Short-term resilience to climate-induced temperature increases for equatorial sea turtle populations

Projection models are being increasingly used to manage threatened taxa by estimating their responses to climate change. Sea turtles are particularly susceptible to climate change as they have temperature-dependent sex determination and increased sand temperatures on nesting beaches could result in the 'feminisation' of hatchling sex ratios for some populations. This study modelled likely long-term trends in sand temperatures and hatchling sex ratios at an equatorial nesting site for endangered green turtles (Chelonia mydas) and critically endangered hawksbill turtles (Eretmochelys imbricata). A total of 1078 days of sand temperature data were collected from 28 logger deployments at nest depth between 2018 and 2022 in Papua New Guinea (PNG). Long-term trends in sand temperature were generated from a model using air temperature as an environmental proxy. The influence of rainfall and seasonal variation on sand temperature was also investigated. Between 1960 and 2019, we estimated that sand temperature increased by ~0.6°C and the average hatchling sex ratio was relatively balanced (46.2% female, SD = 10.7). No trends were observed in historical rainfall anomalies and projections indicated no further changes to rainfall until 2100. Therefore, the sex ratio models were unlikely to be influenced by changing rainfall patterns. A relatively balanced sex ratio such as this is starkly different to the extremely female-skewed hatchling sex ratio (>99% female) reported for another Coral Sea nesting site, Raine Island (~850 km West). This PNG nesting site is likely rare in the global context, as it is less threatened by climate-induced feminisation. Although there is no current need for 'cooling' interventions, the mean projected sex ratios for 2020-2100 were estimated 76%-87% female, so future interventions may be required to increase male production. Our use of long-term sand temperature and rainfall trends has advanced our understanding of climate change impacts on sea turtles.

The ecological importance of the accuracy of environmental temperature measurements

The implications of logger accuracy and precision are rarely considered prior to their application in many ecological studies. We assessed the accuracy and precision of three temperature data loggers widely used in ecological studies (Hobo®, iButton® and TinyTag®). Accuracy was highest in TinyTags (95% of readings were within 0.23°C of the true temperature) and lowest in HOBOs and iButtons (95% of were readings within 0.43°C and 0.49°C of the true temperature, respectively). The precision (standard deviation of the repeat measurements) was greatest in TinyTags (0.04°C), followed by iButtons (0.17°C) and then HOBOs (0.22°C). As a case study, we then considered how modelled estimates of sea turtle hatchling sex ratios (derived from temperature), could vary as a function of logger accuracy. For example, at 29°C when the mean sex ratio derived was 0.47 female, the sex ratio estimate from a single logger could vary between 0.40 and 0.50 for TinyTags and 0.29 and 0.56 for both HOBOs and iButtons. Our results suggest that these temperature loggers can provide reliable descriptions of sand temperature if they are not over-interpreted. Logger accuracy must be considered in future ecological studies in which temperature thresholds are important.

How well do embryo development rate models derived from laboratory data predict embryo development in sea turtle nests?

Development rate of ectothermic animals varies with temperature. Here we use data derived from laboratory constant temperature incubation experiments to formulate development rate models that can be used to model embryonic development rate in sea turtle nests. We then use a novel method for detecting the time of hatching to measure the in situ incubation period of sea turtle clutches to test the accuracy of our models in predicting the incubation period from nest temperature traces. We found that all our models overestimated the incubation period. We hypothesize three possible explanations which are not mutually exclusive for the mismatch between our modeling and empirically measured in situ incubation period: (1) a difference in the way the incubation period is calculated in laboratory data and in our field nests, (2) inaccuracies in the assumptions made by our models at high incubation temperatures where there is no empirical laboratory data, and (3) a tendency for development rate in laboratory experiments to be progressively slower as temperature decreases compared with in situ incubation.

We determined the hatching time in sea turtle nests and compared those with hatching times predicted from nest temperature traces. We found that nest temperature traces overestimated hatching time.

Insights from an ancient gymnosperm lineage: ambient temperature and light and the timing of thermogenesis in cycad cones

PREMISE

Although maintaining the appropriate mid-day timing of the diel thermogenic events of cones of the dioecious cycads Macrozamia lucida and M. macleayi is central to the survival of both plant and pollinator in this obligate pollination mutualism, the nature of the underlying mechanism remains obscure. We investigated whether it is under circadian control. Circadian mechanisms control the timing of many ecologically important processes in angiosperms, yet only a few gymnosperms have been studied in this regard.

