Ocean Acidification in Nigerian Coastal Waters: Present Status, Drivers, and Projected Ecosystem Impacts

Ocean acidification driven by increasing atmospheric carbon dioxide absorption represents a fundamental and largely irreversible threat to marine calcifying organisms, yet its current status, spatial heterogeneity, and projected ecosystem impacts in Nigerian coastal and shelf waters have received almost no observational attention, representing a critical knowledge gap in West African marine science. This dissertation provides the first comprehensive, multi-year observational record of ocean acidification indicators in Nigerian waters and develops regionally calibrated projections of acidification-driven ecosystem impacts to 2100. A three-year monitoring programme (2022 to 2024) deploys autonomous Argo-pH floats and conducts discrete water sampling at 25 stations across a shelf transect from Lagos to Calabar at quarterly intervals, measuring pH (total scale), total alkalinity, dissolved inorganic carbon, and the calcium carbonate saturation states of aragonite and calcite. River-influenced nearshore stations capture the modifying influence of alkalinity inputs from the Niger Delta and freshwater discharge events. A regional acidification budget model quantifies the relative contributions of anthropogenic CO2 uptake, biological productivity, river alkalinity inputs, and upwelling of CO2-rich deep water to observed pH variability. A structured literature-based ecological impact assessment synthesises evidence on the sensitivity of key Nigerian coastal organisms (pteropods, bivalve larvae, echinoderm larvae, coral, finfish early life stages) to projected acidification levels. An ecosystem-level impact scenario model projects changes in secondary production, fisheries yield, and carbonate habitat area under CMIP6 SSP2-4.5 and SSP5-8.5 atmospheric CO2 trajectories. Findings provide the empirical foundation for Nigeria's first national ocean acidification monitoring strategy. Keywords: ocean acidification, Nigerian coastal waters, carbonate chemistry, pH monitoring, ecological impacts