PARAMETERS OF PRODUCTIVITY AND METABOLISM OF CORAL-REEF ECOSYSTEMS OFF CENTRAL VIETNAM

Primary production of phytoplankton in coastal waters off central Vietnam (20-100 mg C m-2 day-1) was depleted over the shallow coral reefs (1-5 mg C m-3 day-1). Planktonic bacteria totalled 0·2-2 × 106 cells ml-1, wet biomass was 50-1250 mg m-3, and productivity was 50-200 mg m-3 day-1 of wet biomass (or 10-40 mg C m-3 day-1). The biomass of planktonic protozoa (ciliates and zooflagellates) in waters off the reefs was 100-300 mg m-3 with depletion by grazing over the reefs being 1-5 mg m-3. Total respiration rates of microplankton were within the range 0·2-1 mg O2l-1 day-1, respiration of bacteria comprising 80-90% of the total. The stock of labile (potentially utilizable by planktonic microflora) organic matter in coastal waters varied from 0·3 to 3 mg C l-1, higher values corresponding with waters over the active coral reef. The excretion of organic matter by corals as well as the respiration and photosynthesis rates in different components of bottom biotopes were measured. The roles of bacteria, algae and planktonic protozoa in coral reef trophodynamics are discussed. © 1991.