Evaluating Centric Diatom Diversity in San Francisco Bay with Scanning Electron Microscopy

Since September 2015, research has been conducted at the University of San Francisco (USF) to study planktonic diatoms in San Francisco Bay. Planktonic diatoms are one of the greatest contributors to the biodiversity in estuary systems. Due to their primary position in the food chain, changes in planktonic diatom communities will affect marine organisms at higher trophic levels. Therefore, the abundance and diversity of diatom species allows for the measurement of the health of the marine ecosystem. A previous study by Keith (2018), focused on documenting changes in species diversity over time, observing seasonal patterns in species richness as well as the effect of environmental factors such as salinity on species succession. In her work, an abundance of centric diatoms were observed, indicating their essential role in phytoplankton communities. Unfortunately, the majority of these taxa cannot be identified with light microscopy. Our ongoing study focuses upon understanding which individual species make up this group of centric diatoms. In particular, this study uses scanning electron microscopy to take images, compare and examine phenotypic characteristics between individuals in preserved samples taken from San Francisco Bay in order to distinguish and classify the individuals at a species level as well as determine relative abundance of individual species over time. By doing so, we will also be able to identify unique and new phytoplankton taxa, and contribute to a better understanding of the ecology of San Francisco Bay.