PROLONGED INUNDATION AND ECOLOGICAL CHANGES IN AN AVICENNIA MANGROVE - IMPLICATIONS FOR CONSERVATION AND MANAGEMENT

The mangrove around Sungei Pemburongunan, just west of Tanjong Batu an d Istana Darul Aman in the Brunei-Muara District, is unique in that it contains the only pure stand of Avicennia marina in Brunei Darussalam . In mid-October, 1990 the mouth of Sungei Pemburongunan was closed du e to a natural build-up of a sandbar across it. The mangrove quickly b ecame flooded and adverse effects on the flora and fauna were observed during the following weeks. In mid-December a channel was dug across the sand bar to reduce the flooding and normalise the ecology. Some of the dying Avicennia and Lumnitzera have since recovered but others su ch as Acrostichum and Casuarina have not. Avicennia showed some intere sting responses to prolonged inundation. Many of the Avicennia that ha d flowered during the flood produced seedlings which are now well root ed and 40-80 cm in height. The survival of large numbers of these seed lings is attributed to the floor-related decrease in the number of gra psid and sesarmid crabs which predate on them. The crab and mollusc po pulations have largely recovered. Unlike periodic short-term flooding which does not seem to have any apparent adverse affect on the ecosyst em, prolonged inundation can result in the loss of the Avicennia and i ts associated flora and fauna. Thus, fragile mangrove ecosystems such as this need to be monitored and managed closely. This work demonstrat es that contrary to conventional wisdom, human intervention and manage ment can be beneficial to more fragile ecosystems, which could otherwi se succumb to natural processes. Furthermore, it highlights the import ance of the dynamic nature of the environment which should be consider ed in management and conservation programmes.