Rising CO2 level, which reached the 400 ppm milestone in 2010s, may disrupt global ecosystems. Biocalcification performed by hard clam contributes to the balance of carbon budget. The current work studies how to promote biocalcification with symbiosis associations. Three symbiotic associations are under investigation. The first one is the symbiosis between micro algae and hard clams. Biocalcification is a pH regulation mechanism. During day time, photosynthesis performed by algae raises pH and boosts biocalcification. During night time, dissolution of calcium carbonate can maintain pH level. However, nutrient is often the limiting factor for the growth of micro algae and calcifying animal. The second is the symbiosis among microorganisms in fermentation for producing synbiotic feeds for clams. Fermentation is environment-friendly since it recycles nutrients from agriculture by-products. The third one is the symbiosis between hard clams and probiotic microorganisms. Probiotic bacteria and fungi can decompose organic waste to create a friendly environment for cultured animals. They can raise the health level of hosts by improving metabolism and the immune system. The ability to maintain proper water clarity is an indicator of the effectiveness and microorganisms. Carbon fixing can be greatly enhanced through these three symbiotic associations.