Valve gape and exhalant pumping in bivalves: optimization of measurement

We examined the effect of sampling frequency of gape angle and exhalant pumping measurements on our ability to determine the behaviour of bivalves. We used the endangered freshwater bivalve Margaritifera margaritifera, the non-endangered mussels Mytilus edulis and Mytilus trossulus, the scallop Pecten maxim us and the cockle Cerastoderma edule. Increasing sampling interval led to an underestimation of the rate of bivalve gape adduction and abduction events detected, an overestimation of the mean duration between gape adduction and abduction events, and a misunderstanding of the form of the gape adduction and abduction events and exhalant pumping profile. Our analyses suggest minimum appropriate sampling rates for archival tags to define gape behaviour of 2, 7 and 40 Hz in M margaritifera, C. edule and P. maximus, respectively, and 18 Hz to describe the metachronal wave in exhalant pumping of M. edulis. We demonstrate that careful consideration has to be given to the selection of sampling intervals when using a non-continuous method of recording behaviour. Our results emphasize the importance of measuring fine-scale behaviour patterns in order to advance our understanding of bivalves. The potential loss of information associated with the choice of particular sampling intervals during measurements of single parameters, and the biases which can result from this choice, are effectively germane to all species.