Tag Archives: ghost crab

Naming sea creatures sometimes had odd results

Published March 7, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
 A ghost crab has a turtle hatchling caught in its pincers. The tiny turtles must pass the crabs to make it to the ocean. ©2016 Susan Scott

A ghost crab has a turtle hatchling caught in its pincers. The tiny turtles must pass the crabs to make it to the ocean. ©2016 Susan Scott

In my Feb. 22 column, I wondered about the origin of the odd fish name “Moorish idol.” About that, Honolulu reader Ned Conklin emailed an excerpt from a 2007 book, “When Languages Die,” by K. David Harrison (Oxford University Press).

The author writes that early European explorers and naturalists disregarded native names for plants and animals, and instead gave them English names relating to something the species reminded them of back home. For instance, on Capt. James Cook’s third voyage, 1776-80, the naturalist aboard named a damselfish with stripes a sergeant, because a British sergeant’s uniform had stripes.

Scientists later learned that the sergeant fish was actually three species. Fish namers stuck with the historic term “sergeant” but added other words to tell the species apart. Hawaii’s endemic sergeant became the Hawaiian sergeant. The damselfish with wider and longer stripes and a wide range is the Indo-Pacific sergeant. And the fish with stripes that lighten and darken, and that has a black spot on its rear, was named the blackspot sergeant.

As to the Moorish idol, Harrison writes, “A fish with a dark-colored face spotted by Capt. Cook’s crew off Hawaii received the exotic name ‘Moorish idol.’”

Another reader, Utah biologist Robert Schmidt, emailed about my Feb. 8 column on ghost crabs. Robert thought he read that ghost crabs blinded or maimed turtle hatchlings before pulling them into their burrows, thereby preventing the hatchlings from escaping. He can’t find a reference to these behaviors and asked, “Do you know anything about this?”

Only what I saw. On Tern Island I watched turtle hatchlings run the ghost crab gauntlet in their race to the ocean. If the crab got hold of only one flipper, the turtle usually got away. But when the crab got a flipper in each of its two pincers the turtle couldn’t escape.

I rescued several hatchlings before they got dragged down a crab hole, and they ran away seemingly uninjured. But I got there too late for some. Lifting one turtle from a crab hole entrance, I found its head missing and the entire body hollowed out. Efficient, those crabs.

Besides being occasional crab food, turtle hatchlings are pupu for seabirds from above and fish from below. Only about 1 hatched turtle in 1,000 makes it to adulthood.

On the bright side, healthy adult turtles are common in Oahu waters, as are ghost crabs performing their daily beach cleanups and sand aeration.

Ned and Robert, thanks for the interesting emails. But I still don’t understand why a naturalist linked the term “Moorish” with “idol.” An exotic name indeed.

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.

Emails reveal shared love of sea creatures worldwide

Published December 29, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

You’ll never hear me complaining about email. It used to be that writing this column was a lonely job. Now each day I get to drink my morning coffee with people who share my love of the ocean and its remarkable inhabitants.

Some readers write to tell me about their own experiences with a subject I’ve written about, and others offer kind corrections or clarifications. Countless people just want me to know how much my articles brighten their Mondays and that brightens the hours I spend at my computer.

Every message has its charm, but a few from 2014 stand out.

Cutest story: Jennifer from Kualoa wrote that she gives the ghost crabs on her beach peanuts. “The big dudes take one in each claw and shuffle another around like a soccer ball … Sometimes they share, as with an apple core that washed in.” Another day, she wrote that her crabs “hold the peanut in one claw and nip off bits to eat with the other. But what about the ones with no claws? I know they will grow back, but in the meantime, what will they do?”

I loved learning that ghost crabs share apples and play soccer with peanuts. The fact that Jennifer worries about injured crabs tells me that we are kindred spirits.

The shortest and sweetest: In this era of information overload, I loved this reader’s economy.

Subject box: “Upside-down jellyfish.”

Message: “Thanks — Really Good.”

Appreciation noted.

Most alarming question: On Feb. 12, Paul wrote, “Aloha Susan, Could the invasive algae be responsible for the missing Honu in the Ala Moana Lagoon? We have only seen one Honu in 4+ months.”

Happiest ending: On Feb. 19, Paul wrote: “Aloha Susan! Had to avoid a large Honu at Ala Moana Lagoon today so that makes 3 in 2 days. A welcome return after many months absence (for whatever reason.)”

Question with the easiest answer: While watching manta rays at night, a Big Island reader, Chris, met a woman who “claimed that there is a day, one time a year, when the world’s oceans all get super excited, and the water is effervescent and the tides change color and sea life large and small all becomes super animated … perhaps tied to a lunar event. Was this gal off her rocker?”

Um. Yes.

Best message from a distant land: Emails arrived from readers in Australia, South Korea, Pakistan and the Czech Republic. These were all fun starts to my day (Wow, Pakistan?) but the one that touched my heart came from the CR. “Hello madam,” Jan wrote. “I’d like to run away from Europe and live a spiritual life. It would be possible to settle in such a paradise? Good luck.”

I already had my good luck. I wished Jan equally good luck in finding his or her paradise.

Favorite video: My neighbor Joanne sent this link — bit.ly/1zad8WG — with the note, “In case you haven’t already seen this 46 times.” I had not seen it even once, but I’m now close to 46.

All my messages this year were positive, entertaining and inspiring. Thank you, dear readers, for making this column so much more than a job. See you in 2015.


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

©2014 Susan Scott