Ross Clark, Earth Matters: A new kelp comes to Santa Cruz — unfortunately

Contributed: The non-native seaweed Undaria pinnatifida has been found in Santa Cruz harbor. In New Zealand, it forms dense beds, replacing native algae and impacting fisheries. In its native Japan, the alga is known as wakame, and is eaten in dishes including miso soup.

Earth Matters
By Ross Clark, Santa Cruz Sentinel

Ocean shipping and fishing operations of the 20th century have helped the world’s marine ports become disembarkation stations for the planet’s marine organisms. Harbors like those in the San Francisco Bay have been invaded by hundreds of species from around the world. The California Department of Fish and Wildlife reports that at least 257 species have invaded California’s bays and estuaries.

Early on, species arrived with oysters and other shellfish that were transported to establish coastal oyster farms. Today, most species arrive by boat, either attached to hulls or floating within ballast water. But measures are in place to limit this transport by requiring large vessels to flush ballast water far from shore. So it was disheartening when I found that a new kelp had come to the Santa Cruz Small Craft Harbor.

The alga Undaria pinnatifida was first spotted in Southern California harbors and had established itself in Monterey by 2001. The kelp is originally from Japan but has spread to harbors around the globe. In New Zealand, it forms dense beds, replacing native algae and impacting fisheries. In its native Japan, the alga is known as wakame, and is harvested and eaten in dishes including miso soup.

Some species cause little harm while others threaten natural ecosystems and human infrastructure. For instance, the giant sea grass Spartina alterniflora has formed dense monocultures that cover San Francisco Bay marsh and mudflats used by the California clapper rail to feed and nest. The state has spent a decade and millions of dollars in an attempt to eradicate the grass, and has ultimately decreased its spread from 2,000 acres to now less than 100 throughout San Francisco Bay.

Many invasive species out-compete the locals for food, substrate and other habitat resources. Once established, some species are impossible to eradicate and quickly become a part of an area’s flora or fauna.

Local agencies acted fast once Undaria was found. The Monterey Bay National Marine Sanctuary partnered with Monterey Harbor in 2002 to initiate a monitoring and eradication program. Volunteer divers searched docks and concrete pier pilings and removed all Undaria encountered.

Initial surveys documented several localized areas within the calm waters of the harbor but the species has since been found elsewhere and initial removal efforts did not eliminate the species. Chad King from the sanctuary noted that eradication seems futile and that boats continue to transit among infested harbors, so a focus on educating boat owners of the importance of removing plants from boat hulls is critical.

When I spotted the kelp growing in Santa Cruz harbor and my identification was confirmed by algal ecologist Dr. Mike Graham at Moss Landing Marine Labs, it became clear the species had hitched a ride to Santa Cruz. Some suggest that the species had been kept away from Santa Cruz and Elkhorn harbors by the freshwater rivers that flow through these two marinas, and that the California drought may have allowed the kelp’s establishment in Santa Cruz with freshwater flows way down.

King pointed out that there is more substrate available in the clear waters of Monterey and Pillar Point harbors — the latter just north of Half Moon Bay — and that limited clarity in Santa Cruz harbor will restrict the species to the tops of the docks.

As yet, there has been little evidence of ecological impacts by the species in Monterey and little impact on harbor operations or fouled vessels. King is focused on continuing long-term monitoring of the open coast, where the species has yet to be seen.

Graham notes that it remains to be seen what impact the species may play in the Monterey Bay, and that future harvest of the species for commercial purposes may help keep our new kelp in check.

Ross Clark is climate action coordinator for the city of Santa Cruz. He’s also director of the Central Coast Wetlands Group and chair of the county Commission on the Environment. Contact him at

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