The purpose of this study was to assess the acute and chronic effects of the macrolide azithromycin (AZI) on the European sea bass (Dicentrarchus labrax) early life stages. Azithromycin is a semi-synthetic antibiotic frequently detected in the aquatic environment, despite this few information about its effects on aquatic organisms were reported. Investigations of AZI acute toxicity on D. labrax early life stages were made using six increasing concentrations (0.625, 1.25, 2.5, 5, 10 and 20 mg/l) during 96 h of exposure. The chronic toxicity was tested at one year old juveniles using two sublethal concentrations (C1 = 0.05 µg/l and C2 = 0.8 µg/l) during 4 and 14 days. Malondialdehyde (MDA), glutathione S-transferase (GST), catalase (CAT) and acetylcholinesterase (AChE) activities were measured in gill and liver tissues of juveniles. The half lethal concentration (LC₅₀), 96 h value of AZI for the European sea bass was determined as 31 mg/l. Results showed that short-time exposure to 20 mg/l of azithromycin induces 18% and 7.5% of larvae mortality and morphological abnormalities, respectively. Azithromycin provoked oxidative stress, peroxidative damage, and neurotoxicity in juveniles D. labrax. Overall, the CAT and AChE activities decreased in gill and liver tissues, while dissimilarity in response in both organs depending on AZI concentrations and time of exposure was observed in MDA and GST levels.

Molecular approaches have proven efficient to identify cryptic lineages within single taxonomic entities. Sometimes these cryptic lineages maybe previously unreported or unknown invasive taxa. The genetic structure of the marine gastropodStramonita haemastomahas been examined in the Western Mediterranean and North‐Eastern Atlantic populations with mtDNACOIsequences and three newly developed microsatellite markers. We identified two cryptic lineages, differentially fixed for alternative mtDNACOIhaplogroups and significantly differentiated at microsatellite loci. The mosaic distribution of the two lineages is unusual for a warm‐temperate marine invertebrate with a teleplanic larval stage. The Atlantic lineage was unexpectedly observed as a patch enclosed in the north of the Western Mediterranean Sea between eastern Spain and the French Riviera, and the Mediterranean lineage was found in Macronesian Islands. Although cyto‐nuclear disequilibrium is globally maintained, asymmetric introgression occurs in the Spanish region where the two lineages co‐occur in a hybrid zone. A first interpretation of our results is mito‐nuclear discordance in a stable postglacial hybrid zone. Under this hypothesis, though, the location of genetic discontinuities would be unusual among planktonic dispersers. An alternative interpretation is that the Atlantic lineage, also found in Senegal and Venezuela, has been introduced by human activities in the Mediterranean area and is introgressing Mediterranean genes during its propagation, as theoretically expected. This second hypothesis would add an additional example to the growing list of cryptic marine invasions revealed by molecular studies.

Imposex was quantified in Stramonita haemastoma from the Bizerta Channel during a one-year study period and the effect of gastropod size and shell fouling by epibiotic barnacles investigated. Butyltin concentrations (tributyltin (TBT) and its derivatives di- and mono-butyltin) were also investigated in the soft tissue of the gastropods to depict temporal trends in pollution. Kelibia Beach was chosen as a reference site (not polluted by organotin) to depict whether barnacle fouling could intervene in imposex development. Imposex incidence in the Bizerta Channel was greater in females fouled by epibiotic barnacles compared to non-fouled females. Considering the size of the gastropods, large females (fouled and non-fouled) always exhibit higher imposex indices than smaller females. The concentrations of organotin compounds were found to be similar in the studied species, independent of sex or fouling condition. For Kelibia Beach, no imposex was recorded in fouled and non-fouled snails, while butyltins were below the limit of detection. Results gathered in the present study confirm the effect of size and epibiotic barnacles as factors affecting imposex quantification in gastropods. The absence of imposex for Kelibia Beach suggests that barnacles do not promote the development of imposex, but could be a secondary factor amplifying the effect of imposex. Furthermore, this investigation showed a significant decrease in imposex and TBT levels in the Bizerta Channel as compared to previous work, reflecting the effectiveness of a TBT ban on a global scale.