The importance of sand albedo for the thermal conditions on sea turtle nesting beaches

At Ascension Island and Cyprus, major nesting areas for green turtles (Chel onia mydas) in the Atlantic and Mediterranean, respectively, visual inspect ion shows some beaches are light in colour while others are darker. We obje ctively measured the albedo of the sand on different beaches, i.e. the perc entage of the incident solar radiation that was reflected from the sand sur face. At sites where albedo was recorded, we also measured the temperature of the sand at nest depths. At both rookeries, the sand temperature was mar kedly higher on darker beaches due to greater absorption of the incident so lar radiation over the diurnal cycle. Temperature loggers buried at nest de pths revealed seasonal changes in temperature on both islands, but showed t hat the lowest temperatures found on the darker beaches rarely dropped belo w the highest temperatures on the lighter beaches. Sea turtles exhibit temp erature-dependent sex determination. Since sand albedo is a major avenue fo r the production of a range of incubation temperatures on both islands, it will also have profound implications for hatchling sex ratios. In compariso n with both Ascension Island and Cyprus, for samples collected from sea tur tle rookeries around the world there was an even greater range in sand albe do values. This suggests that sand albedo, a factor that has previously rec eived little consideration, will have profound implications for nest temper atures, and hence hatchling sex ratios, for other populations and species.