An Accelerometer-Based Sensing System to Study the Valve-Gaping Behavior of Bivalves

Bivalves are extremely sensitive to environmental conditions. The movement of their shells and the gap in-between the valves can serve as indicators of water pollutants entering surface water bodies. This letter proposes a novel sensing system to accurately calculate the valve-gaping angle in bivalves. The sensor unit is comprised of two inertial measurement units for each bivalve to estimate the angle between the two valves. Monitoring of multiple bivalves is possible with several water-insulated sensor units tethered with flexible cables to a central base station housing the processing unit. Miniaturization of the sensor packaging and flexibility of the wires ensured minimum hindrance to the animals' natural behavior. The precision and accuracy of the angle measurement were tested with a benchtop servo motor setup simulating the gaping behavior. The standard deviation of measurements at a steady state was 0.78^\circ, and the average change in measurement during a 10^\circ step was 9.98^\circ. Over 250 h of in vivo validation experiments demonstrated the consistency of the angle measurements using the presented method alongside a magnetic alternative, which had an average correlation coefficient of -0.89. The sensor system provides an accurate study of bivalve gaping behavior and facilitates the potential use of bivalves as environmental sentinels due to their valve-gaping being a biomarker for monitoring water pollution.