The Influence of Beach Sand Characteristics on the Nesting Behavior and Clutch Survival of Green Turtles (Chelonia mydas)

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Abstract
I examined the influence of chemical and physical characteristics of beach sands on nesting behavior and clutch survival of green turtles (Chelonia mydas) at covehead beaches differing in substrate composition on Ascension Id. and Aldabra Atoll. In coarse, dry sand, females have difficulty digging egg chambers, and typically make multiple trial nest holes and re-emerge on successive nights before depositing eggs. At Ascension, clutch mortality is highest at beaches with low substrate water potentials. Calculated substrate water potentials range from -2--320 kPa, and high mortality in the drier conditions suggests that green turtle eggs may be particularly sensitive to desiccation. At the biogenic beaches, mortality is positively correlated with mean particle diameter of the sand, suggesting physiological stress (perhaps desiccation) in coarser sands; sand cave-ins also may cause mortality. Gas diffusion apparently does not limit hatching success at Ascension Id. Clutch survival is positively correlated with nest depth, and negatively correlated with electrical conductivity and volume of air-filled pore space in the substrate. Structure and composition of sand from 34 green turtle nesting beaches from around the world (Atlantic, Indian and Pacific oceans) were analyzed and, together with the Ascension Id. and Aldabra data, indicate that green turtles nest in sands that vary greatly. Factors other than the physiognomy of sand on nesting beaches may be as important, or more important, in nest site selection.