The mystery of the purple puff

April 21, 2023

Last month, reader Carol Wilcox emailed that while snorkeling on Kahala Beach near Black Point she spotted a red filament-like fluid about the size of a baseball oozing from a shallow hole covered with limu. Floating low in the water column, the ooze moved with gentle wave action. Another squirt came out, then a third and a fourth. Some squirts opened like a net, others were opaque and stringlike.

“When I gently lifted a section with my finger it all held together, much like a spider web,” Carol wrote. “The color was a deep purple red… Any ideas?”

Several of us had ideas. I sent Carol’s question to author John Hoover who, like me, wondered if a sea cucumber had ejected its guts. But the tubules that some sea cucumbers expel when disturbed are white and sticky, and sea cucumber gonads, when expelled under duress, aren’t fluid.

John also thought of the hermit crab anemone that ejects pink threads when disturbed, but those aren’t fluid either.

Because neither of these creatures seemed quite right for Carol’s description, John passed the question to Cory Pittman, an expert on Hawaiʻi’s marine invertebrates who, with Pauline Fiene, manages the Sea Slugs of Hawaii website.

Cory agreed that the above animals don’t fit the story and suggested that, most likely, it was a sea hare releasing its defensive ink.

That reminded me of an experience I had while snorkeling on Oahu’s North Shore in 2020. A rapidly rising surf had cut short my swim, and while exiting the water, I found a sea hare rolling at the shoreline. The strong current had dislodged the sluglike animal from its rocky home.

I picked up the sea hare, and the distressed creature began oozing a reddish liquid, much like an octopus’s ink, except purple.

With waves breaking on me, and the current pushing me sideways, my rescue turned into a struggle. (Safe enough in shallow water, but hard work.) By the time I found a proper puka in which to lodge my saved sea hare, I forgot about the creature’s initial purple cloud.

But my camera didn’t forget. After Cory suggested sea hare ink, I remembered the pictures I’d managed to take before swimming back into the surf.

What threw us all off was Carol’s statement that the cloud held together like a web. In all the accounts I’ve found, including my single experience, a sea hare’s ink cloud dissolves like any other liquid. Sea hare ink may be our best guess, but it’s possible Carol saw something else entirely.

Sea hares are plump sea slugs that get their name from sensory organs on their heads that look a bit like bunny ears. Hawaii hosts several species ranging in size from about two inches to 10 inches long. The Hawaiian name for them all is kualakai. All are algae eaters. Kualakai that eat red algae emit reddish-purple fluid when upset. I’ve rescued countless sea hares over the years, but this was the first one that inked me. When red algae is absent from a sea hare’s grazing area, the animal emits no ink.

Most sea hares are nocturnal, hiding during the day and coming out at night to eat. Unlike some of their brightly colored sea slug cousins, sea hares blend with their backgrounds so well it’s easy to miss them.

Researchers have discovered anticancer and antibacterial substances in the ink of a sea hare species found throughout the world’s tropical waters, including Hawaiʻi. You can see photos of that oddly-shaped species, Dolabella auricularia on Cory and Pauline’s site, here. I’ve not this seen one, but now I’ll be looking.

Years ago, my UHM invertebrate zoology professor, Mike Hadfield, took our class to the Diamond Head reef flats at low tide. My first discovery there was a white-speckled sea hare, Aplysia argus. I’ve been admiring (and rescuing) these charming marine bunnies ever since.