2019 Volume 10 Issue 2 Pages 99-108
The authors review the previous studies on the bioaccumulation process of mercury in the marine ecosystem, focusing on the benthic one in enclosed coastal seas. According to the conventional ideas, the mercury content of animals tends to increase discontinuously as the elevation of the trophic level in the biological community. This typical pattern of the bioaccumulation of mercury has been described in the pelagic ecosystem. The mercury contaminated in the water is absorbed by the phytoplankton, and is further biologically magnified in the aquatic animals located at higher trophic levels such as planktivorous fish, piscivorous fish, and sea birds and marine mammals. In the benthic ecosystem in enclosed coastal seas, the mercury transference pathway tends to be more complex due to a variety of diets available for the benthic invertebrates, and the presence of a kind of bioconcentration process of mercury into the sediment. A large amount of organic particles, which are referred to as POM such as dead bodies of phytoplankton and zooplankton and feces excreted from the zooplankton, are always settling on the sea floor as detritus before they have been degraded fully by microorganisms in the water, due to shallow water. The detritus tend to be degraded by microorganisms, but its non-degradable parts, including mercury contaminants, tend to accumulate in the sediment. Some benthic invertebrates burrow into the sediment, and take in the mercury condensed in the sediment through their deposit-feeding activities or suspension-feeding activities to the re-suspended sediment just above the sea floor. The mercury accumulated in the benthic invertebrates is apt to be transferred to benthic and benthopelagic fishes that feed on the infaunal benthic invertebrates preferentially. Here, an accelerated bioaccumulation pathway of mercury exists in the benthic ecosystem, and brings further biologically magnified mercury to the pelagic ecosystem in the enclosed coastal seas.
