<p>Biomineralization has been used for the treatment of calcareous sand to improve its properties. Although many studies have been performed on the biomineralized calcareous sand under freshwater conditions, few studies were focused on the behaviors of calcareous sand in seawater. As the freshwater is scarce in island areas, the freshwater-based biomineralization technology may be unsuitable for the treatment. In this study, seawater-based bacterial enzyme&#xa0;induced carbonate precipitation (BEICP) was proposed to treat calcareous sand. A series of tests were conducted to verify the feasibility and efficiency of this treatment method through investigating the effects of seawater on the biomineralization and the properties of biomineralized calcareous sand in comparison with microbially induced carbonate precipitation (MICP). Test results reveal that seawater leads to the decrease of urease activity of bacterial cells and urease. NaCl, MgCl₂, Na₂SO₄, and CaCl₂ are the main inhibitory components in seawater, of which MgCl₂ and CaCl₂ have a strong influence on the urease activity of bacterial cells and urease, respectively. Compared to MICP treatment, BEICP-treated calcareous sand exhibits higher unconfined compressive strength and better biomineralization effects. The findings of this study can contribute to the application of biomineralization technology in island areas.</p>