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Young green turtles (Chelonia mydas) spend their early lives as oceanic omnivores, which consume primarily animal prey. Once they settle into neritic habitats (recruitment), they appear to shift rapidly into an herbivorous diet in tropical regions. However, the ontogeny of the dietary shift and the relevance of animal prey in the diet of neritic green turtles are poorly understood in subtropical and warm temperate regions. Stable isotopes of carbon and nitrogen in the carapace scutes of 22 green turtles from the eastern Mediterranean, ranging from 28 to 83 cm in curved carapace length (CCLmin), were analysed to test the hypothesis of a rapid nutritional shift following recruitment. Seagrasses prevailed in the stomach contents of all the green turtles that were larger than 30 cm CCLmin, but the concentration of stable isotopes in the carapace scutes revealed that turtles shorter than 40 cm CCLmin derived a negligible amount of assimilated nutrients from seagrasses. The concentration of stable isotopes in the carapace scutes also suggested that the contribution of seagrasses to the nutrients assimilated by green turtles increased steadily with turtle size and that some, but not all, of the turtles larger than 62 cm CCLmin were fully herbivorous. The overall evidence (gut contents analysis and stable isotope analysis) indicates that green turtles in the Mediterranean shift to a seagrass-based diet immediately after recruitment but turtle growth continues to rely on animal-derived nutrients for several years after recruitment. This asynchrony between the dietary and nutritional shifts is thought to be caused by the temperature sensitivity of bacterial fermentation and the low temperatures experienced by green turtles in the Mediterranean, which may result in a poor assimilation of the plant-derived nutrients for most of their neritic juvenile life.

The choice of a suitable nest habitat by oviparous reptiles that deposit eggs into a nest and provide no subsequent parental care is likely to play a major role in the survival of the offspring. In particular variations in nest temperature may influence the rate at which embryos utilise their yolk energy. The effects of nest temperature on total energy use are however complex. High temperatures may advance development and shorten the time to hatching, thereby reducing energy use, but they also stimulate metabolic rate increasing energy use. The net effect of temperature on total energy demands is therefore uncertain. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured by open-flow respirometry during the incubation of loggerhead sea turtle eggs at three temperatures (27.6, 30.0 and 31.8 °C). At each temperature, VO2 and VCO2 showed a peak followed by a decline to hatching. Incubation temperature was negatively related to incubation duration and positively related to the maximum metabolic rate of the embryos. Peak VO2 was 74.8 ml/egg/day at 27.6 °C, 91.9 ml/egg/day at 30.0 °C, and 97.9 ml/egg/day at 31.8 °C. Peak VO2 occurred closer to hatching in eggs incubated at higher temperatures. Total energy expenditure was greatest at the lowest incubation temperature and lowest at the highest temperature. Total VO2 and VCO2 were 1777 ml/egg and 1226 ml/egg, respectively, at 27.6 °C, 1680 ml/egg and 1235 ml/egg at 30.0 °C, and 1613 ml/egg and 1191 ml/egg at 31.8 °C. Using the actual RQ values, this corresponds to a cost of development of 34,963 J/egg at 27.6 °C, 33,403 J/egg at 30.0 °C, and 32,107 J/egg at 31.8 °C. At all temperatures, the calculated respiratory quotient values did not suggest that yolk substrates were oxidised proportionately, but more likely indicated their sequential use. Nest temperatures may play a key role in energy use, with cooler temperature nests increasing the overall energy demands placed on developing embryos.

Female sea turtles typically lay several clutches during each nesting season and rest in the time between laying clutches (the internesting period) in the waters off the nesting beach. Adequate protection of turtles in the internesting area requires knowledge on their spatial behaviour and was so far hampered by methodological limitations. Satellite telemetry data of exceptionally high quality allowed us to scrutinize internesting area use of four loggerhead sea turtles nesting in the Bay of Laganas (Zakynthos, Greece). We assessed the efficacy of two zones of a marine reserve with distinct levels of protection (boats are excluded from one zone). Most of the obtained locations of three of the four turtles were within the bay, a result consistent with a strategy to minimize energy expenditure. Turtles showed no obvious preference for the highly protected area of the bay. The availability of warmer water in the less protected area may be more crucial than avoidance of boat disturbance.

The sandy beaches of Zakynthos Island support the largest single nesting aggregation in the Mediterranean Region of the endangered loggerhead turtle Caretta caretta. The present study attempts to determine possible correlations between a series of habitat variables and nest site selection. Nesting activities, including total and nesting emergences were examined in response to the recorded biotic and abiotic variables. The results of the analysis indicate that beach width is the most critical habitat variable affecting nest site selection. Further analysis of nesting performance implies that sea turtles use multiple environmental cues for nest site selection during the different steps of the nesting processes such as emergence from the surf and nesting. Nevertheless, we caution that a detailed study needs to be conducted over a more extensive period of time to verify these suggestions.

In this paper, we evaluate the effectiveness of different well-tested conservation techniques in an effort to successfully protect sea turtle nests. From an eight-year study on the island of Zakynthos, West Greece, we have experimentally investigated the effectiveness of two different conservation techniques applied to loggerhead sea turtle nests and provided statistical measures to evaluate their conservation value. The categories of nests evaluated include: (i) nests incubated in situ, (ii) translocated into a beach hatchery, or (iii) protected by metal cages. Results of the analysis showed significant interannual variations in hatching success as obtained for each one of the three groups of nests. Significant differences were also observed when comparing hatching success data among the three groups of nests during the eight-year period. Overall, our results indicate that relocation of nests laid at highly threatened locations and the placement of protective cages on nests in situ provide adequate conservation measures that could allow an increase in hatchling production; although their choice and application should be based on the specific conditions and threats of each nest.

Offspring sex ratio is an important demographic parameter and, given its determination by incubation temperature in sea turtles, might be a key factor for their conservation under climate warming. An appealing approach to estimate hatchling sex ratios is to measure sand temperatures at nest depth and deduce hatchling sex ratios from a beforehand-established relationship of hatchling sex ratio and sand temperature. Such estimates will only be accurate though if metabolic heat produced by the embryos is considered. Judging whether metabolic heating has a potential effect on hatchling sex ratios without actually measuring temperature within clutches would greatly facilitate monitoring protocols. We tested for a relationship between the amount of metabolic heating and the number of developed embryos as well as clutch size in the largest known loggerhead sea turtle (Caretta caretta) population of the Mediterranean on Zakynthos (Greece). Temperatures were measured within 20 nests as well as at a reference site in the sand at nest depth. Metabolic heating was detected, but only during the last third of the incubation period did nests heat up considerably (1.6 °C on average) above the temperature of the surrounding sand. During the middle third of incubation, when sex is determined, the amount of metabolic heating was negligible. The amount of metabolic heating during the last third of the incubation duration was significantly correlated to the number of offspring developed to at least about 75% of incubation duration. This factor explained nearly 50% of variation in metabolic heating. Metabolic heating was also significantly correlated to clutch size. Given that clutch size within the Mediterranean is largest in Zakynthos loggerheads, we conclude that metabolic heating can be ignored in the estimate of hatchling sex ratios in Mediterranean loggerhead populations. These results thus provide the basis for a feasible monitoring of hatchling sex ratios in the loggerhead sea turtle in the Mediterranean.