Almost all divers here in Hawai‘i have seen large schools of manini, as they are the most-common fish that lives in shallow water. But most divers do not know how important this fish is to the entire marine ecosystem. The coral reef is a very fragile part of the ocean, and many creatures are needed to help keep it healthy and in balance. Large schools of tangs and surgeon-fish are needed to maintain this balance.
Convict tangs feed on algae that grows on the reef. This algae competes for space on the reef with the corals. The schools of manini graze on the algae, but never completely eat it all, because they feed in the surf, so the waves move them around the reef. This does not give them time to feed in any one spot for long. This keeps the algae short but does not kill it. This is good because other fish on the reef like the little gregory actually farm algae and have their own personal algae garden they protect from the manini by chasing them off when they get near their established home farm. This constant battle between the manini schools and the gregory fish keeps the algae in balance and gives room for the corals to grow.
Without the convict tangs the algae would take over the reef and no corals would grow. The parrot-fish eat live coral and poop out the hard calcium carbonate skeleton of the coral, which washes ashore and makes our beaches. So the manini keeps the algae short so the coral can grow and the parrot-fish can make our famous white, sandy beaches for us to enjoy. Everything in nature is based on the balance between living systems, and this is due to the fact that the Earth is spinning, so nothing ever stays the same!
Manini are usually seen in large schools because their convict stripes confuse predators when the school moves together as one unit. It is hard for a predator like an ulua to single out one manini to try and catch because the moving school of fish causes an optical illusion of which a single fish is hard to see. At nighttime the schools of manini break up and each fish goes its own way to find a place on the reef to sleep. The main predator of the convict tangs is the moray eel, which finds them sleeping by themselves at night.
“Manini” in Hawaiian means “stringy,” and more than likely the name is describing the texture of the meat when the fish is caught for food. Baby manini live their lives in tide pools in small schools, often with baby mamo or sergeant fish that look very similar.
You can see the manini in action in the underwater educational movie “The World’s Guide To Hawaiian Reef Fish” at www.underwater2web.com. I have an entire underwater marine-life series coming out soon for school and tourists education. You can follow my marine-life post on Instagram just under my name.
Terry Lilley is a marine biologist living in Hanalei. He is 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 Hawai‘i go to reefguardianshawaii.org.