The ecology of sandy beaches of the Benguela ecosystem

Abstract

Sandy beaches constitute nearly 46 per cent of the coastline between the Cape of Good Hope and the Orange River along the west coast of South Africa. In addition, shores of mixed sand and rock make up a further 24 per cent although these are not considered here. Sandy beaches are therefore the dominant shore type along the coastline, and most are subject to high wave energy. There are two main ecological beach types along the study coastline: Those that receive a high input of organic matter in the form of stranded kelp and those that do not. Neither type appears to support large stocks of surf-zone phytoplankton, but despite this, even beaches receiving no stranded kelp bear high standing stocks of infauna. This fact may be related to the location of the beaches alongside a highly productive upwelling region. Existing ecological information on sandy beaches along the Benguela coastline is reviewed and integrated to form a composite picture of present understanding of these beaches. The definition of a sandy beach includes not only the sandy intertidal zone but also the surf zone and sand dunes associated with it. Sandy beaches are characterized by the absence of attached primary producers, although in some parts of the world primary production by surf-zone phytoplankton has been found to be important. Secondary production by the infauna usually depends on matter imported into the system, except on beaches supporting important stocks of surf-zone phytoplankton. Imported organic matter is retained by beach sediments which act as a physical sieve, filtering large quantities of water with each wave and tide. © 1987 Taylor & Francis Group, LLC.