METHODS

We subjected cones to different ambient temperature and lighting regimens (constant temperature and darkness; stepwise cool/warm ambient temperatures in constant darkness; stepwise dark/light exposures at constant temperature) to determine whether the resulting timing of their thermogenic events was consistent with circadian control.

RESULTS

Cones exposed to constant ambient temperature and darkness generated multiple temperature peaks endogenously, with an average interpeak-temperature period of 20.7 (±0.20) h that is temperature-compensated (Q₁₀  = 1.02). Exposure to 24-h ambient temperature cycles (12 h cool/12 h warm, constant darkness) yielded an interpeak-temperature period of 24.0 (±0.05) h, accurately and precisely replicating the ambient temperature period. Exposure to 24-h photo-cycles (12 h light/12 h dark, constant ambient temperature) yielded a shorter, more variable interpeak-temperature period of 23 (±0.23) h.

CONCLUSIONS

Our results indicate that cycad cone thermogenesis is under circadian clock control and differentially affected by ambient temperature and light cycles. Our data from cycads (an ancient gymnosperm lineage) adds to what little is known about circadian timing in gymnosperms, which have rarely been studied from the circadian perspective.

Diet reflects opportunistic feeding habit of the Asian water monitor (Varanus salvator)

The Asian water monitor (Varanus salvator) is a large generalist predator and scavenger lizard. This species has a widespread distribution throughout South and Southeast Asia and is frequently encountered around the edges of urban settlements. Here, we present information on diet diversity and habitat utilisation of a population of Asian water monitors inhabiting the University of Malaysia Terengganu campus located on the east coast of mainland Malaysia. The stomach contents of 30 Asian water monitors were examined by stomach flushing, and 47.6% of stomach contents was mangrove crab, 26.2% was human waste and 26.2% was other natural foods consisting of fruits, fishes, leeches, snails, birds and insects. We then recorded the locations and habitats utilised by patrolling the campus area and found Asian water monitors preferred to use water and mangrove forest habitats that fringed and crisscrossed the campus. The broad diversity of stomach contents reflected food available at this location and indicates the opportunistic feeding habit of this species. Given that this species widely distributed in Southeast Asia, its broad diet diversity and habitat variations may promote the adaptation of Asian water monitor to different environments.

Influence of short-term temperature drops on sex-determination in sea turtles

All sea turtles exhibit temperature-dependent sex-determination, where warmer temperatures produce mostly females and cooler temperatures produce mostly males. As global temperatures continue to rise, sea turtle sex-ratios are expected to become increasingly female-biased, threatening the long-term viability of many populations. Nest temperatures are dependent on sand temperature, and heavy rainfall events reduce sand temperatures for a brief period. However, it is unknown whether these short-term temperature drops are large and long enough to produce male hatchlings. To discover if short-term temperature drops within the sex-determining period can lead to male hatchling production, we exposed green and loggerhead turtle eggs to short-term temperature drops conducted in constant temperature rooms. We dropped incubation temperature at four different times during the sex-determining period for a duration of either 3 or 7 days to mimic short-term drops in temperature caused by heavy rainfall in nature. Some male hatchlings were produced when exposed to temperature drops for as little as 3 days, but the majority of male production occurred when eggs were exposed to 7 days of lowered temperature. More male hatchlings were produced when the temperature drop occurred during the middle of the sex-determining period in green turtles, and the beginning and end of the sex-determining period in loggerhead turtles. Inter-clutch variation was evident in the proportion of male hatchlings produced, indicating that maternal and or genetic factors influence male hatchling production. Our findings have management implications for the long-term preservation of sea turtles on beaches that exhibit strongly female-biased hatchling sex-ratios.

