The biological mediation of mineral formation (biomineralization) is realized through diverse organic macromolecules that guide this process in a spatial and temporal manner. Although the role of these molecules in biomineralization is being gradually revealed, the molecular basis of their regulatory function is still poorly understood. In this study, we revealed the incorporation and distribution of the model intrinsically disordered Starmaker-like (Stm-l) protein, which is active in fish otoliths biomineralization, within calcium carbonate crystals. The Stm-l promotes crystal nucleation and anisotropic tailoring of crystal morphology. Intracrystalline incorporation of Stm-l protein unexpectedly results in shrinkage (and not expansion as commonly described in biomineral and bioinspired crystals) of the crystal lattice volume, that is here described for the first time in bioinspired mineralization. A ring pattern was observed in 48h grown crystals, composed of a protein-enriched region flanked by protein-depleted regions. It can be explained as a result of the Ostwald-like ripening process and intrinsic properties of Stm-l, and bears some analogy to the daily growth layers of the otolith.