Consequences of complex connectivity, fishing pressure, and Allee effects in marine metapopulations

Background/Question/Methods Scientists have proposed marine reserves can help protect marine biodiversity and increase population persistence. Moreover, reserves are expected to buffer marine metapopulations from the effects of stochasticity in dispersal. We inquire if marine reserves favor persistence in complex scenarios of fishing pressure, larval connectivity, and density dependence. We constructed a network model to evaluate the effect of spatially heterogeneous fishing pressure, Allee effect, local larval retention, randomized dispersal, and connections between subpopulations in simulated metapopulations with and without marine reserves. In the network model, edges represent direction and strength of larval dispersal, and nodes account for protected and unprotected subpopulations.

Results/Conclusions We found a pattern of persistence with respect to the Allee effect and local larval retention in two fishing pressure scenarios: spatially homogeneous and heterogeneous. Scenarios that assume spatially homogeneous fishing pressure show greater persistence at low dispersal rates. With spatially heterogeneous fishing pressure and without potential Allee effects, persistence also did better when at low dispersal rates. However, with the inclusion of the Allee effect the opposite pattern was found: persistence decreased at low dispersal rates. Moreover, the stronger the Allee effect, the more larvae from other sites were required to persist. Harvested areas depended greatly on larval supply, especially from reserves, to overcome fishing pressure and Allee effects. Our study also reveals that complex connectivity patterns may favor persistence by increasing connections between reserves and harvested subpopulations. Thus, reserve effectiveness may be underestimated by other models. We demonstrate that marine reserves are a good prescription against stochasticity, fishing pressure, Allee effects, and more complex connectivity patterns.