Sand characteristics do not influence hatching success of nests at the world's largest green turtle rookery

Raine Island, located in the northern Great Barrier Reef, hosts the largest green turtle nesting aggregation in the world, but typically experiences low hatching success (20–60%, depending on the number of females visiting the island to nest). To determine whether the low hatching success of green turtle eggs at Raine Island might be explained by local sand characteristics, we investigated the physical properties of Raine Island sand and compared it to sand from other eastern coast Australian sea turtle nesting beaches that have high hatching success (>80%). We also measured the water, salt and organic material content of sand within nests at Raine Island to see whether any of these variables were correlated with the proportion of early embryo death or hatching success. The physical characteristics of Raine Island sand were similar to those of other eastern coast Australian nesting beaches, so it seems unlikely that inherent physical sand properties, water content, salt or organic matter explain the relatively low hatching success observed on Raine Island compared to other Australian green turtle nesting beaches. However, we found that nests that were inundated twice with seawater during spring high tides at the end of their first week of incubation experienced greater early development mortality and lower hatching success than did non-inundated nests, suggesting that embryos drowned during the inundation. Last, we found that hatching success declined towards the end of the nesting season, suggesting that the beach sand in the nesting areas of Raine Island changes in some way, and/or that egg quality decreases as the nesting season progresses.