Bacteria, flagellates and nutrients in island fringing coral reef waters: Influence of the ocean, the reef and eutrophication
Abstract:We sampled subsurface (2 m) eutrophied and non-eutrophied coral reef waters, the adjacent ocean and Harbour bay along the southern coast of Curaçao, Southern Caribbean, and measured nutrient concentrations and microbial variables. In Harbour bay very high ammonium concentrations (up to 35 μM) and bacterial production (up to 11 μgC L−1 h−1) were found. Runoff into the bay increased bacterial production as well as the numbers of bacteria and flagellates. The effects of out flowing Harbour water were limited to the waters in front of the town. Ammonium, nitrite, nitrate and phosphate concentrations were higher close to the urbanized area than at non-eutrophied reef sites over 10 km away. The presence of coprostanol relates this eutrophication to sewage discharge. At the eutrophied site bacterial production was occasionally increased from 0.1–0.5 μgC L−1 h−1 to about 1.2 μgC L−1 h−1 by runoff or because it originated from the Harbour bay, but no stimulation of sewage discharge on bacteria was observed due to rapid dilution of the input. Nitrate concentration were consistently higher in non-eutrophied reef water (0.2–0.6 μM) than in the adjacent oceanic water (0.1–0.3 μM). Bacterial numbers were lower in water over the reefs than in oceanic water. Flagellate bacterivory was similar in both waters. Bacterial production was 2–3 times higher in non-eutrophied reef water than in oceanic water in periods of reduced reef currents and mixing. The coastal reef ecosystem of Curaçao is subjected to short- and long-term fluctuations of nutrients and micro-organisms in the oceanic water mass surrounding the island. We observed such changes at all stations in phosphate concentration, N:P ratio, bacterial and flagellate numbers and bacterial production over a 1-yr period.
Document Type: Research Article
Publication date: 1999-09-01
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