IN-SITU ACTIVITY OF THE SANDY BEACH BIVALVE DONAX-VITTATUS (BIVALVIA DONACIDAE) IN RELATION TO POTENTIAL PREDATION RISKS

Underwater television with time lapse video recording was used to reco rd in situ activity of the tellinacean bivalve Donax vittatus on West Sands Beach, St Andrews on the east coast of Scotland. Individuals eme rged from the sand most frequently immediately before and after low wa ter, when wave action in shallow water caused disturbance of the sedim ent. During this period, emergence was most frequently followed by 'le aping' and/or transport by wave-induced currents. Emergence or partial emergence during mid-tide periods was more frequently followed by sur face or subsurface crawling. These activities resulted in a redistribu tion of the population which affected up to 44% of individuals during each tidal cycle. In all cases, reburial followed quickly. The number of emergence, 'leaping', and reburial events in each 30 min time inter val showed a positive, and the number of crawling events a weak negati ve, correlation with the degree of disturbance by wave action. The sep arate inhalant and exhalant siphons, used to draw in the feeding cur-r ent, remained extended and visible at the sand surface continuously ex cept for periods when wave action was so strong as to stir the sand in to suspension, causing intermittent withdrawal. The significance of th ese activities is discussed in relation to potential predation risks.