Strontium-rich micropearls (intracellular inclusions of amorphous calcium carbonate) have been observed in several species of green microalgae within the class Chlorodendrophyceae, suggesting the potential use of these organisms for 90 Sr bioremediation purposes. However, very little is known about the micropearl formation process and the Ca and Sr uptake dynamics of these microalgae. To better understand this phenomenon, we investigated, through laboratory cultures, the behaviour of two species within the class Chorodendrophyceae: Tetraselmis chui, forming micropearls, and T. marina, not forming micropearls. We show that T. chui growth and micropearl formation requires available Ca in the culture medium, and that the addition of dissolved Sr can partially replace the function of Ca in cells. On the other hand, T. marina can grow without added Ca and Sr, probably due to its inability to form micropearls. T. chui cells show a high Ca and Sr uptake, significantly decreasing the concentration of both elements in the culture medium. Strontium is incorporated in micropearls in a short period of time, suggesting that micropearl formation is, most likely, a fast process that only takes a few hours. In addition, we show that micropearls equally distribute between daughter cells during cell division.