Spatial Ecology of Asian Water Monitors Adjacent to a Sea Turtle Nesting Beach

Nest predation is the main cause of hatching failure for many turtle populations. For green turtles (Chelonia mydas) nesting at Chagar Hutang in Redang Island, Malaysia, Asian water monitors (Varanus salvator) are a potential nest predator. However, no studies have documented the space use of this species in coastal habitat adjacent to a sea turtle nesting beach to assess its potential impact on turtle nests. Here, we used Global Positioning System (GPS) data loggers to quantify space use of Asian water monitors in order to establish the extent to which they use sea turtle nesting areas. Asian water monitors had a diurnal activity pattern and spent most of their time in rain forest habitat behind the sea turtle nesting beach. The home range occupied by Asian water monitors varied between 0.015 and 0.198 km² calculated by the Kernel Brownian Bridge method. The space use patterns of individual Asian water monitors varied between individuals. Two males had relatively small home ranges, whereas one male and the female had a relatively large home range. Because tracked Asian water monitors in this study rarely visited the sea turtle nesting areas, it is probable that only a few individuals are responsible for opening nests.

Egg viability of green turtles nesting on Raine Island, the world’s largest nesting aggregation of green turtles

Egg inviability at oviposition is a possible explanation for the high rate of early-stage embryo death of eggs laid by green turtles at Raine Island, the largest green turtle nesting aggregation in the world. We tested this possibility by assessing egg viability of freshly laid eggs. We found that green turtle eggs laid at Raine Island have high viability at their time of laying, and that there was no relationship between egg viability and early-stage embryo death or hatching success within a clutch. Hence, the inviable egg at oviposition hypothesis cannot explain the high death rate of early-stage embryos that is characteristic of green turtle clutches laid at Raine Island.

Extreme rainfall events and cooling of sea turtle clutches: Implications in the face of climate warming

Understanding how climate change impacts species and ecosystems is integral to conservation. When studying impacts of climate change, warming temperatures are a research focus, with much less attention given to extreme weather events and their impacts. Here, we show how localized, extreme rainfall events can have a major impact on a species that is endangered in many parts of its range. We report incubation temperatures from the world's largest green sea turtle rookery, during a breeding season when two extreme rainfall events occurred. Rainfall caused nest temperatures to drop suddenly and the maximum drop in temperature for each rain-induced cooling averaged 3.6°C (n = 79 nests, min = 1.0°C, max = 7.4°C). Since green sea turtles have temperature-dependent sex determination, with low incubation temperatures producing males, such major rainfall events may have a masculinization effect on primary sex ratios. Therefore, in some cases, extreme rainfall events may provide a "get-out-of-jail-free card" to avoid complete feminization of turtle populations as climate warming continues.

Influence of sand grain size and nest microenvironment on incubation success, hatchling morphology and locomotion performance of green turtles (Chelonia mydas) at the Chagar Hutang Turtle Sanctuary, Redang Island, Malaysia

The nest microenvironment affects hatching and emergence success, sex ratios, morphology, and locomotion performance of hatchling sea turtles. Sand grain size is hypothesised to influence the nest microenvironment, but the influence of sand grain size on incubation of sea turtle eggs has rarely been experimentally tested. At the Chagar Hutang Turtle Sanctuary, Redang Island, Malaysia, green turtle (Chelonia mydas) nests were relocated to sands with different sand grain sizes on a natural beach to assess whether grain size affects nest temperature, oxygen partial pressure inside the nest, incubation success, hatchling morphology and hatchling locomotion performance. Green turtle nests in coarse sand were cooler; however, hatching success, nest emergence success, oxygen partial pressure, incubation length and hatchling size were not influenced by sand particle size. Nests in medium-grained sands were warmest, and hatchlings from these nests were better self-righters but poorer crawlers and swimmers. Hatchling self-righting ability was not correlated with crawling speed or swimming speed, but crawling speed was correlated with swimming speed, with hatchlings typically swimming 1.5–2 times faster than they crawled. Hence, we found that sand particle size had minimal influence on the nest microenvironment and hatchling outcomes.

Sand type influences the energetics of nest escape in Brisbane river turtle hatchlings

Freshwater turtles can construct their nest in a wide range of soil types, and because different soil types have different physical characteristics such as particle size distribution and compactness, soil type presumably affects digging performance and the energetics of nest escape of turtle hatchlings. Previous studies have reported how cohort size affects the energetic cost of nest escape in turtle hatchlings, but no studies have reported the influence of substrate type on the energetic cost of nest escape. The time taken and the energy required by the same number of hatchlings to dig through two different sand types were quantified by open-flow respirometry. Brisbane river turtle hatchlings digging through fine sand escaped faster and spent less energy than hatchlings digging through coarse sand, and a larger cohort size provided a clear energetic advantage while digging in both sand types. Across all group sizes, hatchlings digging through fine sand spent 33.8% less energy compared with hatchlings digging through coarse sand. We conclude that hatchlings emerging from nests constructed in fine sand have an energetic advantage over hatchlings emerging from nests constructed in course sand because they would have greater energy reserves upon reaching the nest’s surface.

