Heavy ionic pollution disrupts assemblages of algae, macroinvertebrates and riparian vegetation.

Urban streams display consistent ecological symptoms that commonly express degraded biological, physical, and chemical conditions: the urban stream syndrome (USS). Changes linked to the USS result in consistent declines in the abundance and richness of algae, invertebrates, and riparian vegetation. In this paper, we assessed the impacts of extreme ionic pollution from an industrial effluent in an urban stream. We studied the community composition of benthic algae and benthic invertebrates and the indicator traits of riparian vegetation. The dominant pool of benthic algae, benthic invertebrates and riparian species were considered as euryece. However, ionic pollution impacted these three biotic compartments' communities, disrupting these tolerant species assemblages. Indeed, after the effluent, we observed the higher occurrence of conductivity-tolerant benthic taxa, like Nitzschia palea or Potamopyrgus antipodarum and plant species reflecting nitrogen and salt contents in soils. Providing insights into organisms' responses and resistance to heavy ionic pollution, this study sheds light on how industrial environmental perturbations could alter the ecology of freshwater aquatic biodiversity and riparian vegetation.

Acanthocephalan parasites reflect ecological status of freshwater ecosystem.

Acanthocephalans' position in food webs, in close interaction with free-living species, could provide valuable information about freshwater ecosystem health through the viability of the parasites' host populations. We explored Pomphorhynchus laevis cystacanths' and adults' intensities of infection, and the prevalence of infected hosts respectively in their Gammarus pulex intermediate hosts and Squalius cephalus definitive hosts in a Mediterranean river. First, we analysed the relationship between P. laevis intensity of infection, its two hosts populations and the other acanthocephalan species found (Pomphorhynchus tereticollis and Polymorphus minutus). Second, we characterised the influence of bacteriological, physicochemical and biological water parameters on these acanthocephalans, and their intermediate and definitive hosts. This research highlights that P. laevis infection was closely related to their two preferential hosts population in the river. Moreover, P. laevis intensity of infection was positively correlated with organic pollution in the river but negatively correlated with biodiversity and with ecological indexes of quality. Pomphorhynchus laevis could thus benefit from moderate freshwater pollution, which promotes their tolerant intermediate and definitive hosts.

Effects of Urbanization on Plant-Pollinator Interactions in the Tropics: An Experimental Approach Using Exotic Plants.

Land-use changes through urbanization and biological invasions both threaten plant-pollinator networks. Urban areas host modified bee communities and are characterized by high proportions of exotic plants. Exotic species, either animals or plants, may compete with native species and disrupt plant-pollinator interactions. These threats are heightened in insular systems of the Southwest Pacific, where the bee fauna is generally poor and ecological networks are simplified. However, the impacts of these factors have seldom been studied in tropical contexts. To explore those questions, we installed experimental exotic plant communities in urban and natural contexts in New Caledonia, a plant diversity hotspot. For four weeks, we observed plant-pollinator interactions between local pollinators and our experimental exotic plant communities. We found a significantly higher foraging activity of exotic wild bees within the city, together with a strong plant-pollinator association between two exotic species. However, contrary to our expectations, the landscape context (urban vs. natural) had no effect on the activity of native bees. These results raise issues concerning how species introduced in plant-pollinator networks will impact the reproductive success of both native and exotic plants. Furthermore, the urban system could act as a springboard for alien species to disperse in natural systems and even invade them, leading to conservation concerns.

Effects of catchment area and nutrient deposition regime on phytoplankton functionality in alpine lakes.

High mountain lakes are a network of sentinels, sensitive to any events occurring within their waterbodies, their surrounding catchment and their airshed. In this paper, we investigate how catchments impact the taxonomic and functional composition of phytoplankton communities in high mountain lakes, and how this impact varies according to the atmospheric nutrient deposition regime. For two years, we sampled the post snow-melt and the late summer phytoplankton, with a set of biotic and abiotic parameters, in six French alpine lakes with differing catchments (size and vegetation cover) and contrasting nitrogen (N) and phosphorus (P) deposition regimes. Whatever the nutrient deposition regime, we found that the lakes with the smallest rocky catchments showed the lowest functional richness of phytoplankton communities. The lakes with larger vegetated catchments were characterized by the coexistence of phytoplankton taxa with more diverse strategies in the acquisition and utilization of nutrient resources. The nutrient deposition regime appeared to interact with catchment characteristics in determining which functional groups ultimately developed in lakes. Photoautotroph taxa dominated the phytoplankton assemblages under high NP deposition regime while mixotroph taxa were even more favored in lakes with large vegetated catchments under low NP deposition regime. Phytoplankton functional changes were likely related to the leaching of terrestrial organic matter from catchments evidenced by analyses of carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in seston and zooplankton. Plankton δ15N values indicated greater water-soil interaction in lakes with larger vegetated catchments, while δ13C values indicated the effective mineralization of the organic matter in lakes. The role played by catchments should be considered when seeking to determine the vulnerability of high altitude lakes to future changes, as catchments' own properties will vary under changes related to climate and airborne contaminants.

