Zonation Patterns of Donax serra Roding (Bivalvia: Donacidae) in Southern Africa

Abstract

The intertidal and shallow subtidal zonation of the sandy-beach bivalve Donax serra was examined on four beaches along the west (cold temperate) and south (warm temperate) coasts of southern Africa. Summer sea temperatures on the west coast seldom exceed 15°C, whereas winter sea temperatures on the south coast seldom fall below 14°C. Juveniles were found in the upper intertidal at all sites. On the south coast, adults also occupied the upper intertidal, whereas on the west coast they were found at or below the spring low tide line. It is proposed that these zonation patterns are the result of a reduction in the burrowing rate of west coast adults due to colder ambient sea temperatures, resulting in the adults being swept downshore by the backwash before they have a chance to reburrow.