SM PIER — Every week, senior aquarist Jose Bacallaos and his team go diving in the Santa Monica Bay looking for algae, kelp and sometimes small animals for the Santa Monica Pier Aquarium.

On Tuesday, Bacallaos was motoring out near Redondo Beach and King Harbor when he noticed something unusual.

“It was pretty foggy, and where we were motoring it was brown everywhere,” Bacallaos said.

The Santa Monica Bay was swept with a phenomenon called the red tide, a discoloration of the water brought on by a rapid increase in certain microorganisms.

Back at the Santa Monica Pier, it was the same story.

Vicki Wawerchak, director of the aquarium, pulled a water sample to check for the algae that cause the red tide.

“Usually with the water sample, you can see a lightish brown color,” she said. “It was literally like pulling up a cup of coffee. It was an intense sample, very dark.”

The water contained the dinoflagellates and diatoms that you see in a red tide, but in unusual concentrations, Bacallaos said.

Heal the Bay personnel theorized that last Wednesday’s heavy rain washed nutrients, fertilizers and other materials that nourish the microorganisms into the water, causing the bloom.

“When you see that nutrient load, something’s going to take advantage of it,” Bacallaos said.

Scientists have yet to find hard evidence tying the blooms to land-based pollutants, but several studies are in the works.

Heal the Bay participates in one of those studies tracking harmful algae blooms, or HABs, a term scientists prefer to “red tide” because not all blooms are red in color or even visible, and many “red tides” contain no harmful organisms at all.

The hope is that they will address the numerous questions that still lurk around the phenomenon.

“It’s hard to determine what causes them, and how long they stick around,” Wawerchak said.

The algae do not directly threaten humans, although some people do have a sensitivity to it which can cause irritation.

“If you went swimming now, you probably wouldn’t get sick unless you ingested a great deal of water,” Bacallaos said.

Some of the diatoms and dinoflagellates naturally produce toxins, but in such small amounts that they don’t affect humans swimming in the ocean.

Where the creatures become a problem is when other sea life, like mussels, consume them and concentrate those toxins.

Mussels, in particular, constantly filter water. They store the toxins in their bodies to a degree that a person eating that mussel could get violently ill.

In general, that’s not a problem because the majority of mussels consumed in restaurants or sold in stores are grown on carefully protected mussel farms, Bacallaos said.

Each year, the Department of Fish and Game and the local Department of Health issue an advisory between May 1 and Oct. 31 to avoid wild-caught shellfish because that’s when most harmful algae blooms, occur.

Another negative impact of the algae comes when the vast swarms of microorganism die off. Other bacteria that feed off of the dead algae use a lot of dissolved oxygen to do so, depleting the supply for the other sea creatures.

This can lead to mass die-offs, similar to that which struck King Harbor in March when hundreds of thousands of sardines went belly up.

Already, the water in the bay seems to be returning to its normal color, both Wawerchak and Bacallaos reported.

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