Persistence of low levels of Pseudo-nitzschia australis on the coast of Maine eight years after its first appearance

About half of the described species in the diatom genus Pseudo-nitzschia are capable of producing the potent neurotoxin domoic acid responsible for amnesic shellfish poisoning. Pn. australis has the highest reported cellular domoic acid concentrations in the genus, making it a species of interest for resource managers; however, Pseudo-nitzschia spp. cannot be easily distinguished by microscopy and blooms typically contain multiple species. We designed a real-time quantitative PCR assay for rapid and accurate detection and quantification of Pn. australis in environmental DNA samples. Estimated cell counts were experimentally derived for this assay. We applied this novel assay to eDNA water samples collected in the western Gulf of Maine to detect and quantify Pn. australis from 2021-2024. Pn. australis abundance via qPCR and particulate domoic acid concentration ([pDA]) peaked in magnitude in the fall when water temperatures were between 14° and 16°C. The magnitude of the signal, length of peak abundance, and [pDA] declined each year from 2021 to 2023. In 2024, no Pn. australis signal was detected. DNA metabarcoding of associated bacterial and eukaryotic communities and macronutrient analysis of select samples were also performed to identify biogeochemical drivers of Pn. australis phenology throughout this time series. This study demonstrates the use of targeted and non-targeted molecular approaches to detect, quantify, and evaluate harmful algal bloom species and their ecology in aquatic systems.

Presentation Preference: Oral

Primary Presenter: Sydney Greenlee, University of Maine (sydney.greenlee@maine.edu)

Authors:

Sydney Greenlee, University of Maine  (sydney.greenlee@maine.edu)

Robin Sleith, Bigelow Laboratory for Ocean Sciences  (rsleith@bigelow.org)

Peter Countway, Bigelow Laboratory for Ocean Sciences  (pcountway@bigelow.org)

Damian Brady, University of Maine  (damian.brady@maine.edu)