Who are the important predators of sea turtle nests at Wreck Rock beach?

Excessive sea turtle nest predation is a problem for conservation management of sea turtle populations. This study assessed predation on nests of the endangered loggerhead sea turtle (Caretta caretta) at Wreck Rock beach adjacent to Deepwater National Park in Southeast Queensland, Australia after a control program for feral foxes was instigated. The presence of predators on the nesting dune was evaluated by tracking plots (2 × 1 m) every 100 m along the dune front. There were 21 (2014–2015) and 41 (2015–2016) plots established along the dune, and these were monitored for predator tracks daily over three consecutive months in both nesting seasons. Predator activities at nests were also recorded by the presence of tracks on top of nests until hatchlings emerged. In addition, camera traps were set to record the predator activity around selected nests. The tracks of the fox (Vulpes vulpes) and goanna (Varanus spp) were found on tracking plots. Tracking plots, nest tracks and camera traps indicated goanna abundance varied strongly between years. Goannas were widely distributed along the beach and had a Passive Activity Index (PAI) (0.31 in 2014–2015 and 0.16 in 2015–2016) approximately seven times higher than that of foxes (PAI 0.04 in 2014–2015 and 0.02 in 2015–2016). Five hundred and twenty goanna nest visitation events were recorded by tracks but no fox tracks were found at turtle nests. Camera trap data indicated that yellow-spotted goannas (Varanus panoptes) appeared at loggerhead turtle nests more frequently than lace monitors (V. varius) did, and further that lace monitors only predated nests previously opened by yellow-spotted goannas. No foxes were recorded at nests with camera traps. This study suggests that large male yellow-spotted goannas are the major predator of sea turtle nests at the Wreck Rock beach nesting aggregation and that goanna activity varies between years.

The effect of on-shore light pollution on sea-turtle hatchlings commencing their off-shore swim

Context Off-shore recruitment impairment of sea-turtle hatchlings because of light pollution is a growing concern to conservation of sea-turtle population throughout the world. Studies have focussed on sea-turtle hatchling sea-finding behaviour, and ignored the possible effect that on-shore lighting might have on hatchlings after they have entered the sea. Aims We experimentally evaluated the effect that on-shore light pollution has on the swimming behaviour of green turtle hatchlings once they have entered the sea and begun swimming off-shore. We also estimated the decrease in off-shore recruitment of hatchlings as a result of light pollution disruption of the off-shore swim. Methods Hatchling misorientation rates were quantified by releasing marked hatchlings to the sea from different land-based locations adjacent to light-polluted beach areas under a variety of environmental conditions. The beach in light-polluted regions was then searched for marked hatchlings returning to shore from the sea. Key results Misorientation rates were highest in trials conducted during moonless nights (66.7% of trials had some hatchlings return to shore) and lowest during trials conducted during moonlit nights (no trials had hatchlings return to shore). Green turtle hatchling off-shore recruitment for the entire 2014–15 nesting season at Heron Island was estimated to decrease 1.0 –2.4% as a result of on-shore lights disrupting hatchling off-shore swimming behaviour. Conclusions On moonless nights, sea-turtle hatchlings after having successfully completed their journey from nest to sea and entered the sea can be lured back to shore again by shore-based light pollution and, this will decrease their off-shore recruitment success. Implications To ensure maximum off-shore recruitment of sea-turtle hatchlings, on-shore light pollution adjacent to nesting beaches needs to be minimised so as to minimise misorientation and disorientation of hatchlings while on the beach and in near-shore waters.

