Marine bacteria play an important role in carbon flow in aquatic ecosystems not only by decomposing detritus but also by providing a trophic pathway, which is called microbial loop, where dissolved organic carbon (DOC) is incorporated into bacterial biomass and returned to the classic food chain through zooplankton grazing on bacteria. Bacteria production (BP) and respiration (BR) rates are fundamental to understanding bacterial carbon metabolism and estimating carbon flux via bacteria to the food web. However, the prefiltration procedure and long incubation time in BR measurement can lead to inaccuracy due to ignorance of particle-attached (PA) bacteria and change in bacterial abundance and composition during incubation. This dissertation investigates methodology problems in BR...[ Read more ]

Marine bacteria play an important role in carbon flow in aquatic ecosystems not only by decomposing detritus but also by providing a trophic pathway, which is called microbial loop, where dissolved organic carbon (DOC) is incorporated into bacterial biomass and returned to the classic food chain through zooplankton grazing on bacteria. Bacteria production (BP) and respiration (BR) rates are fundamental to understanding bacterial carbon metabolism and estimating carbon flux via bacteria to the food web. However, the prefiltration procedure and long incubation time in BR measurement can lead to inaccuracy due to ignorance of particle-attached (PA) bacteria and change in bacterial abundance and composition during incubation. This dissertation investigates methodology problems in BR measurement and proposes approaches to minimize inaccuracy. A field survey was conducted at two coastal sites in Hong Kong water to monitor BP and BR monthly during one-year time. BR of free-living (FL) bacteria was corrected to a better estimation and BR for PA bacteria was estimated from an allometric model. PA bacteria was found to have a significant contribution to total bacterial metabolism rates and therefore total bacterial carbon demand (BCD). They also had higher cell specific production (sBP) rates and most of the time higher bacterial growth efficiency (BGE) than FL bacteria. A set of incubation experiments were done to investigate the effect of incubation during BR measurement on bacterial community. Change of bacterial abundance, productivity and community structures were observed, revealing the effects of long-time incubation and loss of control on bacterial growth when grazers were removed by the prefiltration step. Correlation between relative abundance of major OTUs indicated that taxonomy groups might vary in cellular productivity and have different response to incubation. These bias appeal for shortening incubation time and improved method for BR measurement.