Composition, distribution, abundance and biomass of the macrofauna and meiofauna of four sandy beaches

Abstract

The macrofauna and meiofauna have been investigated quantitatively on four exposed sandy beaches of medium quartz sands. Of the 12 macrofauna species recorded, two bivalves (Donax spp.) and one gastropod (Bullia rhodostoma)made up the bulk of the numbers and biomass values on all beaches. Macrofauna biomass values were 0,01 - 316,46 g/m² on an ash-free, dry mass basis. Diversity index values for the macrofauna were low and on all beaches decreased from LW to HW irrespective of the distribution of densities. Similarity analysis indicated three fauna assemblages, which were less related to tidal heights than to quantities of available food. High meiofauna numbers were recorded (152 - 7056/10 cm²) and these were made up mainly of crustaceans (48%) and nematodes (44%). Meiofauna ash-free dry biomass values were 0,08-3,36 g/m². On all beaches the meiofauna tended to be concentrated at those tide levels where a moderate, but not extreme, degree of desiccation of the sand occurred. Biomass values of macrofauna and meiofauna were extrapolated to 1 m transects of beach giving macrofauna values of 17,5-16553,3 g/transect and meiofauna values of 13,8-76,0 g/transect. Production estimates based on these biomass values indicated that the meiofauna dominated two beaches and the macrofauna two beaches. Two general conclusions are discussed, namely that the meiofauna and macrofauna on these beaches are quite distinct faunal components in all respects, and that the meiofauna, although not part of the macrofauna food chain, are nevertheless of great quantitative importance in the flow of energy.