SAN DIEGO, California (25 Sep 2003) -- It's as if the ocean is blushing. For the past few weeks, the waters off much of Southern California have turned a strange brownish-red. The sea isn't sick. It's a phenomenon known as red tide – a sudden overpopulation of phytoplankton or algae, microscopic plant cells crucial to the oceanic food chain. The species of algae causing the current red tide or algae bloom is not harmful to humans, said Greg Langlois, a marine biologist and biotoxin expert for the state health department. However, public health officials have received anecdotal reports from swimmers and surfers who attribute allergy-like symptoms – eye and throat irritations – to their exposure to red tide, he said. Swimmers and surfers also say the red tide gives the ocean a more pungent odor and taste. The crimson sea will eventually return to its normal hue. The red tide is likely to disappear with the next big storm because this type of algae is very sensitive to turbulence, said Peter Franks, a professor with the Scripps Institution of Oceanography. "We've had a lot of really dense red tides in the past 10 years, but this is one of those off-the-charts red tides," he said. Scientists have yet to figure out what combination of natural processes triggers a red tide. Statistically, more occur between May and September, but they can happen at any time. "The plankton community becomes dominated by one or a few species at extraordinarily high concentrations," Franks said. "It's certainly possible that the growth of the cells is fueled by nutrients brought to the surface by upwelling." | | Upwelling is a wind-driven process in which colder, nutrient-rich water far below the surface mixes with warmer water at the top of the water column. It typically causes the surface water temperature to drop dramatically. The current algae bloom off Southern California is dominated by a species called Lingulodinium polyedrum, which illuminates like a firefly when it is jostled. Such plankton that glow with the flow are known as dinoflagellates. Why do they light up? The most obvious reason is that it may ward off predators. However, the illumination may also act as a sort of burglar alarm in which the flash allows a third-party predator to eat whatever has preyed upon the plankton. "Swift justice," Franks said. A playful scientist, he likes to gather samples of red tide water in clear jars, then, after dark, swirl the containers to watch the blue glow. For more devilish excitement, Franks adds vinegar to the bottle to get an especially bright flash. The acidic vinegar kills all the plankton, however. The plankton bloom affects some types of fishing. Marlin anglers say the discolored water makes it very difficult for their lures to work. Also, the thick plankton blooms have kept scuba-diving enthusiasts from exploring the shallow, rocky reefs such as those at La Jolla Cove. But the bioluminescent plankton make night diving spectacular, dive master John H. Moore said. "If you turn off your lights and wave your hands around in 10 feet of water, the light display is unlike anything that exists above water," he said. "You're surrounded by sparkling blue lights, zillions of them. It's absolutely phenomenal." SOURCE - Union Tribune |
