Sediment reworking by the burrowing polychaete Hediste diversicolor modulated by environmental and biological factors across the temperate North Atlantic. A tribute to Gaston Desrosiers

International audienceParticle mixing and irrigation of the seabed by benthic fauna (bioturbation) have major impacts on ecosystem functions such as remineralization of organic matter and sediment-water exchange. As a tribute to Prof. Gaston Desrosiers by the Nereis Park association, eighteen laboratories carried out a collaborative experiment to acquire a global snapshot of particle reworking by the polychaete Hediste diversicolor at 16 sites surrounding the Northern Atlantic. Organisms and soft sediments were collected during May – July at different geographical locations and, using a common laboratory protocol, particulate fluorescent tracers (‘luminophores’) were used to quantify particle transport over a 10-day period. Particle mixing was quantified using the maximum penetration depth of tracers (MPD), particle diffusive coefficients (Db), and non-local transport coefficients (r). Non-local coefficients (reflecting centimeter scale transport steps) ranged from 0.4 to 15 yr−1, and were not correlated across sites with any measured biological (biomass, biovolume) or environmental parameters (temperature, grain size, organic matter). Maximum penetration depths (MPD) averaged ~10.7 cm (6.5–14.5 cm), and were similar to the global average bioturbation depth inferred from short-lived radiochemical tracers. MPD was also not correlated with measures of size (individual biomass), but increased with grain size and decreased with temperature. Biodiffusion (Db) correlated inversely with individual biomass (size) and directly with temperature over the environmental range (Q10 ~ 1.7; 5–21 °C). The transport data were comparable in magnitude to rates reported for localized H. diversicolor populations of similar size, and confirmed some but not all correlations between sediment reworking and biological and environmental variables found in previous studies. The results imply that measures of particle reworking activities of a species from a single location can be generally extrapolated to different populations at similar conditions

Changes in cellular energy allocation in Enchytraeus albidus when exposed to dimethoate, atrazine, and carbendazim

Cellular energy allocation (CEA) is a methodology developed to evaluate the effects of toxic stress on the metabolic balance of organisms. It consists of the integration of the energy reserves available (Ea; total carbohydrate, protein and lipid content) and energy consumption (Ec) estimated by measuring electron transport system (ETS) activity. The main goal of the present study was to evaluate the effects on the energy budget of the soil invertebrate Enchytraeus albidus (Oligochaeta) after exposure to dimethoate, atrazine, and carbendazim (by testing the reproduction 10% effective concentration, 20% effective concentration, 50% effective concentration and 90% effective concentration) over periods of time from 0 d to 2 d, 4 d, and 8 d. Significant changes in energy reserves were observed with all pesticides, together with effects on energy consumption. Carbohydrates were the first energy source to be used, and clear depletions occurred with all pesticides. Energy consumption increased generally over longer exposures and with higher concentrations of the pesticides. Although clear changes were seen in the individual energy reserve budgets and on Ec, CEA was only significantly reduced with atrazine exposures longer than 4 d. The nearly absent effects on CEA at concentrations known to affect reproduction indicate that the reduction in reproduction is not likely to be caused by a reduction in the total energy budget during the first 8 d of exposure. The present study showed the importance of complementing CEA interpretation with the individual Ea and Ec parameters, in particular if these show opposite balances. The Ea and Ec results were in good agreement with gene transcription results from a parallel study, hence suggesting translation and showing the advantage of combining various effect levels to advance the understanding of mechanisms