Showing papers by "Daniel M. Alongi published in 1994"

The role of bacteria in nutrient recycling in tropical mangrove and other coastal benthic ecosystems

Abstract: Sedimentary bacteria have generally been recognized as an essential food for protists and invertebrates, forming the base of benthic food webs. This trophic role has been well documented, but bacteria play an equally important role as mineralizers of organic detritus and recyclers of essential nutrients. Recent evidence suggests that this latter role is more important than their trophic function in tropical mangrove and coastal sediments. Bacteria in these systems are, on average, more abundant and productive than their counterparts in higher-latitude systems. They account for a disproportionate share of nutrient uptake to the extent that bacterial communities act as a sink for carbon, processing most of the energy and nutrients in tropical aquatic systems. Most bacteria remain unconsumed in tropical deposits, dying naturally and lysing, with the next generation of cells consuming, mineralizing and recycling this material either into new biomass or dissolved material. Bacteria in tropical aquatic sediments are ultimately controlled by inputs of dissolved and particulate detritus, natural mortality and recycling. To replenish damaged ecosystems in the tropics, restoration of the natural geochemical profile in the sediments is necessary to re-initiate the growth of bacteria in order to restore the essential recycling processes which assist in the conservation of nutrients.

Zonation and seasonality of benthic primary production and community respiration in tropical mangrove forests

Abstract: Benthic oxygen consumption and primary production were measured using the bell jar technique in deltaic and fringing mangrove forests of tropical northeastern Australia. In a deltaic forest, rates of sediment respiration ranged from 197 to 1645 μmol O2 m−2 h−1 (mean=836), but did not vary significantly with season or intertidal zone. Gross primary production varied among intertidal zones and seasons, ranging from −281 to 1413 μmol O2 m−2 h−1 (mean=258). Upon tidal exposure, rates of gross primary production increased, but respiration rates did not change significantly. In a fringing mangrove forest, benthic respiration and gross primary production exhibited strong seasonality. In both forests, rates of oxygen consumption and production were low compared to salt marshes, but equivalent to rates in other mangrove forests. The production:respiration (P/R) ratio varied greatly over space and time (range:−0.61 to 1.76), but most values were «1 with a mean of 0.15, indicating net heterotrophy. On a bare creek bank and a sandflat, rates of gross primary production and P/R ratios were generally higher than in the adjacent mangroves. Low microalgal standing stocks, low light intensity under the canopy, and differences in gross primary production between mangroves and tidal flats, and with tidal status, indicate that benthic microalgae are light-limited and a minor contributor to primary productivity in these tropical mangrove forests.