What Is The Role Of Sea Otters In The Ecosystem?

By Sharon Omondi on December 12 2019 in Environment

Sea otter eating a crab in Morro Bay.
Sea otter eating a crab in Morro Bay.

Sea otters (Enhydra lutris) are marine mammals inhabiting the shores of the Aleutian Islands and along the North American coast up to Mexico. They have thick fur that generates heat to keep their bodies warm. Although capable of walking on land, otters may spend their whole lives in water. The males are polygynous as they may take up multiple female partners. Sea otters feed mostly on sea urchins, mollusks, crustaceans, and fish. Sea otters are ‘’keystone species” because of their critical role in maintaining the health and stability of the nearshore marine ecosystems. A keystone species is one that exerts a large, stabilizing influence throughout an ecological community. The specific role of the sea otters in the eco-system is as follows;

1. Sea otters help in preserving the kelp forests that grow underwater

‘’Kelps’’ are brown algae seaweeds growing rapidly underwater covering 25% of the world’s coastlines. They provide crucial habitat and food for other marine organisms and also help to contain coastal erosion. A collection of kelps result in the formation of kelp forests. Sea urchins feed voraciously on kelp forests thereby damaging the eco-system leading to what is known as "urchin barrens." This is an area of the sea without kelp forest cover. Urchin barrens are disastrous to the environment as they result in an increase in carbon dioxide in the atmosphere and the likelihood of coastal erosion and storm surges. Fortunately, sea otters feed on sea urchins resulting in the preservation of the kelp forests. More kelp forests result in fewer urchin barrens, as well as an increase in the absorption of carbon dioxide from the atmosphere through photosynthesis and release oxygen back into the air. Studies show that the presence of otters increased the carbon storage of kelp forests from 4.4 to 8.7 megatons. Thus, the reduction in the numbers of the sea urchins, caused by the presence of sea otters, prevents the decimation of the kelp forests. Places such as British Columbia, Aleutian Islands, and the Big Sur coast of California have had major improvements in the health of their coastal ecosystems due to the re-introduction of otters. 

2. Sea otters manage populations of other marine species by feeding on them

Sea otters reside in the underwater which has extremely cold temperatures. They are adapted to this kind of environment by possessing a dense fur coat which insulates the body from cold. However, this is not enough to keep the sea otters warm. These sea creatures also depend on a high metabolism rate to generate body heat. The high metabolism comes from the food eaten by the sea otters. Thus, to survive the cold temperatures and maintain warmth, the sea otters feed on food amounting to an average of 25% of their body weight every day. To achieve this, the sea otters that are carnivorous feed on various marine species such as crabs, clams, urchins, snails, and worms.

3. Sea otters facilitate the recovery of seagrass beds

Seagrass meadows are significant to the ecosystem as they result in the protection of the coastal regions and preservation of the habitat for fish. Among the widespread species of seagrasses is the Zostera, also known as the eelgrass that has been on the decline in the recent past due to the large population of crabs that have been feeding on them. This challenge has affected even large estuaries such as the Elkhorn Slough Estuary located on Monterey Bay in Central California, US. Nonetheless, the managers of this estuary have recently reintroduced sea otters that have resulted in the sudden increase in the seagrass beds. Such an increase is a result of the food web that forms within this ecosystem formed by the sea otters, crabs, and sea slugs. Sea otters feed on a large number of crabs to retain their body weight. With the reduced crabs in the meadows, the population of the sea slugs increase and feed on the algae seen growing on the leaves of the seagrass. Eventually, the seagrasses become clean and healthy resulting in higher populations.

The Dangers Faced By Sea Otters

First, one of the biggest threats to the existence of sea otters is humans. People affect sea otter populations through direct shootings and trapping sea otters in fishing nets. Secondly, oil spills result in the death of sea otters. Crude oil normally penetrates the fur of the otter destroying the air layer that is trapped next to its skin. Consequently, the sea otters die from hypothermia. Additionally, the damaging physical effects of oil contamination, as well as toxicological effects from ingestion and inhalation can lead to severe, long-term organ damage and other potentially life-threatening conditions. The ‘’Exxon Valdez’ oil disaster that occurred in Prince William Sound on March 24, 1989, proved that the single greatest threat to the otter today is an oil spill. As of 2006, the lingering oil in the area continued to affect the population of these valuable sea creatures.

Thirdly, sea otters expose themselves to diseases and pollutants through their feeding habits. Since they have to consume at least 25% of their body weight each day to stay alive, sea otters prey on filter feeders such as mussels and clams. These filter feeders indiscriminately sieve particles out of the water resulting in them accumulating high concentrations of pollutants and disease pathogens. By repeatedly foraging these contaminated prey, the otters put themselves at risk of harmful diseases. Fourthly, sea otters are also threatened by predators that live underwater like orcas, sea lions, and bald eagles. Some predators like the great white shark may kill the otters but not feed on them. On land, the otters face threats from bears and coyotes.

The Conservation Status of the Sea Otters 

In the recent past, sea otters nearly became extinct due to large-scale commercial hunting for its pelt. However, countries around the globe have enacted legislation outlawing their hunting. Furthermore, countries such as the United States, Russia, and Canada have set up marine protected areas where activities such as dumping of waste and oil drilling are prohibited. Besides existing in the wild, otters are also raised in captivity like public aquariums and zoos. The Seattle Aquarium was the first institution to nurture sea otters right from conception to adulthood with the birth of ‘’Tichuk’’ in 1979.

More in Environment