Biophysical and physiological ecology of loggerhead turtle nests at Zakynthos and Kyparissia, Greece

Sea turtles bury large masses of eggs on beaches. Burying eggs deeply in sand provides a humid environment with fairly constant temperature, but also constrains the diffusion of gases. Zakynthos and Kyparissia, Greece host the largest loggerhead turtle rookeries in the Mediterranean, and the sand on the beaches visibly differs in texture. I used these differences as a natural experiment to determine how the physical characteristics of sand affect the physiology of loggerhead turtle nests in 2009 and 2010. Temperature at nest depth was lower on Marathonissi (26.7 +/- 1.6°C) and Laganas (27.9 +/- 0.8°C) than all other beaches (30.3 +/- 1.5°C) and provided conditions for male hatchling production during this period. Beach temperatures on Kyparissia were higher than ambient weather conditions because topography of the beach allowed for increased absorbance of solar radiation. Based on soil water characteristic curves, eggs on the beaches of Greece were not under hydric stress. Diffusivity varied as a function of air-filled porosity in sand from sea turtle nesting beaches in Greece, Costa Rica and Equatorial Guinea. Conductivity varied as a function of air-filled porosity and median grain size. The oxygen concentration of sea turtle nests can be affected by both diffusion and bulk flow of gases, especially for beaches with large tidal amplitudes. Hatching success of nests was lowest on Kyparissia A (67.6 +/- 4.5%) and maximum nest temperature was lowest on Marathonissi beach (29.4 +/- 0.4°C). All other beaches had a hatching success of 83.0 +/- 4.7% and a maximum temperature of 33.1 +/- 0.4°C. Minimum oxygen concentration within the nest ranged from 17.1 to 20.1 kPa among all nests. Sand grain size characteristics, water content, clutch size, temperature, and ambient sand oxygen concentration predicted nest oxygen concentration when inactive pore space was considered. Gas exchange may limit clutch size, and may be an important factor in the evolution of multiple nesting events in sea turtles. As beaches continue to be developed, eroded or renourished, the undisturbed state of the interstitial environment must be understood in order to properly mitigate and restore the beach ecosystem.