The distribution of epiphytic algae and sessile invertebrates on the seagrass Amphibolis griffithji is not random. The number of epiphyte species increases with increasing seagrass height and there are approximately twice as many epiphytic algal species as Invertebrate species. Epiphytes growing on the stems have a clear apico-basal distribution, with algae such as Haliptilon roseum, Laurencja filiforrnis and Hypnea spp. most abundant on the upper 30 '10 of the seagrass stem, while the bryozoan Celleporjna sp and the hydrozoan Thyroscyphus margjnatus are most abundant near the base of the stem. Other species of algae and invertebrates have intermediate distributions. Eplphyte biomass increases with seagrass height and the bulk occurs on the uppermost 20 cm of the tallest plants. This is mainly due to 1 or 2 algal species. Recruitment of epiphytes also follows a distinct pattern related to plant size (age), with species such as the crustose coralline algae rapidly colonising the leaves and stems of new seagrass plants. Other very early colonisers are the bryozoans Pyripora potita and Electra flagellurn on the stems, and the hydrozoan Plumularia compressa and the bryozoan Thairopora mamjllaris on the leaves.