Application of loop analysis to benthic systems in northern Chile for the elaboration of sustainable management strategies

Abstract

The present contribution is an extension of the trophic models that we have previously designed for benthic communities in Tongoy Bay (north-central Chile). It represents the first attempt to use Levins' loop analysis in a complex harvested system along the Chilean coast. Ecological and extended eco-social models were developed for seagrass, sand-gravel and sand habitats in order to propose sustainable management strategies for the harvest of the red algae Chondrocanthus chamissoi, the scallop Argopecten purpuratus, the snail Xanthochorus cassidiformis and the crab Cancer polyodon. Based on Levins' loop analysis it was possible to estimate both the local stability (sustainability) for each of these model systems and to simulate the changes in the standing stocks of the main groups as response to external factors. Our results suggest that to increase the standing stocks of adult scallops the following man-made interventions should be implemented: (1) seagrass habitat: partial removal of the 3 sea star species Luidia magallanica, Heliaster helianthus and Meyenaster gelatinosus; and (2) sand-gravel habitat: seeding of scallop recruits and juvenile scallops, and removal of the sea star H. helianthus only. According to our results, the sand habitat would not support any harvest. The extended model for the seagrass and sand-gravel habitats were found sustainable only if the fishermen were 'self-damped', that is, when the fishing effort and fish quota were restricted. Even though loop analysis did not allow for explicit quantitative reasoning, 'what if' questions can be answered with sufficient understanding and realism. Therefore, this qualitative modelling appears as a valuable complementary mathematical tool defining and assessing the sustainability of management options within a holistic scope. We also recommend the application of this framework in other benthic management areas along the Chilean coast.