Sea otters are known for their exceptionally thick, two-layered coats, which can have over a million hairs per square inch. Since they lack blubber, they rely on this amazing fur—the densest in the animal kingdom—to stay warm.
Sea otters can be a powerful ally in confronting climate change, according to the Monterey Bay Aquarium in California. In places where they’re thriving, they can maintain and restore kelp forests and coastal wetlands, strengthening our natural defenses against the worst impacts of a warming world.
That’s one of the reasons that we celebrate them annually during the last full week of September. In 2025, Sea Otter Awareness Week runs from September 21 to 27. Events that highlight the importance of sea otters and their ecosystems often include educational activities and presentations from conservation organizations; opportunities to learn from volunteers about sea otters and how to help protect them; and online events, such as virtual visits to coastal locations and social media campaigns.
Sea otters eat 25% of their body weight in food every day. They are predators, whose diets include clams, crabs, mussels and sea urchins, which they’re known to crack open with a tool (such as a rock) and eat while floating in the water. Now, sea otters are showing us that the loss of a predator in one ecosystem can send shock waves into another—in ways that we haven’t understood before. And with climate extremes like marine heatwaves on the rise, understanding how various ecosystem changes can reverberate into other ecologies is central to developing effective conservation strategies.
Sea otters eat a variety of foods, including clams, crabs, mussels, octopuses, sea stars and sea urchins. They are opportunistic hunters, often specializing in different prey depending on local availability and their learned hunting skills. Sea otters are known to use rocks as tools to crack open hard shells.
On the flip side, sea otters are also prey for other animals. Unexpectedly, coastal wolves living in Alaska that eat sea otters have much higher concentrations of mercury than those eating other prey, such as deer and moose.
In honor of Sea Otter Awareness Week, then, let’s take a look at these furry, flexible and fetching marine mammals.
Sea otters reveal the connectedness of ecosystems
Pisaster is a genus of sea stars (also known as starfish). The most well-known species of Pisaster is the ochre sea star (Pisaster ochraceus). In 2013, a sea-star wasting syndrome decimated populations of Pisaster along the West Coast of North America and along the Monterey Peninsula in California. The brownish-red, orange, purple and yellow stars have a hearty appetite for mussels in rocky, intertidal areas. Without the voracious sea stars lurking around, mussel populations exploded, expanding in cover from about 5% to more than 18% within three years. In the wake of the sea-star die-off, mussels became a major prey surplus for sea otters, revealing a surprising link between adjacent intertidal zones and kelp-forest ecosystems. The new research into the phenomenon shows how the loss of a keystone predator (Pisaster) in one ecosystem can change another predator (sea otters) in other ecosystems.
Found on shores from Alaska to California, ochre sea stars sport vibrant colors and five, stout arms covered in small spines. They primarily prey on mussels, helping to maintain biodiversity in tide pools by preventing the mussels from dominating ecosystems.
Monterey Bay Aquarium researchers have been observing sea-otter foraging behavior for decades. Sea otters consume their prey at the surface, which is key to recording what they eat and where they search for food. Following the loss of Pisaster, sea otters more than doubled their mussel consumption, increasing from less than 7% to nearly 18% of their overall diet. The local number of sea otters also increased from a decade (2000–2012) average of 373 to 535 between 2014 and 2024, and the prey surplus supported the increased numbers.
Increases in mussel consumption by sea otters were documented by the Multi-Agency Rocky Intertidal Network (MARINe), a consortium of organizations that conduct long-term ecosystem monitoring. The MARINe group sampled four locations over several decades in intertidal areas along the Monterey Peninsula. For each survey, they recorded information on the number of sea stars, the cover of mussels and how far the mussel beds extended from the upper tide pools toward the water. This long-term monitoring data was pivotal to cinching the correlation between the decline in sea stars and the increase in mussels.
