Conservation prioritization for seahorses (Hippocampus spp.) at broad spatial scales considering socioeconomic costs

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Identifying priority habitats at broad spatial scales is increasingly required for marine species, which generally have large geographic ranges. However, this is challenging due to the lack of techniques and data. Here we initiated prioritization studies for a genus of flagship species, seahorses (Hippocampus spp.), at a national scale (in China) and worldwide. Our target was to protect at least 2000 km2 area of occupancy (AOO) for each species at minimum costs. We first conducted a gap analysis to examine the coverage of existing marine protected areas (MPAs, both multiple-use MPAs and no-take MPAs) on species' AOO. We then used Marxan, a typical prioritization tool, to set priority habitats for species that didn't meet our target. We did this in different socioeconomic scenarios and overlaid their priority solutions to identify spatial convergence and divergence, representing final solutions for no-take reserves and multiple-use areas, respectively. We compared the utility of Marxan's outputs (best solution vs. selection frequency) in deriving better final solutions (more no-take areas, less patchy, lower cost). Our gap analysis indicated that species' AOOs were mainly covered by multiple-use MPAs, flagging the uncertain efficacy of existing MPAs in protecting seahorses. The two outputs of Marxan derived similar priority solutions, with the selection-frequency output tended to perform better than the best-solution output. We identified new priority habitats for seahorses to inform MPA establishment in China and worldwide. Our study provides useful techniques to derive marine conservation priorities under different socioeconomic constraints at very broad spatial scales.