PLANET EARTH Shallow Seas

All across the tropics, humpbacks are heading away from the Equator towards the rich temperate seas of both the southern and the northern hemispheres. These are colder, rougher, and more dangerous waters. Mother and calf must stay close. They can send sound signals to one another, above the roar of the ocean by slapping fins on the surface.



In winter, the temperate seas are lashed by violent storms. The turbulence stirs the water, and draws nutrients up from the depths, but nutrients alone can not support life. There must also be sunlight. In the spring, as the sun daily climbs higher in the sky the algae start to grow, blooms the size of the Amazon Rainforest, turnes the seas green.



Individually the algae are tiny but together, they produce three quarters of all the oxygen in our atmosphere. They're eaten by an array of bewildering creatures. Salps（樽海鞘，纽鳃樽科动物） appear in the plankton soup. Individuals link together to form chains which can stretch for fifteen meters. Pumping water through their bodies they strain out algae and other edible particles.



Comb jellies（红鼻鲈） cruise through the water. They too flourish in this seasonal soup and for short periods, they appear in astounding numbers. Krill, shrimp like creatures. By weight they're the most abundant animals on the planet. A single swarm can contain two million tons of them and that is a lot of fish food.