Toxic dinoflagellates (Alexandrium fundyense and A. catenella) have minimal apparent effects on oyster hemocytes

The possible effect of Alexandrium spp. containing paralytic shellfish poisoning (PSP) toxins on the hemocytes of oysters was tested experimentally. In one trial, eastern oysters, Crassostrea virginica Gmelin, were exposed to bloom concentrations of the sympatric dinoflagellate, Alexandrium fundyense Balech, alone and in a mixture with a non-toxic diatom, Thalassiosira weissflogii (Grun) Fryxell et Hasle. Subsequently, another experiment exposed Pacific oysters, Crassostrea gigas Thunberg, to a mixed suspension of the sympatric, toxic species Alexandrium catenella (Whedon et Kofoid) Balech, with T. weissflogii. Measurements of numbers of oyster hemocytes, percentages of different cell types, and functions (phagocytosis, reactive oxygen species (ROS) production, and mortality) were made using flow-cytometry. During and after exposure, almost no significant effects of Alexandrium spp. upon hemocyte numbers, morphology, or functions were detected, despite observations of adductor-muscle paralysis in C. virginica and measured toxin accumulation in C. gigas. The only significant correlation found was between toxin accumulation at one temperature and higher numbers of circulating live and dead hemocytes in C. gigas. The PSP toxins are known to interfere specifically with sodium-channel function; therefore, the finding that the toxins had no effect on measured hemocyte functions suggests that sodium-channel physiology is not important in these hemocyte functions. Finally, because oysters were exposed to the living algae, not purified toxins, there was no evidence of bioactive compounds other than PSP toxins affecting hemocytes in the two species of Alexandrium studied.     

Stress reactions in Vitis vinifera L. following soil application of the herbicide flumioxazin

In order to evaluate the stress effects of flumioxazin (fmx) on grapevine, a non-target plant (Vitis vinifera L.), physiological parameters such as carbohydrate content, water status or nitrogenous metabolites were investigated on fruiting cuttings and plants grown in vineyard. In the leaves of cuttings, the soil-applied herbicide induced stress manifestations including a decrease of the dry weight percentage and the soluble carbohydrate content during the first week after treatment. Thereafter, a decrease of the osmotic potential was observed, as well as a decrease of total protein content and a parallel accumulation of free amino acids, including proline. Altogether, these results suggest that soil-applied fmx induced a stress in grapevines, leading to leaf proteolysis. However, this stress was partially recovered 3 weeks after herbicide application, suggesting that the cuttings were capable to adapt to the fmx exposure. In the vineyard, the flumioxazin effects were still significant 5 months after the treatment, particularly in the CH cv. They included a decrease of the leaf dry weight percentage and soluble carbohydrate content, as well as an increase of the osmotic potential. The decrease of leaf soluble carbohydrates may have dramatic consequences for the berry growth and the reserve constitution. Moreover, treated plants were characterized by a decrease of the free amino acid content and an accumulation of ammonium, while the protein level did not significantly increase, suggesting a degradation of amino acids. The alteration of carbon and nitrogen status after herbicide treatment may affect the grapevine vigour in a long term.     

The derivation of species response curves with Gaussian logistic regression is sensitive to sampling intensity and curve characteristics

We investigated quantitatively the sensitivity of plant species response curves to sampling characteristics (number of plots, occurrence and frequency of species), along a simulated pH gradient. We defined 54 theoretical unimodal response curves, issued from combinations of six values for optimum (opt = 3, 4, …, 8), three values for tolerance (tol = 0.5, 1.0, and 1.5, sensu ter Braak and Looman [ter Braak, C.J.F., Looman, C.W.N., 1986. Weighted averaging, logistic regression and the Gaussian response model. Vegetatio 65, 3–11]), and three values for maximum probability of presence (p_max = 0.05, 0.20, and 0.50). For each of these 54 theoretical response curves, we built artificial binary data sets (presence/absence) to test the influence of species occurrence, frequency, or number of available plots. With real data extracted from EcoPlant, a phytoecological database for French forests [Gégout, J.-C., Coudun, Ch., Bailly, G., Jabiol, B., 2005. EcoPlant: a forest sites database linking floristic data with soil characteristics and climatic conditions. J. Veg. Sci. 16, 257–260], we compared the ecological response of 50 plant species to soil pH, based first on a small data set (100 randomly sampled plots), and then based on the whole data set available (3810 plots).     

