Seaweed Aquaculture and Waste Stream Integration for Blue Carbon: A Systematic Review of Carbon Pathways and Mitigation Strategies

Abstract

Seaweed aquaculture integrated with waste streams is a promising blue-carbon pathway. This review goes beyond narrative synthesis by introducing three contributions: (i) a cross-system taxonomy of integration modalities, (ii) a concise measurement, reporting, and verification (MRV) protocol accompanied by a practitioner checklist, and (iii) a Crediting Readiness Scorecard (CRS) that operationalizes additionality, durability, leakage, and governability. We systematically reviewed studies published between 2016 and 2025 on coupling seaweed cultivation with aquaculture effluents, municipal wastewater, and flue-gas CO₂, following PRISMA screening and a simple risk-of-bias appraisal; where data permitted, we performed a small quantitative synthesis for nutrient removal and carbon-capture indicators. Our aim is to evaluate operational conditions, carbon pathways (harvest, particulate organic carbon export, dissolved and recalcitrant dissolved organic carbon), and MRV feasibility, while proposing an implementable protocol and scoring tool that standardize assessment across sites and species. Findings indicate that integration generally elevates productivity and carbon capture, but outcomes hinge on nutrient management, residence time and flow distribution, thermal control, and pretreatment addressing pathogens, metals, and co-pollutants. Using the CRS, aquaculture-effluent integrations emerge as nearer-term candidates for conservative crediting; municipal-wastewater and flue-gas routes can approach comparable readiness with stronger pretreatment, clearer system boundaries, and leakage safeguards. MRV remains challenged by air–sea flux attribution, spatial heterogeneity, and inconsistent standards; we map fit-for-purpose metrics net ecosystem exchange/eddy covariance, pCO₂ sensors, ¹³C tracers, and traps/cores to farm, bay, and shelf boundaries with QA/QC routines to constrain uncertainty. Technology assessments highlight artificial upwelling, CO₂ dosing, longline offshore arrays, and automated sensing as promising yet constrained by energy demand, reliability, and permitting; we synthesize indicative readiness ranges to guide deployment. Overall, the review converts disparate findings into actionable guidance through the taxonomy, MRV protocol, and CRS, and sets priorities for MRV optimization, standardized LCA distinctions between avoided emissions and removals, and scaling strategies suited to data-limited tropical contexts.