Bacterial Respiration, Growth Efficiency and Protist Grazing Rates in Mangrove Waters in Cape Rachado, Malaysia
This study was carried out at an inter-tidal site at Cape Rachado (02º24¢48N, 101º51¢31E, Fig. 1) from April 2003 until April 2004. A small mangrove forest populated with Sonneratia and Rhizophora trees was located nearby. Bacterial respiration ranged 0.818–3.208 µM O2 h–1, and the amount of carbon respired was 9.80–38.44 µg C L–1 h–1. Concurrent bacterial production during the incubation was 1.23–3.28 µg C L–1 h–1. Using both these respiration and production values, we calculated the bacterial growth efficiency, and it ranged 4.0–11.1%. The low growth efficiency indicated the lower substrate quality here. However adding nutrients did not significantly increase bacterial growth rates (Student’s t-test for matched pairs: t = 1.883, df = 2, p > 0.10). In this study, protists consumed 0.49 – 5.72 ¥ 104 bacterial cells mL–1 h–1 or 22 ± 15% of bacterial production. In carbon equivalents, grazing ranged 0.15 – 1.81 µg C L–1 h–1. Annual bacterial production at this site is 42.7 g C m–3 yr–1, and carbon consumed by the bacteria was estimated at 585 g C m–3 yr–1. Of this, only 8 g C m–3 yr–1 was channeled onto protists. These calculations showed that effectively only 1% of the carbon consumed by bacteria was passed onto protists. The role of bacteria here was essentially that of a remineralizer, and as a sink for carbon.
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