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

Abstract

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.

Green turtle (Chelonia mydas) hatching success at Raine and Heron Islands

“…This threshold hypothesis could be tested by comparing the abundance of sand microbes from nests with high and low early-stage mortality. Evidence supporting the microbial death hypothesis comes from observations that higher abundance of microbes and higher death rates have been found in sand at high density sea turtle nesting beaches (Honarvar et al 2011;Bézy et al 2014Bézy et al , 2015, and that hatching success of nests decreases at Raine Island towards the end of the nesting season when the abundance of sand microbes is expected to increase due to the accumulation of organic material in the sand from dead eggs and residual egg material left behind in the nest after hatchlings escape the nest (Booth et al 2022) et al 2002;Maulany et al 2012).…”

“…High early embryonic mortality has been noted at Raine island previously (Booth and Dunstan 2018; Booth et al . 2021, 2022), but the cause of this mortality remains elusive, with egg infertility, high nest temperatures and extreme respiratory gas levels being investigated and dismissed as possible causes (Booth and Dunstan 2018; Booth et al . 2021, 2022).…”

“…This study uses data obtained from two sites while conducting other studies: (1) Raine Island, located in the northern Great Barrier Reef (11.5904°S, 144.0352°E), during the 2018–2019 nesting season (Booth et al . 2020, 2022), and (2) Heron Island in the southern Great Barrier Reef (23.4422°S, 151.9146°E) during the 2019–2020 and 2020–2021 nesting seasons (Smith et al . 2021; Young et al .…”

“…The hatching success and therefore recruitment of hatchlings from Raine Island appears to have declined since the mid-1980s, varying between 30 and 60% depending on the female visitation rate (Coffee and Robertson 2021). A definitive reason for the decline in hatching success is unknown, but unusually high rates of embryo death very early during incubation may partly explain the overall low hatching success (Booth et al 2020(Booth et al , 2021(Booth et al , 2022. Here, I compare the hatching success, and the early and late incubation embryo death rates of green turtle nests from Raine Island with those from Heron Island in the southern Great Barrier Reef where hatching success is generally greater (Limpus 2008) to determine if there are genuine differences in early-and late-stage embryo death rates between the two locations.…”

Mitigating the effects of climate change on the nests of sea turtles with artificial irrigation

“…Thus, a substrate's surface temperature and moisture can differ significantly from that at nest depth. Substrate characteristics (e.g., grain size and thermal conductivity) affect the dynamics of water, gases, and temperature in and around the nest (Booth et al., 2022 ; Stewart et al., 2019 ). Sand, soil, and leaf litter, for example, have different thermal properties and interact with moisture changes differently (Hillel, 2003 ).…”