Linking bio-oceanography and population genetics to assess larval connectivity

Abstract

Marine reserves (areas closed to fishing) have been advocated for the management of many species, including the rock scallop Spondylus calcifer in the northern Gulf of California (NGC), Mexico. We developed an explicit coupled biological-oceanographic model (CBOM) to assess connectivity among fished subpopulations of S. calcifer. We focused on the Puerto Peñasco corridor, located in the northeastern portion of the NGC. We validated CBOM's outputs through 2 different techniques: population genetics with 9 microsatellite loci and measurements of spat abundance on artificial collectors. We found strong demographic connectivity between the corridor and southern sources. Sampled localities showed low levels of genetic structure; however, we identified 2 subtly differentiated genetic clusters. On average, the spatial scale of demographic and genetic connectivity is in agreement, suggesting that connectivity decreases when the spatial scale is >100 km. We observed a gradient of higher values of both predicted particles and observed densities of settled spat for the northern and southern sites and lower values for the central sites. Larval recruitment within the corridor could be linked to a large spatial scale of larval inputs, including local sources and subpopulations further south. The absence of a strong barrier to migration suggests that the siting of marine reserves along upstream sites would likely benefit downstream subpopulations. The spatial scale of connectivity (~100 km) could be used as a reference for the strategic siting of marine reserves in the study area. CBOMs and population genetics are powerful complementary tools to assess the relative strength of connectivity among sites.