Quantification of water squirting by juvenile fluted giant clams (Tridacna squamosa L.)

Abstract

The giant clam species Tridacna crocea, T. deresa, T. gigas, T. maxima and Hippopus hippopus are known to exhibit squirting behaviour, ejecting a stream of water either from their exhalant or inhalant siphon. Here, for the first time, squirting in juvenile fluted giant clams, T. squamosa, was measured. By analysing stills from video recordings it was possible to determine the horizontal and vertical distances travelled by each squirt above the water line, the cross-sectional area of the water jet, and the angle of squirt perpendicular to the horizontal axis of the giant clam. The weight of each “aerial squirt” was measured by collecting the displaced water. Using these parameters, the initial velocity, force and pressure exerted by each squirt on an object was calculated. Strong positive correlations were observed between shell length and weight of seawater and force exerted by aerial squirts. We also modelled the pressures that would be experienced by underwater targets. The simulated “underwater squirts” indicate the pressure produced rapidly decreases with distance from the clam.