The role of cannibalism and contaminant source on bioaccumulation in aquatic food webs

Two aspects of bioaccumulation in an aquatic food web are explored. First, the possible implications of cannibalism, including the scavenging of conspecifics, as a factor influencing food web bioaccumulation and biomagnification are explored by examining the behavior of total polychlorinated biphenyls (PCBs) in a simple aquatic food web consisting of plankton, juvenile and adult Mysis relicta, Diporeia, and alewife. From an analysis of trophic transfer efficiencies and food consumption rates, it is concluded that, for M. relicta, a maximum extent of cannibalism in a population is about 10%, although certain individuals may be more cannibalistic. The model suggests that cannibalism and scavenging of dead conspecifics generally result in an increase in concentration by self-biomagnification, but the effect is small and unlikely to exceed 5% on the average. Concentration differences also are likely to result from changes in the relative amounts of the dietary components. Highly cannibalistic individuals may achieve higher levels of bioaccumulation. In extreme cases, the food web model becomes mathematically unstable because of excessive feedback of high concentrations. A major implication is that differences in extent of cannibalism and scavenging probably contribute significantly to natural concentration variation in a population. Second, and more important, is the effect of benthic versus pelagic sources, especially when significant fugacity differences exist between these zones. A simple method is described by which the separate contributions from these sources can be estimated for organisms at higher trophic levels.