SEAGRASS DISTRIBUTION AND SEASONAL BIOMASS CHANGES IN RELATION TO DUGONG GRAZING IN THE MOLUCCAS, EAST INDONESIA

Seagrass distribution and seasonal changes in biomass and total organi c C were studied in relation to dugong grazing, in intertidal meadows dominated by Halodule uninervis (Forssk ($) over circle al) Ascherson between December 1990 and December 1992 in Nang Bay on the east coast of Ambon. Both below-ground and above-ground biomass of Halodule unine rvis significantly increased during the transition period from the dry season to the wet season between February and May. Above-ground bioma ss of Halodule uninervis decreased significantly during the wet season (between May and August), when low tide occurred in day time, and onl y slow recovery took place until November. Below-ground biomass remain ed high until November, resulting in a significant decrease of the rat io of above-ground to below-ground biomass during the period between M ay and August, and in a 'sparse' visible seagrass meadow, with a non-v isible high below-ground biomass between August and November. Total or ganic carbon level in the below-ground plant parts gradually increased between May and August with a peak value in August. Dugong grazing re moved 93% of the shoots and 75% of the below-ground biomass of the upp er 4 cm deep layer of sediment. Seagrass biomass in freshly,orated fee ding tracks was restored to levels of the nearby seagrass bed after 5 months during the onset of the wet season. No significant restoration took place during the dry season. The frequency of dugong grazing show ed a strong positive correlation with total organic C level in the bel ow-ground plant parts,indicating that the dugongs preference for the H alodule uninervis seems to be based on a strategy of a high net rate o f energy intake.