Ecological insights from field and laboratory studies of Akashiwo sanguinea.

Blooms of the dinoflagellate Akashiwo sanguinea occur in coastal ecosystems worldwide and can have significant ecological consequences. Along the central California coast, long-term oceanographic and harmful algal bloom observations indicate that A. sanguinea has exhibited seasonal blooms since approximately 2017, coinciding with negative upwelling anomalies and warm, stratified conditions characteristic of late summer and early fall. In laboratory experiments, three A. sanguinea strains isolated from different sites and/or environmental conditions along the central California coast exhibited variation in growth rates, temperature sensitivity, and transcriptional responses. Under the conditions tested in this study, one strain exhibiting higher maximum growth rates and pronounced late-stage transcriptional responses appeared to be primed for large bloom formation, whereas another strain exhibiting slower growth and early cyst formation appeared to be primed for persistence. Together, these results demonstrate that A. sanguinea bloom dynamics are shaped by both environmental forcing and intraspecific variation, highlighting the importance of incorporating strain-level diversity into predictions of HAB occurrence and impact.