Sea otters are marine mammals that play a significant role in their coastal environments. A common question about their feeding habits concerns their consumption of sea urchins. Sea otters eat sea urchins. Their relationship with these spiny invertebrates extends beyond simple predation, forming an important link in the health of marine ecosystems.
Sea Otters’ Diet
Sea otters are carnivores, primarily eating marine invertebrates. Their specific food choices can vary based on their geographic location and the season. While sea urchins are a well-known component of their diet, they are part of a broader array of prey items. Sea otters also commonly consume bivalves like mussels and clams, crustaceans such as crabs, and gastropods including snails.
Sea otters have a high metabolic rate, requiring them to consume 25% to 30% of their body weight daily. In some areas, individual otters may specialize in eating only a few types of invertebrates, a behavior that can help reduce competition. This varied diet ensures they meet their high energy needs while foraging in their coastal habitats.
How Sea Otters Eat Urchins
Sea otters display adaptations and behaviors when consuming sea urchins and other hard-shelled prey. They often use tools, such as rocks, to crack open the tough exteriors. An otter might dive to retrieve a rock, then float on its back, placing the rock on its chest. The otter then repeatedly strikes the urchin or other shelled prey against the rock until it breaks open.
Beyond tool use, sea otters possess strong jaws and blunt teeth for crushing shells. They also have dexterous forepaws to manipulate prey. When dealing with large, spiny sea urchins, an otter will bite through the underside, where the spines are shortest, and then lick out the soft contents. Some otters that frequently eat urchins even develop a purple hue on their teeth from the pigments.
Ecological Role in Kelp Forests
The consumption of sea urchins by sea otters has a significant impact on kelp forest ecosystems. Sea otters are recognized as a keystone species, meaning their presence has a disproportionately large effect on their environment. By preying on sea urchins, sea otters keep urchin populations in check. This control is important because sea urchins are voracious grazers of kelp, and unchecked populations can devastate kelp forests, creating what are known as “urchin barrens.”
When sea otters are present, they prevent kelp overgrazing, allowing kelp forests to flourish. Healthy kelp forests provide important habitat and food for a wide variety of marine species, supporting greater biodiversity. This relationship creates a trophic cascade, where the otters’ predation on urchins indirectly benefits numerous other organisms that rely on the kelp forest for shelter and sustenance, including various fish and invertebrate populations. Furthermore, thriving kelp forests absorb significant carbon dioxide, regulating ocean chemistry and mitigating climate change.