It’s sea otter awareness week, which seems like a great time to reveal something heroic about this charismatic animal. A recent study from UC Santa Cruz concluded that sea otters are helping to save the ocean—with their appetites.

When you think of sea otters, you may think “cute and cuddly,” but these playful marine mammals are top predators, like great white sharks and tigers, and their hunt for food is helping to maintain ecosystem health along portions of California’s coastline.

The sea otter’s role in ecosystem management begins with one of its preferred foods: crabs. Sea otters eat crabs. Crabs in turn eat sea slugs and small crustaceans. The slugs and crustaceans eat algae off sea plants, keeping them green and healthy. It’s a relatively typical food web but now it’s clear: The healthier the crab-eating otter population is, the healthier the plants tend to be.

Sea plants, like eelgrass, along the west coast are important habitat for fish such as Pacific herring, halibut and salmon. They also protect shorelines from storms and waves, and they soak up carbon dioxide from seawater and the atmosphere.  Thus, a healthy coastal ecosystem has the right mix of otters eating crabs and invertebrates eating algae.

Unfortunately, seagrass meadows have been declining worldwide, partly due to excessive nutrients from agricultural and urban runoff entering coastal waters.  When sewage and agricultural waste like fertilizers spill into the sea, ecosystems suffer. Excessive nitrogen and phosphorus in the water spawns excessive algae growth, which can block sunlight and limit plant growth. Coastal areas that would otherwise be swaying in seagrass and kelp turn brown, murky, and barren of important marine species. But, not when sea otters are around.

Brent Hughes from the University of California, Santa Cruz and his colleagues studied 50 years’ worth of data, comparing areas with or without otters. The team discovered that otters trigger the above ecological chain reaction that protects seagrass meadows and can stave off algal blooms.

“The seagrass is really green and thriving where there are lots of sea otters, even compared to seagrass in more pristine systems without excess nutrients,” Hughes says.

Sea otters were hunted to near extinction in the 19^th and 20^th centuries. Populations on the California coast are slowly recovering now, and one of those places otters have called home since the 1980s is Elkhorn Slough, an estuary in Monterey Bay. Hughes and his colleagues determined that the re-colonization of that estuary by sea otters has been an important factor in the seagrass comeback.

In Tomales Bay, a nearby inlet with far lower levels of incoming nutrients, but no otters, the beds don’t look nearly as good. Hughes told Ed Yong of National Geographic:

The seagrass looks relatively unhealthy: it’s brown, covered in algae, and slumped over. The crabs are four times more abundant and 30 percent bigger than they are in Elkhorn Slough.

The findings in Elkhorn Slough suggest that expansion of the sea otter population in California and re-colonization of other estuaries will likely be good for seagrass habitat—and coastal ecosystems—throughout the state.

“This provides us with another example of how the strong interactions exerted by sea otters on their invertebrate prey can have cascading effects, leading to unexpected but profound changes at the base of the food web,” Hughes says. “It’s also a great reminder that the apex predators that have largely disappeared from so many ecosystems may play vitally important functions.”

The study was published last month in the Proceedings of the National Academy of Sciences.

(Sea otters also play a heroic role in the next Academy planetarium show! Currently in production and set for a fall 2014 opening date, the latest production from our visualization studio will highlight complex relationships in ecosystems—and how humans fit into the picture.)

Jami Smith is a science geek-wannabe and volunteers for Science Today.

Image: Robert Scoles/NOAA

Welcome to Sea Otter Awareness Week! Started 11 years ago to increase the public’s awareness about sea otters, the event “is an annual recognition of the vital role that sea otters play in the nearshore ecosystem,” according to seaotterweek.org.

Tomorrow we will explore that vital role a little more; for today’s article, we checked in with Moe Flannery, from the Academy’s Ornithology and Mammalogy department, to better understand the health of local sea otters.

The US Geological Survey’s Western Ecological Research Center conducts annual population surveys of the southern sea otter (Enhydra lutris nereis), a federally listed threatened species found in California. Flannery says the southern sea otter’s range extends from Pigeon Point near Half Moon Bay down to Point Conception in Santa Barbara County.

This year’s USGS survey was released earlier this month and the news is cautiously optimistic: sea otter numbers are up, due largely to an increase in the number of pups.

In its 2013 report, the USGS estimates the population to be 2,941. For southern sea otters to be considered for removal from threatened species listing, the population estimate would have to exceed 3,090 for three consecutive years, according to the threshold established under the Southern Sea Otter Recovery Plan by the US Fish and Wildlife Service. The USGS has been conducting the population surveys since the 1980s.

“Population growth in central California has faltered recently, so the fact that we’re seeing a slightly positive trend is a basis for cautious optimism,” says Tim Tinker, a USGS biologist who supervises the annual survey. “Certainly, sea otters have made an impressive recovery in California since their rediscovery here in the 1930s.”

“We counted a record number of pups this year, which led to the uptick in the 3-year average,” says USGS biologist Brian Hatfield, coordinator of the annual survey. “A high pup count is always encouraging, although the number of adult otters counted along the mainland was almost identical to last year’s count, so we’ll have to wait and see if the positive trend continues.”

