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 organic 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 uninervis significantly increased during the transition period from the dry season to the wet season between February and May. Above-ground biomass of Halodule uninervis decreased significantly during the wet season (between May and August), when low tide occurred in day time, and only slow recovery took place until November. Below-ground biomass remained high until November, resulting in a significant decrease of the ratio of above-ground to below-ground biomass during the period between May and August, and in a 'sparse' visible seagrass meadow, with a non-visible high below-ground biomass between August and November. Total organic carbon level in the below-ground plant parts gradually increased between May and August with a peak value in August. Dugong grazing removed 93% of the shoots and 75% of the below-ground biomass of the upper 4 cm deep layer of sediment. Seagrass biomass in freshly,orated feeding 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 showed a strong positive correlation with total organic C level in the below-ground plant parts,indicating that the dugongs preference for the Halodule uninervis seems to be based on a strategy of a high net rate of energy intake.