Intraspecific variation in space use of a coastal population of lace monitors (Varanus varius)

The lace monitor (Varanus varius) is a carnivorous scavenger that inhabits lowland forests and coastlines throughout south-eastern Australia. Here we used global positioning system (GPS) devices to remotely monitor adult lace monitor behaviour across two summer seasons in a coastal habitat adjacent to a sea turtle nesting beach at Wreck Rock, Queensland, Australia. GPS tracking showed that lace monitors spent most of their time in woodland habitat away from the seafront dune areas. Both adult males and females occupied relatively large home ranges (0.005 to 1.467 km2 calculated by the Kernel Brownian Bridge method) and individual home ranges overlapped each other to a large extent. The space use patterns of individual lace monitors could be classified as ‘linear’ or ‘clumped’, indicating plasticity in this species’ movement behaviour. Because lace monitors rarely visited the frontal dune area where sea turtles nest, they do not pose a significant threat to sea turtle nests.

Spatial ecology of yellow-spotted goannas adjacent to a sea turtle nesting beach

Nest predation is the main cause of hatch failure for many turtle populations. For loggerhead turtles (Caretta caretta) nesting at the Wreck Rock rookery, adjacent to Deepwater National Park in south-east Queensland, yellow-spotted goannas (Varanus panoptes) are the main nest predator. However, no studies have documented the space use of goannas in costal habitat adjacent to a sea turtle nesting beach. Here we used Global Positioning System data loggers to evaluate the spatial ecology of adult yellow-spotted goannas in order to discover their potential interaction with sea turtle nests. Male yellow-spotted goannas had larger home ranges, spent a greater proportion of their time in the beach dune area where sea turtles nest, and their home ranges overlapped with more sea turtle nests compared with females. Both males and females had a bimodal activity pattern, with peaks in activity in the early morning and mid to late afternoon. Examination of space-use patterns indicates that it is the larger male yellow-spotted goannas that are the main predators of sea turtle nests at the Wreck Rock beach-nesting aggregation. Hence, by inference, it is probable that large male yellow-spotted goannas are responsible for opening nests at other Australian mainland sea turtle beaches, and if a goanna-specific management strategy is implemented to control predation it is these large males that should be targeted.

Thermogenic respiratory processes drive the exponential increase of volatile organic compound emissions in Macrozamia cycad cones

An important outcome of plant thermogenesis is increased emissions of volatiles that mediate pollinator behaviour. We investigated whether the large increase in emissions, mainly the monoterpene ß-myrcene (>90%), during daily thermogenic events of Macrozamia macleayi and lucida cycad cones are due solely to the influence of high cone temperatures or are, instead, a result of increased respiratory rates during thermogenesis. We concurrently measured temperature, oxygen consumption and ß-myrcene emission profiles during thermogenesis of pollen cones under typical environmental temperatures and during experimental manipulations of cone temperatures and aerobic conditions, all in the dark. The exponential rise in ß-myrcene emissions never occurred without a prior, large increase in respiration, whereas an increase in cone temperature alone did not increase emissions. When respiration during thermogenesis was interrupted by anoxic conditions, ß-myrcene emissions decreased. The increased emission rates are not a result of increased cone temperature per se (through increased enzyme activity or volatilization of stored volatiles) but are dependent on biosynthetic pathways associated with increased respiration during thermogenesis that provide the carbon, energy (ATP) and reducing compounds (NADPH) required for ß-myrcene production through the methylerythritol phosphate (MEP) pathway. These findings establish the significant contribution of respiration to volatile production during thermogenesis.

Synchronous activity lowers the energetic cost of nest escape for sea turtle hatchlings

A potential advantage of group movement in animals is increased locomotion efficiency. This implies a reduced energetic cost for individuals that occur in larger groups such as herds, flocks and schools. When chelonian hatchlings hatch in the underground nest with finite energy for their post-hatching dispersal phase, they face the challenge of minimizing energetic expenditure while escaping the nest. The term 'social facilitation' has been used to describe the combined digging effort of sea turtle hatchlings during nest escape. Given that in a normal clutch, a substantial part of the energy reserve within the residual yolk is used by hatchlings in the digging out process, a decreased cohort size may reduce the energy reserve available to cross the beach and sustain the initial swimming frenzy. This hypothesis was experimentally tested by varying cohort size in hatchling green turtles (Chelonia mydas) and measuring energy expenditure during the nest escape process using open-flow respirometry. The energetic cost of escaping through 40 cm of sand was calculated to vary between 4.4 and 28.3 kJ per individual, the cost decreasing as the number of individuals in the cohort increased. This represents 11-68% of the energy contained in a hatchling's residual yolk at hatching. The reduced energetic cost associated with large cohorts resulted from both a lower metabolic rate per individual and a shortened nest escape time. We conclude that synchronous digging activity of many hatchlings during nest escape evolved not only to facilitate rapid nest emergence but also to reduce the energetic cost to individuals.

