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Thursday, October 23, 2014         

OCEAN WATCH


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Organisms stage light show by employing bioluminescence

By Susan Scott

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During a recent nighttime outing at Kualoa Beach Park, reader Alan Chun had a glowing experience. He e-mailed, "We were on a crab hunt and when we turned off our flashlights we saw little sand-grain-sized glowing specks washing up with the gentle waves. Any idea what they are? They had a greenish/yellow glow."

A huge number of marine organisms make light one way or another, in oceans shallow, deep, warm and cold. This Kaneohe flasher was probably a dinoflagellate, a one-celled organism that can be viewed as either a plant with two spindly legs or an animal that grows its own food.

Most dinoflagellates are too small to see with the naked eye, and others look like specks. What they lack in size, though, they make up for in mass. The world's oceans teem with dinoflagellates, and in that, they carry a lot of weight on their shoulders (if dinoflagellates had shoulders). These kicking, solar-powered organisms that straddle the plant and animal kingdoms are a vital link in the marine food chain.

Some dinoflagellates are homebodies (the algae in corals are dinoflagellates), but most are drifters, wandering the oceans as plankton. Dinoflagellates are also the rascals that under certain conditions create poisonous red tides.

Not all dinoflagellates light up but some do so famously. One is called Noctiluca -- "night shiner" in Latin. When waves, boats, people or predators bump Noctiluca (or other light-making dinoflagellates), a temporary dent occurs on the cell's surface. That dent sets off a chemical reaction inside the cell, causing a flash of light lasting about one-tenth of a second.

This might look like a twinkle to us, but to other plankton it's a flashbulb in the eyes. The burst of light might frighten predators or attract potential mates, or it might play a role known only to dinoflagellates.

Sunshine determines the intensity of the nighttime sparkles. When a dinoflagellate basks on a sunny summer day, its spark that night will be brighter than when it spends a short winter day under cloudy skies.

Lakes and rivers have few light makers (only one limpet and a few insect larvae) because the ocean had a better evolutionary recipe for light making than bodies of fresh water. Since ocean water is clear, organisms can see each other, and oceans are so deep that countless creatures live in perpetual darkness. Give oceanic currents a few billion years to stir predators, parasites and prey together in this clear, deep salt water, and you get a stew full of sparkles.

Bioluminescence, or "living light," is a wonder of the world. The organisms illuminate dolphins' routes when they race toward my sailboat, and stick to the dolphins' skin like fairy dust as they ride my bow wave.

I have anchored in bays so ablaze with bioluminescence I could see fish darting around the boat. Recently, in such a bay off Baja, I got in my dinghy and drove around denting billions of dinoflagellate cells. They gave me a light show to die for. And if I can talk a crew member into swimming off the boat (it's cold in there at night!), the glittering green sea angels a person can make in the water put snow angels to shame.

Hawaii's dinoflagellates sometimes bloom bright, but since our islands are in the middle of the Pacific Ocean where we have excellent circulation, they soon spread out. That's why sometimes our bays and beaches put on light shows and other times they're dark.

That's part of the fun of Hawaii's nighttime ocean. Like Alan at Kualoa, you never know when you're going to have a glowing experience.

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Susan Scott can be reached at www.susanscott.net.






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