During the 19th century, sea otters were hunted almost to the point of extinction. when the number of sea otters became very low, it was noticed that the rich ecosystem of kelp bed forests was also disappearing. it was discovered that the sea otters were predators of sea urchins that were in turn predators of the kelp. when sea otter numbers declined, the sea urchin populations grew, destroying the kelp ecosystem and the many species that depended on it. it was then understood that sea otters were in the ecosystem.