onax serra Röding is unusual among intertidal dwelling Donax species in that it does not undergo tidal migrations. We examined the distribution and abundance of the D. serra population along a 200-m section of exposed sandy beach throughout a 96-day period. D. serra was shown to exhibit a semilunar pattern of movement corresponding to the spring-neap tidal cycle. These migrations keep the D. serra band in the zone of water-saturated sand close to the water table. The data also indicate that D. serra exhibits higher abundances on the flatter portions of the beach where the water flow patterns are more suitable for filter-feeding. Distribution and abundance of Donax serra Röding (Bivalvia: Donacidae) as related to beach morphology. I. Semilunar migrations. Available from: