A novel device to monitor small changes in underwater distances

Abstract

Abstract. This study describes a technique to record small (1 cm) distance changes or movements occurring in seawater using a simple electronic circuit and miniature ball electrodes. This low-cost technique was designed to directly measure such changes in a broad range of experiments involving small marine invertebrates while minimizing the mechanical loading of the structures of interest. The circuit detects and amplifies small changes in the resistance of seawater between two electrodes as the distance between them varies; these are then converted to voltage changes. After calibrating the output of the device with known distance measurements, it was evaluated using a test organism by monitoring and recording the body flushing behavior of the sea squirt, Styela plicata. Electrodes were sewn to the tunic at the base of the atrial siphon and changes in its diameter were recorded424-h periods. UsingB3-cm-tall sea squirts, the distance between the electrodes expanded and contracted with a range of 5.5 mm during rhythmic flushings. Flushes occurred on average every 4.1 min and showed a rapid initial contraction, followed by a slower expansion while refilling. Attaching electrodes to the tunic had little mechanical or behavioral effect; the untouched control specimen had similar flushing rates. The movement monitor circuit is stable, sensitive, and performed well in fullstrength seawater experiments where good spatial and high temporal resolution, low inertial loading, and low noise were required. The technique, as shown here, can be used to record a wide range of animal movements and further suggested modifications of the circuit may suit a broad range of other experimental situations.Additional key words: measurement, movement, behavior, electronic distance A frequent difficulty in testing biomechanical functions in marine invertebrates is the accurate and precise measurement of small linear distances over time. Here, we present an electronic circuit design for recording such data with low construction costs and good spatial and temporal resolution. We tested this technique by monitoring the flushing behavior of the leathery (or pleated, or rough) sea squirt, Styela plicata LESUEUR 1823, as quantified by measured changes through time in the base diameter of the atrial siphon (Fig. 1).Directly monitoring changes in distance in seawater can be technically challenging. The chosen technique must be compatible with the high conductivity of seawater. It must minimize the mechanical loading of structures of often small or soft-bodied invertebrates. In addition, it should not interfere with other techniques such as electromyography or pressure measurements. Previously used techniques include a number of methods: sonomicrometric, magnetic, optic, mechanical, and electric. As reviewed below, each has limitations.Ultrasonomicrometry is a common technique that uses piezoelectric crystal transducers. Distance is measured by recording the time taken by ultrasonic waves to travel between crystals. This technique offers high tempo...

Electromyography of the buccal musculature of octopus (Octopus bimaculoides): a test of the function of the muscle articulation in support and movement

“…Beak movements were monitored by a custom movement monitoring circuit (Uyeno and Hsiao, 2006) designed to measure the resistance between two silver/silver chloride ball electrodes affixed with cyanoacrylate glue to the rostra (Fig.·4). The circuit converted the resistance into an amplified voltage output signal that was fed to a Powerlab 4/25 analog to digital conversion unit.…”