Linking changes at sub-individual and population levels in Donax trunculus: assessment of marine stress.

Research in ecotoxicology currently focuses to fill the gap existing between sub-organismal responses (e.g. biomarkers) to toxicants and effects occurring at higher levels of biological organisation (e.g. population). The intra-sedimentary bivalve Donax trunculus commonly found in West Atlantic and Mediterranean coasts is a sentinel species useful for biomonitoring studies in sandy beaches. The objective of this work was to link responses at the infra-individual level (core biomarkers as early and sensitive tools) to supra-individual level (population for its ecological relevance). D. trunculus, originating from a polluted site (Radès Méliane) and a comparatively reference site (Sidi Jehmi) in the Gulf of Tunis (Tunisia), were collected bimonthly from November 2008 to October 2009. An increase in catalase activities was usually observed in bivalves from the polluted site compared to the reference site whereas no differences in TBARs were depicted. The anti-oxydant enzyme (catalase) could be able to prevent the deleterious effect on the lipid membranes. Usually GST activities were decreased in the polluted site. Significantly high inhibition in AChE activities in bivalves from the polluted site suggested neurotoxicity disturbances to their in situ exposure to compounds such as organophosphate and carbamates pesticides, heavy metals. Size-distribution of populations of D. trunculus from the polluted Radès Méliane site consisted of four cohorts whereas five cohorts were depicted in the comparatively reference Sidi Jehmi site. The mean total length size and the growth rate of cohorts were significantly reduced in the impacted site compared to the reference site. In conclusion, it may be suggested that disturbances in responses to chemical stress at the infra-individual level could be linked to the responses observed at the population level.