Honolulu Star-Advertiser © Susan Scott
January 14, 2013
One windy January day in 1983, shortly after moving to Hawaii, I ran into my University of Hawaii physiology lab partner, born and raised on Oahu. Staring at the mask and snorkel in my hand, he asked where I was going.
The beach, I said.
“The beach?” he said. “It’s winter!”
Thirty years later I’m still going to the beach when it’s windy and raining. That’s when I find the best stuff.
What I look for during my blustery beach walks are any of several marine animals that live on the surface of the open ocean. The scientific name for this remarkable group is pleuston, from the Greek root “pleus,” meaning to float or sail. Pleustonic animals do both, floating passively in currents and, when it’s blowing, sailing with the wind.
The common name for these creatures is the wind drift community, a term that hints at one of the downsides of an offshore existence. When the wind overpowers the currents that usually keep the animals at sea where they belong, and the creatures are positioned upwind of land, the drifters blow ashore to their deaths.
One of these animals is a snail called a violet shell or purple snail, names that describe the creature’s shell colors. The adult snail’s fragile lightweight shell, about thumbnail size, is pale lavender on the narrow pointy side and deep purple on the wide, open side.
Such coloration is good camouflage for the little snail. When a fish predator looks up from the deep, the snail’s light underside is hard to see because it blends in with the sky above. If a hungry seabird looks down, the shell’s purple topside colors match the deep blue-purple of the offshore ocean.
The color distribution tells us the snail’s floating position is foot up or, in our view, upside down. The inversion works because the snail floats on a bubble raft it secretes.
The snails hang onto their mucus floats for all they’re worth because to lose their rafts means to lose their lives. They can’t swim.
A violet snail spends a typical day adrift hoping to run into other species like Portuguese men-of-war, by-the-wind sailors or blue buttons, all jellyfish relatives. This is no social call. Violet snails eat their neighbors.
A nomadic lifestyle would seem to make reproducing difficult, but violet snails have that wired. Males discharge sperm in packets that passing females pick up. Females brood their fertilized eggs until they hatch, releasing bubble-rafting babies directly into the sea.
This method seems pretty hit-and-miss, given that the snail’s habitat is millions of square miles of open ocean. It works because oceanic currents usually herd the snails (and their prey) together. Sailors have reported seeing swarms of violet snails up to 200 miles wide. I’ve not seen this yet, but I live in hope.
When strong tradewinds blow, you’ll find violet snails stranded on windward beaches; during Kona blows, on leeward beaches.
Finding these lavender beauties as I did last week was well worth having salt-sprayed glasses, rain-wet hair and sand-filled ears.
But snorkeling? Please. It’s winter.