the functional diversity of coastal bacterioplankton assemblages, their utilization of 31 different carbon sources was analyzed with Biolog-Ecoplates™ in waters from 3 harbours and 2 oligotrophic coastal environments of the NW Mediterranean. Polymers (α-cyclodextrin and glycogen) and carbohydrates (d-cellobiose and N-acetyl-d-glucosamine) were most utilized in the harbours, while carboxylic acids were mainly used in the coastal areas. Seasonal differences in the patterns of carbon source utilization (the so-called ‘functional diversity’) were investigated in 2 spatially close, but contrasting, coastal stations: the oligotrophic coastal site of Blanes Bay, and the Barcelona inner harbour. The existence of a possible seasonal trend in functional diversity of bacterioplankton in the oligotrophic coastal station, but not in the harbour, suggests that the bacterial assemblage of oligotrophic environments can adapt to changing inputs of nutrients and DOC. In contrast, the low water exchange in the harbour provides a pool of DOC of relatively stable composition throughout the year which could allow few potential bacterial metabolisms to persist. We considered the quantity of substrates used (of all those provided in the Biolog plate) as an index of potential functional diversity. The index calculated for the harbour and the coastal station samples was negatively correlated with chlorophyll a concentration, suggesting that the bacterial assemblages of oligotrophic systems have a higher number of metabolic pathways in order to be able to exploit a wide variety of DOC molecules present at low concentrationsThis work was supported by the projects BIOHAB (EVK3-CT99-00015), BASICS (EVK3-CT2002- 00078) and PROCAVIR (CTM 2004-04404-C02-01/MAR) and by a CSIC-I3P post-doctoral contract funded by the Fondo Social Europeo to M.M.S.Peer reviewe