Heterotrophic bacteria typically take up directly dissolved organic matter due to the small molecular size, although both particulate and dissolved organic matter have labile (easily consumed) compounds. Tropical coastal waters are important ecosystems because of their high productivity. However, few studies have determined bacterial cycling (i.e. carbon uptake by bacteria and allocation for bacterial biomass and respiration) of dissolved organic carbon in coastal tropical waters, and none has determined bacterial cycling of total and dissolved organic carbon simultaneously. In this study we followed bacterial biomass and production, and organic carbon changes over short-term (12 days) dark incubations with (total organic carbon, TOC) and without particulate organic carbon additions (dissolved organic carbon, DOC). The study was performed at three sites along the middle stretch of the Great Barrier Reef (GBR) during the dry and wet seasons. Our results show that the bacterial growth efficiency is low (0.1–11.5%) compared to other coastal tropical systems, and there were no differences in the carbon cycling between organic matter sources, seasons or locations. Nonetheless, more carbon was consumed in the TOC compared to the DOC incubations, although the proportion allocated to biomass and respiration was similar. This suggests that having more bioavailable substrate in the particulate form did not benefit bacteria. Overall, our study indicates that when comparing the obtained respiration rates with previously measured primary production rates, the GBR is a heterotrophic system. More detailed studies are required to fully explore the mechanisms used by bacteria to cycle TOC and DOC in tropical coastal waters.

尽管颗粒和溶解的有机物都具有不稳定的（容易消耗的）化合物，但由于分子尺寸小，异养细菌通常直接吸收溶解的有机物。由于其高生产力，热带沿海水域是重要的生态系统。但是，很少有研究确定沿海热带水域中溶解有机碳的细菌循环（即细菌吸收碳以及分配细菌生物量和呼吸），没有一个研究同时确定总有机碳和溶解有机碳的细菌循环。在这项研究中，我们追踪了细菌的生物量和产生情况，以及在短期（12天）黑暗孵化中有机碳的变化，其中有（总有机碳，TOC）和没有添加颗粒有机碳（溶解的有机碳，DOC）。这项研究是在干燥和潮湿季节，沿着大堡礁（GBR）中段的三个地点进行的。我们的结果表明，与其他沿海热带系统相比，细菌的生长效率低（0.1-11.5％），并且有机物质来源，季节或位置之间的碳循环没有差异。尽管如此，与DOC孵化相比，TOC消耗了更多的碳，尽管分配给生物量和呼吸的比例相似。这表明以颗粒形式具有更多可生物利用的底物不会使细菌受益。总体而言，我们的研究表明，将获得的呼吸速率与先前测得的初级生产率进行比较时，GBR是一种异养系统。