The earth is losing biodiversity and ecosystem services due to anthropogenic impacts, and one way to mitigate this is to establish protected areas. Despite an increase in their global coverage, biodiversity is decreasing, while the world’s human footprint and population density are increasing. Effective coastal conservation requires a better understanding of how human activities on land may affect adjacent marine communities, but empirical work is lacking. My dissertation examines the synergistic benefits of co-locating protected areas and examines connections between terrestrial protection and nearshore marine protection by studying seagrass health, (1) a large-scale, multi-island field study of how human use of terrestrial watersheds directly and indirectly affect recipient marine communities, (2) a field experiment measuring the influence of the flux of sediments from human-impacted vs. non-impacted terrestrial watersheds on three adjacent nearshore island marine communities, (3) an exploration of the ecosystem services provided by seagrass beds, specifically small-scale fisheries. Integrating terrestrial with marine protection can improve coastal conservation efficiency. Using the tropical seagrass system, my dissertation provides evidence that terrestrial protection is more important than marine protection for nearshore marine health. Proper management of shallow-water marine resources should take into account stewardship of the adjacent watersheds and coastlines.