Assess students' understanding of the causes of ocean acidification (atmospheric CO2 uptake and anthropogenic emissions), resulting changes to the seawater carbonate system (pH decline, increased H+, conversion of carbonate to bicarbonate, decreased carbonate ion concentration and reduced aragonite/calcite saturation), and consequent effects on marine organisms (reduced calcification, impaired larval development, physiological stress, and food‑web impacts). Students should be able to explain mechanisms, interpret basic carbonate chemistry indicators (pH, [CO3^2-], Ωarag/Ωcalc), and predict organismal responses under different CO2 scenarios.