The coccolithophorid species Pleurochrysis carterae is a common coastal calcifying phytoplankton, which is also able to form dense blooms that harm marine aquaculture. The anti-predator ability of P. carterae is supposed to be one reason why it is a dominant species. In this study, this hypothesis is tested by using brine shrimp Artemia salina as the model predator. Another Prymnesiophyceae species, Isochrysis galbana, which is considered as the benign live food source for A. salina, was used as prey. Changes to the grazing rate or survival rate of A. salina were analyzed when P. carterae was present in the prey mixture. Algal chlorophyll fluorescence efficiency and lipid changes in these two algal species under predation pressure were also studied. Some very interesting P. carterae features were observed, which may provide insights into its anti-predator abilities. These were as follows:(1) When the P. carterae cell numbers increases in the microalgal prey mixture, the brine shrimp A. salina has a lower predation capacity, which is shown by the gradient decrease of chlorophyll content in the brine shrimp intestines. The survival rate is also lower as the number of P. carterae cells increase. Therefore, these results clearly indicated the anti-predator ability of P. carterae.(2) In comparison, the chlorophyll fluorescence(ETR and Fv/Fm) for the two microalgae facing the same predation pressure decreased significantly from 0.75 to 0.60 for Fv/Fm, and from 88% to 65% for ETR, respectively, for I. galbana, but were almost unchanged for P. carterae. This means that photosynthesis of P.carterae is virtually unaffected by the presence of the predator. Such unconstrained ability against the predator was very prominent.(3) Lipidomic analyses, with without the predator, between the two microalgal species indicated that I. galbana did not show any significant changes, whereas P. carterae did significant increase its monogalactosyl diacylglycerol(MGDG), digalactosyldiacylglycerol(DGDG), phosphatidylglycerol(PG), diacylglycerol(DAG), and phosphatidylinositol(PI) contents. Since MGDG, DGDG, and PG are the major components of the chloroplast membrane, the increase in these compounds can have protective effects on the microalgal cell, and both DAG and PI are considered important signals for cell division, so their increase can stimulate the population growth. Hence, the lipid changes clearly provide the biochemical evidence for the physiologically positive changes to P. carterae, in the presence of the predator.(4) Dimethyl sulfoniopro pionate(DMSP) is supposed to contribute in the anti-predator abilities of microalgae. We further studied whether the mortality of A. salina was affected by the algal cellular DMSP content. Cultures containing different cellular DMSP contents were set up by adjusting the phosphorus chemical states in the f/2 culture medium, namely phosphate deficiency, normal f/2, and f/2 medium with ATP as the phosphate supplier. The results showed that, the ambient phosphorus chemical states significantly affect the intracellular DMSP level in P. carterae. After three days of exponential growth, the phosphate deficiency group increased DMSP from 2.35 to 2.42 mg/g lyophilized cells, whereas the normal f/2 medium group reduced DMSP from 2.35 to 2.26 mg/g lyophilized cells, and the ATP enriched group showed the largest decrease in DMSP from 2.35 to 1.90 mg/g lyophilized cells. This indicated that the phosphorus level and chemical state had negative effects on the accumulation of DMSP. Furthermore,, the phosphorus state can affect the preying behavior and mortality of A.salina. Phosphorus deficiency in the culture medium can increase the algal cell's fatal effects on the predator, while ATP, as the sole phosphorus source, may decrease the fatal effects. We conclude that P. carterae contains positive biochemical mechanisms that underlie its anti-predator abilities, possibly through cell membrane component protective reconstruction and DMSP metabolism. Its active anti-preying abilities mean that P. carterae can reach a sustainable population size at the ecological level.