Expanding a network of marine protected areas based on functional rather than structural connectivity is more profitable

One strategy to boost population resilience and stop the long-term loss of ocean biodiversity is to establish networks of interconnected, highly protected areas. In this study, we assess the relationship between profitability and adequacy brought about by structural and functional connectivity in systematic conservation planning (SCP). Twelve sets of conservation plans were explored to protect the hard bottom habitat of the Gulf of Lion (NW Med Sea), varying conservation objectives (10 % and 30 % of the surface area), human activity pressures (including or ignoring existing highly protected areas) and connectivity types: (i) structural connectivity (ii) early summer and (iii) late summer connectivity arising from a week-long larval dispersal. These connectivity are likely estimates of the functional connectivity of gorgonians. Conservation plan profitability - which was defined as the ratio of the population part under protection to protection cost - was assessed using observations of the spatial distribution (that were not used in the SCP) of five gorgonian species Eunicella singularis, Leptogorgia sarmentosa, Eunicella cavolinii, Paramuricea clavata and Corallium rubrum . When functional connectivity replaced structural connectivity, the spatial distribution of highly protected areas was altered, systematically targeting the center of the Gulf of Lion whatever the conservation objective. Profitability drastically increased with functional compared to structural connectivity for four of the five species in the 10 % conservation objective. Including existing highly protected areas also improved profitability but differently according to the species in 10 and 30 % objective. No plan was profitable for P. clavata .