The ocean is our playground, storehouse, transport corridor, driver of weather and coastal change. We’ve learned the hard way that it’s possible for us to exhaust its resources and overwhelm its natural processes. Now, scientists are mapping the web of relationships between the sea, the land and human industry, to figure out how fishing, aquaculture, tourism, land development, and recreation affect its health. What should be permitted, and what prohibited—and where? How can we best strike a balance between using and protecting our seas?