Almost everyone who has gone on a snorkel here in Hawai‘i has seen pohaku puna, the giant lobe coral. But most people can’t actually recognize this very-common coral species.
Some of the lobe corals are hundreds of years old, and can grow as big as a car. But they have adapted to Hawaiian waters quite well, and have many different shapes and colors. The lobe corals look a lot like the giant mound corals, but they are a bit more smooth on their surface, whereas the mound corals are more knobby. They can both be the exact same color and grow side by side.
Pohaku puna is so diverse in shape and color we have had to do DNA tests on Kaua‘i to be sure it was a lobe coral. This coral species can grow flat on the rocks out in the surf and only be an inch tall and bright yellow, or it can grow to 10 feet tall in a calm lagoon and be a tan color. For years these two variations were thought to be totally different corals, but DNA test proved them to be the same coral that can grow completely different in different marine environments!
The color of the coral is caused by the color of the algae that grows within the clear coral polyps. Each giant pokaku puna is like an apartment complex that is made out of a hard calcium carbonate structure, much like concrete. There are thousands of small, soft coral animals that live in the complex, and when they die a new, hard complex is built on top, making the coral larger.
Over time this coral species can form an entire coral reef which is home to millions of marine-life species, just like a large city on land is home to millions of people.
These corals need to live in shallow water where they can receive constant sunshine. The soft, clear coral polyps grow algae within their tissue that produces sugars through photosynthesis, and this helps feed the coral animal. The algae in the coral tissue gives the coral its color. The coral polyp also has tiny stinging tentacles it uses to filter feed plankton from the surrounding water. If pohaku puna is growing in the shallow surf it may grow a yellow algae, but if it is growing in a deep, calm lagoon it may grow a brown algae. Just like on land, certain plants do better with direct sunlight and others do better living in the shade.
If you have a garden at home and you have to remove many weeds or your plants die. You remove them to grow new plants. The butterfly-fish does the exact same thing for pohaku puna. The fish eat the dead or dying coral animals and algae, which makes room for new corals to grow so the entire coral colony can remain healthy. The Hawaiians named the butterfly-fish “kikakapu,” which means “strongly forbidden,” because they know if you removed the butterfly-fish from the reef the corals would die because they would loose their gardener! This is why you find lots of butterfly-fish on a healthy coral reef.
The main thing that can kill the large pohaku puna growing out on our reefs is mud or toxic runoff that covers the surface of the coral complex. Just like in your garden, if it gets covered in mud, the plants will die because they can’t receive any sunlight. This is why it is so important to do construction projects on land that do not cause red dirt to flow into the sea, and we also use nontoxic chemicals in our farmlands. We also have to clean up any cesspools and sewage leaks that go out onto the reef because the nitrates from these pollutants cause bad algae to grow on top of the coral, smothering it.
You can see pohaku puna on my web page, www.underwater2web.com, and also go to the species-identification link to learn what all of our coral species look like with all of their variations.
•••
Terry Lilley is a marine biologist living in Hanalei Kaua‘i and co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawaii go to www.reefguardianshawaii.org.