To fission or to fusion: effects of community size on wild chimpanzee (<Emphasis Type="Italic">Pan troglodytes verus</Emphasis>) social organisation

To balance advantages and disadvantages of group living, some species have fission-fusion social systems in which members of the same group form frequently changing subgroups. This allows flexible responses of group size to external conditions while at the same time retaining group stability. In chimpanzees, subgroup (party) size and composition depend mainly on the presence of receptive females, food availability and the activity of the party. Here we analyse the extent to which fission-fusion parameters are influenced by changes of demographic variables like community size and composition. Data were collected from a habituated West African chimpanzee community (Taï forest, Côte dIvoire) over 10 years, during which total community size decreased from 51 to 21, and the number of adult males decreased from 9 to 2. Taï chimpanzees are highly gregarious, as they spend more than 80% of their time with unrelated conspecifics. With decreasing community size, party size, party duration and male-female association increased. Neither activity nor the presence of receptive females or feeding competition could explain the observed changes in grouping patterns. Thus, the decrease in community size led to an increase of party cohesion and also enhanced cohesiveness between the sexes, while general sociality remained unchanged. Therefore, our data support the notion that small communities are more cohesive and have a less flexible fission-fusion system.Communicated by D. Watts     

Shift in foraging grounds and diet broadening during ontogeny in southern elephant seals from Kerguelen Islands

Highly dimorphic species like southern elephant seals (Mirounga leonina, SES hereafter) frequently exhibit resource partitioning according to sex and/or age classes. We measured carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) of 404 blood samples (136 males and 268 females from Kerguelen Islands, 49°21′S, 70°18′E) from 2004 to 2011. Assuming that the distribution of carbon isotopes (δ¹³C value) reflects the two main foraging grounds (Polar Frontal and Antarctic Zones), we quantified the proportion of SES foraging within each zone in relation with size, a proxy for their age. We found a clear shift from Polar Frontal to Antarctic waters as male SES aged, but no relation as far as females is concerned. We also observed a widening range of nitrogen isotopic (δ¹⁵N) values, suggesting that both males and females expanded their diet spectra with age. Whereas males increased their trophic level, females remained constant on average, with some adult females feeding both at lower and at higher trophic levels than juveniles.     

Assessment and optimisation of VOC mass transfer enhancement by advanced oxidation process in a compact wet scrubber

Dimethyl disulphide (DMDS) removal was investigated in a compact scrubber (hydraulic residence time ≈20 ms), composed of a wire mesh packing structure where liquid and gas flow at co-current and high gas superficial velocity (>12 m s⁻¹). In order to regenerate the scrubbing liquid and to maintain a driving force in the scrubber, ozone and hydrogen peroxide were added to water since they allow the generation of nonselective and highly reactive species, hydroxyl radicals HO. Three ways of reagent distribution were tested. The influence of several parameters (liquid flow rate(s), ozone flow rate, pH and reagent concentrations) was investigated. The best configuration was obtained when ozone is transferred in the scrubbing liquid before introduction at the top of the scrubber simultaneously with the hydrogen peroxide solution, allowing to generate hydroxyl radical in the scrubber. With this configuration, DMDS removal could be increased from 16% with water to 34% at the same gas and liquid flow rates in the scrubber showing the potentiality of advanced oxidation process.     

Effects of intense agricultural practices on heterotrophic processes in streams

In developed countries, changes in agriculture practices have greatly accelerated the degradation of the landscape and the functioning of adjacent aquatic ecosystems. Such alteration can in turn impair the services provided by aquatic ecosystems, namely the decomposition of organic matter, a key process in most small streams. To study this alteration, we recorded three measures of heterotrophic activity corresponding to microbial hydrolasic activity (FDA hydrolysis) and leaf litter breakdown rates with (k_c) and without invertebrates (k_f) along a gradient of contrasted agricultural pressures. Hydrolasic activity and k_f reflect local/microhabitat conditions (i.e. nutrient concentrations and organic matter content of the sediment) but not land use while k_c reflects land-use conditions. k_c, which is positively correlated with the biomass of Gammaridae, significantly decreased with increasing agricultural pressure, contrary to the taxonomic richness and biomass of Trichoptera and Plecoptera. Gammaridae may thus be considered a key species for organic matter recycling in agriculture-impacted streams.     

Defining Chlorophyll-a Reference Conditions in European Lakes

The concept of “reference conditions” describes the benchmark against which current conditions are compared when assessing the status of water bodies. In this paper we focus on the establishment of reference conditions for European lakes according to a phytoplankton biomass indicator—the concentration of chlorophyll-a. A mostly spatial approach (selection of existing lakes with no or minor human impact) was used to set the reference conditions for chlorophyll-a values, supplemented by historical data, paleolimnological investigations and modelling. The work resulted in definition of reference conditions and the boundary between “high” and “good” status for 15 main lake types and five ecoregions of Europe: Alpine, Atlantic, Central/Baltic, Mediterranean, and Northern. Additionally, empirical models were developed for estimating site-specific reference chlorophyll-a concentrations from a set of potential predictor variables. The results were recently formulated into the EU legislation, marking the first attempt in international water policy to move from chemical quality standards to ecological quality targets.