Sahara Mustard weeds, foreground, are robbing local wildflowers of water at the Brookhurst Marsh in Huntington Beach. (KEVIN CHANG / March 21, 2013)

There's an invasion happening along Pacific Coast Highway between Brookhurst and Magnolia streets. They've come by the hundreds and more are on their way, slowly consuming Brookhurst Marsh and threatening the areas around it.

It's the Sahara mustard, an invasive weed that has been in Southern California since 1927 but has boomed in population over the last 20 years, according to the California Invasive Plant Council.

It has overwhelmed the Anza-Borrego Desert State Park in San Diego and now it has made its way to Huntington Beach.

"We have two major issues that we constantly struggle with. One is trash coming down the flood channel and blowing over from the beach and the other one is weeds," said Dr. Gordon Smith, chairman of the Huntington Beach Wetlands Conservancy. "We've got the usual clovers, foxtails and dandelions, but this is a new one."

Smith said California State Parks environmental scientist David Pryor found the North African-native weeds a few weeks ago along the shoulder of Pacific Coast Highway and upon closer inspection found them growing in the sand dunes along the north side of the highway.

"It completely surprised me and it's scary," Pryor said. "It's like it was planted there."

An average driver traveling along PCH probably wouldn't think twice about the vegetation growing alongside the road, but to a trained eye the presence of the mustard is truly apparent.

"This has all happened in the past few months," Smith said. "We watch things along here pretty closely for weeds, and it's just astonishing how fast these have grown."

The Sahara mustard is adaptive to dry, sandy locations, Smith said.

Dr. Elizabeth Brusati with the Invasive Plant Council said that the weed has a serious ecological impact.

 It's unknown how the weed made its way to Huntington Beach, but Smith believes that its seeds may have gotten stuck underneath a vehicle and were then blown into the marsh.

Pryor said the mustard has a quick germination period and would probably negatively affect the bright yellow beach primrose that grows along PCH — along with other native vegetation — by robbing it of the water and sunlight it needs. Its growth could also hurt the indigenous animals.

If the Sahara mustard overwhelms the area, it could kill off plants these local animals feed on, endangering their survival in the process, Pryor explained.

The weed has been spotted in the Brookhurst Marsh dunes, but that doesn't mean its coverage stops there. Smith said it has the potential to move toward the Magnolia Marsh and even the Bolsa Chica Wetlands.

Restoration ecologist Austin Parker, who is with the Bolsa Chica Conservancy, said Sahara mustard has been on the wetlands for a while and the group has done what it could to contain the weed.

"We need to get rid of all the invasives and we'd like to restore ... [the plants in the wetlands] all to native species," Parker said. "But it's not something that's going to happen like that. There's no silver bullet. You can cut them all down or pull them by the roots, but there's years of seed banks in the soil, so it's going to come back."

When the weed is young and green, the seed pods remain intact, but as they begin to dry and wither, the pods explode when they're pulled from the ground, Pryor said.

"We'll see a lot more of it next year for sure," he said.

Smith has begun to hire contractors to help eradicate the Sahara mustard and is beginning to organize cleanup events, asking volunteers to pull and bag the weeds, he said. A special spray will be used in the fall to try to prevent their growth next season, he added.

"We're vigilant and if it gets too big, we'll bring out the troops," Pryor said.

anthonyclark.carpio@latimes.com

Twitter: @acocarpio