Abstract
lgal forests represent the most extensive coastal habitat in the ocean, believed to play an important role in supporting biodiversity and carbon fluxes in the ocean. Yet, reliable estimates of the area and global production of algal forests are not available, and estimates available in the literature have been carried over along a chain of citations from estimates, representing best guesses rather than empirical assessments, for nearly half a century. Here we build on new developments on global data on environmental drivers and observations of macroalgal presence and production around the world to provide a first estimate of their global extent, production and trends in marine algal forests globally.