Ocean Watch
By Susan Scott
Friday, August 24, 2001
Last week, after a whirlwind trip to Bangladesh, where the time difference from Hawaii is eight hours, I found myself drowsy during the day and wide awake at night. The ocean teems with
light-making animalsMy first day back, I drooped around the house all afternoon, and then when evening came, perked up like it was morning. It seemed a good opportunity to take a night walk on the beach.
The sky was moonless that night, and because the tradewinds had been blowing strong, the surf was up. This made for breaking waves on a jet-black night, perfect conditions for watching the ocean's bioluminescence.
Bioluminescence is the term for the release of light by animals. Where I grew up in Wisconsin, we knew about this phenomenon from fireflies. But it's in the ocean that light-making animals truly shine. There, bacteria, dinoflagellates, jellyfish, brittle stars, worms, mollusks and fish also make light.
When concentrated, this light can be astonishing. While sailing off the coast of Venezuela once, my husband and I heard about an inlet that had extraordinary bioluminescence. After motoring down the long, narrow entrance to the small bay, we anchored and waited for nightfall.
When the last light of day disappeared, we saw that the stories we heard had not been exaggerated. Glowing, green light outlined the entire hull of our boat, and when Craig jumped into the water, the explosion of his plunge made liquid fireworks.
We played in the water for a long time, making "snow" angels and experimenting with arm and leg movements to make psychedelic light trails.
Even getting out of the water was fun. As we stood on the deck, we glowed like fireflies.
The light-making animals in that bay were dinoflagellates, concentrated there by limited circulation. These tiny drifting organisms are part plant, part animal and exist in many shapes and sizes. More than 2,000 species of dinoflagellates live in the world's oceans. Some of these make light.
Dinoflagellates don't have to be concentrated in bays to produce astonishing light shows. I once saw masses of greenish-blue dinoflagellates stuck to the skin of several dolphins riding the bow wave of our sailboat.
The sight was unforgettable.
Why do some tiny dinoflagellates make light? Researchers speculate that dinoflagellate glow is a device for discouraging predators. Small animals called copepods eat dinoflagellates. But when a copepod swallows a flashing dinoflagellate, the light makes a bright spot on the copepod's body.
Copepods that eat blinking green meals don't last long.
Animals give off light in two ways. Some absorb light during the day.
Others make their own light with a chemical reaction involving oxygen. In the case of dinoflagellates, this reaction takes place when the organism is jostled.
Fish and squid have the most highly developed light-producing organs. Some squid not only produce light, but also reflect light of other squid and use flaps of skin as blackout curtains.
When Columbus approached the North American coast, he reported seeing something like "candles moving in the sea." Researchers think these were Bermuda fireworms, which produce green light and swarm near the surface at mating time.
Because most of the organisms that make light move around, seeing them is usually unpredictable. I saw none during my nighttime beach walk, but the randomness of the ocean's light shows is half the fun. I'll keep looking.
Marine science writer Susan Scott's Ocean Watch column
appears weekly in the Star-Bulletin. Contact her at susanscott@hawaii.rr.com.
