Monthly Archives: February 2016

Wrasses and parrotfishes are good for our coral reefs

Published February 29, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
The humphead wrasse is a friend of coral and eats crown-of-thorn starfish. ©2016 Susan Scott

The humphead wrasse is a friend of coral and eats crown-of-thorn starfish. ©2016 Susan Scott

At Hanauma Bay I often see and hear parrotfish chomping on living coral, their beaverlike teeth leaving distinct scars in the coral head’s skeleton. This can’t be good for the coral, yet natural populations of parrotfish are essential to healthy reefs.

To look into how this works, I found a 2014 study on the roles of parrotfish on tropical reefs. But as often happens when delving into the intricacies of marine systems, I got sidetracked by something unexpected: “The most corallivorous (coral eating) of all parrotfishes,” the researchers wrote, “is the bumphead wrasse.”

What? Are the terms “wrasse” and “parrotfish” interchangeable in Brazil and Australia, the authors’ home bases? No. The writers made a mistake in calling the coral-eating bumphead parrotfish a wrasse. But wrasses and parrotfish are so closely related, and regional common names vary so widely, it’s easy to get them mixed up.

The wrasse family has 450-some species, including one that grows 6 feet long called the humphead wrasse. The giant fish’s other names are Napoleon wrasse, Maori wrasse and Cheilinus undulatus.

The parrotfish family has about 100 species. The biggest at about 4 feet long is the bumphead parrotfish, or Bolbometopon muricatum.

Hawaii hosts 45 wrasses and nine parrotfishes but neither of the above giants.

The International Union for the Conservation of Nature lists the humphead wrasse as endangered and the bumphead parrotfish as vulnerable, because they’re slow-growing and overfished in most places. I’ve been lucky. I’ve seen the fish in French Polynesia, in Palau and at the Great Barrier Reef, but only in protected areas.

You can easily tell the fish apart by their lips: The humphead wrasse has large, plump lips. The bumphead parrotfish barely has lips at all, just skin stretched tight over jutting, fused white teeth.

But back to my original inquiry. Except for the bumphead parrotfish and a few other parrotfishes that eat live coral, most parrotfishes eat algae growing on dead coral rock. While feeding, the fish bite off pieces of old calcium carbonate skeleton, digest it into tiny pieces and expel it as sand.

Algae-eating parrotfishes, therefore, not only help keep algae growth in check, but also load reef floors with clean white sand. Even though the humphead wrasse doesn’t eat algae or manufacture sand, it’s still a friend of coral. The big fish eats, among other things, crown-of-thorn starfish.

A friend recently asked whether I ever run out of column topics. Never. Marine life is so interconnected that looking up a subject is like wandering a maze with a treat at each turn. And the subjects are virtually endless.

Common name for this fish is in need of an origin story

Published February 22, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
The Moorish idol is an omnivore that has a relatively large brain. Courtesy Russell Gilbert

The Moorish idol is an omnivore that has a relatively large brain. Courtesy Russell Gilbert

While snorkeling I recently saw five Moorish idols zipping along from one coral head to another. With their triangular body shape and black-and-yellow markings, the 8-inch-long fish reminded me of the traffic signs warning drivers of a possible animal encounter: CAUTION: MOORISH IDOL CROSSING.

Watching the perky fish commute made me wonder where they got that odd name. If Moors are a historical Muslim group, and if “idol” is taken to mean a false god, the name Moorish idol for a fish seems offensive. But looking into the name on the Internet opened a can of worms. The Hawaiian name, kihikihi, was easier. It means angular, curved or zigzag.

The Hawaiians chose this versatile word to describe three fish, the Moorish idol, kihikihi; hammerhead sharks, mano kihikihi; and threadfin jacks, ulua kihikihi. The Moorish idol’s scientific name, Zanclus cornutus, is also straightforward. The first name comes from the Greek “zancion,” meaning sickle, referring to the white, sickle-shaped filament that trails behind the fish’s upper fin. Because of this long fin, people often mistake Moorish idols for angelfish or butterflyfish. They are not related. The Moorish idol is its own unique family of one.

