Keystone Species and Biodiversity — Sea Otters and Kelp Forests.
By: Thomas O'Grady
Tags: Environmental Health, Biodiversity, Ecology And Environment, Environment, Biology

An ecosystem is a community of organisms interacting directly and indirectly in their environmental roles. They are neither completely ordered nor in complete chaos. The appearance of a species within an environment occurs because the organism lives in a habitat that is suitable to their particular adaptations. In each community that makes up an ecosystem, there are different trophic levels of organisms present which will affect the population sizes of other species already present. Those species with the most pull in an ecosystem are referred to as keystone species. The removal of the keystone species from an ecosystem may be devastating to the entire ecosystem and can lead to the decline and near extinction of other organisms present, and also allow for organisms not currently present to invade and alter the entire structure of the ecosystem.

Sea otters are large-bodied, agile because of their relation to weasels, have cat-like whiskers covering the face, and typically have lazy or lethargic expressions. The sea otter, scientifically known as the Enhydra lutris, is anything but lazy or lethargic in practice and is a keystone species that is of particular importance along the Pacific Coastal line. The seashore is the natural habitat of sea otters in the wild.

Sea otters extend over a range of land from as far north as Alaska and south to Southern California. By the end of the nineteenth century, Enhydra lutris was in danger of becoming extinct, due to the extensive predation of the animal for their fur.

Vanishing completely from parts of their natural habitat, the missing sea otter leads to a chain of events occurring. The primary diet of sea otters includes a diet rich in sea urchins. Because of the lack of pressure, the sea urchins population grew exponentially in size after sea otters disappeared as a natural predator. Sea urchins eat kelp as a nutritional source. Large populations of sea urchins consumed much of the kelp and seaweeds that were close to shore. Heavy kelp in an intact habitat acts as a veritable forest of the marine area, and it is essential to the anchoring of the sea bottom. While the sea otter was present equilibrium was reached which allowed for sea otter, sea urchin, and kelp to survive and flourish. After the keystone otter species disappeared much of the underwater terrain near the coast was turned into desert-like regions. While the decline in sea otter populations directly caused sea urchins to overpopulate, the absence of the sea otter indirectly caused other organisms to vanish with the kelp.

Photo by Photoholgic on Unsplash

It’s important to ask why the indirect impact of disappearing kelp and the subsequent desertification would even matter. The impacts can be far-reaching. The kelp forests are rich marine habitats that provide shelter and food to many other species of marine animals. Without a place to hide from predators and without food these species will disappear with the kelp. This includes the disappearance of fish that humans may consume.

After a significant amount of time, the sea otter was restored to its original habitat and biodiversity. Two places where the sea otter was able to survive well were in the Aleutian Islands, at the northern end of their original terrain, and also in Southern California. A new equilibrium was reached between sea otters and sea urchins. With the sea otter populations rising, the very large populations of sea urchins began to decline in size. With this new equilibrium reached, fewer sea urchins were grazing on the sea kelp at the bottom of the ocean. Many of the once luxurious kelp forests were able to grow back and eventually began to resemble something of the past. After the sea otter was again introduced into the ecosystem as a keystone species, algae along with crustaceans, squid, and fish species also moved into the ecosystem. Gray Whales were able to bring their young into the shore and let them rest in the kelp edges. During these times adult gray whales would feed on the plankton animals that were present in high concentrations. This is only one example of how a keystone species can drastically affect the ecosystem present.

How does this relate to the present day? Over the past several years there has once been a stark decrease in the presence of kelp forests along the Pacific Coastal waters. The main culprit this time is not the disappearance of the keystone species the sea otter. The main culprit this time is the warming of the environment and waters. While it may seem like a more difficult problem to overcome it is possible to reverse the impact of disappearing biodiversity and bring back equilibrium.