Tidal exchange of larvae of Sesarma catenata (Decapoda, Brachyura) in the Swartkops Estuary, South Africa

Abstract

The tidal exchange of larve of the salt-marsh grapsid crab Sesarma catenata was studied in a tidally driven, shallow estuary in Algoa Bay. Zoea I larvae were found in all sampling sessions, with highest abundance during noctural ebb tides. Seasonal peaks of abundance were detected in November and February-March. These coincided with recorded peaks of percentage abundance of gravid females in the adult population. Megalopa larvae were recorded mainly during flood tides from January-March. Over 70% of all S. catenata larvae moving through the tidal inlet of the Swartkops estuary in either direction were exported in any given sampling session. There was net export of zoea I larvae in all cases but one, and net import of megalopa larvae in all cases. The possibility that S. catenata larvae may become entrapped in the surf zone circulation system throughout development, as a mechanism to avoid offshore dispersal, is discussed. -from Author