The species name, cornutus, comes from the Latin “cornut,” meaning horn. Adult Moorish idols have a tiny hornlike spine in front of each eye, larger in males.

Along with surgeonfish, Moorish idols are the Einsteins of reef fish, having large brains compared with body size. Both fish families need high IQs because they’re roving omnivores without harems and therefore must distinguish colors, shapes and patterns to find food, mates and places to hide from predators.

After learning verifiable facts about the Moorish idol, I returned to my search of its name. A Wikipedia entry said the Moors of Africa believed the fish brought happiness, but with no reference cited, the statement is void.

I read nearly endless opinions, conjectures and rants about the word “Moor” and settled on academia, the Oxford Islamic Studies Online website. Moor, the authors write, is a medieval term once used to describe dark-skinned Muslims of Arab or Berber decent who invaded Spain in 711. The origin of the term is uncertain, but it probably meant people from Mauritania or Morocco.

So the name Moorish idol might indeed be insensitive. Or not. I went again with Oxford and read their dictionary’s second definition of idol: “a person or thing that is greatly admired, loved or revered.”

Could this mean the name might have come from early Moroccans who greatly admired the fish? Not likely. Moorish idols are found only in the Indian and Pacific oceans.

Some fish enjoy the perks of a committed relationship

Published February 15, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
Hawaii divers have plenty of opportunities to see synchronized swimming butterflyfish: Of the 25 species of the fish in isle waters, at least a dozen are known to live in pairs. Courtesy Russell Gilbert

Hawaii divers have plenty of opportunities to see synchronized swimming butterflyfish: Of the 25 species of the fish in isle waters, at least a dozen are known to live in pairs. Courtesy Russell Gilbert

Last week I watched two fourspot butterflyfish glide around a coral head so close together they were almost touching. Was this a male and female? I wondered. Whenever I’ve seen two butterflyfish together, I’ve always assumed they were male and female, but to what end? Because butterflyfish release their eggs and sperm into open water, these parents don’t have to feed or protect eggs or offspring.

So with plenty of fish in the sea, as they say, and the kids drifting off before they’re even born, what’s the advantage of lifetime liaisons?

It’s clearly a benefit in some butterflyfish species. The world’s coral reefs host about 130 kinds of butterflyfish. Some hang together in schools; others live solitary lives. But at least 78, or about two-thirds, form pairs.

My idea that butterflyfish couples are male and female is mostly accurate. Researchers haven’t studied each species yet, but they have looked at the behavior of some that live in pairs.

One benefit to being a fish couple is that no romancing is required. Neither male nor female has to waste energy searching for a partner or performing elaborate courtship rituals. In one butterflyfish species, couples swim to the reef’s outer edge to spawn during periods of strong tidal currents. This sweeps the precious sex cells away from the reef’s many plankton eaters. And that’s that. The two go back to eating, while trying to avoid being eaten themselves. It’s here that monogamy has other perks. Butterflyfish have varied diets. Some species eat tiny shrimp and crabs, others prefer plankton and many graze on the soft bodies of live corals. One theory about butterflyfish pairing is that when it comes to finding shrimp and crabs hiding in sand and reef cracks, four eyes are clearly better than two.

Another notion is that because the minuscule animals and corals that certain butterflyfish eat live scattered across large areas of the reef, the fish have to travel far and wide to dine. Such roving prevents a male from creating and guarding a harem. But a monogamous male doesn’t have to. He simply keeps his female with him.

Researchers have also noted that some couples watch each other’s back. While one nibbles, the other functions as lookout, signaling when to flee from an approaching predator.

Of Hawaii’s 25 butterflyfish species, at least 12 live in pairs, giving us snorkelers and divers lots of chances to watch synchronized swimming in fish. It’s a marvelous sight to behold, two bright fish waltzing together in matching outfits of yellow, black and white, with the occasional blue or orange accessory. And that may be another reason some butterflyfish pair up. They love ballroom dancing.

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.

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