High‐resolution modelling of ocean circulation can reveal retention spots important for biodiversity conservation

Abstract

Abstract Larval transport by ocean circulation and its emerging property at the population level, i.e. connectivity, has received increasing attention thanks to the Aichi target 11 of protecting 10% of ocean surfaces through well‐connected marine protected area (MPA) networks. Furthermore, it is also important to investigate retention within a site, as it determines the self‐persistence of a population in an isolated MPA. Mediterranean rocky substrates host a conspicuous and diverse biota, which explains why MPA designations have targeted rocky habitat. Retention rates in the fragmented rocky habitat of the Gulf of Lion were established at two spatial scales (10 and 1 km2) using dispersal simulations. To this end we computed three‐dimensional flow simulations with high spatial resolution nearshore (80 m), combined with a high density of release spots (every 100 m). This study shows that among the six rocky 10‐km2 patches, the four with highest average retention rates for pelagic larval duration (PLD), of up to 42 days, were designated MPAs. Furthermore, within each MPA, small zones where special protection measures are applied correspond to 1‐km2 subpatches where the highest local retention rates were found. Yet the 2% most retentive subpatches of the rocky habitat do not exhibit retention rates large enough to ensure the local persistence of most species.