BEHAVIORAL-CHARACTERISTICS OF THE JUVENILE JAPANESE SURF CLAM PSEUDOCARDIUM-SACHALINENSIS IN RESPONSE TO SAND EROSION AND DEPOSITION ASSOCIATED WITH OSCILLATORY WATER-FLOW

This study examined the behavioral characteristics of juvenile Japanes e surf clam Pseudocardium sachalinensis in response to sand erosion an d deposition under laboratory conditions, then estimated the fluid con ditions critical to wash the clams out of the sand. The juveniles star ted burrowing downward into sand when their burying depth decreased to less than 1.5 times the shell length due to erosion, and moving upwar d when the depth increased to more than 2.5 times the shell length due to deposition of sand. Burrowing and climbing actions of the juvenile continued until the depth reached 1.7-2.1 times the shell length once again. The burrowing and climbing speeds were about 1.8 times higher than the speed of erosion or deposition of sand. It was concluded that the juveniles would maintain their position actively in order to avoi d being washed out or buried too deeply by adapting their behavior to the dynamic conditions of sand movement. The juveniles were washed out of the sand when the erosion speed exceeded 3.5 mm/min, and such eros ion occurred when oscillatory water flow speeds over a sandy bottom wi th median particle diameter of 0.3 mm exceeded more than 45 and 55 cm/ s at periods of 4 s and 8 s, respectively.