Chemical interactions between filter-feeding mussels and Ulvaprolifera: The role of dissolved organic matter and secondary metabolites in growth promotion and competition inhibition of algal species.

This review examines the chemical and ecological interactions between filter-feeding mussels and the green macroalga Ulva prolifera in integrated multi-trophic aquaculture (IMTA) systems. Mussels are crucial for nutrient recycling, as they filter water and release bioavailable compounds such as ammonium (NH4+), urea (CO(NH2)2), and dissolved organic matter (DOM). These compounds promote Ulva growth and enhance microbial activity. In turn, U. prolifera produces sulfated polysaccharides, phenolics, and halogenated metabolites that can influence microbial communities, suppress competitors, and potentially affect mussel physiology at high concentrations. The review emphasizes the interconnectedness of nutrient exchange, DOM cycling, and microbial genes such as pmoA and mcrA, highlighting the novelty of integrating microbial ecology with biogeochemical cycles and ecosystem outcomes, illustrating both the synergies and risks present in co-culture systems. While moderate production of metabolites helps control biofouling and maintain ecosystem stability, excessive DOM or allelochemical accumulation can hinder mussel filtration and lead to hypoxia. Maintaining specific thresholds, such as DOM concentrations below 5 mg C/L and labile-to-refractory DOM ratios above 1:1, is essential for balance. This synthesis integrates microbial ecology, metabolite feedbacks, and biogeochemical processes to provide a framework for resilient IMTA design. It also emphasizes practical strategies like adjusting stocking densities, optimizing water exchange, and employing microbial monitoring tools to promote sustainable IMTA practices. By linking molecular interactions to ecosystem-scale outcomes, the review offers guidance for sustainable aquaculture systems that enhance productivity, minimize environmental risks, and improve resilience in the face of climate stress.