Graduation Date
Fall 2024
Document Type
Thesis
Program
Master of Science degree with a major in Biology
Committee Chair Name
Paul E. Bourdeau
Committee Chair Affiliation
HSU Faculty or Staff
Second Committee Member Name
Erik S. Jules
Second Committee Member Affiliation
HSU Faculty or Staff
Third Committee Member Name
Bret C. Harvey
Third Committee Member Affiliation
Community Member or Outside Professional
Fourth Committee Member Name
Gina M. Contolini
Keywords
Kelp Forest, Kelp Forest restoration, Rock crabs, Purple urchins, Bull kelp, Cancer productus, Romaleon antennarium, Strongylocentrotus purpuratus, Kelp forest ecology, Experimental Ecology, Applied Ecology, Kelp Forest Conservation, Northern California, Marine Ecology, Marine Biology
Subject Categories
Biology
Abstract
Kelp forests are threatened by regional abiotic and biotic stressors, including overgrazing by sea urchins. On the north coast of California, purple sea urchins (Strongylocentrotus purpuratus) are prolific grazers of kelp and with the regional extinction of their main predator (sunflower stars, Pycnopodia helianthoides), it is unknown whether any remaining mesopredators could exert top-down control of purple urchin populations. Other known predators of purple urchins in northern California include rock crabs, which have been shown to control sea urchin populations in Atlantic urchin barrens and indirectly cause phase shifts back to kelp forests. Yet, little is known about the importance of these predators in mediating purple urchin distribution, abundance, and grazing behavior in the eastern north Pacific. To better understand the ecological effects of rock crabs on purple urchins in northern California, I conducted laboratory mesocosm and field experiments to determine: (1) the feeding rates of two common rock crab species (Romaleon antennarium and Cancer productus) on urchin barren and kelp forest urchins; and (2) the influence of crab risk cues and damaged conspecific urchins on urchin grazing rates. In mesocosms, actively feeding rock crabs of both species and all adult sizes consumed approximately two urchins per day, regardless of urchin condition. The effect of the presence of non-feeding rock crabs on urchin grazing depended on urchin condition, with crab risk cues strongly suppressing grazing by well-fed urchins compared to the presence of crushed conspecific urchins and no-cue controls, but only weakly suppressing the grazing of starved urchins. In a natural urchin barren, risk cues from caged rock crabs reduced urchin grazing by 64% when compared to no-crab plots. As we search for novel restoration efforts, our findings provide insight into potential strategies for suppressing urchin grazing, through rock crab consumptive and non-consumptive effects. Together, my findings suggest that rock crab enhancement could be incorporated with other methods as a tool for kelp forest restoration until sunflower stars can be re-introduced to these vital ecosystems.
Citation Style
APA
Recommended Citation
Traverso, Sandra E., "ASSESSING THE EFFECTS OF REMAINING NORTHERN CALIFORNIA KELP FOREST MESOPREDATORS ON PURPLE SEA URCHIN ABUNDANCE, DISTRIBUTION, AND FEEDING ACTIVITY" (2024). Cal Poly Humboldt theses and projects. 806.
https://digitalcommons.humboldt.edu/etd/806
Included in
Biodiversity Commons, Biology Commons, Ecology and Evolutionary Biology Commons, Marine Biology Commons