Beating Back Invasive Seaweed

invasive seaweed
Image Credit: Scripps

Invasive seaweed is disturbing native ecosystems in the rocky reef off of the Southern California coast. The seaweed species, Sargassum horneri, has spread aggressively from Santa Barbara to Isla Navidad, inhibiting native algae growth and altering marine ecosystems. Santa Barbara Coastal LTER researchers compared approaches for clearing the invasive from California’s coastal ecosystems, to determine the most effective and efficient methods.

From field experiments conducted off of Santa Catalina Island, California, the researchers determined that plants with severed leaves are unable to regenerate and will eventually die. This shows that slashing seaweed leaves, instead of removing whole plants, may be effective in killing plants and stopping propagation. Researchers also found that the most effective places to remove the seaweed are those that haven’t been completely overtaken by the invasive yet.

In addition to general best practices, divers determined the most efficient seaweed removal methods when different resources are available. They found that using an underwater suction device had the highest efficiency of seaweed removal, but only allowed two divers to work at a time and had significant startup costs and logistical challenges associated with the suction equipment. This shows that groups that have limited volunteers, but ample funds, should use the suction method.

The second method tested in this study was the “line and bag method,” in which divers filled mesh bags with detached seaweed. This method was less efficient than the suction method, but was less expensive, required little training, and allowed for more than two divers to work at a time. From these results, researchers concluded that groups with many volunteer divers but limited funds should use the line and bag method.

These findings will directly help groups find effective strategies to control the spread of invasive seaweed and contribute to the health of coastal California ecosystems.

Original article in Management of Biological Invasions

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