Graduation Year


Document Type

Open Access Senior Thesis

Degree Name

Bachelor of Science


Environmental Analysis

Reader 1

Sarah Gilman

Reader 2

Branwen Williams


ENSO (the El Nino-Southern Oscillation) is a periodic ocean phenomenon that results in warm periods (El Nino) and cooling periods (La Nina). ENSO influences the upwelling patterns along the California Coast and by extension, the ability of marine invertebrate larvae to recruit back to shore. During La Nina years, when upwelling is strengthened, the rising deep sea water causes offshore advection that diverts mobile larvae away from the intertidal habitats which the adults inhabit. Contrastingly, El Nino periods weaken upwelling and could increase larval recruitment. I tested the relationship between ENSO state and larval recruitment by analyzing a 10-year time series of mussel (Mytilus californianus) and barnacle (Chthamalus spp/Balanus glandula) populations with a Mixed-Model ANOVA; shifts in population size served as an indicator of changes in recruitment. I also tested for differences in the effect of ENSO among three regions: CA North, CA Central, and CA South. The results reveal that barnacles (Chthamalus spp/Balanus glandula) are more sensitive to ENSO conditions while mussels (Mytilus californianus) are not affected by it. Barnacle percent cover increases by 0.200% for each unit increase in the ENSO value index. Despite this minuscule increase, the experiment does provide proof that ENSO’s effect on upwelling influences larvae recruitment for certain intertidal species. Understanding how ENSO influences barnacle percent cover shows that certain species are sensitive to extreme weather events and these induced alterations to percent cover could influence the surrounding ecological structure.