A NUMERICAL ANALYSIS OF THE DISTRIBUTION OF A SHALLOW SUBLITTORAL SAND MACROFAUNA ALONG A TRANSECT AT LAMBERTS BAY, SOUTH AFRICA

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Abstract
Samples were collected by a diver-operated suction sampler along a transect at stations between Om (J.W.S.) and a depth of 33 mat Lamberts Bay on the west coast of South Africa. The samples were subdivided into either 2 or 4 subsamples from different levels between the sediment surface and a depth of 60 cm. Numerical analyses by classification and ordination using the Bray—Curtis similarity coefficient defined 3 depth zones within the turbulent depth zone, each with a defined faunistic grouping. Characteristic species for each faunal grouping were obtained using information statistic analyses. It is shown that 42,4%of species penetrate below 30 cm depth of sediment, while 25,0%of species and 59,4%of individuals are found only below a sediment depth of 10 cm. The highest percentage of dry weight biomass per sediment level from all stations was found on average to be between the sediment depths of 10 and 20 cm. However, the highest value for densities of individuals was found between 0 and 10 cm sediment depth. Correlations are given between the mean percentage of clay in the sediment column at stations from 5 to 20 m inclusive and the total dry weight biomass, polychaete and deposit-feeding polychaete dry weight biomass. The rarefaction method of Sanders and the random reduction method of Hurlbert for interpolating the number of species present in a known population size are compared against actual values using data from the samples at the 10 m station. Sanders's method is slightly more accurate. Both methods are used to calculate the number of species at each station for a population of 14 and the 3 depth zones in the sea are again shown. Levels 2 and 3 in the sediment between 10 and 30 cm were speculated to be more favourable for the fauna than levels 1 or 4 between 0–10 and 30–60 cm depth of sediment. Turbulence and sediment texture are suggested as the most important factors which regulate the distribution of species and individuals within the turbulent depth zone.