This Adorable Sea Slug is a Sneaky Little Thief | Deep Look

Nudibranchs may look cute, squishy and defenseless ... but watch out. These brightly-colored sea slugs aren't above stealing weapons from their prey.


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DEEP LOOK is a 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.

The summer months bring low morning tides along the California coast, providing an opportunity to see one of the state’s most unusual inhabitants, sea slugs.

Also called nudibranchs, many of these relatives of snails are brightly colored and stand out among the seaweed and anemones living next to them in tidepools.

“Some of them are bright red, blue, yellow -- you name it,” said Terry Gosliner, senior curator of invertebrate zoology and geology at the California Academy of Sciences in San Francisco. “They're kind of designer slugs.”

But without a protective shell, big jaws or sharp claws, how do these squishy little creatures get away with such flamboyant colors in a habitat full of predators?

As it turns out, the nudibranchs’ colors serve as a warning to predators: These sea slugs are packing some very sophisticated defenses. And some aren’t above stealing weapons from their prey.

Gosliner and Brenna Green and Emily Otstott, graduate students at San Francisco State University, were out at dawn earlier this summer searching tidepools and floating docks around the Bay Area. They want to learn more about how these delicate little sea slugs survive and how changing ocean temperatures might threaten their futures.

Nudibranchs come in a staggering variety of shapes and sizes. Many accumulate toxic or bad-tasting chemicals from their prey, causing predators like fish and crabs to learn that the flashy colors mean the nudibranch wouldn’t make a good meal.

--- What are nudibranchs?
Nudibranchs are snails that lost their shell over evolutionary time. Since they don’t have a shell for protection, they have to use other ways to defend themselves like accumulating toxic chemicals in their flesh to make them taste bad to predators. Some species of nudibranchs eat relatives of jellyfish and accumulate the stingers within their bodies for defense.

--- Why do nudibranchs have such bright colors?
The bright colors serve as a signal to the nudibranch’s predators that they are not good to eat. If a fish or crab bites a nudibranch, it learns to associate the bad taste with the bright colors which tends to make them reluctant to bite a nudibranch with those colors in the future.

--- What does nudibranch mean?
The word nudibranch comes from Latin. It means naked gills. They got that name because some species of nudibranchs have an exposed ring of gills on their back that they use to breath.

---+ Read the entire article on KQED Science:
https://www.kqed.org/science/1929993/...

---+ For more information:

Learn more about Terry Gosliner’s work with nudibranchs
https://www.calacademy.org/staff/ibss...

Learn more about Chris Lowe’s work with plankton
http://lowe.stanford.edu/

Learn more about Jessica Goodheart’s study of nematocyst sequestration
https://onlinelibrary.wiley.com/doi/f...

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