Incidence of intersex and reproductive status in the clam Scrobicularia plana from 13 sites in NW France
Résumé
The endobenthic clam Scrobicularia plana is important for the structure and functioning of estuarine and coastal mudflats, and thus the reproduction success of this species is a topic of interest for environmental conservation. In thirteen estuaries from NW France differing by their degree of contamination (as documented by the data of RNO for Réseau National d'Observation, now ROCCH, Réseau d'Observation de la Contamination Chimique du milieu marin at http:// wwz.ifremer.fr/envlit/), intersex and different parameters linked to reproduction (sex-ratio, gonadosomatic index) were examined in S. plana collected at the beginning of gametogenesis and at the peak of sexual maturity. Both temporal and intersite differences were shown. Some reports exists showing that the presence of several endocrine disrupting chemicals (EDCs) may be directly linked to the incidence of intersex in S. plana and, in other bivalve species, an induction of female-biased sex ratios were observed after exposure to EDCs at the larval stage. Thus, the presence of EDCs in superficial sediments collected in parallel to clams was investigated by using an approach combining quantitative chemical analyses of the main classes of EDCs and a battery of in vitro bioassays allowing the quantification of receptor-mediated activities, namely estrogen (ER), androgen (AR) and dioxin (AhR) receptors. In addition, the reproductive success may be impaired indirectly when species used as food are impacted in contaminated sites, limiting food availability and then energy ressources devoted to the reproduction of consumers. This hypothesis was tested concurrently with endocrine disruption by determining hepatosomatic indices and measuring chlorophyll and phaeopigments in superficial sediments, the microphytobenthos of which is a major food source for deposit-feeding bivalves such as S. plana.