Reliable detection of harmful algal species is essential for understanding how red tide blooms form, tracking their movement, and developing strategies to manage them. In a new study, researchers developed and tested a real-time DNA-based method that can accurately detect as little as a single cell of Karenia brevis, the toxic dinoflagellate responsible for frequent red tide blooms impacting Gulf Coast communities from Texas to Florida.
Until now, red tide monitoring has relied largely on microscopes to count algal cells in water samples. While effective in many cases, this approach has limitations. K. brevis closely resembles other harmless microalgae, making it easy to misidentify. It is also difficult to detect the harmful algae species when cell numbers are very low–such as at the beginning or end of a bloom–when early warning information is most valuable.
To overcome these challenges, NCCOS-supported scientists developed a new real-time polymerase chain reaction (qPCR) test, a DNA-based technique that targets a gene sequence unique to K. brevis. This method allows scientists to detect the species directly from environmental samples with high accuracy, even when only a few cells are present. In laboratory and field tests, the approach consistently identified K. brevis without confusion from closely related species and performed well with samples containing many different types of microalgae. The method was also able to detect K. brevis at levels below what can typically be seen under a microscope, supporting earlier identification of blooms and giving scientists and managers more time to respond.
The researchers also showed how the new DNA-based detection method can be paired with a classic dilution experiment to improve understanding of red tide ecology. Using this approach, the team compared how quickly K. brevis populations were growing with how fast they were being consumed by tiny plankton grazers. The scientists also examined these processes for the broader algal community using chlorophyll measurement. Results showed that K. brevis grew faster than the grazers consumed it, while growth and grazing were more balanced across the overall phytoplankton community. This difference may help explain how red tide blooms begin, persist, and intensify over time.
Overall, this study introduces a powerful new tool for red tide research and monitoring. By allowing precise, species-specific detection of harmful algae at very low levels, the method supports earlier detection, improved tracking, and a clearer understanding of the biological processes that drive red tide events.
This research was led by Dr. Yida Gao and Dr. Deana Erdner (University of Texas at Austin) as part of a project funded by the NCCOS Ecology and Oceanography of Harmful Algal Bloom (ECOHAB) Program.
NOAA is authorized to advance research for HAB detection through the Harmful Algal Bloom and Hypoxia Research and Control Act (33 U.S.C. §§ 4001 et seq.).
Citation: Gao, Y., & Erdner, D. (2025). Development of a novel quantitative PCR assay for the toxic dinoflagellate Karenia brevis and its application for measuring in situ microzooplankton grazing impact. Journal of Applied Phycology, 37(5), 3843-3854.