The effect of rearing temperature on development, body size, energetics and fecundity of the diamondback moth

Temperature is arguably the most important abiotic factor influencing the life history of ectotherms. It limits survival and affects all physiological and metabolic processes, including energy and nutrient procurement and processing, development and growth rates, locomotion ability and ultimately reproductive success. However, the influence of temperature on the energetic cost of development has not been thoroughly investigated. We show that in the diamondback moth [Plutella xylostella L. (Lepidoptera: Plutellidae)] rearing temperature (range 10-30°C) affected growth and development rates, the energetic cost of development and fecundity. Rearing at lower temperatures increased development times and slowed growth rate, but resulted in larger adult mass. Fecundity was lowest at 10°C, highest at 15°C and intermediate at temperatures of 20°C and above. At a given rearing temperature fecundity was correlated with pupal mass and most eggs were laid on the first day of oviposition, there was no correlation between total eggs laid and adult longevity. The highest production cost was incurred at 10°C; this decreased with increasing temperature, was minimized in the range 20-25°C, and then increased again at 30°C. These minimized production costs occurred at temperatures close to the intrinsic optimum temperature for this species and may reflect the rearing temperature for optimal fitness. Thus at sub-optimal temperatures greater food resources are required during the development period. Predicted increased temperatures at the margins of the current core distribution of P. xylostella could ameliorate current seasonal effects on fecundity, thereby increasing the probability of winter survival leading to more resilient range expansion and an increased probability of pest outbreaks.

An assessment of ‘turtle-friendly' lights on the sea-finding behaviour of loggerhead turtle hatchlings (Caretta caretta)

Context It is well established that artificial light can disrupt the sea-finding ability of sea turtle hatchlings, and some manufactures are now marketing ‘turtle-friendly’ lights that are supposed to be minimally disruptive to this sea-finding behaviour. However, there have been no studies that have tested whether ‘turtle-friendly’ lights are benign to hatchling sea turtle sea-finding ability. Aims We tested two different types of ‘turtle-friendly’ lights (LED amber-light peak intensity 620 nm and LED red-light peak intensity 640 nm) to see whether they are disruptive to the sea-finding ability of eastern-coast Australian loggerhead turtle hatchlings. Methods Using standard circular-arena experiments, we assessed the directional preference of newly emerged loggerhead turtle hatchlings from the Woongarra Coast of Queensland, Australia, during different moon phases without artificial lighting and in the presence of ‘turtle-friendly’ lights. Key results Contrary to expectations, sea-finding ability of hatchlings was disrupted by the amber lights, particularly in the absence of a moon. The less intense red lights were less disruptive to hatchlings; however, misorientation and disorientation events still occurred when lights were within 4 m of hatchlings. The disruptive impact on sea-finding ability increased with the cumulative impact of multiple lights increasing light intensity. Conclusions The ‘turtle-friendly’ lights we used disrupted the sea-finding ability of eastern-coast Australian loggerhead turtle hatchlings, with the most pronounced disruption occurring under moonless conditions. Implications The use of amber and red LED lights adjacent to the nesting beaches of loggerhead sea turtles should be managed because this lighting has the potential to disrupt the sea-finding ability of sea turtle hatchlings.

Incubation temperature, morphology and performance in loggerhead (Caretta caretta) turtle hatchlings from Mon Repos, Queensland, Australia

Marine turtles are vulnerable to climate change because their life history and reproduction are tied to environmental temperatures. The egg incubation stage is arguably the most vulnerable stage, because marine turtle eggs require a narrow range of temperatures for successful incubation. Additionally, incubation temperature affects sex, emergence success, morphology and locomotor performance of hatchlings. Hatchlings often experience high rates of predation in the first few hours of their life, and increased size or locomotor ability may improve their chances of survival. Between 2010 and 2013 we monitored the temperature of loggerhead (Caretta caretta; Linnaeus 1758) turtle nests at Mon Repos Rookery, and used these data to calculate a mean three day maximum temperature (T3dm) for each nest. We calculated the hatching and emergence success for each nest, then measured the mass, size and locomotor performance of hatchlings that emerged from those nests. Nests with a T3dm greater than 34°C experienced a lower emergence success and produced smaller hatchlings than nests with a T3dm lower than 34°C. Hatchlings from nests with a T3dm below 34°C performed better in crawling and swimming trials than hatchlings from nests with a T3dm above 34°C. Thus even non-lethal increases in global temperatures have the potential to detrimentally affect fitness and survival of marine turtle hatchlings.

