See Sea Slugs Scour Seagrass by the Seashore | Deep Look

Eelgrass sea hares may look like lazy, zebra-striped spoonfuls of jello, but these sea slugs are actually environmental heroes. Their voracious appetite for algae helps keep underwater meadow ecosystems in balance–which is great news for sea otters.

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DEEP LOOK is an ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Explore big scientific mysteries by going incredibly small.

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Eelgrass sea hares are tiny aquatic slugs named for the bunny-like tentacles on top of their head. They can be found munching on the microscopic algae that grow on the surface of eelgrass, a type of marine seagrass. Also known as the Taylor’s sea hare, these humble, zebra-striped slices of green jello are actually crucial to the health of their ecosystem.

They don’t eat the grass itself; instead they help the meadows grow by clearing the way for sunlight to reach the plants, scraping the blades of grass clean with their rows of tiny teeth. The seagrass, in turn, serves as a safe haven to lay their eggs, and protection from predators like crabs and fish.

The blades of grass also protect more than just these voracious little cleaners. At Elkhorn Slough, a large winding estuary off of Monterey Bay, the eelgrass beds form a habitat for a diverse community of animals and plant life, which includes sea otters, Dungeness crabs, clams, skeleton shrimp and various fish.

For decades, nutrient overload from agricultural runoff has caused excessive algae blooms in Elkhorn Slough, as the thick algal mats block out the sunlight needed for the grass to grow. But with the reintroduction of sea otters to Elkhorn Slough in the 1980’s, ecologists observed a balancing effect on the system. The otters started eating the crabs that eat the sea hares. Because of this trophic cascade, the slug population grew, and their appetite for algae helped keep the eelgrass clean, counterbalancing the effects of the algal blooms.

--- Is a sea hare a nudibranch?

Nudibranchs and sea hares are both different types of sea slugs. There are various species of nudibranchs and sea hares. All sea slugs are a kind of mollusk.

--- What is a trophic cascade?

A trophic cascade occurs when the addition or removal of a top predator has a dramatic effect on the food web, drastically changing the structure of an ecosystem, and how nutrients cycle through it.

---+ Read the entire article on KQED Science:

https://www.kqed.org/science/1970711/...

---+ For more information:

Paper on the ecological effects of sea otters, and their relationship to eelgrass and sea hares, by Brent Hughes, Sonoma State University -
https://www.pnas.org/content/110/38/1...

Katharyn Boyer’s Lab at San Francisco State’s Estuary and Ocean Science Center, focusing on eelgrass ecology and restoration work in the San Francisco Bay
http://online.sfsu.edu/katboyer/Boyer...

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