Kelp forest

Last stance against a trophic cascade: Why sea otters play an integral role in the preservation of kelp forests

In the coastal waters of the northeast Pacific, what were once biodiverse and dense kelp forests have now become barren wastelands ravaged by an uncontrollable menace. There is currently an overwhelming number of sea urchins present in kelp forests along the west coast of the United States. Here, these urchins decimate the ecosystem by grazing on kelp, leaving the region stripped of its luscious greenery and myriad of species. As a result, these kelp forests can no longer support the rich biodiversity that once inhabited this environment. The oversaturation of sea urchins in kelp forests is caused by the lack of a natural predator: sea otters. 

In a typical kelp forest environment, sea otters provide balance to the ecosystem. They are referred to as a keystone species, which means they play an integral role within a specific ecosystem by exerting a top-down effect on lower trophic levels via predation. Moreover, their removal from an environment leads to major changes pertaining to abundance of other species. With regard to kelp forests, sea otters control sea urchin populations by predation. As sea urchin populations decrease, grazing pressure decreases and kelp forests flourish. However, in recent years, sea otter populations have significantly declined, thus leading to the creation of urchin barrens. 

In the 18th and 19th centuries, humans began hunting sea otters due to a high demand for their fur, leading them to near extinction. As a result, in the 20th century, various national and international protections, including the Fur Seal Treaty of 1911 and the Marine Mammal Protection Act, helped lead sea otter populations to a slow recovery. Nevertheless, new rising environmental issues such as pollution and climate change pose threats to sea otter populations. For instance, recent studies show that Alaskan sea otter populations have significantly decreased by 90% in some regions.

Humans are not solely responsible for the decrease in sea otter populations along the coasts of the Pacific Northwest. Predation by cetaceans, specifically orcas, has been shown to play a role in significantly altering sea otter populations in regions near southern Alaska. An increased predation pressure on sea otters is often linked to an insufficient food supply in an altered habitat. Therefore, orcas must resort to feeding on sea otters, consequently impacting their populations. 

As sea otter populations decline in the Pacific, kelp forests are ravaged, which has a multitude of negative impacts on local environments. Healthy, dense kelp is imperative to coastlines because it is a foundation species. Foundation species establish the structure of an ecosystem. Kelp forests provide shelter for countless species, foster biodiversity, and greatly increase oceanic productivity. Additionally, these forests are important because they act as a barrier to coastlines, protecting communities against erosion and wave energy. 

The outbreak of sea urchins in kelp forests is an epidemic. If sea otter populations are not recovered, these environments could permanently change for the worse and urchin barrens could surround the coastlines of the Northwest Pacific. Protections must be put in place to further the restoration of sea otter populations and conserve their positive impact on the growth of kelp forests. Organizations such as The Sea Otter Foundation & Trust have contributed to the rescue and rehabilitation of injured sea otters to help increase their numbers within these regions, but these populations are far from healthy. Overall, the preservation of sea otters is necessary to save kelp forests, one of the most important ecosystems on the planet.