Living in the twilight zone

The sea gooseberry is just one of the many species that inhabit the mesopelagic region of the ocean, which is between 100 m and 1000 m below the surface. The mesopelagic is home to most of the world’s fish, but how they get enough food has largely been a mystery. Using information from satellites and in situ instruments, scientists have worked out that a ‘seasonal mixed-layer pump’ moves 300 million tonnes of carbon from the surface waters to the depths below. This is an important addition to the ‘rain’ of fast-sinking organic aggregates of dead plankton and waste products from organisms that live near the surface.