Tag Archives: Parrotfish

Extracted teeth tell the tale of a truly extraordinary fish

Published May 9, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
Parrotfish have protruding beaklike teeth, used to bite off pieces of coral rock to get to the algae growing on the surface, or to scrape live coral heads to get to the corals’ soft bodies. ©2016 Susan Scott

Parrotfish have protruding beaklike teeth, used to bite off pieces of coral rock to get to the algae growing on the surface, or to scrape live coral heads to get to the corals’ soft bodies. ©2016 Susan Scott

While snorkeling I found a big, pink parrotfish head bumping along the sand near the shorebreak. The freshly dead fish had such striking teeth jutting from its mouth, I picked it up for a closer look. When I clutched the rolling head, though, my fingers touched the fish’s pharyngeal mill, a special set of teeth embedded in the throat. I knew about this parrotfish trait but had never seen it. So I took the head home. After two days of bleaching, cutting, boiling, drying and scrubbing my apartment of fish smell, I had the teeth free of flesh for examination. It was well worth the work.

In addition to their rainbow-colored bodies, parrotfish resemble parrots in their protruding beaklike teeth, two massive uppers and two lowers, each pair with a gap in the middle. Parrotfish also talk, sort of, making distinct crunching sounds as they bite off pieces of coral rock. Most species eat rocks to get the algae growing on the surface. Other parrotfish excavate hard sand surfaces to get algae stubble so short it’s unavailable to other plant-eating fish.

Still other parrotfish, two in Hawaii, scrape live coral heads to eat the corals’ soft bodies. These parrotfish leave conspicuous patches in the shape of their teeth.

Whether they eat algae or live coral, parrotfish bite off more than they can chew because the nutrients they need are growing on, or living inside, chunks of solid limestone. And that’s where the pharyngeal mill comes in.

Throat teeth AKA pharyngeal mill. ©2016 Susan Scott

Throat teeth AKA pharyngeal mill. ©2016 Susan Scott

This second set of teeth in the parrotfish’s throat works like a coffee grinder. Molars on plates move back and forth, pulverizing the rocks to bits. As the tiny stones move on, the parrotfish’s digestive system extracts the nutrients, churns the rubble into fine sand and expels the grains through the anus.

In addition to their jaw-dropping beauty, these extraordinary fish change sex as needed, sleep in self-made mucus sleeping bags and play a large role in keeping our reefs healthy. Parrotfish bite marks on living coral open up spaces for other animals to settle and grow. Parrotfish also mow the reef’s lawns and supply much of the sand that houses countless fish and invertebrates.

Spearfishers have killed the good-tasting parrotfish to the point they’re now rare in Hawaii waters outside of protected areas. You can help Hawaii’s parrotfish, and in turn our coral reefs, by not spearing parrotfish or ordering them in restaurants.

Of course, without supporting tissue, my parrotfish teeth fell apart. Still, I treasure them. The little mound of teeth now sits on my shelf as a tribute to a truly remarkable fish.

Parrotfish teeth cleaned: Pharyngeal mill (top three pieces). Mouth teeth (bottom four pieces.) ©2016 Susan Scott

Parrotfish teeth cleaned: Pharyngeal mill (top three pieces). Mouth teeth (bottom four pieces.) ©2016 Susan Scott

Creatures show that gender is neither rigid nor constant

Published May 2, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
Most anemonefish are born male and change to female as the need arises. This is a Clark’s anemonefish swimming off Palau. ©2016 Susan Scott

Most anemonefish are born male and change to female as the need arises. This is a Clark’s anemonefish swimming off Palau. ©2016 Susan Scott

North Carolina politicians recently passed a law that requires people in public buildings and schools to use the bathroom corresponding to their gender at birth. When an NPR reporter asked the Rev. Alex McFarland, a North Carolina evangelist, why he supports this legislation, he replied, “This is an issue of natural law … and natural law is the recognition that there are males and females.”

Excuse me, but what natural law would that be? It’s certainly not one of Mother Nature’s. Researchers have discovered hundreds of hermaphrodite fish species in at least 20 families, and marine invertebrate hermaphrodites are so numerable, they’re uncountable. Because animals with both testes and ovaries employ them in such a variety of ways, researchers sort hermaphrodites into three categories: those that permanently have both ovaries and testes, those that start life as males and turn into females, and those that go the other way, from female to male. And given nature, each group has variations galore.

How do these dual-sexed animals reproduce? One can barely count the ways. One example is a kind of sea bass with both testes and ovaries, and it stays that way. This fish doesn’t fertilize itself, but when it meets another of its kind, they both go off, releasing sperm half the time and eggs the other half.

Some deep-sea hermaphrodite fish do fertilize themselves. This doesn’t do much for the gene pool, but it’s handy for keeping the species going when a fish can’t find a mate.

Anemonefish have another tactic. They inhabit anemones in groups of one large male, one large female and several small, immature males. Only the two big sexually mature fish lay eggs and shed sperm.

The little anemonefish in the clan are biding their time. When the breeding female dies, her mate turns into a female, and the largest juvenile matures to become the new breeding male. If the male dies, same thing. A lucky juvenile moves on up.

Some fish that change sex can swing both ways. In Japanese reef gobies, a female in a group becomes male if the dominant male leaves. If a larger male joins the group later, the changed fish reverts to her former female form.

Parrotfish, wrasses, hagfish, lizardfish, sharks, scorpionfish and other fish families all have members of various genders, being male, female, both, in-between, and changing as the situation requires. A heading in my fish textbook says, “When the going gets tough, the tough change sex.” The Rev. McFarland’s belief that there’s a dividing line between male and female organisms on our planet is wrong. In nature, of which we humans are a part, gender is anything but clear-cut.

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.

