Abstract: The biological function and mechanism of the calcareous skeletons of planktonic foraminifera are not fully understood. Previous studies have suggested that the shell plays a role in regulating the force balance of planktonic foraminifera by providing negative buoyancy. However, few studies have reconstructed and quantitatively analyzed the individual development process of planktonic foraminifera to reveal the function of the shell throughout their life cycle. We used synchrotron X-ray tomography to reconstruct the individual development of planktonic foraminiferal chambers from six different genera in sediment cores from the tropical western Pacific. By calculating the total mass of the shell and cytoplasm before and after the formation of each chamber, we were able to determine the average density variation pattern during the entire individual development process. We found significant differences in the patterns of average density among different ecological niche genera, suggesting that buoyancy regulation may be related to vertical migration during the life cycle, especially for non-spinose planktonic foraminifera genera. The density patterns also reveal the range of buoyancy regulation throughout the entire individual development process, which may be one of the factors on the vertical migration of non-spinose planktonic foraminiferal genera. Furthermore, the morphological evolution of planktonic foraminifera chambers may involve adaptation to changes in the vertical structure of the living water column.