Target gastropods for standardizing the monitoring of tar mat contamination in the Arabian Gulf

This study proposes a standardization process for monitoring the level of tar mat contamination in the Arabian Gulf. In the study, we selected target gastropod species and evaluated the ecological and ecotoxicological effects of tar mats on their populations, the bioaccumulation of heavy metals, and these species’ potential as bioindicator taxa for tar mat-associated heavy metals. The study was carried out at two sites on the Qatar coast on shoreline rocks, both of which have areas of tar mat coverage and areas without tar mats. The species selected as representative species for the ecoregion were the endemic Clypeomorus bifasciata persica (Houbrick, 1985) in the intertidal zone and the Echinolittorina arabica (El Assal, 1990) in the supratidal zone. Both are grazers and are niche restricted to hard substrates and daily scraping/grazing on the tar mat deposition zone of the shorelines. The key heavy metal indicators chosen were As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni and Zn, and the gastropod species were divided into classes according to their size. Tar mat presence was found to negatively affect both the overall population size of Clypeomorus and different size classes, and lead to high levels of assimilation of heavy metals. Tar mat presence also negatively affected different size classes of Echinolittorina where large sizes were found to be most significantly affected. The results also demonstrated that Cu and Ni are the heavy metals most associated with tar mat contamination of this kind. Overall, our results confirmed that grazer gastropods are good bioindicators of tar mat-associated contaminants in shoreline ecosystems. Our study provides the database on the heavy metal contamination of the proposed target gastropods, and offers information that will be relevant for further monitoring and comparisons among threatened coastal areas in the Arabian Gulf.