Effect of Particle Size and Shape of Sandy Soil on Burrowing of Surf Clam, Donax semigranosus (Dunker) under Standing Conditions

Abstract

A series of burrowing experiments was conducted on a typical bivalve, Donax semigranosus, which lives in a sandy beach shoreline area, using sandy substrates of various particle sizes and shapes under standing conditions. As a result, the success rate of burrowing varied and decreased to below 30% when the particle diameter was over 0.8 mm and the vane shear resistance was less than 0.018 kN/m² or greater than 0.14 kN/m², or the friction coefficient tan Φ was less than 0.46 or greater than 0.88. This is thought to be due to the fact that the D. semigranosus cannot excavate the substrate with increasing hardness with a larger particle size over 0.8 mm under given dense packing states, and that the substrate is not strong enough to take the burrowing posture at low values of vane shear resistance and friction coefficient defined by tan Φ. In addition, it was considered that some individuals foot did not reach the substrate. These results suggest that the burrowing behavior of D. semigranosus is presumably adapted to sand dynamics in the shoreline area of the sandy shore, such as uprush and backrush, coastal gradients, and drifting sand.