The influence of mercury on the burrowing behaviour ofCorophium volutator

The burrowing behaviour ofCorophium volutator (Pallas) has been recorded in sediments treated with seawater solutions of 0.001, 0.1, 10, and 1000 ppm HgCl₂. Heterotrophic sediment bacteria have also been counted. Non-choice and choice experiments have been conducted. In non-choice experiments no individuals burrowed in the sediment treated with 1000 ppm HgCl₂ solutions. The same numbers of individuals burrowed in the sediments treated with 0.001, 0.1, and 10 ppm HgCl₂ solutions as in the control. Bacterial numbers were lower in the sediments treated with 10 and 1000 ppm HgCl₂ solutions. Hence, a mercury concentration that killed bacteria (10 ppm) did not inhibit burrowing. In choice experiments, individuals avoided all the mercury-treated sediments, particularly that treated with 1000 ppm HgCl₂ solution. Bacterial numbers were only lower than the control in the sediments treated with 10 and 1000 ppm HgCl₂ solutions. Hence, individuals avoided treated sediments (0.001, 0.1 ppm HgCl₂) in which no bacterial mortality had occurred.