Tag Archives: shells

Diverse array of ‘pennies’ comes from marine critters

Published May 28, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
Australians call these foram shells mermaid’s pennies; they’re common on the Great Barrier Reef. ©2016 Susan Scott

Australians call these foram shells mermaid’s pennies; they’re common on the Great Barrier Reef. ©2016 Susan Scott

Goldsmith Island, Queensland, Australia >> While sailing north through the reefs and islands of Great Barrier Reef National Park, our routine is to sail in the morning, choose one of the nearly endless protected island anchorages, stop there for the night and explore. Although each island is rich with its own charming gangs of kangaroos, parrots and coral-ringed islets, we rarely spend more than one night in the same place. We just never know what this amazing park has in store for us down the line.

One day last week, for instance, after anchoring in a picture postcard bay, we headed to shore in our dinghy and struck it rich. Countless pennies lay scattered over the white sand.

Mermaid’s pennies, that is, according to Australians. To me they were puka shells, but odd ones. It looked as if someone had spilled a truckload of washers on the beach.

The shell washers ranged in diameter from so tiny I could barely pick them up to about an inch wide. The holes in the center also varied from none to most of the shell. Nor were these disks pure white and wavy like puka shells. Their flat surfaces came in all shades of gray, brown and cream. The shells are from a species of marine creature called a foraminifera, foram for short. Being close to the beginning of the food web, forams are vital for healthy oceans, and to human enterprises as well. Egypt’s pyramids are made of zillions of calcium carbonate foram shells squished together over geologic time. Geologists also use foram deposits as clues to the location of underground oil.

Forams deliver beauty as well, decorating some of the most exquisite shorelines on the world. Beaches in Hawaii, Palau, Bermuda and more are carpets of forams finely ground by ocean waves.

Forams are animals like bacteria are animals. They eat, reproduce, walk around, prey on other organisms and die. But even the largest ones are only a single cell. They’re like amoebas with shells arranged in countless shapes of disks, spheres, spirals and tubes. Most are too small to see with the naked eye, which is what makes the mermaid’s pennies (and the white puka shells of the South Pacific) special.

Forams line all ocean floors and drift in marine plankton in astronomical numbers. In his study, one researcher found an estimated 70,000 forams per square yard on the ocean bottom. The number is on the low side for some areas. In one place, “foram ooze” was 6,600 feet thick.

At this writing, we’ve explored beaches and reefs of about 10 islands and found shells of snail species we know and many we don’t. Curiously, we’ve seen no more mermaid’s pennies, but the handful I have make me feel rich indeed.

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