Spatial homogeneity of benthic macrofaunal biodiversity across small spatial scales

- Spatial homogeneity of macrobenthic species density is little known.
- Such was re-investigated in intertidal seagrass in the Knysna estuarine bay, RSA.
- As expected, macrofaunal abundance was heterogeneous at all spatial grains.
- Yet species and guild density were homogeneous right down to 0.0015 m2 grain.
- Similar such densities across sites at very small scale however are scaling artefacts.

Spatial heterogeneity of biodiversity has been extensively researched, but its spatial homogeneity is virtually unstudied. An intertidal seagrass system at Knysna (South Africa) known to display spatially homogeneous macrobenthic species density at scales ≥0.0275 m2 was re-investigated at four smaller spatial grains (0.0015 m2 - 0.0095 m2) via a lattice of 8 × 8 stations within a 0.2 ha area. The aim was to investigate the null hypothesis that spatial homogeneity of species density is not a fixed emergent assemblage property but breaks down at small spatial grains within given spatial extents. Although assemblage abundance was significantly heterogeneous at all spatial grains investigated, both species density and functional-group density were significantly homogeneous across those same scales; observed densities not departing from those expected on the basis of independent assortment. Spatial homogeneity is therefore an emergent assemblage property within given spatial extents at Knysna and probably at equivalent sites elsewhere. Equivalent species density in South Africa, Australia and the UK at spatial grains <0.03 m2, however, is a scale-related sampling artefact, as may be temporal homogeneity of species density at Knysna over a 3 year period, but close similarity in shape of their species occupancy distributions remains unexplained.