Temporal Variation of Bacterial Respiration and Growth Efficiency in Tropical Coastal Waters

We investigated the temporal variation of bacterial production, respiration, and growth efficiency in the tropical coastal waters of Peninsular Malaysia. We selected five stations including two estuaries and three coastal water stations. The temperature was relatively stable (averaging around 29.5°C), whereas salinity was more variable in the estuaries. We also measured dissolved organic carbon and nitrogen (DOC and DON, respectively) concentrations. DOC generally ranged from 100 to 900 M, whereas DON ranged from 0 to 32 M. Bacterial respiration ranged from 0.5 to 3.2 M O2 h 1, whereas bacterial production ranged from 0.05 to 0.51 M C h1. Bacterial growth efficiency was calculated as bacterial production/(bacterial production respiration), and ranged from 0.02 to 0.40. Multiple correlation analyses revealed that bacterial production was dependent upon primary production (r2 0.169, df 31, and P < 0.02) whereas bacterial respiration was dependent upon both substrate quality (i.e., DOC/DON ratio) (r2 0.137, df 32, and P 0.03) and temperature (r2 0.113, df 36, and P 0.04). Substrate quality was the most important factor (r2 0.119, df 33, and P 0.04) for the regulation of bacterial growth efficiency. Using bacterial growth efficiency values, the average bacterial carbon demand calculated was from 5.30 to 11.28 M C h1. When the bacterial carbon demand was compared with primary productivity, we found that net heterotrophy was established at only tw