No association between the use of Bti for mosquito control and the dynamics of non-target aquatic invertebrates in French coastal and continental wetlands.

The environmental safety of Bacillus thuringiensis subsp. israelensis (Bti) is still controversial, mainly because most of the previous field studies on its undesired effects were spatially limited and did not address the relationship between community similarity and application time and frequency. No general statement can therefore be drawn on the usage conditions of Bti that insure protection of non-target organisms. The present study was conducted in eight sites distributed over the main geographical sectors where mosquito control is implemented in mainland France and Corsica. Changes in non-target aquatic invertebrates were followed at elapsed time after repeated applications of two Bti formulations (VectoBac® WDG or 12AS) up to four consecutive years. We examined the influence of both larvicide treatments and environmental variables on community dynamics and dissimilarity between treated and control areas. As it can be argued that chironomids are the most vulnerable group of non-target invertebrates, we scrutinised potential Bti-related effects on the dynamics of their community. The use of VectoBac® WDG and 12AS in coastal and continental wetlands had no immediate or long-term detectable effect on the taxonomic structure and taxa abundance of non-target aquatic invertebrate communities, including chironomids. This applied to the main habitats where mosquito larvae occur, regardless of their geographic location. Flooding, whose frequency and duration depend on local meteorological and hydrological conditions, was identified as the main environmental driver of invertebrate community dynamics. Our findings add support to the environmental safety of currently available Bti formulations when following recommended application rates and best mosquito control practices.

Effects of Bacillus thuringiensis israelensis and spinosad on adult emergence of the non-biting midges Polypedilum nubifer (Skuse) and Tanytarsus curticornis Kieffer (Diptera: Chironomidae) in coastal wetlands.

To optimize their efficacy, some insecticides used for mosquito control are introduced into aquatic ecosystems where mosquito larvae develop (marshes, ponds, sanitation devices) and cannot escape from the treated water. However, this raises the question of possible effects of mosquito larvicides on non-target aquatic species. Bacillus thuringiensis var. israelensis (Bti), which is well-known for its selectivity for Nematocera dipterans, is widely used for mosquito control all over the world. Spinosad, a mixture of spinosyns A and D known as fermentation products of a soil actinomycete (Saccharopolyspora spinosa), is a biological neurotoxic insecticide with a broader action spectrum. It is a candidate larvicide for mosquito control, but some studies showed that it may be toxic to beneficial or non-target species, including non-biting midges. The present study was therefore undertaken to assess the impact of Bti and spinosad on natural populations of Polypedilum nubifer (Skuse) and Tanytarsus curticornis Kieffer (Diptera: Chironomidae) in field enclosures implemented in Mediterranean coastal wetlands. Unlike Bti, spinosad had a strong lethal effect on P. nubifer and seems to affect T. curticornis at presumed recommended rates for field application. Differences in the sensitivity of these two species to spinosad confirm that population dynamics need to be known for a proper assessment of the risk encountered by chironomids in wetlands where larvicide-based mosquito control occurs.

Ecology of leishmaniasis in the South of France. 22. Reliability and representativeness of 12 Phlebotomus ariasi, P. perniciosus and Sergentomyia minuta (Diptera: Psychodidae) sampling stations in Vallespir (eastern French Pyrenees region).

This study was conducted around Céret (Pyrénées-Orientales, mean elevation 200 m) to test the statistical reliability of 12 stations devoted to sampling the Leishmania infantum vectors Phlebotomus ariasi and P. perniciosus in the South of France. Each station included a retaining wall and the surrounding phytoecological environment (total area: 2,000 m(2)). The wall had rectangular drainage cavities (weep holes) in which flight interception traps (sticky paper) were inserted and stretched every 10 days from May to October. For both vector species, the statistical analysis of 10-day and annual frequencies led to the following conclusions: (1) P. ariasi densities were significantly higher than P. perniciosus densities, (2) densities per species were significantly different at the 12 stations : none of them could be considered as representative of local vector densities, which depend on the wall structure (exposure, shade, vertebrate hosts), (3) the 10-day variation trends were not significantly different between stations, indicating that these variations are not determined by the station structure but rather by a common external factor (likely meteorological) and (4) the phytoecological features at the stations were not correlated with the sandfly densities. Most of the observations obtained with P. ariasi and P. perniciosus are also relevant for the non-vectorial species S. minuta. In conclusion, future research on the dynamics of leishmaniasis outbreaks relative to climate change and agricultural-silvicultural modifications should be very cautiously carried out, while focusing especially on the vector sampling quality and the use of phytoecological maps as vector density indicators.

Chitobiase activity as an indicator of altered survival, growth and reproduction in Daphnia pulex and Daphnia magna (Crustacea: Cladocera) exposed to spinosad and diflubenzuron.

