SANTA CRUZ, CA--In nature, there's no accounting for taste. New research shows that a common type of marine algae may prefer urea, an organic nitrogen compound found in urine and in agricultural and urban runoff, over inorganic fare such as ammonium and nitrate that occurs naturally in the ocean. When excess nutrients cross their paths, these single-celled organisms, called dinoflagellates, can grow into potentially toxic blankets of algae commonly known as red tides.

The new findings, published in the current issue of Aquatic Microbial Ecology, suggest that urea in urban and agricultural runoff may play a greater role than previously thought in triggering or sustaining harmful algal blooms found growing off California's coastline.

"The particular bloom we looked at, which extended from the upper Baja peninsula in Mexico to the Monterey Bay, occurred after heavy urban runoff events in the southern California region," said Raphael Kudela, assistant professor of ocean sciences at the University of California, Santa Cruz. "Our data suggests it was probably triggered by the increased concentration of urea introduced to the ocean by urban runoff," Kudela said.

Kudela and coauthor William Cochlan of San Francisco State University's Romberg Tiburon Center for Environmental Studies examined the physiology and ecology of the bloom, which occurred in 1995 and was the largest and most widespread red tide found off California's coast since 1902. Though marine scientists usually monitor marine ecosystems for high concentrations of common inorganic nutrients known to spur harmful algal blooms, urea is generally ignored, the researchers said.

Previous studies have shown that urea can nourish the growth of dinoflagellates under laboratory conditions. The new study shows for the first time, however, that the naturally occurring red-tide dinoflagellate responsible for the 1995 bloom--known scientifically as
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Contact: Tim Stephens
stephens@cats.ucsc.edu
831-459-2495
University of California - Santa Cruz
23-Feb-2000