Spring 2016

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)


Science & Environmental Policy


The rocky intertidal zone serves as an important nighttime high tide foraging habitat for the California spiny lobster (Panulirus interruptus) but the role of this habitat in supporting this valuable species may vary with fine-scale differences in the habitat. On Catalina Island, variation in the proportions of crabs, mussels, and limpets that lobsters target may reflect variation in prey availability or consumer population demographics, independent of fishing pressure. I estimated the relative contribution of three important lobster prey taxa by applying Bayesian mixing models in MixSIAR to δ15N and δ13C signatures of lobsters and their prey from both a fished and a protected site. Mixing models indicated that mussels represented a greater proportion of the diet of lobsters from the fished site which has persistent mussel beds, a known foraging habitat for lobsters. Mixing models that incorporated demographic variables also indicated that foraging site, sex, and carapace length were important variables in explaining variation in spiny lobster diet. Manly selectivity analyses indicated that overall lobsters selectively forage for mussels at both sites but prey use and selectivity also varied between individuals. The strategy of closing areas to fishing can impact local trophic dynamics but habitat quality, regardless of fishing pressure, remains an important factor in determining prey availability and community trophic dynamics. This study provides evidence suggesting that fine-scale differences in foraging habitat equate to differential foraging potential and influence consumer diets.