Turf algae redefine the chemical landscape of temperate reefs, limiting kelp forest recovery

In temperate regions experiencing rapid ocean warming, kelp forests are being replaced by chemically rich turf algae. However, the extent to which these turf algae alter the surrounding chemical environment or affect the rebound potential of kelp forests (through chemically mediated interactions) remains unknown. Here, we used underwater visual surveys, comprehensive chemical profiling, and laboratory experiments to reveal that turf algae release bioactive compounds into the water that fundamentally alter the reef "chemical landscape" and directly suppress kelp recruitment. Therefore, our study reveals that chemical ecology is critical in shaping modern kelp forest ecosystems and their resilience. Further, it demonstrates that reversing climate-driven state shifts will require not only curbing global carbon emissions but also implementing targeted local interventions that break harmful ecological feedback loops and foster recovery.