Beach Sand Properties Drive Microclimate and Hatching Success of Olive Ridley (Lepidochelys olivacea) Turtles Under Automated Incubation

Beach sand mediates the egg-adjacent microclimate that determines sea turtle embryonic development and hatching outcomes. This study examines how native sands from four East Java beaches shape in-sand temperature and moisture under automated incubation and how these conditions relate to performance of olive ridley turtles (Lepidochelys olivacea). Despite identical incubator setpoints, sands produced distinct depth microclimates. Sensor data revealed strong ambient–substrate coupling: room humidity predicted sand moisture (R = 0.95, R² = 0.906; $Y = 1.704X − 44.4$), and room temperature correlated positively with sand temperature, demonstrating that cabinet air readings are insufficient proxies for embryo environments. Hatching success was 77.5% (31/40), with the highest rate in the Kilikili sand box (90%). Failure analysis (9/40) distinguished developing-stage arrests (n= 5) from non-developing eggs (n= 4), concentrated in lighter-egg classes. Egg mass scaled with hatchling body mass (r= 0.491, P= 0.004) and carapace length (r= 0.709, P< 0.001), but not width (r= 0.042, P= 0.818), indicating trait-specific responses under stabilized conditions. Findings show that substrate choice, depth-resolved sensing, and mass-aware management are practical levers to improve outcomes and manage temperature-dependent sex determination risks. Integrating native sand selection with sensor-guided control provides actionable guidance to enhance reproductive success and climate resilience in coastal conservation programs.