# Recent Developments on Biomineralization for Erosion Control
## 1 Introduction
While seawalls and breakwaters effectively reduce the loss of coastal soil and offer long service life, they can cause secondary erosion. The construction of these structures requires significant amounts of concrete, which not only causes a large amount of carbon emissions, but also forms a permanent cementation on the beach, threatening the normal growth and activities of organisms. Riprap and beach nonurishment, while avoiding environmental pollution, require ongoing maintenance. The long plant growth cycle of mangrove afforestation also needs to be considered, although this technology comes from nature. In general, these conventional approaches, while protective, can be costly and environmentally damaging when considering material, energy, time, cost, and environmental impact. Therefore, it is very meaningful to seek sustainable and environmentally friendly methods to prevent coastal erosion of sandy slopes and liquefaction of the seabed. Drawing inspiration from the natural soil diagenesis process mediated by bacteria, microbially induced calcium carbonate precipitation (MICP) presents a novel method to enhance the engineering properties of sand while offering notable environmental advantages over conventional reinforcement techniques. This process utilizes urease-producing bacteria, such as _Sporosarcina pasteurii_, which hydrolyze urea and precipitate calcium carbonate in the presence of calcium ions. The resulting CaCO\({}_{3}\) strengthens the sand by bonding particles, clogging pores, and coating grains, thereby improving its strength, stiffness, and resistance to erosion [36]. MICP offers benefits such as controllable reactions, eco-friendliness, and low carbon emissions. The bacterial solution (BS) and cementing solution (CS) used in MICP have very low viscosities, allowing them to penetrate farther and deeper compared to Portland cement and other chemical agents. Moreover, the calcium carbonate generated by MICP does not fully occlude the pores, which supports biological processes and promotes plant growth [37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47]. Additionally, MICP is highly suitable for marine environments due to the alkaline pH conditions and the alkaliphilic nature of _Sporosarcina pasteurii_. Furthermore, the presence of calcium and magnesium ions in seawater enhances the rate of carbonate precipitation [48; 49]. Since the discovery by [PERSON] et al. (1973) that certain microorganisms can induce calcium carbonate precipitation via their metabolic processes, research on the reaction mechanisms and engineering applications of MICP has been continuously advancing worldwide [50]. The National Research Council of the United States has recognized MICP technology as a key research focus for the 21 st century. [PERSON] (2004) was the first to utilize MICP for reinforcing loose sand, enhancing its strength and stiffness [51]. Later, [PERSON] and [PERSON] (2005) highlighted the wide-ranging applications and significant potential of MICP in engineering [52]. To date, MICP technology has been widely used in the fields of ground improvement [53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65], erosion control [66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77], crack repair [82; 83; 84; 85; 86; 87], liquefaction mitigation [88; 89; 90; 91; 92; 93; 94; 95; 96; 97], corrosion protection [98; 99], etc. There are a large number of review articles that have comprehensively summarized MICP from the aspects of technical principles, influencing factors, application scenarios, and reinforcement efficiency [100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 110], but there has been no comprehensive review of MICP technology in ocean engineering. Unlike previous reviews focusing on land-based applications, this work evaluates MICP performance in oceanic environments subject to wave and tidal loads.