Identifying Pseudo-nitzschia, A Domoic Acid Producing Diatom

In the Fall of 2016, a phytoplankton bloom in Narragansett Bay led to shellfish closures because of the potential for seafood to be toxic, thus harmful to humans. Although cases are generally not fatal, consuming contaminated shellfish could lead to Amnesic Shellfish Poisoning (ASP).

This event started with a marine diatom (a common type of phytoplankton) called Pseudo-nitzschia that can produce a toxin called domoic acid. This toxin ends up in shellfish feeding on phytoplankton and causes problems for other species feeding on contaminated shellfish.

In 2017, Dr. Lucie Maranda received a Rhode Island Sea Grant to identify at the species level the toxin-producing Pseudo-nitzschia of Narragansett Bay. In order to distinguish this diatom from others, she needed to see its fine structural elements that are otherwise not visible with a regular light microscope. This led Dr. Maranda and Joe Barnes, an undergraduate student from the University of Rhode Island, to use the desktop Scanning Electron Microscope (SEM) housed at the Nature Lab. The SEM enabled them to view diagnostic features of a culture of Pseudo-nitzschia pungens at 40,000X magnification (100X is generally the absolute maximum magnification of a light microscope).

Dr. Lucie Maranda states: "One of the goals of this project is to establish the occurrence, abundance, and distribution of toxin-producing Pseudo-nitzschia in Rhode Island Sound and Lower Narragansett Bay. The ultimate purpose is to help provide shellfish managers and fishermen with timely information on relevant phytoplankton dynamics to ensure safe seafood products."