Effects of mercury on the behaviour and oxygen consumption of Monodonta articulata

The trochid snail Monodonta articulata Lamarck was exposed to mercuric sulphate at concentrations of 0.2, 0.5, 0.8 and 1 ppm Hg⁺⁺. At 24 h, retraction into the shell was observed in 0.8 and 1 ppm Hg⁺⁺; this retraction increased in these concentrations at 36 h. Retracted snails died if retained in the solutions, but generally recovered within 24 to 48 h if transferred to uncontaminated sea water. Immersionemersion behaviour and interface activity were studied over 24 h by means of an aktograph; snails in normal sea water spent more time below than above the water surface, and exhibited frequent periods of activity. Exposure to mercuric sulphate at concentration of 0.25, 0.5, 0.8 and 1 ppm Hg⁺⁺ progressively reduced both the length and frequency of activity periods. From 0.5 ppm Hg⁺⁺ upwards, emersion periods increased, and immersion periods decreased. Oxygen consumption of snails was measured in sea water and in mercuric sulphate at concentrations of 0.2, 0.5, 0.8 and 1 ppm Hg⁺⁺. Oxygen consumption decreased significantly with each progressive rise in mercury concentration. It is considered that mercury affects M. articulata by interfering with respiration, initially reducing interface activity, then forcing the snail for longer and longer periods out of the water. Retraction occurs when activity is no longer possible. It is concluded that respiratory and behavioural alterations of this nature would afford a good indicator of the presence of sub-lethal concentrations of pollutants.