THE BIOLOGY OF LANGEBAAN LAGOON: A STUDY OF THE EFFECT OF SHELTER FROM WAVE ACTION

Abstract

The physical characteristics of the Saldanha Bay-Langebaan Lagoon system are described and it is shown that there are graded changes in wave action, substratum, temperature and salinity between the bay and the head of the lagoon. None the less the lagoon is not an estuary but a sheltered inlet of the sea. Two transects of rocky shores and four transects of sandy shores are described and these are then used to illustrate the effects of increasing shelter on physical factors of the environment and the vertical zonation of the fauna. On sandy shores it is shown that zonation is more closely related to the depth of the water-table than to tidal levels. An annotated list of species is given in the appendix which shows changes in species and their relative abundance throughout the system. This list is analysed to determine the changes in faunistic composition which occur with increasing shelter. On rocky shores there is an impoverishment of the fauna but no essential change in composition. On sandy shores there is an enrichment of the fauna and significant changes in composition. One part of the sheltered water fauna is derived from exposed rocky shores, another part is restricted to sheltered waters and a third is derived from species which elsewhere occur only below tide marks. The whole fauna of a sheltered inlet is very similar to that of the middle and lower reaches of an estuary. It is concluded that most so-called estuarine species are merely calm-water species.