Seasonal and diel variation in movement rhythms of sand dollar, Peronella lesueuri (Valenciennes 1841), in Cockburn Sound, Western Australia

Abstract

Rates and direction of movement in the sand dollar Peronella lesueuri were measured in summer and winter in Cockburn Sound, a large coastal embayment in south-western Australia. P. lesueuri was found to have a diurnal activity pattern throughout the year and had a greater movement rate in the summer (mean of 5.3 cm h−1, day; 3.9 cm h−1, night) than in the winter (mean of 2.7 cm h−1, day; 2.0 cm h−1, night). Seasonal change in temperature and physiological requirements by the sand dollar are the most likely reason for the seasonal differences. Reasons for diurnal variation were not clear. Direction of movement was found to be random at both times of the year. Based on these movement rates, one sand dollar can bioturbate an approximate area of 0.1 m2 day−1 and 36.4 m2 year−1. At a conservative density estimate of 0.5 sand dollars per m2 it takes approximately 20 days for the sand dollars to rework the entire area of the sediments in the habitats they occupy.