Modeling trophic interactions to assess the effects of a marine protected area: case study in the NW Mediterranean Sea

The present study describes the food web and evaluates the effects of a marine protected area (MPA), the Port-Cros National Park (NW Mediterranean Sea), on the marine ecosystem inside the reserve and its potential to sustain resources outside the reserve. We built an Ecopath model of the Port-Cros MPA which comprised 41 functional groups and represented an average situation for the period 1998 to 2008. At a high trophic level, fish were dominated by the amberjacks and large dusky grouper groups, 2 abundant top predators playing a central role in the ecosystem in terms of keystone species and trophic cascades. The biomass accumulation rate estimated with Ecopath could reach 10% yr(-1) for large dusky groupers, which is consistent with field observations, suggesting that the MPA succeeded in protecting the species. The total export from the MPA was estimated at a maximum of about 100 tons yr(-1), which limits the benefits at a local scale. EcoTroph fishing scenarios showed that the current state of the ecosystem inside the reserve was close to the unexploited state, and that current fishing practices had an insignificant impact. The major effects of the MPA were to protect the high trophic level groups and thus to maintain the functional biodiversity within the reserve. In summary, trophic modeling seems to be a relevant approach to study the effects of MPAs and to improve their management.