Hydro-Oceanographic Controls on Water Quality and Artificial Reef Sustainability in a Data-Limited Tropical Coastal System

Artificial Reefs (ARs) are utilized as ecological engineering tools to rehabilitate degraded coral reefs; however, their long-term performance strongly depends on local hydro-oceanographic conditions. This study presents a practical field and data-processing protocol for seawater quality monitoring around cube-shaped ARs deployed in 2017 at Damas Beach, Prigi Bay, East Java, revisited in August 2024 during the southeast monsoon. Six stations surrounding the ARs were surveyed for in situ temperature, salinity, Dissolved Oxygen (DO), pH, current speed, turbidity, and q depth (water clarity), while nitrate and phosphate concentrations were analyzed ex-situ. The Secchi Depth (SD) ranged from 1.3–4.5 m and turbidity from 19.00–35.78 NTU, indicating highly turbid conditions. The currents were very weak (0–0.1 m/s, mean 0.07 m/s), favoring local sediment deposition around the structures. In contrast, the temperature (24.69–25.77 °C), influenced by monsoon-driven upwelling, salinity (34.00–34.52 ppt), DO (6.68–6.80 mg/L), and pH (7.3–8.0) were within the range suitable for coral reef organisms. Nutrient concentrations were enriched, with nitrate concentrations of 1.746–1.842 mg/L and phosphate concentrations of 0.0947–0.3307 mg/L, consistent with terrestrial inputs from the watershed. Overall, the Damas case demonstrates how the proposed minimum parameter set and workflow can generate a replicable hydro-oceanographic baseline to support routine monitoring and adaptive management of AR sites in data-limited tropical coastal systems.