DEMOGRAPHIC PATTERNS OF THE PALAEMONID PRAWN MACROBRACHIUM-INTERMEDIUM IN SOUTHEASTERN AUSTRALIA - SPATIAL HETEROGENEITY AND THE EFFECTS OF SPECIES OF SEAGRASS

The effects of species of seagrass (Zostera capricorni and Posidonia australis) on spatial and temporal heterogeneity in the demography of estuarine populations of the palaemonid prawn Macrobrachium intermedium across 65 km of the Sydney region, southeastern Australia, were examined. Three estuaries were sampled in 1983 and 1984 to assess the magnitude of intra- and inter-estuary variability in demographic characteristics among populations. Species of seagrass had no effect on the demographic patterns of populations: differences in the magnitude and directions of change in abundances, recruitment, reproductive characteristics, size structures and growth were as great among populations within each species of seagrass as those between the 2 seagrasses. Abiotic factors, such as the location of a meadow in relation to depth of water and distance offshore, and the interactions of these factors with recruiting larvae are hypothesised to have greater influence than the species of seagrass in determining the distribution and abundance of these prawns. Spatial and temporal heterogeneity in demography was similar across all spatial scales sampled: among meadows (50 m to 3 km apart) in an estuary and among meadows in all 3 estuaries (10 to 65 km apart). Variability in demographic processes among populations in the Sydney region was most likely due to stochastic factors extrinsic to the seagrasses themselves. I conclude that the demography of seagrass-dwelling estuarine populations of M. intermedium is basically the same throughout the Sydney region, but differs to that of populations of M. intermedium in seagrasses occurring at higher latitudes in southeastern Australia. This study emphasises the need to consider spatial and temporal heterogeneity in the demographic processes of a species over various scales to assess the magnitude of flexibility in its life history throughout its distribution.