Variability of particulate beam attenuation coefficient at 532 nm (cp (532)) and microbial planktonic community
(heterotrophic bacteria and phytoplankton) was analyzed in coastal waters of Southern California. The goal of this study
was to explore heterotrophic bacteria (HB) response (cell abundance, BA, and carbon production, BCP) with respect to
different particle characteristics (concentration, size distribution, and composition) related with cp(532). We observed a
fairly complex pattern of HB response and particle dynamics during seven experiments throughout the summer and
winter, which reflected variations in cp(532). The first experiment showed relatively high values of cp(532), in
conjunction with high chlorophyll a concentration (chl) of about 5.4 mg m-3. For experiments 2 and 3, a sharp decrease
of chl was accompanied by an increased role of detrital particles (non-living matter) as evidenced by increased detrital
absorption (ad). The highest values of particle-attached (>1 μm) and free living (<1 μm) BA and BCP were observed in
experiment 3. These changes in particle assemblage including HB maintained cp(532) at relatively high level,
comparable to that observed when phytoplankton dominated. A significant decrease of cp(532) was observed in
experiment 4 and 5, which coincided with relatively low BA, BCP, and ad values. In experiment 7, cp(532) magnitude
was comparable to the first experiment and was accompanied by high chl, BA and SPM (suspended particulate matter).
Greatest changes in cp(532) coincided with greatest variations in BA, even though our estimates of the direct contribution
of heterotrophic bacteria to cp(532) for all experiments remained quite low (<10%).