Tag Archives: starfish

Starfish that dines on coral is a management challenge

Published February 1, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott

A crown-of-thorns starfish eats rice coral in New Caledonia. Research is inconclusive on whether the animal does lasting harm to coral reefs. ©2015 Susan Scott

Published February 1, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott

‘If I see one in an area, I leave it,” a knowledgeable Palauan dive guide told me recently. “But if there’s two or more, I kill them.”

This was the reply to my query about whether crown-of-thorns starfish have been a problem on reefs in Palau. The guide’s explanation didn’t answer my question, but it made clear one fact: Most people see the crown-of-thorns starfish as a coral killer that deserves the death penalty.


Crown of thorns. ©2015 Susan Scott

But before giving this native Indo-Pacific reef animal a lethal injection, we should consider the 1,200 observations on the subject. That’s the approximate number of crown-of-thorns-starfish-related research papers published, most since the 1960s and ’70s outbreak that devastated Australia’s Great Barrier Reef.

Because that amount of data is so large, it’s been hard to ferret out the facts. So workers from James Cook University joined workers with the Australian Institute of Marine Science to consolidate the studies. Their resulting 2014 report draws only one sobering conclusion: “Many questions about the biology of (the species) remain unanswered, which greatly limits the understanding and hence the potential to manage outbreaks.”

The recent study of studies, however, did answer one question: Do the starfish search out a particular kind of coral or go for whatever is in their paths?

Crown of thorns close-up. ©2015 Susan Scott

Crown of thorns close-up. ©2015 Susan Scott

Both, it turns out, an answer that shows the difficulties researchers have in learning about the starfish and planning its management.

According to seven studies across the Pacific, given a choice, the starfish have, by far, two favorites: rice coral (Montipora) and plate and staghorn coral (Acropora). Although Hawaii has several species of both types, the starfish hasn’t caused much damage here.

If not given a choice, however, such as when corals are scarce and the creatures are starving, they’ll eat any and all corals they can find.

One fact I know about these giant (18 inches across) starfish that wasn’t mentioned in the 2014 report is that they’re beautiful. The color variations are endless, but often the tops of the bodies bear circles of green, red and blue; and the spikes that rise from them often have orange or purple bands. And on its thousands of fat tube feet below, the creature wears pretty yellow socks.

Like sharks and jellyfish, myths about crown-of-thorns starfish live on. And also like sharks and jellyfish, these native species have vital roles in the health of coral reefs. Until scientists know what causes the crown-of-thorns starfish to out-reproduce their coral resources, we should grant the creatures parole.

Crown of Thorns. Courtesy Scott R. Davis

Crown of Thorns. Courtesy Scott R. Davis

A snorkeler adrift in Palau finds underwater rewards

Published November 16, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott

A crinoid walks along the sea-bed in the waters of Palau. ©2015 Susan Scott

A crinoid walks along the sea-bed in the waters of Palau. ©2015 Susan Scott

PALAU >> In some of my favorite snorkeling spots here in Palau, I don’t have to stroke my arms or even move my fins to see vast stretches of coral reef. With Palau’s tidal range of 6 to 7 feet, and two high and two low tides daily, the current along the edges of deep channels is sometimes strong enough that we snorkelers have little choice of where to go. There’s nothing to do then but relax and let the ocean have its way.

Drifting effortlessly above colorful coral reefs is fantastic, but it’s hard to get a good look at a particular organism. By the time I turn around and swim up-current, I’ve often lost sight of what I wanted to look at. Also, there are no handholds to help a person steady a camera. Touching coral is a strict no-no, and it’s almost all coral.

But drift snorkeling has a big plus. Moving water offers free delivery to suspension feeders such as sea fans, soft corals and other wonders. Among those wonders are feather stars, also known as crinoids.

Crinoids (not found in Hawaii) are starfish and sea urchin relatives but have a shape and lifestyle all their own.

Crinoids get to touch the coral. The black, green and orange creatures stand in the open on coral heads, positioning their multiple feathery appendages in the current.

