11:10 〜 11:30
[ACG41-03] Seagrass distribution and adaptation in a turbid tropical estuary (Brunei Bay, Borneo)
★Invited Papers
Seagrass studies have been predominantly conducted in coastal marine environment such as coral reefs, but estuarine seagrass have been behind in research because of its lower abundance. However, the uniqueness of seagrass physiology or adaptation to the environment would be more exerted in estuaries, where water and sediment properties are not stable compared to marine environment. In order to get a better understanding of estuarine seagrass, recent studies on seagrass and water properties at the tropical estuary, Brunei Bay, Borneo are overviewed in this presentation. A total of eight species of seagrass have been recorded in this estuary during 2016-2019, and most of them were found at intertidal zones because the Brunei estuarine water is turbid and sufficient light is not available at subtidal zones. Among the eight species, Halodule pinifolia was most tolerant to muddy sediment conditions, while Halophila minor, Halophila ovalis, and Thalassia hemprichii preferred a relatively coarse sediment. Three species (Halodule pinifolia, Halodule uninervis, and Halophila beccarii) were found most upstream, where the surface water salinity fluctuated between 8.5-21. Laboratory experiments showed that Halophila ovalis, which is now found only in the downstream estuary, could also survive the conditions of this most upstream seagrass habitat. The spatial and temporal variations in basic water properties showed a wide range of salinity, pH, and dissolved oxygen from the upstream river to the downstream estuary. In particular, the upstream pH was lowest for the estuaries recorded in Southeast Asia. Because Brunei is covered with much more pristine forest than neighboring countries, surface and groundwater discharged from the abundant forest would be contributing to forming this unique gradient of water properties along the estuary. Seagrass has adapted to this environmental gradient using its species-specific physiological advantage. Amid continuing coastal disturbance such as dredging, upstream estuary may function as a shelter for seagrass and therefore needs to be carefully monitored for conservation of the ecosystem.