Movement and behavior of the sand dollar Mellita tenuis (Echinodermata: Echinoidea)

ABSTRACT Mellita tenuis occurs in large aggregations in the eastern Gulf of Mexico, and are. major bioturbators of sandy environments. In this laboratory study, M. tenuis were placed in a laboratory enclosure under varying treatments (Time of Day, Size, Predatory Cues, Feeding History, Density), and video recorded for 3–4 hr. Five variables were analyzed: time in forward plus rotational movement (Movement), time in forward movement alone (Progression), time covered by sand (Covered), distance moved (Distance), and how fast they moved (Speed). There was no diel rhythm pattern found for any of the variables studied amongst Time of Day treatments. Large individuals covered less often, moving further and nearly two times faster than small individuals. Neither Feeding History nor Predatory Cues had an effect. Lower density aggregations spent more time in Movement and Progression. Both larger and smaller individuals contribute to bioturbation activitiespotentially impacting the habitat across 24 hr.