Dynamical simulation of mass-balance trophic models for benthic communities of north-central Chile: assessment of resilience time under alternative management scenarios

Within Tongoy Bay (north-central Chile), four different habitats (seagrass, sand-gravel, sand and mud) were identified and subsequently considered as subsystems for the construction of trophic mass-balance models. By using the ecosim software package of Walters et al. (Ecosystems, 2 (1997) 539), different management scenarios were simulated for these subsystems and for an overall integrated system (combining all habitats) in order to explore strategies of sustainable resource use. System Recovery Time (SRT) as well as single species responses differed with the scenario simulated. The most important findings were: (1) an increase in the harvest of the scallop Argopecten purpuratus would not drastically affect the global properties of the systems; (2) a depletion of its principal predator, the sea star Meyenaster gelatinosus, greatly improved the availability of scallops in the subsystem seagrass, sand-gravel as well as in the integrated model; (3) a biomass reduction of the snail Xantochorus cassidiformis would produce only a small negative impact on the SRT, while a simulated harvest on the clam Mulinia sp. drastically changed the system properties. This clam may thus be considered as a keystone species; (4) predictions of the maximum sustainable yield (MSY) of the scallop were lower than those obtained by single species approaches. Our simulations allow us to conclude that: (1) a strong fishery of the scallop predator, the sea star M. gelatinosus, would greatly increase the yield of the scallop and the other populations or resources of the systems; (2) trophic mass balance models and their simulated scenarios offer great possibilities for the planning of interventions or manipulations of natural systems.