Antler corals in Hawai‘i are some of the most beautiful coral species that can grow to about three foot tall and are usually brown, golden or green colored, but in one location on Kaua‘i they are bright yellow.
This stunning coral has branches that grow upwards, and they start out as a single, floating coral polyp that looks like a soft, upside-down jellyfish. The tiny, fertilized coral polyp swims in the open ocean, then finds a place on the reef to attach and start growing. The soft polyp needs protection so it builds a hard calcium-carbonate home to keep it safe just like us humans build a hard concrete building to keep us safe. After the coral polyp builds its hard, stony home, more coral polyps are produced, and they build their homes on top of the original coral polyp, producing a coral colony that grows upwards. After about 20 years this coral colony can be three feet tall and house hundreds of thousands of coral polyps, much like a giant apartment complex us humans might live in.
The calcium-carbonate coral skeleton is white in color and the coral polyps are clear, but out on the reef the antler corals all have colors from brown, green to the unusual Kaua‘i yellow antler coral. These colors come from an “algae garden” the coral polyps grow in their tissue. The algae produces sugars and other byproducts through photosynthesis which help give the coral food, much like us humans would grow a vegetable garden to supplement our need for food. Antler corals need to grow in shallow water from three feet deep to about 60 feet deep so they are close to the sunlight of which the algae needs to photosynthesise. The coral polyps also collect food with their soft, movable, stinging tentacles they use to filter feed in the saltwater currents.
Most antler corals grow green or brown algae in their tissue, but for some reason the Kaua‘i antler corals at ‘Anini Beach grow yellow algae and are extremely beautiful to look at. Our nonprofit Reef Guardians Hawai‘i puts on a Coral Reef Summer Camp for kids, and we have been visiting these yellow antler corals since 2016 when they started to grow, and some of the corals are over two foot tall, which is an unusually fast growth rate for a coral. Over 100 of these antler corals in one part of the lagoon at ‘Anini are all yellow, whereas the rest of the antler corals on Kaua‘i are green or brown.
As scientists, we are finding new discoveries all of the time about coral health and growth and the super-fast-growing Kaua‘i yellow antler corals are quite a mystery. The kids in our marine-science camp are getting to measure and track the growth rate of these corals, and one day we will unlock the mystery to their unusual color.
The public can help out with our nonprofit coral-reef research project and school educational program by becoming ambassadors for the coral reef. You can find some information about the program reefguardianshawaii.org.
You can also follow our daily marine life educational program on Reef Guardians Hawaii Facebook page.
Terry Lilley, author of The Critter Of The Week, is a marine biologist living in Hanalei, 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 reefguardianshawaii.org.