DIATOMS AS EPIPHYTES ON SEAGRASSES IN SOUTH SULAWESI (INDONESIA) COMPARISON WITH GROWTH ON INERT SUBSTRATA

The epiphytic diatom assemblages on the seagrasses Enhalus acoroides ( L.f) Royle and Thalassia hemprichii (Ehr.) Ascherson were studied in a n estuarine sandy mudflat and a coral reef-flat habitat in South Sulaw esi, Indonesia. A comparison was made with the diatom flora developing on inert substrata (suspended microscope slides) and the sediment flo ra in the same habitats. The epiphytic diatom floras on seagrasses rep resented a selection from the sediment flora, strongly favouring light ly silicified diatom species. The two seagrass species did not differ in their epiphytic diatom floras. Diatom floras on leaves of the same seagrass species, but in different habitats, differed considerably. De velopment of diatoms on suspended slides indicated that colonisation i s a random process, in which an important role is played by 'seeds': f ragments of decaying seagrass leaves carrying portions of old diatom a ssemblages. These will blur a potential succession of the developing e piphytic diatom assemblage. Diatoms were among the very first organism s to colonize the slides and completely dominated the eventual flora, which did not differ essentially from that on the seagrass leaves. Sea grass leaves were more sparsely colonized than suspended slides expose d for a comparable duration, probably due to grazing, from which the s lides were protected.