Construction of Dichotomous Taxonomic Keys for San Francisco Bay Planktonic Diatoms

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), undergraduate 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 project was intended to use scanning electron microscopy to examine phenotypic characteristics of cells from field collections of Keith (2018) and clonal cultures to identify the species that make up the assemblage of dominant centric diatoms. Five centric diatom species were identified prior to the COVID-19 pandemic: Coscinodiscus curvatulus, Actinoptychus senarius, Coscinodiscus oculus-iridis, Coscinodiscus lentiginosa, and Thalassiosira nordenskioeldii. However, due to temporary sampling site closures and limited access to laboratories because of stay-at-home orders from the pandemic, the project was modified to be done remotely. The project was modified to analyze and compile present literature on diatom taxonomy based on morphology and develop taxonomic keys specific to diatoms in San Francisco Bay for use by both specialists and non-specialists, including school-aged children. In the construction of the keys, genera and species were considered significant if they were observed in ≥50% of the samples in the study by Keith (2018) from September 2015 - December 2017, including Chaetoceros spp., Ditylum brightwelli, Pseudo-nitzschia spp., Rhizosolenia setigera, Skeletonema costatum, Thalassiosira spp., and Trieres mobiliensis. Here, two keys are constructed – “A Technical Key to Common Planktonic Diatoms in San Francisco Bay” and A Basic Key to Common Phytoplankton in San Francisco Bay” – and the challenges of constructing the keys are discussed. These keys will aid in the assessment of diatom biodiversity in San Francisco Bay. Additionally, open-source diatom taxonomy websites have been collected to further support specialists and non-specialists in their scientific education and study of phytoplankton

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

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