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

The conference gave the same opportunity to younger scientists, through the AGU’s Bright STaRS program. “The program began in 2003 to get schools kids to the AGU meeting,” according to Pranoti Asher, manager of education for the AGU. She also reports that the number of middle and high school students attending has grown from 31 in 2003 to 128 this year.

Two teams from the Academy’s Careers in Science (CiS) intern program were among the Bright STaRS participants. The CiS program serves youth from communities traditionally underrepresented in the sciences with opportunities to immerse themselves in the natural world, develop life and job skills, receive college and career mentorship, and learn science and sustainability concepts in an authentic, paid work environment.

In a poster session that included 2,500 posters from professional and young scientists, CiS interns presented two very diverse posters—one on volcanism on the Moon and the other on sand crabs that live on Ocean Beach.

The first team worked with a scientist at NASA/JPL, using data and images gathered by the Lunar Reconnaissance Orbiter (LRO). The high schoolers decided to look at a volcanic structure on the far side of the Moon called the Compton-Belkovich Feature (CBF). Their question: How similar or different is CBF to volcanoes on the near side of the lunar surface?

The young researchers looked at albedo, elevation, radioactive thorium concentration and the surrounding geology. The youth found that Compton Belkovich is very different from other lunar volcanoes. Next, the team will attempt to identify potential sites that will yield the safest landing location and most scientific benefit.

A little closer to home, the second team looked at the influence of wastewater effluence on the population of sand crabs on San Francisco’s Ocean Beach. The Oceanside Treatment Plant lies just south of the beach and deposits copper, zinc and ammonia into the ocean.

The interns wondered what effect these chemicals have on the native Pacific mole crabs (Emerita analoga), which are a big part of the local ecosystem. Looking at previous studies on marine invertebrates, the team hypothesized that all three chemicals would negatively affect the abundance of these sand crabs.

The CiS interns have been studying the Pacific mole crabs on Ocean Beach for the past ten years. Using the data they collected between 2007 and 2010 and studying EPA data for the same four years, these young scientists found that while copper and zinc were bad for the populations, ammonia actually increased the abundance of these crustaceans.

Both teams enjoyed presenting to other researchers and their own Bright STaRS peers. Professional scientists seemed to thoroughly enjoy the presentations and gave the youth advice on where to take their research next.

And the high schoolers?

“My favorite part of AGU was presenting our research,” says senior Mollie. “Just like when teaching a lesson on the public floor of the museum, Angel and I had to gauge our visitor’s level of interest, and previous scientific knowledge. By tailoring our presentations and focusing on clearly and succinctly communicating our research, I felt I became more familiar with our project and its subtleties. Additionally, visitor’s suggestions and critiques of our project invigorated my interest in taking our Pacific mole crab research further in future years.”

“It was my first time at AGU and I had a wonderful time meeting scientists and presenting the research on lunar volcanoes to all,” says senior Rabiya. “It was definitely an amazing experience to be in a place where everyone is excited and curious about the same thing—the sciences!”

Image: Careers in Science Interns (from left to right) Mollie, Angel, Joseph, Reina, and Rabiya