Surveys of Invasive Algae at CINMS
NOAA Diver Ryan Freedman holds up an invasive Undaria pinnatifida sub-adult during an algae survey dive at Channel Islands National Marine Sanctuary.
From April 4-6th, the Channel Islands National Marine Sanctuary (CINMS) Dive Team and National Park Service divers, working as reciprocity partners, conducted a series of survey dives to search for an invasive algae, Undaria pinnatifida.
While Undaria has been established on the mainland for some time, sighting it within CINMS is a recent discovery. Surveys from this year have found that the invasive has expanded its range both west and east from the original site on the north side of Anacapa Island. For now, the algae has not been spotted on the south side of Anacapa Island or on the next closest island, Santa Cruz (although surveys were not conducted on Santa Cruz during this particular expedition).
Pairs of divers used drift dives to cover a large area of habitat offshore of Anacapa Island, where the algae was first discovered approximately a year and a half ago. Drift diving is a technique used by divers to cover large survey areas without having to swim. Instead, divers let the water current transport them.
The three days of dive surveys found that Undaria was quite abundant on the north side of Santa Cruz along with Sargassum horneri, another algal invasive. Despite being a Marine Reserve and Marine Conservation Area, the invasive has become quite established in multiple habitats including sandy bottoms, rocky reefs and near eelgrass beds. Divers documented a number of species feeding on Undaria on this trip as well. It may be a preferred food source compared to Sargassum, which has been shown to be undesirable in feeding experiments for a number of herbivores. CINMS aims to continue to monitor the expansion of this invasive and track the potential for environmental degradation.
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Significance: The Channel Islands National Marine Sanctuary works to protect and conserve the natural resources around the islands for the enjoyment of all. The introduction of invasive algae could outcompete local kelp, Macrocystis pyrifera, which provides important biological habitat for fishes and other economically and environmentally important species. Monitoring invasives and understanding their impact and spread is critical for effective sanctuary management.