Research Technical Report

Status of the Invasive Alga Undaria pinnatifida in Monterey Harbor

Lonhart, S. (November 2003)

Oral presentation at the Western Society of Naturalists conference, Long Beach, CA

ABSTRACT

In the last decade, the invasive brown alga Undaria pinnatifida has spread throughout the Northeastern Atlantic and Southwestern Pacific, and most recently to California. In March 2000 it was detected in Los Angeles Harbor, and subsequently spread northward, reaching Monterey Harbor in 2001. Undaria is considered a threat because it can grow and spread quickly, and has the potential to overgrow native algae, although few studies have assessed its actual ecological impact. In October 2002 research divers surveyed the floating docks in Monterey harbor and mapped the distribution of Undaria. Volunteer divers used this information to begin a removal effort, diving the harbor monthly from December 2002 until April 2003. For each individual removed, researchers recorded total length, damage, reproductive status, and location. In one year volunteers removed almost 2000 Undaria, many of which were prereproductive. However, a dockside survey of the harbor in September 2003 indicated that despite these efforts the alga has spread within the harbor and is more abundant than last year. It remains unclear whether a more concerted and systematic effort can reduce the spread of Undaria. This program is an ongoing collaboration between the Sanctuary Integrated Monitoring Network (SIMoN) at the Monterey Bay National Marine Sanctuary, Elkhorn Slough National Estuarine Research Reserve, Department of Fish and Game, City of Monterey (Volunteer Services and Office of the Harbormaster), Moss Landing Marine Laboratories, and the University of California at Santa Cruz.