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

While elephants and tigers may have won for now, an initiative to put an end to international trophy hunting and commercial trade in polar bear parts was defeated. CITES also voted down a proposal to ban the hunting of Atlantic bluefin tuna and opted for no protection of four vulnerable species of sharks.

The proposal to protect polar bears was put forward by National Resources Defense Council (or NRDC) lawyers, who asserted the bears are hunted at unsustainably high rates for trophies, pelts, paws and teeth.

“There has been a lot of positive momentum in polar bear conservation recently, this is a real setback,” said Andrew Wetzler, the Director of NRDC’s Endangered Species Project.

A study of the total polar bear population done by the U.S. Geological Survey “conservatively” predicted a decline of over 70% in the next 45 years as global warming literally melts their habitat.

Commerce also trumped science as CITES refused to protect Atlantic bluefin tuna, in spite of receiving reports that defended the research. Bluefin qualifies for the highest level of protection for protected species given its population has declined by 80% since 1970, and continues to plummet due to overfishing and international trade.

The U.S., Norway and Kenya offered outright support for the ban, while the European Union asked that any actions be delayed until May 2011 to provide more time to respond to claims of overfishing.

Japan, which imports 80% of Atlantic bluefin conceded that stocks were in trouble. However, one bluefin can go for $175,000 on the Tokyo fish market, making it a highly desirable commodity. Japan echoed a growing theme that CITES should have no role regulating marine species, and trade quotas should come from the International Commission for the Conservation of Atlantic Tunas.

Four species of shark — the scalloped hammerhead, oceanic white tip, porbeagle and spiny dogfish — also remain unprotected. “Despite fast declining populations of the ocean’s apex predators, CITES government delegates turned a blind eye to science,” said Matt Rand, director of global shark conservation for the Pew Environment Group.  “Four threatened species of sharks were refused protections even though the evidence of international trade’s harmful effects was plentiful. Inaction can and will set these sharks on a course toward total population collapse.” The shark trade kills an estimated 73 million sharks annually.

As the BBC article summarizes, “There is a feeling among many conservationists that Doha may have been our last chance to give real, meaningful protection for some species — and that we missed it.

“However, for all its faults, CITES is the one international convention specifically targeted at controlling trade in endangered species, so it is the international legal framework with which we have to work.”

Creative Commons image by Johan Lantz

Now here’s the topper: cork is sustainable and good for biodiversity!

For hundreds of years vintners have used cork from oak cork trees as wine bottle stoppers. Grown mostly in southern Europe and northern Africa, the forests that contain these trees are also home to various endangered bird and animal species, including the Iberian lynx.

Cork trees can live for 200 years and stripping the cork bark from the tree to make wine stoppers is quite sustainable. The bark will grow back in about nine years to be harvested again. It is also harvested by hand, creating very little impact on the land.

Several years ago, a few wine-makers switched over to screw-tops and synthetic corks, because the quality of corks can be inconsistent. But corks are still atop about 80% of all wine bottles and cork producers are ensuring better quality.

Used corks can also be recycled—and made into floors, walls and other items.

So raise a glass or two this weekend, because the more you drink, the healthier you are and the more you protect biodiversity!

Creative Commons image by Wavering