Ocean Watch

Susan Scott

Friday, March 19, 2004

Hanabatas of the
ocean link food chain

Let's talk about mucus. I know it's disgusting, but marine life is full of the slimy stuff and some researchers just love to study it.

In a recent investigation on Australia's Great Barrier Reef, a team of scientists found that every square yard of coral there produces about a gallon of mucus a day. Some dissolves and becomes an important food source for the ocean's natural bacteria, a basic link in the marine food chain.

The rest forms sticky, drifting spheres that trap tiny plants and animals. The weight of these organisms causes the slime balls to sink to the bottom, where they become meat-and-veggie meals for bottom-dwelling animals, including corals.

Using mucus to trap food is a common strategy in the marine world, but when it comes to slime, nothing beats hagfish. Also called slime eels, these cold-water bottom fish are the monarchs of mucus, famous for excreting massive gobs of gunk when alarmed, like when they're caught in traps.

The decks of hagfish boats must look like scenes from "Alien," but for some anglers the mess is worth it. People in Korea eat about 5 million pounds of hagfish per year, and in Japan broiled hagfish is a treat called anago-yaki.

Also, the tough skin of hagfish makes good leather. Products from it are usually sold as eel skin.

Fishers in the Atlantic and Pacific oceans often catch hagfish using so-called Korean traps. These plastic tubes have conical covers on the ends, each bearing fringes that allow hagfish to swim in but not out.

Hawaii beachcombers are familiar with these black trap parts, shaped like porous dunce caps, because they frequently break loose and wash ashore.

Other mucus in the news has to do with cleaner wrasses. These colorful little fish hover in specific areas of the reef waiting for fish clients burdened with skin parasites. When such a fish drops in, it allows the wrasse to eat pests off its skin.

Sometimes, however, cleaner wrasses also nip a bit of mucus from a fish. Because mucus coating reduces a fish's drag, and is therefore of value, mucus snatching angers the customer fish. When this happens, it either chases the wrasse from the area or moves to another cleaning station, never to return.

Researchers wanted to know why these wrasses would hazard losing a client, and therefore a full meal, for a sip of slime. Turns out, they do it for the same reason most of us would rather eat candy than carrots: It tastes better.

To learn wrasse motives, biologists gave cleaner wrasses their choice of mucus, worm parasites or crustacean parasites called isopods. The wrasses always liked the worms, but when faced with a choice of crustaceans or mucus, they chose mucus. To a cleaner wrasse, mucus is apparently a delicacy worth the risk.

To most of us, however, it's just gross. This slippery mixture of protein (called mucin in vertebrates), water and inorganic salts is sometimes hard for the most professional of people to embrace, even in strictly clinical conditions.

"I should never have been an anesthesiologist," a friend of mine sighed one day after work.

"Really? I thought you liked your job," I said.

"Oh, the work is fine," she said. "It's the mucus I can't stand."

Marine biology wouldn't be her next best choice.

See the Columnists section for some past articles.

Marine science writer Susan Scott can be reached at


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