Investigating diet and diet switching in green turtles (Chelonia mydas)

Understanding the dietary ecology of animals provides information about their habitat requirements, facilitating informed conservation. We used last-bite diet and stable isotope analysis to assess the diet of juvenile and adult green turtles (Chelonia mydas) at two different habitats located 10 km apart within Port Curtis, Queensland, Australia. Last-bite diet analysis indicated that turtles had distinctly different diets in these two habitats: in one the diet was dominated by red macroalgae and in the other the diet was dominated by seagrass. Only juveniles (n = 12) were caught in the habitat where red macroalgae dominated the diet, while both juveniles (n = 9) and adults (n = 38) were captured in the habitat where seagrass dominated the diet. In the seagrass habitat there was no difference in diet between juveniles and adults, and no difference in diet between adult males (n = 17) and females (n = 21). Because the red macroalgae and seagrass had distinctly different carbon stable isotope ratios, it was possible to detect a change in diet by comparing the carbon stable isotope ratio between serum and epidermal tissue sampled from the same turtle. In this region, a switch in diet would reflect a shift in foraging habitat. Such comparisons indicate that ~50% of turtles switched diet, and therefore changed foraging habitat between the time when blood serum and epidermis were formed. This implies that switching foraging habitat by green turtles within this region is a common occurrence, which is somewhat surprising because previously it was thought that foraging green turtles had high site fidelity with relatively small home ranges.

Kinematics of swimming and thrust production during powerstroking bouts of the swim frenzy in green turtle hatchlings

Hatchling sea turtles emerge from nests, crawl down the beach and enter the sea where they typically enter a stereotypical hyperactive swimming frenzy. During this swim the front flippers are moved up and down in a flapping motion and are the primary source of thrust production. I used high-speed video linked with simultaneous measurement of thrust production in tethered hatchlings, along with high-speed video of free swimming hatchlings swimming at different water speeds in a swim flume to investigate the links between kinematics of front flipper movement, thrust production and swimming speed. In particular I tested the hypotheses that (1) increased swimming speed is achieved through an increased stroke rate; (2) force produced per stroke is proportional to stroke amplitude, (3) that forward thrust is produced during both the down and up phases of stroking; and (4) that peak thrust is produced towards the end of the downstroke cycle. Front flipper stroke rate was independent of water speed refuting the hypothesis that swimming speed is increased by increasing stroke rate. Instead differences in swimming speed were caused by a combination of varying flipper amplitude and the proportion of time spent powerstroking. Peak thrust produced per stroke varied within and between bouts of powerstroking, and these peaks in thrust were correlated with both flipper amplitude and flipper angular momentum during the downstroke supporting the hypothesis that stroke force is a function of stroke amplitude. Two distinct thrust production patterns were identified, monophasic in which a single peak in thrust was recorded during the later stages of the downstroke, and biphasic in which a small peak in thrust was recorded at the very end of the upstroke and this followed by a large peak in thrust during the later stages of the downstroke. The biphasic cycle occurs in ∼20% of hatchlings when they first started swimming, but disappeared after one to two hours of swimming. The hypothesis that forward thrust is produced during both the up and down stroke was only supported relatively rarely in hatchlings that exhibited the diphasic cycle, the majority of time forward thrust was only produced during the downstroke phase. The hypothesis that peak forward thrust is produced during the end of the downstroke was supported in both the monophasic and biphasic thrust producing stroke cycles.

