Abstract
Density of epiphytic foraminifera varies spatially from sub-leaf to regional scales within Posidonia australis meadows of south Western Australia. Foraminiferal populations on individual seagrass leaves show compositional zoning 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 densities on individual plants, and are distributed evenly throughout seagrass samples from meadows at a given geographic site. Only species associated with patchy epiphytic algae within the meadows show spatial heterogeneity at the local scale. Spatial homogeneity within the seagrass meadow reflects repetition 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 may have homogeneous and heterogeneous distributions. Abundance of individual species is uniform, sporadic, or shows a gradient pattern along the coast. Patterns of variation in foraminiferal populations regionally, partly reflect the climate gradient, but also factors operating at micro- and local scales. Regionally distinct assemblages could be defined for different climatic regions along the coast. Thus, populations of the various foraminiferal species are regulated by environmental or biotic variables at different scales. This study shows how sample composition at each site reflects spatial variation of species at micro-, local and regional scales and how these differences can be used to define assemblages which characterize microhabitats, localities and regions.