Description

Swirling algae blooms in the Baltic Sea surround Gotland, Sweden’s largest island. These massive blue-green clouds are composed of cyanobacteria — a type of marine bacteria that capture and store solar energy through photosynthesis. Large blooms can cause an oxygen-depleted dead zone where other organisms cannot survive. For a sense of scale, Gotland is 1,229 square miles (3,184 sq km) in area — about twice the size of London.