SUMMARY Marine turtles spend more than 90% of their life underwater and have been termed surfacers as opposed to divers. Nonetheless turtles have been reported occasionally to float motionless at the surface but the reasons for this behaviour are not clear. We investigated the location, timing and duration of extended surface times (ESTs) in 10 free-ranging loggerhead turtles (Caretta caretta) and the possible relationship to water temperature and diving activity recorded via satellite relay data loggers for 101–450 days. For one turtle that dived only in offshore areas, ESTs contributed 12% of the time whereas for the other turtles ESTs contributed 0.4–1.8% of the time. ESTs lasted on average 90 min but were mostly infrequent and irregular, excluding the involvement of a fundamental regulatory function. However, 82% of the ESTs occurred during daylight, mostly around noon, suggesting a dependence on solar radiation. For three turtles, there was an appreciable (7°C to 10.5°C) temperature decrease with depth for dives during periods when ESTs occurred frequently, suggesting a re-warming function of EST to compensate for decreased body temperatures, possibly to enhance digestive efficiency. A positive correlation between body mass and EST duration supported this explanation. By contrast, night-active turtles that exceeded their calculated aerobic dive limits in 7.6–16% of the dives engaged in nocturnal ESTs, probably for lactate clearance. This is the first evidence that loggerhead turtles may refrain from diving for at least two reasons, either to absorb solar radiation or to recover from anaerobic activity.

Ectothermic species are strongly affected by thermal changes. To assess the viability of these species under climate change constraints, we need to quantify the sensitivity of their life history traits to temperature. The loggerhead marine turtle (Caretta caretta) nests regularly in the Oriental Basin of the Mediterranean Sea. The different populations are separated because of time (< 12,000 yrs) and very different thermal habitats; it is hotter on the southern coast (Libya) than on the northern ones (Cyprus, Greece, and Turkey). Patterns of embryo growth response to incubation temperatures have been searched for these 2 populations. We found that both populations have similar thermal reaction norms for embryonic growth rate. This highlights that 12,000 yrs is not enough time for this species to adapt to specific thermal habitats and raises the question of the persistence of these populations in the context of rapid climate change.

In order to elucidate genetic structure within the royal tern Thalasseus maximus, genetic analyses and phylogenetic reconstructions were performed on royal terns Thalasseus maximus albididorsalis from the West African breeding population and compared with sequences from American populations Thalasseus maximus maximus. The analysis shows that royal tern as currently defined is a paraphyletic species: West African royal tern is genetically distinct from American breeding populations of the nominate subspecies and forms part of a genetic cluster with lesser crested terns Thalasseus bengalensis (of all subspecies) and greater crested terns Thalasseus bergii. This represents the first published analysis of the genetic relationship between the two subspecies of royal terns, suggests that the West African population should be treated as a distinct species, and provides support to previous studies suggesting that morphological and genetic similarities are poorly correlated in the genus Thalasseus. Conservation and taxonomic implications are discussed.