Abstract
Microalgae and cyanobacteria reconfigure pigment-protein complexes as environments change, coupling light harvesting, photochemistry, and redox homeostasis. This review synthesizes the mechanisms driving shifts in chlorophylls, carotenoids, and phycobiliproteins in response to abiotic and anthropogenic stressors, including irradiance, temperature, salinity, nutrient limitation, and pollutants. Pigment measurements are most informative when interpreted as profiles of individual pigments, absolute abundances, and diagnostically relevant ratios, and when analyzed together with photosystem performance and independent oxidative-damage markers. Key strategies include chlorophyll antenna remodeling to rebalance light capture and protection; carotenoid-mediated nonphotochemical quenching, excitation quenching, reactive oxygen species scavenging, membrane stabilization, and, in some taxa, secondary carotenoid accumulation during prolonged adaptation. In cyanobacteria, phycobiliprotein plasticity enables redistribution of excitation energy and supports antenna-level energy dissipation, while extracellular UV-screening pigments such as scytonemin provide an additional protective layer.