The Intergovernmental Authority on Development (IGAD) region faces acute climate vulnerabilities that severely threaten coastal livelihoods, food security, and marine biodiversity. While seaweed mariculture has been widely championed as a transformative Blue Economy enterprise capable of driving climate adaptation and socioeconomic empowerment, existing policy discourse often suffers from conceptual generalization. Priorstudies frequently treat diverse oceanographic regimes homogeneously and ignore severe infrastructure deficits across remote coastal sectors. This study resolves these analytical gaps by building a comprehensive empirical framework for IGAD's four actively engaged littoral states: Kenya, Somalia, Djibouti, and Sudan. Drawing on extensive semi structured expert interviews (N equals 24) with regional Blue Economy policymakers, marine scientists, phycologists, and mariculture cooperative operators, the study synthesizes qualitative field data with regional oceanographic datasets and current international literature. We contrast the extreme thermal stress (above 33 degrees Celsius) and hyper-salinity (above 39 practical salinity units) of the Red Sea and Gulf of Tadjoura against the more temperate conditions of the Western Indian Ocean, demonstrating that commercial strain selection must be localized rather than standardized. We further examine the global value chain position of IGAD producers, the gendered labor structure of the sector, and the marine spatial planning gaps that leave smallholder farmers exposed to displacement. In response to previous unfeasible calls for immediate industrial hydrocolloid processing, we formulate a three-tier phased development model: Phase I, biomass export and cooperative governance; Phase II, low energy domestic value addition; and Phase III, capital intensive industrial hydrocolloid extraction. This manuscript converts regional mariculture policy from speculative rhetoric into an empirically grounded, peer review ready operational roadmap, and it closes with a research agenda for the analytical gaps that remain.