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

Scientific American considered the effects on endangered sperm whales in the area in a recent podcast.

The NOAA ship Pisces discovered a dead sperm whale on June 15—a possible victim of the ongoing oil spill in the Gulf of Mexico…

…It is known that such sperm whales feed on deepwater squid that may be impacted by plumes of dispersed oil. The endangered whales have also been spotted surfacing into the slick. How the millions of liters of oil will impact sperm whales and other cetaceans is an ongoing, unintentional science experiment.

Meanwhile, The New York Times is following researchers tracing the movement of manatees along the Florida coast. About 100 manatees (out of a total population of 5,000) migrate each summer to Mobile Bay, Alabama which means they could be swimming right into the oil.

As oil spreads into the bay, these travelers are now in danger of having their migratory routes and habitats contaminated, putting at risk a group that Dr. Carmichael believes may represent the scouts for the larger population. “So much is unknown,” she said. Manatees eat 10 percent of their body weight in sea vegetation per day. If oil clings to the sea grass, the animals could eat it, get the oil on their bodies and pass it to others by contact. After a 1983 oil spill in the Persian Gulf, between 38 and 60 dugongs, a species that is similar to manatees, died from exposure.

LiveScience focuses on those sea grasses in its recent story, “Small Creatures Will Be Oil Spill’s Biggest Victims”. The article includes an interview John Caruso, an ecology and evolutionary biology professor at Tulane University:

In particular, the cord and Spartina grasses that grow on the coast of Louisiana are crucial to the ecosystem and especially sensitive to the oil leak, Caruso said. These grasses form the foundation of the local food chain, and their root systems lessen the erosion of the small islands that protect inland Louisiana from hurricanes, Caruso said.

The other small creatures they include are phytoplankton and zooplankton:

During the spring and early summer, plankton and other organisms at the base of the food chain reproduce in the shallow water on the Gulf of Mexico. The newborn critters that result are particularly vulnerable to the oil, Caruso said.

New Scientist poses the possibility that phytoplankton are already being affected:

In fact, it’s possible – but difficult to prove at this point – that the dispersants and oil are already killing phytoplankton, which could account for low oxygen levels recorded in near-surface waters.

One thing is for certain, the oil will affect life for a long, long time. Again, from LiveScience:

As for vertebrates like birds and sharks, the major consequences of the oil leak will occur later, said Caruso. Even though birds coated in oil will die, or face difficulty after cleaning, the degradation of the food chain will cause larger problems for these animals over a longer span of time, Caruso said.

(Watch Academy researchers’ thoughts on the Gulf of Mexico wildlife and the oil spill here.)