Spatial variability in epiphytic foraminifera from micro- to regional scale

Density of epiphytic foraminifera varies spatiallly from sub-leaf to region al scales within Posidonia australis meadows of south Western Australia. Fo raminiferal populations on individual seagrass leaves show compositional zo ning and aggregation around algae and serpulid worm tubes. Such microscale spatial heterogeneity could reflect microhabitat, leaf growth history, food source and recruitment patterns. Most foraminifera have homogeneous densit ies on individual plants, and are distributed evenly throughout seagrass sa mples from meadows at a given geographic site. Only species associated,vith patchy epiphytic algae within the meadows show spatial heterogeneity at th e local scale. Spatial homogeneity within the seagrass meadow reflects repe tition of seagrass leaf substrate and microhabitats, and the uniformity of ambient environmental variables at scales larger than the seagrass leaves. Spatial homogeneity in this environment permits characterization of a given geographic site based on three samples. At regional scales, foraminifera m ay have homogeneous and heterogeneous distributions. Abundance of individua l species is uniform, sporadic, or shows a gradient pattern along the coast . Patterns of variation in foraminiferal populations regionally, partly ref lect the climate gradient, but also factors operating at micro- and local s cales. Regionally distinct assemblages could be defined for different clima tic regions along the coast, Thus, populations of the various foraminiferal species are regulated by environmental or biotic variables at different sc ales. This study shows how sample composition at each site reflects spatial variation of species at micro-, local and regional scales and how these di fferences can be used to define assemblages which characterize microhabitat s, localities and regions.