Using Scanning Electron Microscopy and Morphologic Characteristics to Identify Centric Diatom Species in San Francisco Bay

Planktonic diatoms exhibit high biodiversity in marine systems and make a significant contribution to water column primary productivity. This makes research on planktonic diatoms particularly important in measuring the health of coastal marine ecosystems. At the University of San Francisco (USF), research has been conducted since September 2015 to study planktonic diatoms in San Francisco Bay. A previous study by Keith (2018), Planktonic Diatom Species Succession in San Francisco Bay, documented changes in species diversity over time, observing seasonal patterns in species richness as well as the effect of environmental factors such as salinity, temperature, and rainfall on species succession. In her work, an abundance of centric diatoms was present, indicating their essential role in local phytoplankton communities; however, the majority of observed centric taxa could not be identified with light microscopy. The current study is using scanning electron microscopy to examine phenotypic characteristics of cells from field collections and clonal cultures to identify the individual species that make up the assemblage of dominant centric diatoms. As of April 2020, five species have been verified: Actinocyclus curvatulus, Actinoptychus undulatus, Coscinodiscus oculus iridis, Thalassiosira lentinginosa and Thalassiosira nordenskjoldii.