Crabs, Clams, and Other Critters: The Sea Otter's Menu
Introduction
Sea otters might look like they spend their days floating around and being adorable, but there’s serious work happening beneath the surface. These marine mammals are dedicated, high-energy hunters whose feeding habits shape entire underwater ecosystems. Their ever-changing menu reflects both their adaptability and the wide variety of life found along the seafloor.
Crabs: A Shell-Cracking Favorite
Crabs rank among the most reliable items on a sea otter's menu. Otters hunt them along the seafloor, using their sensitive front paws to feel around rocks and crevices. Once caught, the otter brings the crab to the surface and smashes it against a rock balanced on its chest until the shell breaks open.
Ocean crustaceans like crabs are calorie-dense, making them worth the effort. A single otter may eat dozens in a day.
In California's Elkhorn Slough, southern sea otters have been feasting on European green crabs. Green crabs, native to coastal Europe and North Africa, are a highly destructive invasive species that has damaged oyster and seagrass beds and depleted the small invertebrates that shorebirds depend on for food. Researchers estimate a single otter can consume between 50,000 and 120,000 green crabs in a year, making them one of the most promising natural methods for controlling the invaders.
Clams: The Hidden Meal Beneath the Seafloor
Clams take a little more digging. Buried in sand or tucked under sediment, they require otters to root around on the seafloor before they can even begin the cracking process.
The payoff is worthwhile. Crabs and clams together form the backbone of what many otters eat day to day, and clams offer a hearty, protein-rich reward for the effort involved.
Like crabs, clams get the rock treatment at the surface. Otters will sometimes keep a favorite rock tucked in a loose fold of skin under their arm, carrying it from dive to dive. Efficiency matters when you need to eat a quarter of your body weight every single day.
Other Critters: A Flexible and Opportunistic Diet
Sea otters aren’t picky. The sea otter diet shifts based on season, location, and what happens to be available. This flexibility is part of what makes them such effective predators.
- Sea Urchins
Sea urchins are a staple for many otter populations, especially along rocky coastlines. Otters keep urchin numbers in check, which directly protects kelp forest health. Without predators like otters, urchin populations explode and mow down kelp beds from the bottom up.
- Snails and Gastropods
Snails and other gastropods round out the menu nicely. They are slow-moving and easy to collect, making them a low-effort option that still delivers nutrition. Otters forage for them along rocky reef areas and in shallower coastal zones.
- Mussels and Other Bivalves
Mussels cling to rocks in clusters, and otters have figured out how to pry them free. Like clams, they’re broken open at the surface. The foraging behavior involved in collecting mussels is often learned from mothers, passed down through generations within the same region.
- Fish and Fast-Moving Prey
Fish are a smaller part of the diet for most otters, since catching them requires more speed and coordination. Some individuals develop a taste for certain fish species and become skilled at hunting them, but it’s not the norm across the board.
- Worms, Crustaceans, and Small Invertebrates
Worms, shrimp, and other small invertebrates fill in the gaps. Sea otter prey is remarkably diverse, and individual otters often develop personal preferences based on what they learned to hunt early in life.
A Life of Constant Foraging
Otter feeding habits impact the entire ocean ecosystem. As a keystone species woven into the kelp forest food web, otters regulate the populations of the animals they hunt. Their role in the marine food chain keeps ecosystems in balance, supporting everything from kelp to the fish that shelter within it.
At the Sea Otter Foundation & Trust, we work to ensure the survival and recovery of sea otters in their habitats by building funds to support research, conservation, and education. You can learn more about the all-important efforts of our grant recipients by watching our interviews with them. These efforts are funded directly by our supporters, so consider advancing our crucial work by adopting an otter or making a donation today!