Scientists ponder unusual ulva blooms along Monterey Bay shoreline.

About a dozen Monterey Bay area scientists are studying green algal mats on Monterey, Seaside, Sand City and Moss Landing beaches. Their diagnosis: a genus of green algae called ulva, generally a bad sign for ocean health but possibly natural in light of El Niño conditions.

Ulva is usually found in estuaries, recently disturbed areas or nitrogen-polluted waters, according to Andrew DeVogelaere, research coordinator for the Monterey Bay National Marine Sanctuary and director of the Sanctuary Integrated Monitoring Network.

“It’s known as an ephemeral species. It comes and goes," he says. “It’s not the sign of what you would generally consider a healthy open-coast ecosystem."

The good news: It's not harmful to humans, and this event might be more a sign of natural El Niño conditions than of manmade pollution.

“There’s weird stuff going on in the ocean right now," DeVogelaere says. "It’s warmer and calmer than usual. We think the nitrate levels in the ocean right now from upwelling are lower in this season than they have been in 12 years.”

Although pollution could have been a suspect, the scientists think it's an unlikely culprit: the ongoing drought means little agricultural runoff, and urban outfalls are not active in the summer. Nutrient levels are low these days in Monterey Bay, which means relatively clear water.

That clarity allows light to penetrate farther down in the water column than usual. The ulva may have bloomed in the sand and in offshore shale reef, DeVogelaere says, and internal waves could have swept it onto the beach.

Ulva blooms have appeared on local beaches about six times over the last 12 years, he adds, but never in the quantity seen this July. Beaches in Sand City and Seaside were hit hardest, though the blooms now appear to be diminishing.