Wanted! The Whereabouts of Sargassum horneri

Tom Boyd-S.horneri







In 2003, an unexpected stowaway on a container ship found its way into the Port of Long Beach and was introduced into our nearshore ocean. If you have been strolling on the beach or have been diving along the rocky reefs in Southern California, you may have seen it. It is a brown algae called Sargassum horneri and it has spread as far north as Santa Barbara and south into Baja, Mexico. Originating in the warm waters of Japan and Korea, this invasive alga’s distribution and persistence along the West Coast has generated concern as it poses a potential threat to native ecosystems.

In 2012, Los Angeles Waterkeeper partnered with NOAA to seek out populations of non-native algae and remove them with a specialized mechanical suction device called the “Supersucker” that was designed for sub-tidal algae removal. The first attempts using this device was conducted at Ship Rock on Catalina Island with members from NOAA, UCSB, and LAW staff and volunteers. The main target was S. horneri and over 100lbs of this algae was removed in a single day in September 2013. While removal did not have any significant impact in a small 100m2 plot, this pilot study was used to guide and improve future removal efforts through research conducted by UCSB.

While LAW continued its contribution to kelp forest restoration, the spread of S. horneri became better documented along the California coast and offshore Islands. In 2014, after a series of summer storms and long period of unusually warm water, the kelp forest at the Casino Point Dive Park on Catalina Island virtually disappeared and became displaced by this algae, which by now is commonly referred to as the “devil weed”. This caused great concern amongst the dive community, having lost an iconic dive site in California that was known for easy access to a thriving kelp forest. Unfortunately, with little action towards abating its spread and proliferation, S. horneri has become well established in our waters.

Today, we are still seeing this “devil weed” up and down the coast as many divers in Los Angeles and Orange County are still reporting sightings in their favorite dive sites. There still is great concern about how this invasive algae is affecting our native kelp forests and much research is currently being done to explore this question. With the recent summation of our kelp forest restoration work, we believe it is a natural transition to continue protecting these environments by embarking on new efforts that will contribute to the work currently being done. In the coming months, we will be back on the water with our scientific dive team to begin looking for areas where this algae dominates the landscape.

–Ian Jacobson, Marine Programs

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