Tag Archives: algae

Weird Palau find offers a lesson in flora, fauna

Published March 4, 2017 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2017 Susan Scott

More than 2,000 tunicate species are found throughout the world, with at least 45 varieties found in Hawaii. Pictured are the green barrel sea squirt variety found in waters off Palau. ©2017 Susan Scott

I’m home from my snorkeling trips to Palau and Yap, and in sorting through my pictures, I came upon a favorite: something so new, I didn’t know whether it was plant or animal. When I showed the real thing to our knowledgeable Palauan guide, he didn’t know either, but guessed it was a kind of alga.

Soft, thimble-size barrels with pores in them didn’t look like any alga I had ever seen, but then, some weird plants grow in the world’s oceans. One common one looks like a small Japanese glass float that filled up with water and sank to the bottom. Some call this one-celled seaweed bubble algae. (Singular is alga, but no one calls it that.) I prefer its more colorful common name: sailor’s eyeball.

After a few tries of describing my mystery organism, Google came up with “green barrel tunicate, scientific name, Didemnum molle” with a photo that matched mine.

Over 2,000 tunicate species are found throughout the world, with Hawaii hosting at least 45.

Years ago, in a zoology course at UH, I learned that these filter feeders have baglike bodies with two openings. One draws water in with tiny beating hairs, and the other directs water out. This human-heart-type image was the picture I had of all tunicates.

But like so many marine invertebrates, tunicates come in various forms. Some exist in colonies, where their bag bodies join at the base. The colonies can spread over coral and rocks in matlike patches with lots of inhalant and exhalant holes for sharing food. Often this spreading, combined with brilliant colors, makes some colonial tunicate species look like sponges.

The barrels in my photos are not visibly attached to one another, but runners creeping along the rock base connect individuals and give rise to new ones.

An individual green barrel sea squirt, also known as the tall urn ascidian (a class of tunicate), can grow to 4 inches in diameter in deep water. Shallow-water communities, such as those in my photos, are less than an inch wide.

The green tinge comes from a bacterium that lives in the tunicate’s tissues. Although not technically a plant, the bacteria produce oxygen, essential to the tunicate, the same way plants do, through photosynthesis. In this symbiotic relationship, the sea squirt produces a chemical sunscreen that protects its bacteria from UV radiation.

I’m not discouraged about not knowing those little barrels were sea squirts, or that I have surely incorrectly identified some tunicates as sponges. Learning new facts about the marine world is the thrill that keeps me dunking my face in water until it hurts.

Now I need to learn another fact: how one tells a tunicate from a sponge.

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