## 1 Introduction  
The precipitation of solid matter from dissolved substances in seawater occurs either abiotically (governed by inorganic thermodynamics and reaction kinetics) or biotically (as a metabolic consequence of living organisms). This process is primarily controlled by the biochemistry of organisms including algae, foraminifera, cyanobacteria, and corals but is also influenced by the marine conditions where they live. Beachrock (Figure S1) is a carbonate sedimentary product with an anchoring effect for dynamic islands and provides protection from erosion [1; 2; 3]. The sedimentary characteristics of beachrock have been investigated; however, many things about its origin and properties remain unknown or are subject to debate. Outcrops of beachrock are valuable records of the past climate of the low-lying reef islands generally found in tropical and subtropical areas with generally warm seawater [4; 5; 6]. Carbonate cement occurs as precipitation from interstitial seawater and or seawater waves [7; 8], coastal aquifers featuring the mixture of saltwater and freshwater [9], or at sea level due to CO\({}_{2}\) degassing [1], with biological activity as an additional agent [10]. Indonesia's coastline is among the largest of any country, and Indonesian beaches face unique issues. Compounding effects and conflicts arise in a complex manner with emergent and cross-scaled impacts, including manifold potential change drivers (e.g., climate change, urbanization, tourism development, and marine resource exploitation) [11; 12; 13; 14; 15].  
Beachrock in some areas has not yet been subjected to study. The beachrock found on Krakal-Sadranan Beach is distributed parallel to the coastline, with a coverage of around 10-30 m\({}^{2}\). The research area is located on a coastline that extends along the south of Java Island (the South Coast). It is included in the Wonosari-Punung Formation according to the regional geological map [16; 17; 18; 19; 20] (Supplementary Materials S1-S3) of the Surakarta-Giritontro sheet [20]. The authors chose this particular location due to the unexplored sedimentary and diagenesis beachrock in the area around Krakal-Sadranan Beach, as well as the lack of records on beachrock occurrence. The aim of this study was to identify the ureolytic bacteria that induced the natural beachrock. This study serves as an initial exploration of beachrock sedimentary processes in the area and as a basis for future studies. These might include studies of the rocks' age based on carbon dating and the development of artificial beachrock using microbially induced carbonate precipitation (MICP) to resolve coastal erosion or other issues. As an initial step towards achieving this goal, native indigenous ureolytic strains were isolated from Indonesian beachrock and beach sand and their bioaugmentation potential. Upon receiving more successful results for MICP treatment using a marine ureolytic bacterium for the desired engineering application, further studies were carried out to (i) isolate a local strain of ureolytic bacteria from natural beachrock, (ii) optimize the growth and enzymatic activity of the isolated strain, and (iii) explore the chemical compounds in the natural beachrock cementation material in nearshore environments as an alternative technique for sand stabilization.