Areas starved of oxygen in open ocean and by coasts have soared in recent decades, risking dire consequences for marine life and humanity

A fisherman on a beach blanketed with dead sardines in Temuco, Chile. In coastal regions, pollution can cause algal blooms and when the algae decompose oxygen is sucked out of the water.
A fisherman on a beach in Temuco, Chile that is blanketed with dead sardines, a result of algal blooms that suck oxygen out of the water. Photograph: Felix Marquez/AP