Abstract

This paper aims to assess Tunisian coastal water quality using the clam Ruditapes decussatusembryos and larvae bioassays tests. Water samples collected from four stations (Monastir lagoon, Chebba, Mahres and Zarat), was used for chemical analysis and clam bioassay tests (embryogenesis, larval growth and metamorphosis). The results, based on chemical analysis, showed the highest metal contamination in Mahres and Zarat while the lowest ones were recorded in Chebba station. The Monastir lagoon is characterized by the highest level of mercury (18.1±2.16 µgL^-1). Compared to control, reduction of clam embryogenesis is up to 40, 60 and 67% respectively in Monastir, Zarat and Mahres while no reduction were observed in Chebba (p>0.05). Larval growth rate was significantly (p<0.05) reduced in all stations except Chebba this also shown when daily growth rate (DGR) is calculated for larvae reared in water collected from each station. A significant (p<0.05) reduction in larval survival is also shown in Monastir (74%), Zarat (70%) and Mahres (52.8%) compared to control (94.5%). Compared to control (82%), metamorphosis success is significantly reduced only on two stations (Zarat: 68% and Mahres: 64%) conversely survival in this stage was affected in three stations (Monastir: 69±6.7%; Zarat: 52±6.1% and Mahres: 44±5.2%) compared to the control (83±4.7%). This work showed that both clam embryos and larvae are sensitive to contaminants and can be used to evaluate seawater contaminations and monitoring pollution.  

Key words: Bioassay, coastal water, embryogenesis, larvae, metamorphosis, Ruditapes decussatus.