NASA At dusk, the greatest migration of biomass on Earth unfolds through the oceans in near silence, largely unnoticed. Trillions of often tiny creatures – zooplankton, krill, lanternfish – rise in synchrony from the depths, drawn by blooms of phytoplankton in the uppermost layers of water. They feast through the night, safe from predators that hunt by sight, then retreat as the sun rises. The ebb and flow of the sun and moon dictate the behaviour of many sea creatures. But in recent decades, large areas of the ocean surface have mysteriously been darkening. Tim Smyth, a marine scientist at Plymouth Marine Laboratory in the UK, and his colleagues were the first researchers to spot this pattern in the open ocean last year. Since then, he has continued to study how the oceans are shifting in response to global warming alongside changes in land use – and the crucial role that light plays within these habitats.…