Efficacy of intensive seawater irrigation in mitigating climate-driven increases in incubation temperature of green sea turtle (Chelonia mydas) nests.

Sea turtles exhibit environmental sex determination and face risks of over-feminization, heat-induced embryonic failure, and hatchling mortality due to rising global temperatures. Mitigating these impacts of climate change may necessitate interventions to reduce sand temperature. One proposed strategy is to irrigate nests with seawater, but uncertainties exist regarding turtle egg tolerance to saline nest sand. To test the hypothesis that sea turtle embryos can tolerate a regimen of irrigation with seawater at a management-relevant scale, we investigated the impact of two levels of large-scale irrigation using cooled seawater on green turtle nests and embryos, assessing the effects on important nest environmental factors and developmental success. Irrigation which simulated 200 mm of rain reduced the temperature in clutches by up to 5.6 {degrees}C (1.34 {+/-} 0.10 mean {+/-} SD) without adversely affecting clutch oxygen levels, sand water potential, or sand moisture content, but our irrigation regimens resulted in very low hatching success (1.5%). However, late-stage embryonic mortality predominated, suggesting that early embryos may have an unexpected tolerance to saline sand and increasing our understanding of sea turtle resilience to seawater irrigation. The observation that younger embryos may be less susceptible to seawater-associated mortality than mature embryos near hatching further informs the limitations and potential applications of seawater irrigation as a management strategy.