Date of Award

Spring 5-18-2018

Degree Type

Honors Thesis



Degree Name

Bachelor of Science



First Advisor

Deneb Karentz

Second Advisor

James Sikes

Third Advisor

Naupaka Zimmerman


Since Hutchinson first described the “Paradox of the Plankton” in 1961, research has been done to determine how and why the coexistence of so many different species of phytoplankton is possible. A critical part of this question is species succession, or how the assemblage of phytoplankton in a region changes over time. This study examines the succession of planktonic diatoms in San Francisco Bay, CA (USA) from September 2015 through December 2017 using phytoplankton samples and environmental data. Periodic sampling was conducted at a site in the Golden Gate Strait and taxa were identified using light microscopy and scanning electron microscopy. Relative abundance, relative biovolume, and diversity measures were calculated for each sample date. Over the course of the study, 46 unique taxa were identified, some of which persisted over time while others were seen on only one occasion. A seasonal pattern in species richness was observed, in which high species richness was consistently seen in fall and winter and low species richness was seen in spring and summer. Seasonal clusters were also seen when a non-metric multidimensional scaling (NMDS) ordination was used to visualize community similarity. Fall and spring sampling dates formed the most distinct clusters, indicating that communities during these seasons are consistently similar to one another. Diatom assemblages differed greatly between drought and non-drought periods, suggesting that certain environmental conditions (e.g., salinity) play a large role in species succession in San Francisco Bay. Further studies could examine additional environmental variables (e.g., nutrients, water column mixing, solar radiation) to determine their role in shaping phytoplankton communities.