The 2013 sea-star wasting event was abrupt; by late 2013, the local population of stars had nearly collapsed. Predators like sea stars and sea otters are essential to maintaining resilient ecosystems. When these predators are removed, everything crumbles, said the researchers, who coined the term keystone interdependence, where the loss of a predator in one ecosystem doesn’t just affect that particular ecosystem, it also extends to adjacent ecosystems, even benefiting other predators.
In a surprising coastal ecosystem ripple effect, it was found that the collapse of one marine predator can benefit another. The mass die-off of ochre sea stars created a mussel boom—offering sea otters an unexpected prey buffet. After sea stars recover, sea otters may have to shift their diets once again.
Although sea otters thrived in response to the increased availability of mussels, researchers caution this might only be temporary. With fewer sea stars, more mussels survived to reach maturity, and their average size grew larger. Now that mussels are reaching sizes that are too large for sea stars to consume, a return to the previous balance may be slow—even after Pisaster recovers. However, the scientists hypothesize that sea otters might have to shift their diets once again, after they deplete the overabundance of large mussels and after Pisaster eventually recovers.
The study also highlights how climate change compounds the effects of ecosystem shifts. Shortly before the mussel population increase, the largest marine heatwave on record occurred in the northeast Pacific Ocean, from 2014 to 2016. In the sweltering sea temperatures, kelp-eating sea urchin numbers exploded, kelp forests declined and sea otters switched their diets toward eating more sea urchins. Later, the sea otters swiveled again; this time, toward mussels as this prey surplus became available.
The scientists state, in their article published in the journal Science Advances in April 2025, that conservation efforts rarely consider how adjacent ecosystems are connected. Their findings demonstrate that predators are important for enabling ecological resilience; and that when they decline in one ecosystem, the consequences may manifest in another.
Sea otters eat both purple and red sea urchins, but they primarily target purple sea urchins due to their larger size and nutritional value. Sea otters are a keystone species in kelp-forest ecosystems, as their consumption of sea urchins prevents them from overconsuming the kelp that’s vital for marine life.
Coastal wolves expose the mercury in sea otters
In late 2020, a female coastal wolf collared for a study on predation patterns unexpectedly died in southeastern Alaska. The wolf, No. 202006, was only four years old.
After researchers at the Alaska Department of Fish and Game conducted a necropsy and different analyses of the wolf’s tissues, it was discovered that the cause of her death was unprecedented concentrations of mercury in her kidneys, liver and other tissues.
Mercury is a naturally occurring element that humans release from the Earth’s crust through coal combustion and small-scale gold mining. It’s a metal that can be liquid at room temperature or a vapor. When mercury gets into the atmosphere in its elemental form, it can travel for very long distances.
Coastal wolves are a genetically distinct subspecies of gray wolf found along the coasts of Alaska and Canada. Unique for their semiaquatic lifestyle, coastal wolves swim between islands and forage for marine-based foods like salmon, shellfish and marine mammals.
Mercury can also get converted into methyl mercury when it’s introduced into aquatic environments. Because methyl mercury is an organic form of mercury that moves efficiently through the food web, it can reach high concentrations in predators that are tapped into aquatic food sources. So, higher concentrations of methyl mercury are seen in coastal wolves.
In a study conducted by researchers at the University of Alaska Fairbanks and at Canada’s University of Calgary, published in the journal Science of the Total Environment in June 2025, wolves from Pleasant Island—located in the Alaska Panhandle region, west of Juneau—are compared with the population on the mainland adjacent to the island, as well as with wolves from interior Alaska. The highest mercury concentrations were found in the wolves from Pleasant Island. The researchers state that while there could be a number of factors driving the higher concentrations of mercury, the mainland population mostly feeds on moose and the odd sea otter.
Since it remains unclear exactly what caused the death of wolf No. 202006, the scientists are also doing more work to determine mercury’s role in impacting wolf health. However, years of collected data show that 70% of the island wolves’ diet is sea otters. It may be that the coastal wolves are eating so many sea otters that they’re ingesting high doses of mercury that accumulate over time. As other populations of wolves in Alaska—as well as in British Columbia—appear to be eating sea otters, this phenomenon might be more widespread than originally thought.
