Researchers have measured critically low oxygen levels in King Harbor after a massive die-off in the Redondo Beach marina.
Brent Scheiwe, program director at the SEA Lab in Redondo Beach, said he took dissolved oxygen level readings in the harbor after the first reports of the dead fish came in Tuesday morning and found them at almost zero.
“The levels were critically low," he said. "There was pretty much no oxygen in the water."
Scientists are working to determine what caused oxygen levels to drop so steeply that fish estimated to be in the millions suffocated and deposited a silver sheen of carcasses, many of them sardines, among the rows of docked boats. It may be days before the precise cause is known.
Marine biologists at USC installed oxygen sensors in King Harbor after an algal bloom caused a mass fish die-off in 2005. They are now probing the harbor for clues about the cause of the latest kill, said biological sciences professor David Caron.
“What we're trying to tease apart is whether it's a consequence of algal buildup, a fish buildup or something toxic in the water,” Caron said.
Massive, stinking fish kills also struck King Harbor in 2003 and 2005. Both times, algae blooms robbed the harbor waters of life-enriching oxygen, causing fish to suffocate and die.
Despite efforts by boat owners to scoop up the dead fish, the rafts of decomposing flesh unleashed a powerful stench that plagued the harbor for weeks after each episode. Some boat owners complained of feeling sick from the smell. Others were driven off their boats to seek refuge inland. Waterfront restaurants suffered steep declines in customers, unable to compete with the unsavory odor that hugged the harbor.
Such fish kills have been popping up around the world in what one Louisiana scientist calls “dead zones.” She has spent a career studying America’s largest one, which strikes nearly ever year in an expanse of the Gulf of Mexico about the size of the state of New Jersey.
The cause of the die-off is nearly always decaying algae. Although the oceans are awash in algae, these microscopic organisms bloom when fed by nutrients such as fertilizers and human and animal waste washing off the land. Stoked by such nutrients and exposed to sunlight, algae flourish and then die and sink to the bottom. Bacteria then take over, breaking down the plant matter and sucking the oxygen out of seawater. That leaves little or none for fish and other marine life.
Robert Diaz, a professor at the Virginia Institute of Marine Science, and other scientists have identified hundreds of these around the world, choking the life out of harbors, bays and estuaries.
Writing up a report to Congress last September, Diaz found that nearly half of U.S. bays, estuaries and other waterways surveyed have suffered from low-oxygen dead zones. These episodes do not necessarily happen ever year. They strike when the conditions are just right.
The episode in King Harbor follows unusually heavy rainfall in Southern California, which washed lawn fertilizer, dog droppings and similar nutrients into coastal waters. Algae have begun to bloom along the coast as the days grow longer, providing needed sunlight. Recent winds have further enriched waters by stirring up nutrients that these tiny plants need from deeper waters.
Scientists believe such dead zones will increase as ocean waters continue a warming trend in a changing climate. Warmer waters prompt faster biological growth, just like molds and bacteria will more quickly devour food left out of the refrigerator.
Some scientists, such as Jeremy Jackson at Scripps Institution of Oceanography, have suggested the oceans are reverting back to primeval seas of millions of years ago, when algae, bacteria and jellyfish ruled the oceans. He playfully dubs this the “rise of slime.”
- Tony Barboza and Kenneth R. Weiss
Photo: A couple troll their little boat through a mass of dead fish in the King Harbor Marina. Credit: Don Bartletti / Los Angeles Times