Trace metals from industrial effluents discharged into Malaysian mangrove ecosystems, in Sarawak in particular, are of growing concern. Concentrations of trace metals (copper, manganese, iron, and zinc) were determined in sediment, surface water, pore water, green and red filamentous macroalgae (Chaetomorpha sp. and Bostrychia sp., respectively) and the rock oyster Saccostrea cucullata from three estuarine mangrove habitats in Sarawak (Kuala Nyalau, Bakam, and Miri), Malaysia. Trace metal concentrations detected in sediment of these mangrove ecosystems (except for Zn concentration in K. Nyalau) were considerably higher than those specified in USEPA sediment quality guidelines. Sediment trace metal concentrations differed significantly (p Mn > Zn > Cu, Fe > Zn > Mn > ...