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Invasive Weed Threatens Kelp Forests Off San Diego Coast

San Diego's iconic kelp forests are facing a threat from warm ocean temperatures and an invasive species called "devil weed."

Sargassum horneri thrives in warm ocean waters like the conditions common off the coast of San Diego this past summer and fall.

Photo by Nicholas McVicker

Devil Weed off the coast of the Channel Islands in this undated photo.

San Diego's kelp forests are facing a threat from El Niño fueled storms and an invasive weed.

Ed Parnell is a researcher at the Scripps Institution of Oceanography who worries the quick growing plant will out-compete kelp that might be displaced by El Niño fueled storms.

It is already happening near Catalina Island, Parnell said.

"This species here covers so much of the bottom it can interfere with recruitment of the giant kelp, so it can keep it from coming back," Parnell said.

The kelp might be helped by a return of colder ocean waters because the invasive weed prefers warmer water temperatures.

The situation in the Channel Islands could happen here.

"I'm very concerned that the same thing is going to happen down here off San Diego and really exacerbate its competition with giant kelp, and change the fundamental nature of kelp forests off San Diego County," Parnell said.

If the invasive weed gains a foothold here, Parnell worries that the region's kelp forests may not be able to recover from the beating strong winter storms typically deliver.

Storms can do a lot of damage, but kelp usually recovers over the next year.

Without kelp forests the ocean off San Diego would not be as vibrant because so many species rely on the habitat for reproduction, for nourishment and for protection from predators.

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