Vol. 48: 137-145, 1988 MARINE ECOLOGY - PROGRESS SERIES Mar. Ecol. Prog. Ser. Published September 21 Preliminary assessment of benthic community metabolism in a south-east Asian mangrove swamp Erik Kristensen, Frede Ø. Andersen, Lars H. Kofoed Institute of Biology, University of Odense, DK-5230 Odense M, Denmark ABSTRACT: Preliminary data are presented on benthic metabolism, i.e. carbon, oxygen and dissolved inorganic nitrogen (DIN) dynamics in a tropical, south-east Asian mangrove swamp. Primary production by benthic microalgae, measured as 14C assimilation and O2 production, was low compared to other intertidal areas. Benthic production comprised 4 to 20 % of production estimates obtained from the literature on the mangrove Rhizophora apiculata. Factors responsible for the relatively low benthic primary production appeared to be shading by R. apiculata and DIN availability. Oxygen penetration into water-covered sediment showed significant differences between light (2.5 mm) and darkness (1.5 mm). In air-exposed sediment, however, O2 penetration depth was similar in both light and darkness. Oxygen uptake by the sediment obtained from core incubations was 20 to 55 % higher than the rate estimated from vertical O2 profiles. The estimated O2 demand needed to support the decay of produced algal cells was ca 73 % of the measured total O2 uptake by the sediment. Water sampling in a tidal channel indicated that suspended particles transported by incoming tides were trapped in the mangrove system. This tidal import was evident as an upper sedimentary silt-zone (0 to 5 cm) superposing a lower peat containing root-zone (> 5 cm) in the sediment. INTRODUCTION Mangrove swamps are usually considered to be areas of high primary productivity which support highly developed detritus-based food webs (e.g. Odum & Heald 1975, Dye & Lasiak 1986, Robertson 1986). It has long been recognized that mangrove trees, e.g. Rhizophora spp. and Avicennia spp., are the most important primary producers (Christensen 1978, Bunt et al. 1979, Twilley et al. 1986b). During the last decade various studies have been reported on primary production and sessile mac- roalgae in mangrove swamps (Wium-Andersen 1979, Ricard 1984, Davey & Woelkerling 1985), but the role of benthic microalgae has not yet been addressed. Benthic microalgae, known as important producers of organic matter in intertidal flats all over the world (e.g. Colijn & Jonge 1984), may be of significance for nutrient and detritus dynamics in mangrove swamps. The decay of organic matter in mangroves has usu- ally been determined as the time dependent weight loss of litter (Boonruang 1978, Cundell et al. 1979, Rice & Tenore 1981). This has provided valuable informa- tions about leaching and microbial attack on intact leaves, but less about the overall microbial activity in mangrove sediments. Oxygen exchange, generally accepted as a measure of autotrophic and heterotrophic (aerobic as well as anaerobic) activity in sediments (Jørgensen 1983, Andersen & Hargrave 1984, Kristensen & Blackburn 1987), may provide the basis for an estimate of primary production and decomposition by the benthic commu- nity. The results can without serious error be converted to carbon flux using a conversion factor of