Reef Check News

Invasive Algae Sargassum horneri Found in Monterey


2020-06-25

During a dive along the Breakwater in Monterey, California in early June, Melanie Moreno, a Reef Check volunteer diver, observed what she suspected might be the invasive species, Sargassum horneri.

Sargassum horneri has been nicknamed "devil weed" as it has the ability to take over ecosystems and supplant lush kelp forests with bushy fields. It is native to Japan, Korea and China, and most likely arrived on a commercial vessel coming from Japan. It was first identified in California in Long Beach Harbor in 2003 and has since spread from the Northern Channel Islands to Guadalupe Island, Mexico. If Melanie's observation was correct it would be first sighting north of Point Conception.

Concerned that her find might represent the beginning of an invasion of this problematic species, she sent a photo of it to Reef Check to confirm the identification of the specimen. Reef Check staff confirmed the observation and immediately planned a dive to locate the specimen and look for others.

After several dives searching the site for the plant came up empty, Reef Check divers Dan Abbott and Maxwell Seale, stumbled upon it while practicing fish transects. It measured 12 cm (5 in) in diameter, meaning it was a juvenile and had not yet reached a reproductive stage. The dive team did an extensive search of the area but only found this single plant. Photos and GPS coordinates were taken and the California Department of Fish and Wildlife was immediately notified. Since this site is located within the Ed Ricketts State Marine Conservation Area, a scientific permit is required for the removal of most species, including invasives. As news of this observation spread quickly in the local research and management community, calls for the removal of this specimen were made.

A dive team from the California Department of Fish and Wildlife coordinated with Reef Check to search the site and remove the plant if found. Not only did they do so, but they found a second plant which they were able to remove. Removal of these new invaders before they have a chance to reach a reproductive state is key to protecting Monterey's productive kelp forest ecosystems, and none of it would have occurred without the watchful eyes of a Reef Check volunteer.

When asked for permission to credit the photos and her observation, Melanie said:

"Please just credit a 'Reef Check volunteer diver'. If I hadn't been trained and required to recertify for Reef Check every year I would not have been as focused on looking for invasive seaweeds. Not everyone who is trained goes on to complete Reef Check surveys, but the education provided puts hundreds of eyes out in the water to watch what's going on in our marine environment."

Reef Check California volunteers continue to look for new and potentially invasive species whether during a Reef Check survey or while diving recreationally. If you notice anything unusual during a dive, please contact your Reef Check California regional manager. Together, we can help protect these incredibly important Kelp Forest Ecosystems.