Michel Girardin

Development of a fish-based index to assess the ecological quality of transitional waters: the case of French estuaries.

The Water Framework Directive requires the assessment of the ecological status of transitional waters considering the fish component. An original methodology, based on a pressure-impact approach, was established to develop a multimetric fish-based index to characterize the ecological quality of French estuaries. An index of contamination, based on the chemical pollution affecting aquatic systems, was used as a proxy of anthropogenic pressure. The fish metric selection was based on their response to disturbances tested via statistical models (generalized linear models) taking into account sampling strategy and estuarine features. Four metrics, for which discriminating responses to level of pressure were demonstrated, were retained to constitute the estuarine multimetric fish index. This new tool appeared particularly relevant to detect the contamination effects on fish communities in estuaries. It could help managers to take decisions in order to maintain or reach the good status required by the Water Framework Directive for 2015.

Reproductive Biology of Palaemon longirostris (Decapoda: Palaemonidae) from Gironde Estuary (France), with a Comparison with Other European Populations

Abstract Our study details key parameters of the reproductive biology of the shrimp Palaemon longirostris, e.g., spatio-temporal variation of the sex-ratio, migration pattern, breeding period, fecundity, size at the onset of maturity, and egg volume. While P. longirostris population was very little studied in its distribution area, our fist aim was to complete that lack of knowledge and to provide a basis for understanding its population dynamic. Finally, our results were also compared with those reported from different studies on this species within Europe, in order to test the reported latitudinal cline of reproductive parameters in decapods. During a one-year survey, P. longirostris have been collected monthly across a large part of the Gironde estuary (France). Biometric measurements and determination of sex and maturation stages were carried out on preserved subsamples. Eggs were counted and measured for ovigerous females. In the Gironde, the breeding period was restricted from March to July, and related to water temperature. The size of the ovigerous females ranged between 7.1 and 14.6 mm cephalothorax length; according to their size, these females brought between 78 and 1391 eggs (547 on average). These results were compared with available data from the literature on French or foreign populations. For two reproductive parameters a latitudinal cline was noticed: e.g., an increase of the maximum females size and a restriction of the breeding period with latitude. Due to the weakness of available data on the reproductive biology of P. longirostris, it was very difficult to compare fecundity (number of eggs brought per female) and egg volume between localities. As expected fecundity could decrease with latitude, but this trend remains to be confirmed by more extensive studies on the species populations.

Exoskeletal deformities in Palaemonidae: Are they a threat to survival?

Shrimps of the Palaemon genus have been affected for over 15 years by a problem of exoskeletal deformities, particularly in the Gironde estuary (France). Given the large numbers of individuals affected, this study focus on a better description of the phenomenon to estimate its impact on shrimps. This study, on Palaemon longirostris and Palaemon macrodactylus, is based on samples collected from 1992 to 2007 in the Gironde estuary with particular focus on the year 2007, and on a 4-month rearing of adult shrimps in experimental system. The different approaches reveal the relative persistence of the phenomenon since 1992 (with on average more than 58% of ovigerous females affected) and its persistence during shrimp life cycle, even after several moults. Important consequences associated with deformities at the individual level were demonstrated: a higher mortality, a lighter egg mass and a lower weight for a given size. The presence of exoskeletal deformities is now a major phenomenon, with profound effects on individual shrimps, and which may in turn have an important impact on the survival of the P. longirostris population in particular.

Growth Modeling and Spatio-Temporal Variability in the Body Condition of the Estuarine Shrimp Palaemon longirostris in the Gironde (Sw France)

Abstract Growth and morphometric characteristics of the caridean Palaemon longirostris Milne Edwards, 1837, were studied in the Gironde estuary population. Their first comparison with earlier studies in this estuary and in the Mira River provided the first step towards developing environmental indicators using a species represented at the European scale. Mean individual growth was modelled for each sex using the classical von Bertalanffy growth model and the seasonal model that integrates periods of lower growth. Morphometric relationships, in particular the spatio-temporal variability in the relative weight of individuals, were explored according to sex and physical parameters of the environment. Females grew to larger size than males. Growth estimates showed the importance of accounting for the seasonal variations to evaluate non-biased growth. Sex and the presence of eggs for females showed significant interaction within the carapace length – total length relation as well as for the carapace length – weight relation. Body condition was significantly greater in spring and summer for both sexes and was significantly correlated with salinity, but only for males. Comparison with the Mira River was limited to the range of data available. However, the population of the Gironde estuary, being similar in both recent and historical studies, showed morphometric differences when compared to that of the Mira River. Indeed, the growth performance index was higher in the Gironde estuary and likely linked to temperature constraints. Conversely, differences between males and females were much higher in the Mira River than in the Gironde estuary.