Variation in meiofaunal abundance and composition across an estuarine bay: Do they comprise a coherent and distinct entity displaying contrasting patterns to the macrofauna?

Patterns of meiofaunal distribution, abundance and composition were investigated across the disparate regions of the warm-temperate Knysna estuarine bay, South Africa's premier site for estuarine biodiversity and conservation. This locality was represented by five seagrass and five adjacent bare-sediment sites for which earlier data on the equivalent macrofaunal patterns were available. Thus it was possible to compare meiofaunal and macrofaunal responses to the same suite of contrasting habitats. Nematodes, copepods and ostracods, totalling 95.7% of numbers, dominated the Knysna epibenthic meiofauna which showed low (but not necessarily locally atypical) abundance: per core sample values of 19-886 (mean 211) ind. 10 cm-2. Meiofaunal abundance was subequal or greater in seagrass beds than in bare sediment, and peaked in the clean delta sands of the mouth. Each major component benthic taxon, whether macrofaunal or meiofaunal, responded individually to the estuarine gradients concerned and no common within-group or contrasting between-group macrofaunal or meiofaunal responses were apparent. Thus the macrofauna and meiofauna did not appear to behave as distinct and discrete ecological entities, as has been claimed. The macrofaunal 'opportunistic polychaete to amphipod' and meiofaunal 'nematode to copepod' ratios, used as indices of ecological quality, yielded differing (but in both cases unrealistic) results.