<![CDATA[Mangrove ecosystems play a crucial role in climate change mitigation, particularly through blue carbon sequestration and the protection of coastal areas. This study aims to identify the initial characteristics of the coastal waters on the western side of Lancang Besar Island, Thousand Islands, based on parameters including depth, pH, temperature, and total dissolved solids (TDS). The findings are compared against relevant seawater quality standards, specifically those stipulated in Government Regulation of the Republic of Indonesia Number 22 of 2021 concerning the Implementation of Environmental Protection and Management. Measurements were conducted on October 8, 2026, along a single transect comprising 21 observation points, spaced at 50 cm intervals, extending from 0 to 1,000 cm from the shoreline. Data were analyzed using descriptive statistics and by examining parameter profiles in relation to the distance from the shore. The results indicate that water depth ranged from 4 to 60 cm (mean: 28.19 cm); pH ranged from 8.1 to 9.0 (mean: 8.50); and temperature ranged from 32 to 33 °C (mean: 32.33 °C). Following adjustment based on the instrument's multiplier factor, TDS values ranged from 172 to 8,790 mg/L. A preliminary comparison with Appendix VIII of Government Regulation Number 22 of 2021 reveals that pH values do not consistently fall within the 7.0–8.5 range established for marine biota. Similarly, temperatures within the mangrove ecosystem do not entirely align with the 28–32 °C reference range, although a deviation of up to 2 °C is permitted. TDS values cannot yet be categorized as compliant or non-compliant based on the provided standards, while water depth serves as a physical characteristic of the aquatic environment. The data obtained can serve as a basis for planning the assessment of vegetation structure, mangrove biomass, and sediment organic carbon content to support the estimation of blue carbon stocks.]]>