Chitobiase is involved in exoskeleton degradation and recycling during the moulting process in arthropods. In aquatic species, the moulting fluid is released into the aqueous environment, and chitobiase activity present therein can be used to follow the dynamics of arthropod populations. Here, chitobiase activity was used for monitoring the impact of mosquito candidate larvicides on Daphnia pulex and Daphnia magna under laboratory conditions. Both species were exposed to spinosad (2, 4, 8 µg L(-1)) and diflubenzuron (0.2, 0.4, 0.8 µg L(-1)) for 14 days. Bacillus thuringiensis var. israelensis (Bti; 0.25, 0.5, 1 µL L(-1)) was used as the reference larvicide. Chitobiase activity, adult survival, individual growth and fecundity, expressed as the number of neonates produced, were measured every 2 days. Average Exposure Concentrations of spinosad were ten-fold lower than the nominal concentrations, whereas only a slight deviation was observed for diflubenzuron. In contrast to Bti, spinosad and diflubenzuron significantly affected both species in terms of adult survival, and production of neonates. As compared to D. pulex, D. magna was more severely affected by diflubenzuron, at low and medium concentrations, with reduced adult growth and much lower chitobiase activity. Chitobiase activity was positively correlated with the individual body length, number of neonates produced between two consecutive observation dates, and number of females and neonates. In addition, the significant positive correlations between chitobiase activity measured on the last sampling date before the first emission of neonates and the cumulative number of neonates produced during the whole observation period strongly support the potential of the activity of this chitinolytic enzyme as a proxy for assessing the dynamics of arthropod populations exposed to larvicides used for mosquito control.

Population-level effects of spinosad and Bacillus thuringiensis israelensis in Daphnia pulex and Daphnia magna: comparison of laboratory and field microcosm exposure conditions.

Because exposure to toxicants not only results in mortality but also in multiple sublethal effects, the use of life-table data appears particularly suitable to assess global effects on exposed populations. The present study uses a life table response approach to assess population-level effects of two insecticides used against mosquito larvae, spinosad (8 µg/l) and Bacillus thuringiensis var. israelensis (Bti, 0.5 µl/l), on two non target species, Daphnia pulex and Daphnia magna (Crustacea: Cladocera), under laboratory versus field microcosms conditions. Population growth rates were inferred from life table data and Leslie matrices under a model with resource limitation (ceiling). These were further used to estimate population risks of extinction under each tested condition, using stochastic simulations. In laboratory conditions, analyses performed for each species confirmed the significant negative effect of spinosad on survival, mean time at death, and fecundity as compared to controls and Bti-treated groups; for both species, population growth rate λ was lower under exposure to spinosad. In field microcosms, 2 days after larvicide application, differences in population growth rates were observed between spinosad exposure conditions, and control and Bti exposure conditions. Simulations performed on spinosad-exposed organisms led to population extinction (minimum abundance = 0, extinction risk = 1), and this was extremely rapid (time to quasi-extinction = 4.1 one-week long steps, i.e. one month). Finally, D. magna was shown to be more sensitive than D. pulex to spinosad in the laboratory, and the effects were also detectable through field population demographic simulations.

Tributaries under Mediterranean climate: their role in macrobenthos diversity maintenance.

The taxonomic richness erosion and the role of tributaries in the maintenance of the taxonomic richness were considered in a Mediterranean catchment in southeastern France. Nine stations were chosen along the Arc stream (three stations downstream from an organic effluent and one station upstream from the pollution source) and on two groups of tributaries (three intermittent and two perennial). High biodiversity erosion was noticed in the main stem, revealing diffuse sources of pollution added to the expected effect of the localized organic pollution. Jackknife richness estimator and beta diversity indicated that the intermittent tributaries had the highest richness values and harboured 70% of the taxa recorded at the catchment scale. The intermittent flow tributaries seem to play a major role in maintaining the taxonomic richness in such catchments, highly impacted by anthropogenic activities. The detailed examination and the preservation of these ecosystems should be an important step in catchment management, and support the need for catchment-scale conservation of freshwater invertebrates.

[A new approach to biodiversity: morphological plasticity of a fresh-water diatom]. / Une nouvelle approche de la biodiversité: plasticité morphologique chez une diatomée d'eau douce.

Population responses of a planktonic freshwater diatom, Asterionella formosa Hassal, to the hydrodynamic anthropic disturbances were studied at the landscape scale, along a series of nine reservoirs, for a period of 18 months. The analysis of biotic descriptors as cell abundance, cell length and architecture has shown a strong morphological plasticity of this diatom. The morphological variability of A. formosa in response to hydrodynamic conditions favours the colonization of lacustrine freshwater ecosystem for this species. The determination of architectural indices allowed us to distinguish a modification of biodiversity along a disturbance gradient for population level.