Wildlife Conservation Article on Bioluminescent Bays

Tom Verde wrote:

The first thing you notice is the wake - a luminous, emerald path of foam lingering below the stern. There are other boats here on Mosquito Bay at night, but you can barely see them- only their wakes, glowing like the lights of distant cities. Suddenly, thereís a flash of the bow. A startled porgy bursts through the water, leaving a cometlike trail. Then another. And another. Soon the water explodes with porgies, mullets, and halfbeaks in an underwater fireworks display

Its biological classification is no longer a mystery, but just why Pyrodinium flashes is a puzzle that scientists have not yet been able to definitively solve.

"The function is not well understood," says Paul Dunlap, a specialist in bioluminescence at the Woods Hole Oceanographic Institute in Massachusetts. "In other bioluminescent organisms- certain fish, for example we know they use it to attract prey or mates. Or to scare off predators."

Dunlap and most other scientists suggest that the later explains why dinoflagellates are bioluminescent. Some think that the organism flash as a "direct" warning to predators. Then there is also the "indirect" theory thet they are signaling their predatorís predator.

"Mosquito Bay is surrounded by mangroves, and as you can see, their roots reach down into the water, " she says, panning the floodlightís beam across the tangled rows of vegetation. As the roots and fallen leaves of the mangroves decompose, scavenging bacteria produce vitamin B12, an essential nutrient for the dinoflagellates.

Because of the opening to the sea is narrow, Grasso explains, B12 and other nutrients stay in the bay rather than being flushed out to sea. The shallowness of the bay means that the evaporation rate is high. With evaporation, the surface water becomes saltier and sinks to the bottom. This heavier water moves out to sea, leaving populations of Pyrodinium thriving at the surface.

Itís a delicate balance. Alter the channel, and the exchange rate of water is thrown off; disturb the mangroves, and B12 source is imperiled.

"These conditions are rare," Grasso says. "People say there maybe six or seven places like it in the world."

There used to be more. New Providence Island in the Bahamas had a bioluminescent bay, until its opening to the sea was widened and the dinoflagellates population declined. A bioluminescent bay in Hawaii suffered a similar fate. Others in the Caribbean have been lost due to industrial or boat pollution, the cutting of mangroves for charcoal, the overgrazing by cattle of nearby fields, which produces water-clouding runoff, and the increase in artificial lights, which reduces the phenomenonís brightness, according to Barabara Bernache Baker, a retired biologist who has worked hard to preserve the Mosquito Bay.

"La Paguera used to be the most spectacular bay," says Eduardo Cintron, a marine biologist with Puerto Rican department of natural resources. Now itís "one-tenth as bright as Mosquito Bay."

Aside from being aesthetically offensive, decomposing garbage could threaten the bioluminescence. Marine biologist Timothy Goertemiller of Smithsonian Institutionin Washington, D.C., ... says "that while the mangroves may filter some waste, or fertilizers," he explains. "Household garbage could do it too."

Since Pyrodinium are known to be sensitive to change, such chemical imbalances could imperil the population. Grasso sees gasoline and oil from power boats as another threat.