Variability in the outcome of outdoor mesocosms with three-spined Stickleback (Gasterosteus aculeatus) populations in control conditions : data from 20 replicates in two annual experiments
Résumé
Ecotoxicology aims at protecting ecosystems and populations. Population level is rarely studied in ecotoxicity tests. However, the population level can be monitored with high realism relative to ecosystems through experiments in outdoor mesocosms. At INERIS, we focus on the three-spined Stickleback, Gasterosteus aculeatus, because it is a well-studied species, autochthonous in French rivers, and a promising species to assess the impact of contaminant. All studies already performed in mesocosms suffer from an important variability between replicates for a same treatment (more than 50 % of variation is generally observed on biological variables). Temporal replicability of mesocosms' outcomes is also an issue. In our study, we aimed at identifying the major causes of inter and intra annual variability in control conditions. Thus ten populations per year, for two years experiments were monitored between March and October 2010 and 2011. At the beginning of experiments, each compartment of the ecosystem (weight of macrophytes, number and masse of invertebrates, number, length and sex ratio of fish...) were introduced in standardized conditions. At the end of the experiments, all populations were defined by characteristics such as total number of fish, sex ratio, and percentage of mature organisms. We found that, in 2010, the proportion of males and females fish introduced in the system was the most influent parameter to account for the population characteristics (total number of fish and structure of the population) at the end of the experiment. Inter-annual variability was mainly due to differences in water temperature profiles. Intra-annual variability can be reduced through a better sex determination of the fish introduced at the beginning of the experiment. We developed an original methodology to achieve that (see another poster of de Kermoysan et al. : "A non-invasive method based on head morphology to sex mature three-spined Stickleback (Gasterosteus aculeatus) in rearing conditions"). Inter-annual variability, in link with temperature, could be quantified provided the influence of temperature on the main components of G. aculeatus population dynamics are understood and modelled.