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Research Technical Report

Assessing the Invasiveness of the Non-native Kelp Undaria pinnatifida in Monterey Harbor and Implications for its Management

Jeffries, S. (May 2011)

A Capstone Project at California State University, Monterey Bay, 27pp.


The annual subtidal alga Undaria pinnatifida has been federally declared an invasive species and has spread rapidly across the globe from its native range in northern Asia. The ability of this alga to complete its life cycle determines its success in a particular location, and several abiotic factors have been found to be important in determining reproductive success in kelps. Laboratory zoospore culture experiments were conducted monthly to test the effects of temperature and nitrate concentrations on microscopic stage production throughout a year. Cultures were grown under two temperatures (12, 18° C) monthly and three nitrate concentrations (1,5,10 µmol) three months during the year. Each month sporophytes were produced in both temperatures, and densities were either higher in the 18°C treatment or there was no difference between temperatures. Sporophytes were also produced in all nitrate treatments, but there was no consistent nitrate effect observed. Finally, field measurements and sporophyll punches were obtained to test the relationship between zoospore output and the physical features sporophyll size and blade length for U. pinnatifida in Monterey Harbor. These results revealed a non-linear relationship for individual plants, and a linear relationship at a population (average) level. Visual predictors of the reproductive status of an individual that can be used before it is removed (trauma can cause zoospore release) is essential to the success of programs seeking to avoid the further spread of this species, such as the Monterey Bay National Marine Sanctuary Undaria program. Alternately, information regarding abiotic influences on U. pinnatifida is important as microscopic stage production is vital in supporting future cohorts. Similar culture experiments have been conducted on other native central California kelp species, a majority of which were unable to produce sporophytes in all treatments. This suggests that U. pinnatifida is a condition-flexible alga whose reproductive physiology allows it to enter and thrive in new areas. The methods developed and used in this study should be implemented in other locations throughout U. pinnatifida's range in order to inform local management efforts and provide a more complete understanding of the ability of this species to continue to spread.

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