Catherine Aliaume

Effects of waterborne uranium on survival, growth, reproduction and physiological processes of the freshwater cladoceran Daphnia magna.

Acute uranium toxicity (48 h immobilisation test) for Daphnia magna was determined in two different exposure media, differing in pH and alkalinity. LC(50) varied strongly between media, from 390+/-40 microgL(-1)U at pH 7 to 7.8+/-3.2 mgL(-1)U at pH 8. According to the free ion activity model uranium toxicity varies as a function of free uranyl concentration. This assumption was examined by calculating uranium speciation in our water conditions and in those reported in the literature. Predicted changes in free uranyl concentration could not solely explain observed differences in toxicity, which might be due to a competition or a non-competitive inhibition of H(+) for uranium transport and/or the involvement of other bioavailable chemical species of uranium. Chronic effects of uranium at pH 7 on mortality, ingestion and respiration, fecundity and dry mass of females, eggs and neonates were investigated during 21-day exposure experiments. A mortality of 10% was observed at 100 microgL(-1)U and EC(10) for reproduction was 14+/-7 microgL(-1)U. Scope for growth was affected through a reduction in feeding activity and an increase in oxygen consumption at 25 microgL(-1)U after 7 days of exposure. This had strong consequences for somatic growth and reproduction, which decreased, respectively, by 50% and 65% at 50 microgL(-1)U after 7 days and at 25 microgL(-1)U after 21 days. Uranium bioaccumulation was quantified and associated internal alpha dose rates from 2.1 to 13 microGyh(-1) were estimated. Compared to the toxicity of other alpha-emitting radionuclides and stable trace metals, our results confirmed the general assumption that uranium chemical toxicity predominates over its radiotoxicity.

Assessment of coastal lagoon quality with taxonomic diversity indices of fish, zoobenthos and macrophyte communities

Lagoons and marshes account for more than 50% of the coastal area in the Languedoc Roussillon region (South of France, Mediterranean Sea). The lagoons are very different in their physical and chemical characteristics, eutrophication level and resource exploitation mode. In this study, different levels of taxonomic diversity and two indices (Δ+ and Λ+) based on macrophyte, zoobenthos and fish communities are used to compare three lagoons (Ingril, Prévost and Mauguio). Whilst the taxonomic diversity of the fish community seems not influenced by the lagoon characteristics, the benthos community is strongly related to their eutrophication status. With the same sampling effort we identified 7 benthic species in Mauguio, the most impacted lagoon, while 24 species were found in the Ingril lagoon, which is the less impacted one. Overall, the variance of taxonomic distinctness Λ+ appeared as the best indicator of the lagoon eutrophication level. This index is always highest for the Mauguio lagoon, whatever the biotic compartment considered. In a more stable environment like in the Ingril lagoon (lower variations of salinity, temperature or turbidity), Λ+ is low, i.e., the structure of the taxonomic tree is very regular with a relatively homogeneous partition of species among phyla. By contrast, when salinity variations are wide, like in the Mauguio lagoon, the taxonomic tree becomes irregular with some lineages less constrained (many species belonging to the same family), while others are more impacted with a limited number of species in these phyla.

Growth of Juvenile Centropomus undecimalis in a Tropical Island

Age, growth rates and hatching dates were determined for juvenile common snook, Centropomus undecimalis, collected in several Puerto Rican estuarine systems. Two growth models (von Bertalanffy and power curve) were used and compared based on the fitting, the residual distribution and homogeneity of variances. A multiple linear regression was also fit to predict age from otolith weight, fish weight and standard length. Hatching dates back-calculated from age estimates, suggested that spawning occurs throughout the year but peaks from May to October. Early juveniles (age < 100 d) recruited during the wet season (August to November) showed a significantly higher growth rate (0.67 mm d−1) than the dry season (December to July) recruits (0.41 mm d−1). These results are compared with snook collected in west Florida.

Growth of sand whiff Citharichthys arenaceus and bay whiff Citharichthys spilopterus (pleuronectiformes: bothidae) in Puerto Rico (greater antilles) and North Carolina (USA), with comments on growth rate comparisons

Abstract Sagittal otoliths from two bothid flatfish species ( Citharichthys arenaceus and C. spilopterus ) collected in Puerto Rico were microstructurally examined and periodic increments counted. C. arenaceus length-at-age (33 to 246 days) data were best fitted by a Gompertz growth model whose parameters were estimated to be SL ∞ = 170 mm and K = 0.0166. Adult size is reached in less than one year. The peak period of hatching occurred in late spring, and settlement took place 39 days later. Due to a smaller age range (71 to 150 days), growth of C. spilopterus was described by a linear relationship with slope = 0.693 and intercept = −15.1 days. Hatching occurred in winter and spring. These two species showed no significant difference in age at settlement. After settlement, growth of C. spilopterus (0.69 mm·d −1 at 71 to 113 days old) was significantly slower than that of C. arenaceus (1.00 mm·d −1 at 71 to 113 days) possibly due to poorer environmental (abiotic or food-related) conditions during the dry, cool season (December–April). C. spilopterus from North Carolina, hatched in the same period, settled about two weeks older than in Puerto Rico. Growth after settlement was significantly slower in North Carolina (0.44 mm·d −1 at 71 to 113 days) than in Puerto Rico. Environmental conditions (including temperature), distance between spawning areas and settlement grounds, and/or food availability, might explain the dissimilarity in growth observed between the two geographic areas. We recommend absolute field growth to be compared by using growth rates obtained by deriving the growth curve formula.

Community-wide scan identifies fish species associated with coral reef services across the Indo-Pacific

Determining whether many functionally complementary species or only a subset of key species are necessary to maintain ecosystem functioning and services is a critical question in community ecology and biodiversity conservation. Identifying such key species remains challenging, especially in the tropics where many species co-occur and can potentially support the same or different processes. Here, we developed a new community-wide scan (CWS) approach, analogous to the genome-wide scan, to identify fish species that significantly contribute, beyond the socio-environmental and species richness effects, to the biomass and coral cover on Indo-Pacific reefs. We found that only a limited set of species (51 out of approx. 400, approx. 13%), belonging to various functional groups and evolutionary lineages, are strongly and positively associated with fish biomass and live coral cover. Many of these species have not previously been identified as functionally important, and thus may be involved in unknown, yet important, biological mechanisms that help sustain healthy and productive coral reefs. CWS has the potential to reveal species that are key to ecosystem functioning and services and to guide management strategies as well as new experiments to decipher underlying causal ecological processes.

A statistical test to detect vortices in the current fields of bodies of water

Vortices could play an important role in the occurrence of certain biological phenomena, such as the massive proliferation of harmful algae in bodies of water. Many measures exist to detect vortices in fluids, but little is known about the stochastic behavior of these quantities with data that contain statistical noise. Consequently they do not provide control over the probability of false positives and give little information about the risk of false negatives. Obtaining such control requires a statistical testing procedure. In this paper, we develop a test for vortices in random current fields using only the directions of the current observed at points on a regular grid. We construct a change-point test for spatially ordered angular data to detect the presence of a local vortex. A global vortex detection procedure based on this test is developed and applied to a data set from a lagoon located in the south of France. It is shown that this procedure can detect the presence of multiple vortices with good accuracy.