Parrotfish may be a suspect in the case of the weird blob

Published March 24, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

The Riggins’ blob. Courtesy Heather Riggins

While snorkeling in four feet of water off Kauai’s North Shore, readers John and Heather Riggins found a blob.

John emailed me a slightly blurred photo of it, describing it as “4 to 5 inches in diameter and slightly trans­­parent. It appeared to be pulsating (that could have been from current but nearby algae and sea grasses were not moving). The pulsating made the object appear to be alive.”

John and Heather thought this might be the nighttime cocoon of a parrotfish.

Digging into that subject, I was soon immersed in the extraordinary world of parrotfish where changing sex, manufacturing sand and oozing sleeping bags is all in a day’s work.

Of the 90 species of parrotfish in the world, Hawaii hosts only seven. Of those, three — yellowbar, spectacled and regal — are found only in Hawaii.

Good luck identifying these striking natives.

Parrotfish change colors like Lady Gaga changes hairstyles. A fish’s colors and patterns vary widely in a single species depending on age, activity, surroundings and sex.

To further complicate matters, two parrotfish species occasionally produce hybrids.

And speaking of sex, talk about hormone storms. Some parrotfish females change to males as the need in a population dictates.

Those fish, called supermales, establish territories and keep harems.

Parrotfish are grazers, scraping algae off rocks and dead coral, and sometimes eating live coral. Big parrotfish (Hawaii’s largest, the spectacled, grows to 26 inches long and weighs nearly 15 pounds) have powerful jaws and strong dental plates that remove bits of coral skeleton as they eat.

When snorkeling, you can hear the crunch as nearby parrotfish bite down. Their “beaks” leave distinct marks on the rock.

Parrotfish. Courtesy Scott R. Davis

Parrotfish. Courtesy Scott R. Davis

The stony material that a parrotfish swallows gets ground into fine particles in the fish’s throat, passes through the digestive system and out the anus. In this way, parrotfish are major producers of sand.

Come dusk, some parrotfish make themselves a sleeping bag for the night. Glands near the gills produce mucus that exits through the mouth. It takes a parrotfish about 30 minutes to encase itself in this clear, 3-inch-thick sac that has two holes for breathing.

Researchers believe the cocoon protects the parrotfish from nighttime parasites as well as predators, such as moray eels, that hunt by smell. Come dawn, parrotfish abandon their sleeping bags, which, being made of mucus, dissolve in the water.

I don’t know what’s more remarkable: transgender fish, pooping sand, mucus pajamas or that after all my searching, I still have no clue about the identity of John and Heather’s blob. Help is welcome.

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

©2014 Susan Scott


The shifting times of sand due to people and nature

Published November 10, 1997 in the “Ocean Watch” column, Honolulu Star-Advertiser ©1997 Susan Scott

I received some interesting questions about sand lately.

One reader, an avid spearfisherman, has observed that parrotfish have become pretty scarce around Oahu over the years.

He asks: Since parrotfish make sand, is their decline in numbers decreasing the amount of sand we have on our beaches?

It’s true that parrotfish make sand. Some parrotfish bite off pieces of dead coral rock (limestone) in order to get the algae growing on it. Other species eat live coral, biting into the limestone skeletons that support the living coral animals. Still others eat algae growing on the surface of the sand, swallowing some sand in the process.

Special bones in the fish’s throat grind up both food and coral rock. The food gets used by the fish’s body; the ground-up coral gets discharged through the anus.

If you go to places where fish are protected, it’s easy to watch both ends of this process in action. While snorkeling in the sanctuary waters of Midway Atoll recently, I watched enormous parrotfish (2 feet long) take noisy bites from living coral.

With loud crunching sounds, they scraped their beaklike teeth over the surface of coral heads, leaving characteristic tooth marks.

At the same time, passing parrotfish excreted clouds of fine, white sand that fell to the reef floor.

So. We know parrotfish make sand. And we also know that fishing has depleted parrotfish stocks in many unprotected areas of Hawaii. It seems obvious then, that a lack of parrotfish means significantly less sand for Hawaii’s beaches.

However, it’s not true. And that’s because ground-up coral makes up such a small proportion of Hawaii’s white beach sand.

In many cases, tiny seashells called foraminifers compose 50 percent of the grains on a Hawaii white sand beach. The other components are snail shells, coralline algae pieces, sea urchin and starfish shells and, running a distant fifth, coral fragments.

In rare cases, at its most concentrated, coral makes up 20 to 25 percent of a white Hawaii beach. On the average local beach, however, the number is less than 10 percent.

So where is all this sand that parrotfish produce?

On the ocean floor. Much of the ground-up coral that comes from parrotfish is so fine and powdery, it rarely reaches shore. Rather, most of it falls into cracks and channels and remains near the reefs.

So, in answer to my reader’s question, depletion of parrotfish doesn’t do much to Hawaii’s beaches, but it does lessen the amount of sand found in and around our reefs. Thus, these fish play an important role in the health of Hawaii’s coral reefs.

Another reader wants to know if the beaches off Aina Haina were ever sandy.

Probably not, at least not since humans have been here.

The Wailupe Peninsula, a residential site seaward of Aina Haina, was once an enormous fishpond.

Ancient Hawaiians built their fishponds in areas where freshwater mixed with salt water, usually meaning some silty runoff from the land. Such conditions often produce muddy shores rather than sandy beaches.

This is true also of Waikiki, where the white sand beaches are mostly man-made.

Sand is periodically trucked there to replace that which is carried away both by water and people.

Beach changes often occur through human interference, but some changes are natural.

During my last trip to French Frigate Shoals, a pristine atoll in Hawaii’s northwest chain, I was shocked to find one of my favorite islands, Whale-Skate, completely gone.

Biologists there assured me it would be back in its own good time, that is, at the whim of ocean currents.


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