PLANET EARTH Shallow Seas

An army of sea urchins（海胆） is mounting an attack. The urchin plague strikes at the kelp's holdfasts, their crucial attachments to the rock. Holdfasts are extremely tough, but each urchin has five teeth, which are self-sharpening and are replaced every few months. Urchins fell vast areas of kelp forest creating clearings know as urchin barrens, yet barrens is a poor description.



Millions of invertebrates（无脊椎动物） invade the seabed. The most fearsome predator here is a giant. The sunflower starfish（向日葵海星） is a meter across, with an appetite for brittle stars. It uses its feet to taste for prey. When it's actions are speeded up, it becomes clear that the predator's fondness for the brittle stars is almost matched by the brittle stars ability to get out of the way.



Sand dollars flat sea urchins cluster together as a defense, but it doesn't seem to work against the sunflower starfish. The predator extrudes it's stomach, and wraps it around its victims liquefying（液化） their soft parts. Nothing is left of them, except their white skeletons.



The Californian upwellings are seasonal and relatively small but in Southern Africa they're so big they create seas rich enough to support colonies of over a million seals. The Benguela（本格拉，安哥拉西部港口城市） Current sweeps along the western coastline of Southern Africa driving nutrient rich waters up to the surface and then, at the southern tip of Africa it meets the Agulhas Current, arriving from the east. The result: even richer waters.