Monthly Archives: February 2013

Crowds of Palmyra’s crabs chow down on rats’ remains

Published February 25, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

Strawberry hermit crabs on Palmyra atoll. ©2013 Susan Scott

My recent column about the successful elimination of rats from Palmyra Atoll, a National Wildlife Refuge 1,000 miles south of Hawaii, garnered some good questions and comments.

A reader, Jean, emailed, “So the rat poison destroys the rats and the curlews had to be removed. But how are the rats disposed of?”

They were recycled. In 24 hours, Palmyra’s amazing land crabs gobbled up every last morsel of rat, including fur and bones. All that was left, I was told, were little piles of teeth.

Six kinds of native land crabs roam Palmyra’s 25 islets. Most people know about the colossal coconut crabs weighing up to 10 pounds with 3-foot-wide leg spans. While I worked in Palmyra, however, the far more numerous strawberry hermit crabs, named after their dimpled red bodies the size of jumbo strawberries, stole my heart.

Like all hermit crabs, strawberry hermits live in empty seashells to protect their soft, vulnerable backsides. On Palmyra the shell of choice is a white spiraled snail shell. When wearing those “turbans,” the bright red crabs look like walking strawberries dipped in swirls of white chocolate.

crab

The total number of crabs of all species on Palmyra is hard to estimate because populations are high in some areas, low in others. One rough estimate was about 100,000 individuals. With the rat population at the time of eradication around 30,000, that’s at least three crabs for each rat.

The researchers easily found rat carcasses simply by looking for piles of crabs.

In the same column, my statement that bristle-thighed curlews are the only shorebirds known to use tools prompted reader David to send me a video of a green heron using bread to catch fish (“Clever Bird Goes Fishing” at goo.gl/R9dPj). I had seen this remarkable clip before, but I can’t watch it enough times.

Although this bird is standing on the shore, as most herons do, the tool-using green herons are classified as water birds, a separate category from shorebirds.

Hawaii’s shorebirds, including bristle-thighed curlews, or kioea, are here right now in all their glory. Molokai reader Arleone Dibben-Young emailed that a curlew satellite-tagged on Oahu’s North Shore flew to Molokai for lunch last week.

The kioea, Arleone writes, has recently been named the official bird of Kaunakakai. Fans hope the designation will raise awareness of the species’ special role in Molokai’s culture and natural history, and help protect these rare native treasures.

Thanks, all, for taking the time to write.


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

©2013 Susan Scott

Spaghetti worm gets name from noodlelike tentacles

Published February 18, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

A spaghetti worm’s feeding tentacles, which can extend up to 3 feet, capture plankton particles. ©2013 Susan Scott

 

Last week I braved the North Shore’s bone-chilling cold to go snorkeling. It was worth the chicken skin. I got to look down the throat of a spaghetti worm.

Having grown up in Wisconsin, I’m joking about Hawaii’s cold, but only partly. Thyroid hormones regulate body temperature, but after living on Oahu for 30 years, my heat glands have apparently retired. With Oahu’s water temperature at its winter low of 76 degrees and the morning air in the mid-60s, I had to force myself to plunge in.

And there was the worm of my dreams.

I don’t really dream about worms, but I do admire them. I’m particularly fond of the kind that spend their entire lives inside self-made tube homes, such as spaghetti worms, even though I never actually see them. If the creatures didn’t stick their tongues out to eat, I wouldn’t even know they were there.

A spaghetti worm makes its cylindrical home under a rock or inside a reef crevice by gluing together sand and bits of gravel with a mucuslike secretion from a gland near its head. Also around the head are corkscrew tangles of red gill filaments, the creature’s breathing organ.

An adult spaghetti worm’s body is 5 to 6 inches long and about an inch thick, but you won’t see it because it stays hidden all its life. An excellent photo of a Hawaii spaghetti worm is at goo.gl/0E2Zz.

The parts of the worm we do see are its multiple fettuccinelike feeding tentacles that extend from the head. Each “noodle” is about a quarter-inch wide and can extend up to 3 feet. When plankton particles drop out of the current onto the tentacles, tiny beating hairs move it along a groove, like a rain gutter, into the mouth.

The worm can also use its elastic tentacles to lasso larger food items and drag them to its mouth.

When danger approaches, such as one of the worm’s major predators, a blue-stripe butterfly fish or a cone snail, it can withdraw its tentacles completely into its head. The worm is slow in its retreat, but if a noodle gets nipped it’s no big deal. The worm can regrow its tonguelike tentacles.

Spaghetti worms usually build their tubes so deep that I rarely see the origin of the white pasta that looks spilled on the reef. But during my brutally cold snorkeling venture, I found a spaghetti worm with its head above the surface of the ocean floor (above).

The worm wore a sand and seaweed hat cemented over its head, but I got a brief glimpse of its mouth hole before it hauled in its feeding tentacles.

Now I know where it lives. Before I revisit, though, I’m buying a neoprene vest.


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

©2013 Susan Scott

Palmyra’s native species rebound after rats’ removal

Published February 11, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

A bristle-thighed curlew. ©2013 Susan Scott

Last week I came home from a trip to a good-news email. A year after a team of workers made an enormous effort to get rid of rats on Palmyra Atoll, a national wildlife refuge 1,000 miles south of Hawaii, its islands remain rat-free.

The workers are breathing a sigh of relief, as are the atoll’s plants and animals. In one year, biologists found a 367 percent increase in native crabs, insects and spiders and a 130 percent increase in native tree seedlings.

Researchers believe that rats arrived in Palmyra between 1940 and 1945 during the Navy’s construction of buildings, runways, roads and wharves. With no predators and native crabs, insects and seeds to eat, the black rat population grew to an estimated 30,000 on Palmyra’s 25 islets.

That’s a lot of rats for a land mass of less than one square mile, and those rodent rascals grew bold. When I was there in 2005, I often found them munching, in broad daylight, on snacks from my gear.

rat

Rat eradication is tricky business for a lot of reasons, one being that no biologist likes exterminating animals that are there through no fault of their own. But when the time comes that it’s crucial, as it clearly was in Palmyra, you have to make sure you’re not hurting the species you’re trying to save.

rat

The Palmyra rat project took seven years of planning to make sure that no native animals, particularly a migratory shorebird called the bristle-thighed curlew, were harmed.

In that workers succeeded. Recent counts show no change in the number of curlews in the atoll.

Curlews were worrisome because, unlike seabirds, which eat only fish and squid, bristle-thighed curlews eat anything they find, including the anticoagulant bait put out for the rats. (The substance does not affect invertebrates.) Because not all curlews fly to their Alaska breeding grounds each spring, workers captured 13 of the birds that summered in Palmyra, and cared for them while the bait was spread.

Later, when the birds were set free, they went back to their normal, extraordinary lives.

Bristle-thighed curlews are the only shorebirds known to use tools. At Midway the 17-inch tall birds throw rocks at abandoned albatross eggs to break them open. In Palmyra, curlews drop rocks on hermit crabs to break shells.

The imperiled bristle-thighed curlew, down to only about 7,000 individuals in the world, is the only shorebird that migrates exclusively to oceanic islands, including here in the main Hawaiian Islands.

Rat eradication in refuges is hard, unglamorous work, but without it the areas are not the havens they are intended to be. Congratulations to all the workers on a job well done.


Bonus picutre of a Coconut Crab on Palmyra,
which is way to big to be bothered by a bird throwing stones.

crab


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

©2013 Susan Scott