Tag Archives: violet shells

Clinger crabs are members of wind drift community

Published February 3, 2018 in the
“Ocean Watch” column, Honolulu Star-Advertiser ©2018 Susan Scott

A pregnant clinger crab fits in the palm of a hand. ©2018 Susan Scott

When the wind is howling and the surf is busy salting everything in my house, I hit the beach. Those aren’t the best conditions for soaking up sun or playing in the water, but for us avid walkers it’s prime time for finding marine treasures.

Because I make mosaics from litter I find in albatross nests at Midway and on beaches in the Pacific, my gems are usually bits and pieces of colored plastic. Last week, though, my prize was alive. When I got home and dumped my junk in a colander for rinsing, there on a barnacle- and algae-encrusted toy truck clung an offshore crab.

This species of crab is a member of the wind drift community, a diverse bunch of animals that float on the surface eating anything they run into, including each other. They’re called wind drifters because they are indeed adrift, their direction and speed controlled entirely by current, wind and waves.

Common jelly-type critters floating offshore are Portuguese men-of-war (Physalia), by-the-wind sailors (Velella) and blue buttons (Porpita).

You might not expect snails to be members of this community, but two species are common: violet snails (Janthina) and snails-without-shells called nudibranchs (Glaucus).

Another unlikely offshore mariner is a little crab I call the clinger crab because it doesn’t have its own float system, as the others do, nor does it swim. Rather, the clinger crab spends its life hanging onto a piece of wood or debris. (I can’t find a common or scientific name for this little crab. If you have one, please write.)

Clinger crabs are about the size of a quarter and come in shades of blue or brown, depending on which object they’ve chosen to call home. This clinger was brown, a perfect match to the brown seaweed that grew on its floating toy.

You can tell a male crab from a female by the flap on the center of its underside. Narrow is male; females have wide flaps that hold their eggs.

When I examined my crab’s belly, I discovered, with some excitement, that I had a female with eggs. Hoping to raise some baby clingers, I rushed back to the ocean for a bucket of water, half filled my rescue tank and gave my pregnant crab her tiny truck, a pile of rocks to reach it and some frozen brine shrimp for energy.

A pregnant clinger crab fits in the palm of a hand. The eggs are the yellow mass under the flap. ©2018 Susan Scott

Alas, a tank being the utter opposite of her natural habitat, she did not survive. Even so, I was happy to have had a wind drift pet, even if just for a day.

During my beach walks I sometimes forget to bring a bag, and have to go trash-can diving for containers. Failing at both those things last week, I called Craig to come get me in the car, because I couldn’t walk home. After stuffing my pockets full of flotsam, I then filled my Crocs.

I have lived in Hawaii long enough that I sometimes think it’s too cold to go snorkeling. Never, ever, though, is it too cold for beachcombing.

Violet snails build their own bubble rafts and float away

Published November 9, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott
Violet snails shells are left behind by animals that survive by eating Portuguese men-of-war.©2015 Susan Scott

Violet snails shells are left behind by animals that survive by eating Portuguese men-of-war. ©2015 Susan Scott

AIRCRAFT BEACH, EURIMBA NATIONAL PARK, Australia » For me, beach walking is often as rewarding as snorkeling. Sure, marine animals lying on beaches are dead or dying, but that means I can pick them up or turn them over and admire to my heart’s content. The long-dead animals I found stranded on this 2-mile-long sand beach, suitable for small plane landings, are the largest violet snail shells I’ve ever seen, nearly 2 inches long and an inch high. The exquisite shells, lavender above and purple below, lay 50 or so feet above the high tide line, suggesting that storm winds drove the snails toward shore and high waves spit them out. Most violet snails have better luck. Healthy ones float offshore, upside down, on self-made bubble rafts. Some believe that the snail agitates water with its foot to make bubbles. Another theory is that the snail blows bubbles from air it has taken into its shell. In either case, the creature secretes mucus from its foot to coat its bubbles, creating a rubbery raft.

It’s a precarious existence. To lose the raft is to sink to the bottom and drown. These air-breathing snails can’t swim.

Nor can they steer. Throughout the world’s tropical oceans, violet snails and other members of their drifting community, including Portuguese men-of-war (called blue bottles here in Australia), are at the mercy of winds and currents. That’s why during strong onshore winds, we find both species stranded on beaches.

Unlike us, violet snails don’t get a sting when they bump into blue bottle tentacles. They get a meal. Portuguese men-of-war are violet snails’ main food.

When an animal can’t control its course, it’s tough for the sexes to get together. As a result, when a male violet snail senses a female in the area — they can’t see each other because violet snails have no eyes — he ejects sperm in her general direction. When the sperm hit their target, the female lays eggs and carries them with her beneath her bubble raft.

Eggs hatch into a drifting underwater form. When they mature, the tiny snails build their own bubble rafts and continue the nomadic existence.

I’ve often found violet snail shells on Hawaii’s windward beaches, and could fit about 10 in my palm. Here two barely fit. The snails might be different species, or the big ones might have grown large due to these nutrient-rich waters. On the same beach, I also found the biggest Portuguese man-of-war I’ve ever seen. Whatever their size, violet shells on any beach give me a fine marine animal fix. And I don’t even have to get wet.


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2015 Susan Scott