Adaptations to feast and famine in different strains of the marine heterotrophic dinoflagellates Gyrodinium dominans and Oxyrrhis marina

Marine planktonic organisms endure fluctuations in food abundance and quality during their life. The degree of resource variability in each specific environment may have forced adaptive survival responses on the organisms inhabiting them. We studied the adaptations to feast and famine of 2 strains of the heterotrophic dinoflagellates Gyrodinium dominans (GYR-DK from Denmark; GYR-BCN from Barcelona) and Oxyrrhis marina (OXY-BCN from Barcelona; OXY-CRB from the Caribbean). Overall, the OXY strains showed contrasting results in terms of feeding, metabolism, and biochemical composition, whereas both GYR strains presented similar responses to the variables measured. OXY-BCN exhibited higher maximum ingestion rates, better capacity to exploit a pulse of food, higher carbon assimilation efficiency and lipid storage capacity, and longer survival time to starvation. When feeding on a fatty acid-rich alga (Rhodomonas salina, RHO), OXY-BCN displayed very high (75%) gross growth efficiencies (GGE), but showed no growth when conditioned to one that was more fatty acid deficient (Dunaliella tertiolecta, DUN). In contrast, both GYR strains had higher GGE when feeding on DUN (>50%) compared to a diet of RHO (16 to 22%). OXY-CRB showed low GGE (<2 0%), despite feeding actively on both prey. All strains maintained their carbon and nitrogen stoichiometry after 5 d starvation, but lost some fatty acids, especially OXY. Additionally, when starving, respiration rates decreased by 70% in OXY-BCN, 50% in GYR-DK, and by 25% in OXY-CRB. Our results demonstrate that OXY-BCN is a more opportunistic organism, perfectly adapted to heterogeneous or unstable environments; although it requires a suitable biochemical composition in its prey. On the other hand, GYR seems better conditioned to more stable habitats, such as coastal and open waters. This study also stresses the phenotypic differences between strains (especially of OXY) originating from different ecosystems.