Sea otters are a familiar sight in coastal marine environments. Their position within the intricate marine food web often sparks curiosity: are they truly apex predators? Understanding their ecological role requires defining an apex predator and examining how sea otters interact with other species.
Defining an Apex Predator
An apex predator occupies the top position in a food chain, typically having no natural predators of its own. These organisms are at the highest trophic levels, consuming other animals without being regularly hunted. Apex predators play a significant role in maintaining ecosystem balance. Their presence influences the populations and behaviors of other species below them in the food web.
Sea Otters in the Marine Food Web
Sea otters primarily consume a variety of marine invertebrates. Their diet largely consists of sea urchins, mollusks like clams, mussels, and abalone, as well as crustaceans such as crabs. They often use rocks as tools to dislodge prey and open shells. Despite their role as consumers, sea otters are themselves prey for several larger animals.
Killer whales, also known as orcas, are a significant predator of sea otters. Great white sharks also prey on sea otters. Young sea otter pups can face threats from bald eagles, while on land, they may be vulnerable to coyotes and bears. These predator-prey relationships indicate that sea otters are not at the very top of their food chain.
Their Ecological Significance
While sea otters are not apex predators, they play a disproportionately large role in shaping their marine environment. They are considered a keystone species, meaning their presence has a substantial impact on the structure and function of their ecosystem. Sea otters help maintain the health of kelp forest ecosystems by managing sea urchin populations.
Sea urchins graze on kelp. Without sea otters to control their numbers, urchin populations can increase dramatically, leading to the destruction of kelp forests and the creation of “urchin barrens.” By consuming sea urchins, sea otters allow kelp forests to thrive, which provides habitat and food for numerous other marine species, supporting biodiversity. This interaction, where a predator affects lower trophic levels and the ecosystem as a whole, is known as a trophic cascade. Their influence also extends to coastal protection and carbon sequestration, as healthy kelp forests absorb carbon dioxide from the atmosphere.