Short-term oil exposure impacts on the harmful algal bloom (HAB) species Pseudonitzschia australis and the coccolithophore Emiliania huxleyi were studied by investigating physiological responses in growth, production of transparent exopolymer particles (TEP), P. australis domoic acid (DA) content, and E. huxleyi calcification, with the goal of better understanding the potential effects of the 2015 oil spill near Refugio State Beach in the Santa Barbara Channel, California (USA). While oil exposure negatively impacted growth of both species, P. australis appeared to be more sensitive to oil exposure compared to E. huxleyi. Increased cellular TEP (both species) and DA (P. australis), and abnormal calcification (E. huxleyi) were observed in the presence of oil. The physiological changes detected in these locally important phytoplankton species have implications for other ecosystem processes, human health, and the fate of the spilled oil. The results from this study enhance our understanding of the repercussions of oil pollution events, but further research is necessary to explore ecosystem-wide impacts and chronic or long-term effects of oil in marine environments.