TRANSFER OF MERCURY FROM BENTHIC INVERTEBRATES TO FISHES IN LAKES WITH CONTRASTING FISH COMMUNITY STRUCTURES

We examined the flow of mercury (Hg) from benthic invertebrates to fis hes in lakes with contrasting fish community structure. The study was carried out in two whole lakes in southcentral Ontario in 1992. Both w ere remote from direct sources of contamination and were chosen becaus e of their physical and chemical similarities. Although the fish commu nities in the mio lakes were qualitatively similar, the total number o f fishes in Ranger Lake was an order of magnitude smaller than that in Mouse Lake. As a result of the lower net predation from benthivorous fishes, documented in earlier studies, Ranger Lake benthic invertebrat e populations were significantly higher. However, benthic invertebrate taxa in Mouse Lake were generally larger and had higher Hg concentrat ions. This was partly attributed to the stunted growth of Mouse Lake f ishes, which did not allow them to prey on larger benthos as a result of gape limitations. Despite the lower Hg concentrations in Ranger Lak e benthos, total benthic invertebrate Hg pools were higher in this lak e as a result of its higher total benthic invertebrate biomass. Howeve r, the transfer of total Hg from benthic invertebrates to fishes was h igher in Mouse Lake due to the higher consumption rates of benthivorou s fishes.