Sea Hares: Nature's Underwater Alchemests

Drifting quietly through the seagrass beds of the Indian River Lagoon is a creature that looks part rabbit, part cloud, and part magician. Meet the sea hare, one of the lagoon’s most unexpected (and oddly charming) residents.

Normally these marine mollusks don’t make headlines like dolphins or manatees, but recently there’s been a bit of an online “freakout” about them. Words like invasion and toxic have been tossed around as apparently quite a few washed up on some Treasure Coast Beaches in recent weeks.

Let’s be clear up front. Sea Hares are toxic to dogs, not humans.

So…What Exactly Is a Sea Hare?

Sea hares belong to the Aplysiidae family, a group of soft-bodied sea slugs with a talent for both disguise and drama. Their name comes from their rabbit-like appearance—complete with two floppy, ear-like appendages called rhinophores that help them “smell” their surroundings. They basically look like part snail, and part ray, as they also sport wing-like flaps called parapodia, which they can use to swim in slow, graceful pulses like a living, breathing piece of silk. Some can grow up to 30 inches but most average 8-12 inches.

Sea hares like in warm, shallow coastal waters, and gravitate toward sheltered zones like tide pools, rocky intertidal shores, seagrass beds, bays, and mangrove areas where abundant algae and gentle currents protect them from the open ocean. Parts of our coastline, along with the Indian River Lagoon fit that description well, making the Treasure Coast and the lagoon a dream neighborhood for these gentle creatures.

The Great Ink Escape

Here’s where things get interesting.

When threatened, sea hares release a dramatic cloud of purplish ink into the water—a move that looks a little like a smoke bomb. But it’s not just for show. This ink can actually interfere with a predator’s sense of smell and taste, buying the sea hare enough time to make a slow but successful getaway. And, by the way, it’s that ink that’s toxic specifically to dogs.  If you walk your dog on the shore, it’s best to try and keep it from licking at anything on the sand.

Here is a very cool video of how a Sea Hare swims and squirts ink, from Southwest Florida Television.

Why They Matter (More Than You’d Think)

Sea hares are underwater gardeners. As herbivores, they spend their time munching on algae, keeping it from taking over seagrass beds and crowding out other marine life. In a system like the Indian River Lagoon, where balance is everything, that quiet grazing makes a real difference. Without sea hares you might be looking at a much greener lagoon, and not in a good way.

Tiny Brains, Big Science

Despite their laid-back lifestyle, sea hares have made a big splash in the world of science.

Their relatively simple nervous systems have made them a favorite for researchers studying memory and learning. In fact, they’ve helped scientists better understand how brains, ours included, store information. Additionally, compounds found in their ink and tissues are being explored for potential medical uses. Not bad for a creature most people have never heard of.

Spotting Sea Hares, A Little Magic Beneath the Surface

If you’re snorkeling or wading along the lagoon, you might just spot one.

They’re slow-moving, often blending in with their surroundings, but once you notice that soft, undulating movement, it’s hard to miss. And despite their dramatic defenses, they’re completely harmless to humans. Watching one move feels a bit like discovering a secret—like the lagoon letting you in on something quietly cool and wonderful.

Sea hares may not be the stars of the show, but they’re part of what makes the Indian River Lagoon so endlessly fascinating. Strange, subtle, and surprisingly important, they remind us that even the quietest creatures can shape an entire ecosystem—and maybe even hold a little mystery along the way.