Biomonitoring a stressed Kuwait Bay environment revealed a differential and collective transfer of mercury (Hg) between the primary producer and primary and secondary consumers, in addition to possible Hg bioconcentrations and bioaccumulation in such marine organisms that attributed harmful effects to humans at the tertiary level of the food chain. Selected live samples were collected from five bay sites and exposed for 96 h and 30 d in aquarium tanks. Samples analyzed by direct mercury analyzer (detection limit of 0.0015 ng.g^-1) revealed Hg concentrations in the sequence of Barbatia helblingii >Acanthopagrus berda>phytoplankton>zooplankton at sites IV>V>III>I>II during the summer and winter seasons, respectively. Bioaccumulation factor (BAF) was >1 in most of their trophic transfer, although Hg-BAF was <1 in a few trophic levels. Seasonal variations, anthropogenic sources, vestiges of Hg from the shut-down chlor-alkali plant, urbanization, slow water current, and nutrient upwelling attributed to the persistent Hg accumulation in the marine ecosystem. Since Hg is a ubiquitous pollutant in the bay, their transfer through the medium, diet, and net accumulation in higher predators is of importance to marine life and is a concern to tertiary consumers, including humans.