Long-term degradation of algal-derived dissolved organic matter (ADOM) by particle-associated and free-living opportunistic pathogens and their contribution to refractory DOM accumulation

Seawater samples were collected from three stations within an offshore kelp aquaculture area and from three additional offshore stations located outside the aquaculture zone. Sufficient volumes of seawater were collected for subsequent indoor simulation experiments. The experimental treatments contained kelp detritus, while the control treatments consisted of offshore seawater without added detritus. Microbial degradation experiments were conducted for 120 days for both treatments. During the incubation period, microorganisms with different lifestyles (free-living and particle-associated) were periodically collected from both treatments, accompanied by measurements of DOM-related parameters and environmental variables. This study focused on evaluating the contributions of opportunistic bacteria with different lifestyles to the degradation of algal-derived DOM and the formation of refractory DOM (RDOM), as well as the temporal dynamics of microbial community succession over time.