Sea otters live along the coasts of the Pacific Ocean in North America and Asia. Ever since their population plunged in the early 1900s, sea otters have been in danger of extinction. It would be especially devastating for sea otters to go extinct because they are a keystone species. National Geographic defines a key stone specie as, “a plant or animal that plays a unique and crucial role in the way an ecosystem functions.” (1)
As you can see in Figure 1, sea otter populations reached a low in the early 1900s. As a result of the fur trade, sea otters were almost hunted into extinction.(3) Sea otters populations once numbered several hundred thousand. So even though this graph shows growth, the population now, a mere 2,000, is nowhere near where it once was.
The reason sea otters are considered to be a keystone species is because of the role they play in their food web. In the figure 2, kelp and other algae serve as primary producers. This means that they are autotrophs and are able to make their own food through photosynthesis. The next trophic level includes sea urchins. They are known as primary consumers because they get their energy from consuming the primary producers. From there, sea otters would be secondary consumers because they eat the sea urchins. When this system works, each level keeps the level below them from overpopulating. However, when one species within the web experiences a decline in population, it affects the entire system. In the case of the sea otter, they are considered the most important, keystone species because they keep the urchin population controlled.
In 1900, when the otters dwindled in numbers, the sea urchin population exploded. This caused the urchins to consume so much kelp that they destroyed the kelp forest.(2) This is an example of a trophic cascade. A trophic cascade happens when population control of prey by their predators affects the next level down, in the case, kelp.(2) This ecosystem needs the otters to prevent another trophic cascade. If the otter population continues to grow, this fragile ecosystem will be restored.