Degraded but not too much: the carbon metabolism of pristine and urban marine forests in the NW Mediterranean SeaMacroalgae and Ecosystem Services (sponsored by Annals of Botany)

Fabio Bulleri¹, Chiara Ravaglioli¹, Ludovica Pedicini¹

¹Università di Pisa, Italy

Macroalgal forests are declining worldwide due to compounded anthropogenic perturbations. Despite the large attention given to the rise of algal turfs globally, along urbanized coastlines of the Mediterranean, forests are often replaced by shrub-like assemblages. In this study, we measured rates of carbon turnover due to photosynthesis, respiration, calcification and CaCO3 dissolution, in benthic communities on reefs along an urbanized coast and at a pristine island in the NW Mediterranean, by means of in-situ incubations under dark and light conditions. The diversity and biomass of primary producers and invertebrates, as well as community production (NCP) and respiration (CR), were similar between pristine and urbanized sites. Thus, despite differences in the identity of dominant macroalgal and associated species, benthic communities at pristine and urbanized reefs provide similar ecosystem services (e.g., carbon uptake, enhancement of biodiversity). These results suggest that the replacement of marine forests by alternative assemblages does not always cause the collapse of biodiversity and ecosystem functioning. While pursuing the conservation of marine forests remains a priority, evaluating the ecological value of alternative macroalgal assemblages, generally labelled as degraded, appears warranted to inform the management of temperate rocky reefs.