5. Conclusion
C. polykrikoides blooms photosynthesize at high rates, outcom-pete other plankton for vitamin B12, and more rapidly assimilate ammonium than other plankton. These attributes may provide this harmful alga with a competitive edge that likely contributes toward bloom persistence. While the presence of C. polykrikoides has been shown to alter the microplankton community via the release of allelopathic and toxic compounds, this study demon-strates that C. polykrikoides patches harbor a distinct planktonic consortium including picoeukaryotes and heterotrophic bacteria. C. polykrikoides blooms can turn over labile nitrogen species (ammonium, nitrate, and urea) and vitamin B12 in the bloom in 1.5 and 10 days, respectively, outside the bloom, potentially making acquisition of these limiting elements more difficult for other plankton. C. polykrikoides may rely on its ability to vertically migrate and a B12 producing and nitrogen re-mineralizing microbial community to supply its nitrogen and vitamin requirements. In conclusion, the presence of C. polykrikoides blooms fundamentally changes the microbial community and resource cycling of the coastal marine ecosystem.