Coastal wolves that eat sea otters have much higher concentrations of mercury than those eating other prey, such as deer or moose. Some coastal wolves have diets that are 70% composed of sea otters, so it could be that they’re ingesting the high doses of mercury that accumulate in sea otters over time.
Additionally, there’s a potential link to climate change, due to Alaska’s shrinking glaciers. Glaciers can release a tremendous amount of mercury; and in coastal Alaska, glaciers are retreating at some of the most rapid rates in the world. With that melting, particulate bedrock is released; and some of that bedrock contains mercury. The fate of that mercury is not known. It may get buried in sediments, or it may actually be available for conversion to methyl mercury and get into the food web.
Female sea otters demonstrate how tool use helps them survive a changing world
In the southern sea otter’s range of coastal Central California, some of their preferred prey—such as large abalone and sea urchins—are not difficult to break open. However, these food resources sometimes dwindle or disappear. This leads sea otters to prey more often on clams, crabs, mussels and small marine snails, whose hard shells can damage a sea otter’s teeth in the process of prying them open.
Tooth condition is important for survival because when sea otters’ teeth become too damaged or worn, the animals could starve. Using tools helps sea otters meet their caloric needs by allowing them to branch out into different types of prey.
Sea otters sometimes use rocks (like the one on mom’s belly, here) as tools to access their food. Those that do use tools are able to eat larger prey while reducing tooth damage. Females tend to raise offspring, and they are often the ones that pass down tool-use behaviors.
To better understand how sea otters use tools in a rapidly changing environment, a research team from the University of California, Santa Cruz; the Monterey Bay Aquarium; and the University of Texas at Austin monitored how sea otters use tools—such as rocks, shells and trash—to break open prey and identified links to the animals’ dietary patterns and dental health. The scientists and their volunteer “otter spotters” followed 196, radio-tagged southern sea otters off the coast of California.
The results, published in the journal Science in May 2024, showed that female sea otters are more likely to use tools than male sea otters. It could be that the females are using tools to overcome their smaller body size and weaker biting ability in an effort to meet their caloric demands. Raising pups takes a lot of energy, and the females need to be efficient in their foraging. In fact, females were able to consume prey that were up to 35% harder compared with that of males that used tools. And female sea otters had less tooth damage than male sea otters did. This was the first time that researchers had found that the use of tools among female and male sea otters led to a reduction in tooth injuries.
Sea otters court contemplation with their cuteness
Sea otters are the smallest marine mammals in North America. Approximately 90% of the world’s sea otters live in coastal Alaska. Many reside in the waters surrounding public lands, including Glacier Bay National Park, Kenai Fjords National Park and Kodiak National Wildlife Refuge. Southern sea otters live along the mainland coastline of California from San Mateo County to Santa Barbara County and on San Nicolas Island, the most remote of California’s Channel Islands.
Fluffy fur, large eyes and “puffy cheek buns” contribute to the cuteness of sea otters. Their habit of floating on their backs and holding hands in “rafts” adds to their adorable image.
Hunted to the edge of extinction by fur traders in the 18th and 19th centuries, the few remaining sea otters (estimated to be a mere 1,000 to 2,000 individuals) were first protected by the International Fur Seal Treaty in 1911. Sea otters in the United States received additional protections with the passage of the Endangered Species Act and the Marine Mammal Protection Act in the 1970s. Today, it’s thought that there are about 125,000 to 130,000 sea otters worldwide. The current southern sea otter population averages around 3,000 individuals.
I hope you’ll give a thought to them during this year’s Sea Otter Awareness Week. With those large, furry faces and small, dexterous “hands” (or forepaws), they’re just too cute not to.
Here’s to finding your true places and natural habitats,
Candy
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