Tag Archives: crabs

Attempt to aid crab heals faith in humanity

Published January 14, 2017 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2017 Susan Scott

Tiny mole crabs live in Hawaii, just below the sand and often along the water’s edge. A deceased female’s belly shows a mass of orange eggs clinging to it. ©2017 Susan Scott

One morning last week the news of hate crimes, science denial and war atrocities left me feeling hopeless about the human race. Wanting to block out the whole wretched world, I plugged my ears with headphones, pulled a hat down to my eyes and walked to the beach.

And something wonderful happened. Standing near the shore break, an elderly couple peered down at a tiny white object in the sand.

“We wanted to help it,” the man said, when I approached, “but we didn’t know if it could sting. It seems to be tangled in something orange.”

The creature they were trying to rescue was a charming little mole crab.

Hawaii’s cream-colored mole crabs, about 1.5 inches long, live under the sand along some shore breaks, moving up and down with the tides. The little crabs manage to survive in this turbulent area because their egg-shaped bodies are smooth, allowing water and sand to slide over them with minimal resistance.

With its strong back legs, a mole crab can dig a hole in wet sand and back into it in a split second. This happens so fast that even while watching you can lose the crab’s location. If you know what to look for, though, it’s sometimes possible to find buried mole crabs.

The crabs position themselves upright in their burrows, facing the incoming waves with two stalked eyes peeking out and a pair of feathery antennae lying flat and forward, as a kind of brace. Another pair of plumed antennae stand upright, directing water to the gills for breathing.

All four antennae filter the water washing over them, gathering tiny plants and animals, dead or alive, for food.

The mole crabs’ organs are so tiny, and the wave action so swirly, that the minuscule dimple they make in the sand is barely visible. One easy tell, though, is when a crab has found a Portuguese man-of-war. Even as waves wash back and forth over the shipwrecked creature, it looks as if its long blue tentacle is stuck in the sand.

It is. A mole crab is reeling it in to eat at its leisure. I’ve found crabs with blue tentacles rolled up on the crab’s belly like a bright skein of yarn.

The mole crab the couple found was alive, but barely. I picked her up, explaining that these filter feeders have no pincers and don’t sting. I say her because the orange mass on the abdomen was a bundle of eggs. Small holes, likely a bite, in the crab’s back proved to be fatal.

To remember those kind people, who not even knowing what it was tried to save a tiny crab’s life, I took the creature home and gave it a photo memorial. The pictures remind me to try to focus on the good side of human beings — and to take more beach walks.

Ghost crabs keep low profile along atoll’s sandy beaches

Published February 8, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
The horn-eyed ghost crab, the larger of Hawaii’s two species of ghost crabs, is known to dig M-shaped burrows. ©2016 Susan Scott

The horn-eyed ghost crab, the larger of Hawaii’s two species of ghost crabs, is known to dig M-shaped burrows. ©2016 Susan Scott

While walking a beach at Midway recently, I noticed a lot of ghost crab holes with flat smooth sand around them, no mounds, sprinklings or claw prints in sight. Ghost crabs (also called sand crabs) are famous for building large, complex burrows. So what, I wondered, had these crabs done with their sand?

You can see ghost crab holes on nearly every tropical, subtropical and temperate beach on the planet. But good luck seeing the holes’ architects. The world’s 22 ghost crab species make their mansions mostly at night and hunker down in them during the day. Ghost crabs use their burrows the way we use houses. The dwellings provide refuge from predators and bad weather, are a private place to change clothes (in the crab’s case, to molt), and when the time is right, they’re love shacks. A crab hole generally has a funnel shape at the top leading to a tunnel that ends in a chamber. Depending on species, ghost crab burrows look like the letters Y, J, I and U. The larger of Hawaii’s two species, the horn-eyed ghost crab, sometimes digs M-shaped burrows. This is usually the result of a new resident re-excavating an abandoned burrow.

The side branches of Y and M shapes are either escape routes or places to hide from predators that dig, such as coyotes, foxes, mongooses and dogs. How deep a crab’s tunnel goes depends on the sand’s moisture. The drier the sand, the deeper the burrow, because ghost crabs have lungs and gills that both need water to absorb oxygen. When we see ghost crabs taking dips in the surf zone, they’re wetting their breathing organs.

Here in the main islands, ghost crabs often leave evidence of their quarries, either throwing excavated sand willy-nilly or piling it in mounds. During the reproductive season, Hawaii’s horn-eyed males build copulation burrows in an S shape. To advertise their bachelor pads to females, males shape their scooped-out sand into pyramids.

Scattered sand, mounds and pyramids, however, are like arrows directing predators to a crab’s location. And that’s where those Midway crabs’ holes with no tailings make sense. To mask their whereabouts, ghost crabs sometimes trample their excavated sand, expertly erasing all traces of digging.

In addition to eating dead plant and animal material that washes up, ghost crabs are ecosystem engineers. Their burrows create passageways for air and water to mix sand, bacteria, soil and sediment, crucial factors in maintaining healthy beaches.

Besides being useful, ghost crabs are fun to watch and beautiful to behold. Please be kind to these native species. Our beaches need them.

Coconut crab in the road no monster, merely thirsty

Published January 5, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott

This coconut crab was photographed south of Hawaii on Palmyra. ©2015 Susan Scott

Coconut crabs got a lot of attention recently when residents found one walking down Salt Lake Boulevard. A thoughtful person coaxed the non-native animal into a box and notified authorities. When news of this got out, the crab became a celebrity.

As it should. But not because of the sensational reporting, which made the crab sound like the spawn of Godzilla whose presence in Hawaii was a plot toward world domination. No, the coconut crab deserves publicity because it’s a magnificent creature that urgently needs international protection.

On Palmyra Atoll I fell in love with coconut crabs after helping weigh and measure them. The crabs are protected there, but lack of data prevents the overhunted species from being officially listed as endangered.

The coconut crab is a land crab, but its survival depends on the sea. After mating, the female carries her eggs tucked under her folded abdomen until they’re ready to hatch. She then walks to the shore and drops her tiny offspring into the ocean.

After three to six weeks adrift, the lucky survivors, being of the hermit crab family, look for snail shells to call home. Two years later the crabs have outgrown all seashells and spend the rest of their long lives, up to 60 years, naked.

crab

Such exposure leaves the hermit crab vulnerable to dehydration, making a high-humidity environment crucial to its survival. As natives of the steamy rain forests of certain tropical islands in the Pacific and Indian Oceans, coconut crabs cannot live in Hawaii’s relatively cool, dry climate.

Coconut crabs come in a rainbow of stunning colors arranged in dots, spots, bars and blotches. With two red stalked eyes, four waving antennae and eight gangly walking legs, the crabs look like a cross between a spider and a lobster. This makes the animals creepy to some but beautiful to those of us who admire nature’s amazing designs.

crab

Part of the coconut crab’s fame is its two big front claws, which generate silly headlines like “Coconut crabs ate Amelia Earhart!” But those mismatched pincers have practical functions. One claw strips husks off green coconuts; the other cuts into the hard inner shell. Even with such efficient tools, it takes a mature crab 24 hours to get to the center of a coconut.

No one knows who brought the 4-pound crab (they grow to 8) to Hawaii, or why it was wandering down a city street, but it’s in good hands now with a coconut crab expert guiding its care.

After being kidnapped, chilled, desiccated and deserted, and then portrayed as a vicious monster, I hope our unwilling visitor is treated to a big bag of shredded coconut.


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

©2015 Susan Scott