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

Two years ago, we produced a video about the remarkable work that scientists at Mote Marine Laboratory and the Academy are doing on spotted eagle rays. Little is known about these stunning elasmobranchs, but Kim Bassos-Hull of Mote and Anna Sellas from the Academy are continuing their studies to discover more about the rays and perhaps protect them along the way.

Bassos-Hull recently came to the Academy, and she and Sellas took the time to give Science Today an update on their long-term project.

Satellite Tagging & Genetics
They were excited about a satellite tag (a location-only SPOT tag) they deployed on a ray in April. Unlike sharks and marine mammals, rays are hard to tag because they have no prominent fins. The scientists’ colleague, Matt Ajemian of the Harte Research Institute, has had some luck with tagging rays, and he visited Mote to work with Bob Hueter, Mote’s expert on tagging sharks, to give the team some tips and best practices.

Generally, Ajemian has had satellite tags stay on animals for up to a few months, though the batteries last up to six months. Ajemian recently presented these findings at a special symposium on stingrays hosted by the American Elasmobrach Society in Albuquerque, New Mexico. Bassos-Hull says that the tag isn’t too invasive to the ray and that “many of the rays carry remoras larger than these tags.”

The first tag from April was unsuccessful, but in late May, Hueter and the team put a six-month pop-up archival satellite tag on a large female eagle ray.  If all goes well, this tag will pop off as programmed in about six months and give scientists more data on these mysterious rays.

Sellas is hoping the tag reveals information on the spotted eagle rays’ movements. The rays are generally found near Mote, off the coast of Sarasota in the Gulf of Mexico, from March through November. Few of the rays are seen in the summer months, and hardly any in the winter. Spotted eagle rays are also found on the Atlantic side of Florida, as well as off the coasts of Mexico and Cuba, but these rays could come from the same or different populations.

Sellas’ genetic work has revealed little genetic difference between rays found off Mexico and those found off Cuba, suggesting they are likely from the same population. Greater genetic differences seem to exist between rays sampled off Sarasota and those sampled off Mexico, suggesting limited movement across the Gulf. The satellite tagging data could confirm this “weak, but significant, genetic structure,” as Sellas calls it.

Sellas also hopes these tags can reveal how deep the rays are swimming and which habitats they frequent. Bassos-Hull says that habitat usage is particularly important off Sarasota, where there is proposed sand dredging in the Big Sarasota Pass Inlet for beach renourishment. But the Mote team knows the rays use this area to feed and that additional data could help protect this habitat for the rays.

Gulf Oil Spill
Since the Gulf Oil Spill, the Mote team has observed the number of spotted eagle rays off their coast decreased by about half. They began measuring and documenting the rays in 2009 and 2010, but in 2011 and 2012 the numbers per unit of measure had decreased. And, while the season isn’t finished this year, the lower population trend seems to have continued into 2013.

In addition, the Mote team has observed species rarely seen in the area—devil rays and whale sharks have started appearing in higher numbers than previously recorded. “It might be that these fish moved away from where the oil contaminated water was,” says Sellas.

Overseas collaborations
Bassos-Hull and Sellas have been working with Mexican scientists to collect tissues of spotted eagle rays for genetic sampling. Unlike the Florida samples, these tissues don’t come from live animals, but rather dead rays sold at local fish markets for consumption. One of their Mexican colleagues, Juan Carlos Perez-Jimenez, visited Mote in May to update them on the catch rates of spotted eagle rays in their fisheries.

Sellas and Bassos-Hull are also excited that this type of collaboration has expanded to Cuba.  A colleague there has similarly collected market samples for Sellas to conduct genetic work on here at the Academy.

Citizen Scientists on the Job
In the meantime, Bassos-Hull has received funding to utilize citizen scientists to learn more about these rays off the Florida Keys. She’s distributed small cards to dive shops there that, like the back of a milk carton, show a picture of one of these beautiful rays and ask, “Have you seen me?” Citizens can then refer to the back of the card which directs them to a website where they can report their sightings.

Mote is hoping that divers might spot these rays and input their sightings into the database, including pictures and location information. The small cards also give divers clues about where on the rays they might find small “spaghetti tags.” These tags indicate whether the ray has been caught before by Mote.

Bassos-Hull says that these citizen scientist sightings can help researchers understand where the hot spots for spotted eagle rays are in the Keys and where researchers should direct their attention for future studies.

Recognition and Recaptures
If you remember the video we produced in 2011, one of the most astonishing aspects of Mote’s work with these rays is the spot recognition software they use to identify the rays. The program, called I³S, is based on star recognition software and allows the researchers to recognize rays they’ve previously captured and released. Like fingerprints, no two rays’ spot patterns are the same.

Based on the data Mote has collected over the past few years, approximately 5% of the rays sampled are recaptures. This suggests that a certain number of rays are either remaining in the same area or returning to that area over time.

Busy Summer
Bassos-Hull and Sellas still have a lot of work ahead of them to understand these charismatic creatures and to share that knowledge with the world. In the meantime, this summer has kept them busy with a recent presentation at a professional conference on stingrays and forthcoming publications on their findings. And with more seasonal captures, they’ll undoubtedly learn more about the rays and their habitats. “We’re documenting the flux of nature,” Bassos-Hull says.

That could take a while.

Bob Hueter of Mote is also a principal investigator on this project. The researchers receive support and funding from the National Aquarium, the Disney Worldwide Conservation Foundation, the PADI Foundation, the Save Our Seas Foundation, and the California Academy of Sciences.

Image: Kim Bassos-Hull, Mote Marine Laboratory