Graduation Date

Spring 2018

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Dr. Sean Craig

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Brian Tissot

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Paul Bourdeau

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Dr. Joe Tyburczy

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



Red abalone and sea urchins are both important herbivores that potentially compete with each other for resources like food and space along the California coast. Red abalone supported a socioeconomically important recreational fishery during this study (which was closed in 2018) and red sea urchins support an important commercial fishery. Both red sea urchins and red abalone feed on the same macroalgae (including Pterygophora californica, Laminaria setchellii, Stephanocystis osmundacea, Costaria costata, Alaria marginata, Nereocystis leutkeana), and a low abundance of this food source during the period of this project may have created a highly competitive environment for urchins and abalone. Evidence that suggests competition between red abalone and red sea urchins can be seen within data collected during the years of this study (2014-2016): a significantly higher red sea urchin density, concomitant with a significantly lower red abalone density, was observed within areas closed to commercial sea urchin harvest (in MPAs) compared to nearby reference areas open to sea urchin harvest. In addition, a significant negative relationship was found between red abalone and red sea urchin abundances when examined at the 60 m2 transect level: transects with higher abundances of red sea urchins contained fewer red abalone. Designating MPAs that are closed to sea urchin harvest, in the absence of sea urchin predators such as sunflower stars (Pycnopodia helianthoides), sea otters (Enhydra lutris), spiny lobster (Panulirus interruptus), and predatory fish species, (such as the sheephead (Semicossyphus pulcher) found in Southern California), may all have contributed to an increase in red sea urchin abundances and a concomitant decrease in red abalone within the Cabrillo MPA studied in this project.

Citation Style



Thesis/Project Location