Sea otters and their role in the kelp forest

An ecosystem is a biological community. It includes plants, animals, and microorganisms. Yet ecosystems can change. The living things within these communities need to adapt.

A keystone species is an organism that an entire ecosystem depends on. If the keystone species were to disappear from the ecosystem, the environment would be different. No other species would be able to fill its role. New organisms could take over the habitat, but it would not be the same.

Sea otters are an example of a keystone species. When a sea otter population drops, it starts a chain of events that changes the region's food web. This happened in the Pacific Ocean off the coast of the western United States from the mid 1700s until the early 1900s. Humans hunted sea otters for their fur, and animals just about disappeared.

Sea otters typically eat sea urchins. If sea otters disappear, the sea urchin population can explode. More sea urchins can mean less of a certain type of seaweed called kelp. That's because sea urchins can eat huge forests of kelp if left unchecked. These changes, then affect many fish and other marine animals that rely on kelp for shelter. The loss of kelp forests forces these fish into different habitats.

The loss of a keystone species affects its prey and other organisms in a food web. In fact, their removal can change the entire ecosystem. Without a keystone species, the ecosystem becomes much less diverse.