Tiny tube feet tipped with sticky mucus stick out from both sides of each arm. When the moving water brings tiny plants and animals to the crinoid, they get stuck in its glue.

This starts the crinoid’s ingestion assembly line. The outer tube feet flick the food to inner tube feet that cover it in slippery mucus and then deposit the catch in a groove at the center of each arm. There tiny hairs act like conveyor belts, transporting the meal to the creature’s mouth at the center.

Although they can walk and even swim, most crinoids find a spot they like and park there. Because crinoids have rootlike feet, a walking feather star looks a mutant flower searching for a sunnier spot.

Compared with 500 million years ago when they covered the ocean floors, crinoids are rare today. But their fossils are not. Among other places, they’re abundant in the Midwest. Missouri’s state fossil is the crinoid.

Drift snorkeling here isn’t scary because at the end of the channels, the water spreads out and the current stops. In addition, the boat goes with you. Palau’s boat drivers follow snorkelers and divers, so you can get out of the water when you like.

I’m soon starting my second Palau tour as a naturalist for the Oceanic Society, and even though I don’t know what I’ll see, I know one thing for sure. I will go with the flow.

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

©2015 Susan Scott

Hawaii’s starfish protected from fatal wasting disease

Published December 23, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

One of my favorite activities during visits to the Puget Sound area is starfish gazing. At the ferry docks I’m in awe of the orange, purple and red starfish sprawled on the pilings like so many ornaments, and at my husband’s family cabin on Orcas Island, I’m the first to don rubber boots at low tide and splash out on a sea star trek.

Now, sadly, starfish (aka sea stars) are in trouble, and not just in Washington state. From Southern California to Alaska, sea stars of several species are dying by the thousands from a disease called wasting syndrome. No one knows the cause of the mysterious ailment, but the stakes are high. Starfish play a key role in the health of Pacific rocky intertidal zones.

Scientists are hard at work looking for answers, a massive job given the range involved. A key element is mapping the areas affected, a project that requires information gathered from researchers and lay people alike. You can see the affected areas at data.pisco­web.org/marine1/seastardisease.

Wasting disease has not affected Hawaii’s starfish. Because a bacterium or virus is the suspected cause of the starfish illness, being more than 2,000 miles away from the sick individuals seems to be, so far, an effective quarantine.

In addition to being isolated by distance, Hawaii’s mountaintop islands and steep ocean drop-offs offer starfish few shallow marine environments, the preferred habitat of many species. Of the 1,900 or so sea star species in the world, Hawaii hosts only 20 in shallow water and 68 in deep water.

In Hawaii, snorkelers and divers see starfish, but not during every excursion and never by the dozens. Finding a star here is a treat that for me is always worth a stop.

If you pick up a starfish, it’s common to see thousands of the creature’s yellowish, water-filled tube feet, tipped with suckers, extending from grooves on the animal’s underside. You might also see a tan, jellylike mass at the center of the radiating arms. This is the creature’s stomach, turned inside out to digest its meal of a live animal, or the remains of one.

But look fast. A disturbed star quickly pulls its feet and stomach back inside its protective skin, embedded with moveable calcium carbonate rods and plates. (Please return all admired sea stars to the spot you found them, belly side down. The creatures can walk, and even turn themselves over, but it’s slow going and energy-intensive.)

If there’s hope for any beleaguered class of marine animals to make it through a crisis, though, it’s these classic symbols of the sea. Starfish have remarkable powers of regeneration. In addition to releasing sperm and eggs into the water to make new starfish, an adult star can regrow a lost arm, and in some species a detached arm can grow into a complete new starfish.

It’s hard to picture Puget Sound without sea stars hugging the pilings and festooning the tide flats. But with dozens of private and public organizations and individuals teaming up to help researchers on both coasts map and study wasting syndrome, and sea stars’ doing their part with their remarkable powers of regeneration, let’s hope we won’t have to.

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

©2013 Susan Scott

Lacking certainty of harm, starfish should not be killed

Published March 4, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

Crown-of-thorns starfish. ©2013 Susan Scott