Imposex in the marine neogastropod Hexaplex trunculus from Tunisian coasts: Geographical distribution and development intensity

The superimposition of male sexual characteristics in neogastropod females, or imposex, was used as a reliable bioindicator for the evaluation of sea water tributyltin (TBT) contamination. We recorded in Tunisian coasts the first observations of this phenomenon in Hexaplex trunculus in 16 stations, among 19 investigated sites, from Bizerta to Djerba. Imposex indices revealed a frequency of 100% in high shipping activity areas such as the Bizerta channel, Menzel Bourguiba, Menzel Abderrahmen, NPK Sfax, Sfax Harbour and the Adjim channel, with a VDS index value varying between 4 and 5 in the Cement factory station, generating a sterility of 8%, while the RPL index values oscillated between 29.96 and 69.13. In the other stations, the imposex rate varied from 0 to 93% with a variable VDS index of 0 to 3.32 and an RPL index ranged from 0 to 8%. A classification (tree clustering), of all the stations where this anomaly was found, taking into account the female length of the penis and VDS index, enabled us to highlight three groups of sampling intensity of imposex.