Fig. 4. Effect of inorganic Hg on (A) the duration and (B) frequency of shell gaping activity of the vent mussel B. azoricus during 3 weeks in seawater (Control) followed by 3 weeks of daily exposure to 20 µg g^-1 inorganic Hg, and an additional 3 weeks in Hg-free seawater (Recovery). Vertical bars represent means of replicate mussels ± S.E.M. (N=3). Statistical significance of Hg on shell gaping was tested by one-way analysis of variance, and post-hoc tests were performed to detect differences at different experimental moments, indicated by asterisks (^**P=0.001 and ^***P<0.001). See Table 1 for further details.