Rise of Turfs: A New Battlefront for Globally Declining Kelp Forests

Abstract

Kelp forests are structurally complex habitats, which provide valuable services along 25% of the world's coastlines. Globally, many kelp forests have disappeared and been replaced by turf algae over the last decade. Evidence that environmental conditions are becoming less favorable for kelps, combined with a lack of observed recovery, raises concern that these changes represent persistent regime shifts. Here, we show that human activities mediate turf transitions through geographically disparate abiotic (warming and eutrophication) and biotic (herbivory and epiphytism) drivers of kelp loss. Evidence suggests kelp forests are pushed beyond tipping points where new, stabilizing feedback systems (sedimentation, competition, and Allee effects) reinforce turf dominance. Although these new locks on the degraded ecosystems are strong, a mechanistic understanding of feedback systems and interactions between global and local drivers of kelp loss will expose which processes are easier to control. This should provide management solutions to curb the pervasive trend of the flattening of kelp forests globally.