Host Phosphorus Limitation Triggers Trade‐Off Between Stoichiometric Homeostasis and Production in the Micro‐Parasite Amoebophrya ceratii

Phosphorus (P) is a chemical element essential for life that can drive dynamics of microorganisms in marine environments. Nutrient acquisition by parasitic organisms is mainly done through infection. In the case of micro-parasites, how host diet limitations affect parasite stoichiometry and parasite-host interaction has not been thoroughly studied yet. This study focused on the free-living stage of Amoebophrya ceratii, a micro-parasite (Syndiniales, Dinoflagellates) of marine dinoflagellates. It aims to examine how host P limitation prior to infection affects parasite stoichiometry and infection cycle. To this end, Scrippsiella acuminata was used as a host and cultivated under P-replete or P-limiting conditions. Infection and parasite production were monitored, and elemental quotas and stoichiometry of the freshly produced dinospores were determined. In P-replete conditions, elemental quotas and ratios of the parasites were similar to their host, showing a strong need for P. While the host's stoichiometry was greatly impacted by P limitation, parasites were able to maintain stoichiometric homeostasis and elemental cell quotas. Finally, host P limitation mainly affected the dinospore production, exhibiting a trade-off between dinospores quotas, stoichiometric homeostasis, and production. These findings have implications for host-parasite interactions and biogeochemical cycling in coastal waters.