The relative significance of bacteria, meio- and macrofauna on an exposed sandy beach

Abstract

A survey of the intertidal biota of a sandy beach on the west coast of South Africa has shown standing stocks of macrofauna, meiofauna and bacteria of 241.23, 200.17 and 663.07 g dry wt m-1 of shoreline respectively, an approximate biomass ratio of 1:1:3. The distribution of the macrofauna was the reverse of the usual pattern, with highest biomass occurring at the level of the current driftline. This appears to be related directly to the ready availability of food in the form of drift algae. Peak meiofaunal numbers were also found below the driftline and it is proposed that meiofaunal distribution is governed by dissolved organic matter (DOM) levels in the interstitial environment. Bacteria were abundant up to 1.2 m below the sediment surface, with the highest concentrations occurring at low tidal levels. The significance of the various biotic components in the energetics of the sandy intertidal is discussed. Turnover estimates suggest that bacteria may account for about 87% of annual production, with meiofauna and macrofauna making up 10 and 3% respectively. Despite this overwhelming importance of bacteria, the macro-and meiofauna probably play a vital role in making small organic particles available to bacteria for mineralization and in optimising conditions for microbial growth.