Background/Question/Methods Kelp forests are found along over 25% of the world’s coastlines and are the largest marine biome in the world, covering 1.5-2 million square kilometers. Human activities have had a profound influence on kelp forests across their range, and these habitats have declined over the past half century. Many of the current threats to kelp forests are linked to, or compounded by, climate change. When kelp forests become unstable, abrupt transformations can take the form of regime shifts to sea urchin barrens or to turf-dominated reefs. These shifts occur when biotic or abiotic stressors overcome stabilizing feedbacks that maintain the kelp-dominated state. Restoration of these states can be a challenging, and these shifts have consequences on ecological function of the coastal zone.
Results/Conclusions Over the last decade, an emerging pattern has been that kelp forests increasingly are replaced by turfs, changing the reef seascape from a complex forest to a structurally simple mat of low-lying algae. The loss of forest-forming seaweeds and the rise of turfs across four continents consistently resulted in the miniaturization of underwater habitat structure, with seascapes converging towards flattened habitats with smaller habitable spaces. Surprisingly, such habitat convergence occurred despite turf seascapes consisting of vastly different species richness and with different taxa providing habitat architecture, as well as across disparate drivers of marine forest decline. These changes have consequences for associated fauna, nutrient cycling and carbon storage. Climate change and other human stressors are eroding the resilience of kelp forests and resulting in less stable temperate reefs.