Sea Otters Helping In The Fight Against Poor Water Quality
August 27, 2013

Returning Sea Otters Helping Recovery Of California Seagrass Meadows

redOrbit Staff & Wire Reports - Your Universe Online

Scientists studying seagrass beds in one of the largest estuaries in central California are crediting its recovery on the return of sea otters to the coastal region, according to new research published in this week’s edition of the Proceedings of the National Academy of Sciences.

According to Suzi Gage of BBC News, seagrass at Elkhorn Slough in Monterey County was “heading for extinction” due to an increase in pollution in coastal waters blamed on an increase in the use of nitrogen-rich fertilizers.

Seagrass meadows worldwide are suffering a similar fate, the study authors said. These regions, which provide coastal protection and are an essential habitat for fish, are being harmed by the growth of algae on seagrass leaves. Those blooms are caused by nutrients and prevent the meadows from receiving enough sunlight.

However, when sea otters began returning to Elkhorn Slough in 1984, it marked the beginning of a remarkable chain of events that saw the seagrass there begin its recovery process, explained Brent Hughes, a Ph.D. candidate in ecology and evolutionary biology at the University of California, Santa Cruz and first author of the study.

Hughes and his colleague said that while the otters had no direct effect on the landscape, they do consume a tremendous amount of crabs, reducing the crustacean population in the slough. With fewer crabs to prey on them, sea slugs and other grazing invertebrates became larger and more abundant.

Those creatures, as well as small crustaceans known as Idotea (which also increased in number when the crab population is controlled by sea otters) feed on the algae growing on the seagrass leaves, keeping them clean and helping them remain healthy. The researchers call this type of chain reaction in a food web a “trophic cascade.”

“This estuary is part of one of the most polluted systems in the entire world, but you can still get this healthy thriving habitat, and it's all because of the sea otters,” Huges told Gage on Monday. “So it's almost like these sea otters are fighting the effects of poor water quality.”

“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,” added co-author Tim Tinker, a wildlife biologist with the US Geological Survey (USGS). “It's also a great reminder that the apex predators that have largely disappeared from so many ecosystems may play vitally important functions.”