USGS scientists also annually update a database of sea otter strandings—the number of dead, sick or injured sea otters recovered along California’s coast each year. Flannery leads the Academy as one of the organizations that responds to these strandings as part of the national Marine Mammal Stranding Network.

This year’s stranding number was 368. Flannery says that a remarkable number of sea otters wash up with shark bites. “The shark populations have been increasing because elephant seal populations are increasing,” she says. “The sharks appear to take a bite of the sea otters, but don’t consume them. As bony, skinny and furry as sea otters are (with up to one million hairs per square inch!), they’re probably less desirable than fat, blubbery elephant seals.”

Sharks aren’t the only threat to sea otters. Mainland diseases, such as toxoplasmosis from cat fecal matter, also plague the animals.

Because of their threatened status, all sea otter necropsies (animal autopsies) are performed by the California Department of Fish and Wildlife. However, many of the specimens end up here, in the Academy’s collections. The result is that we have the largest collection of southern sea otter specimens in the world. The number was up to 1,300 specimens last year, but several hundred have yet to be cataloged and processed, according to Flannery.

Researchers come from all over the world to study the specimens—last year scientists from UC Davis came to study dental pathologies in 1200 sea otter skulls!  They found that 93% of our southern sea otter specimens had problems with their teeth.

Luckily, most of us don’t have to study 1200 sea otter skulls to learn more about these engaging animals. For events around Sea Otter Awareness Week, including this week’s Nightlife at the Academy, click here. Celebrate!

Image: Mike Baird/Wikipedia

Once upon a time, there were close to a million of the California sea otters and their range extended many miles. According to SFGate, they “frolicked from Alaska’s Prince William Sound to Baja California.”

Over a period of 150 years, however, they were hunted so extensively for their fur that it was believed they had gone extinct.

Then, in 1938, “a small colony of about 50 was discovered south of Monterey… They have been listed as threatened under the Endangered Species Act since 1977.” [UPI] And since then, their numbers had been rising fairly steadily and their range extended “from Pigeon Point to Gaviota State Park” [SFGate], or about 270 miles. That is, until this year. From Wired:

Annual surveys of the California sea otter population, which are averaged over three years to compensate for variability in observation conditions, show the overall population has declined by nearly 4 percent compared to estimates in 2009, and the number of sea otter pups has declined by 11 percent. The otter’s range along the central California coastline has also shrunk by nearly 30 miles.

We contacted Andrew Johnson, Manager of the Sea Otter Research and Conservation program (SORAC) at the Monterey Bay Aquarium, via email to clarify what might be causing the decline.

The numerous and varied threats faced by sea otters include natural factors, such as attacks by white sharks, El Niño events, and changes in prey availability, and anthropogenic factors, such as pollution inputs from land-based sources, entrapment in fishing gear, boat strikes, gunshot, etc. The sheer diversity of these threats makes recovery difficult… The population has a high rate of infectious disease—upwards of 50% of annual deaths occur as a result of disease, much of which transfers into the ocean from land sources.

The California sea otter population currently rests at just above 2,700, a very low number indeed. In addition, Scientific American reports today that another number has dropped for these protected animals—their funding:

Some of the money available to study sea otters and help save them comes from California’s Sea Otter Fund, which pays for much of the research on the species and is voluntarily funded by California taxpayer contributions. This year’s donations are $31,000 short of target, leaving the fund vulnerable to termination by the state tax board. Board spokesman John Barrett told The Sacramento Bee that the fund likely will be eliminated this year if donations do not increase immediately.

Why should we care about these creatures? Well, their health tells us a lot about the health of the ocean. SORAC’s Johnson had this to say:

As the apex predator in this system, sea otters indicate problems throughout the system, such as contaminant and pathogen pollution, disease, mismanagement… of watersheds, presence of biotoxins, and climate change effects… In other words, sick sea otters equate to a sick system. Eventually, the problems within the system will become more evident—contaminated shellfish, closed beaches, die-offs of plants and animals, systematic changes that will never resolve. So, the sea otter is trying to tell us something important, and we need to listen to this message before irreparable damages occur throughout the entire nearshore system.

So what can you do? At the end of September, look for Sea Otter Awareness Week and Sea Otter Days at the Monterey Bay Aquarium and here at the California Academy of Sciences. Also, Johnson says we can all help by doing small things everyday:

People can… make sure that they don’t deposit toxic materials (e.g., motor oil, lawn-care chemicals) where they can wash into streams or the ocean; they can reduce their carbon footprint; they can lobby legislators to pass ocean-friendly legislation; they can dispose of garbage and waste in a proper manner; they can consume seafood items harvested from sustainable fisheries… We need to support major renovation of our water management infrastructure in coastal areas to protect delicate marine ecosystems. The biggest help will come from local, state, and federal decisions that support better wastewater and watershed management.

Let’s turn those numbers around.

Creative Commons image by Mike Baird