Artificial lighting and disrupted sea-finding behaviour in hatchling loggerhead turtles (Caretta caretta) on the Woongarra coast, south-east Queensland, Australia

Coastal development adjacent to sea turtle nesting beaches can result in an increase in exposure to artificial lighting at night. That lighting can repel nesting females and interfere with the orientation of hatchlings from the nest to the sea. Disrupted hatchling orientation is a serious source of turtle mortality, sufficient to reduce recruitment and contribute to a long-term marine turtle population decline. The purpose of this study was to assess whether artificial lighting disrupts hatchling sea-finding behaviour at the largest loggerhead rookery in the South Pacific, the Woongarra coast, south-east Queensland. The crawling tracks of hatchlings that emerged from nests, as well as staged emergences, were used to assess the effect of lighting conditions at several local beaches on hatchling sea-finding behaviour. Disrupted orientation was observed at only a few locations, excluding the majority of the main nesting beach at Mon Repos Conservation Park. At the sites where orientation was disrupted, normal orientation was restored when a full moon was visible, presumably because lunar illumination reduced the perceived brightness of the artificial lights. The controlled use of lights used for guided turtle-viewing tour groups within Mon Repos conservation Park did not interfere with the sea-finding behaviour of hatchling turtles. Further coastal development, especially at the nearby town of Bargara, requires that a light management plan be formulated to ensure that development does not adversely affect the marine turtles that utilise the local nesting beaches.

Blood concentrations of lactate, glucose and corticosterone in dispersing hatchling sea turtles

Natal dispersal of sea turtles is an energetically demanding activity that is fuelled primarily by aerobic metabolism. However, during intense exercise reptiles can use anaerobic metabolism to supplement their energy requirements. We assessed anaerobic metabolism in dispersing hatchling loggerhead and flatback turtles by measuring the concentrations of blood lactate during crawling and at different times during the first four hours of their frenzy swim. We also measured concentrations of blood glucose and corticosterone. Blood lactate (12.13 to 2.03 mmol/L), glucose (6.25 to 3.8 mmol/L) and corticosterone (8.13 to 2.01 ng/mL) concentrations decreased significantly over time in both loggerhead and flatback hatchlings and no significant differences were found between the species. These results indicate that anaerobic metabolism makes a significant contribution to the dispersal phase of hatchling sea turtles during the beach crawl and the first few hours of the frenzy swim.

Effect of nest temperature on hatchling phenotype of loggerhead turtles (Caretta caretta) from two South Pacific rookeries, Mon Repos and La Roche Percée

La Roche Percée, in New Caledonia, is the most important loggerhead turtle rookery outside of Australia for the eastern Pacific genetic stock. The females nesting on this beach are genetically similar to the females found at the Mon Repos rookery in Queensland, Australia. This study shows how nest temperature affects the phenotype of genetically similar populations. During the 2010–11 breeding season, mean nest temperatures were significantly higher at La Roche Percée (31.8°C) than at Mon Repos (29.5°C) and the mean for the three-days-in-a-row maximum nest temperatures was also significantly higher at La Roche Percée (34.6°C), than at Mon Repos (31.7°C). Differences were found in mean hatching success (La Roche Percée 83 ± 3%, Mon Repos 96 ± 2%) and emergence success (La Roche Percée 76 ± 3%, Mon Repos 93 ± 3%). Hatchlings from La Roche Percée also had significantly lower fitness characteristics, having smaller carapace size (La Roche Percée 1565 ± 7 mm2, Mon Repos 1634 ± 5 mm2), slower self-righting times (La Roche Percée 4.7 ± 0.1 s, Mon Repos 2.7 ± 0.1 s) and slower crawling speed in terms of both absolute speed and body lengths per second (La Roche Percée 2.5 ± 0.2 cm s–1 or 0.57 ± 0.05 body lengths s–1, Mon Repos 4.6 ± 0.1 cm s–1 or 1.04 ± 0.02 body lengths s–1). Nest temperatures at La Roche Percée approached the upper limit of embryo thermal tolerance towards the end of incubation (34°C) and this condition may contribute to the lower hatching and emergence success and lower fitness characteristics of hatchlings at the La Roche Percée rookery.

Locomotor activity during the frenzy swim: analysing early swimming behaviour in hatchling sea turtles

Swimming effort of hatchling sea turtles varies across species. In this study we analysed how swim thrust is produced in terms of power stroke rate, mean maximum thrust per power stroke and percentage of time spent power stroking throughout the first 18 h of swimming after entering the water, in both loggerhead and flatback turtle hatchlings and compared this with previous data from green turtle hatchlings. Loggerhead and green turtle hatchlings had similar power stroke rates and percentage of time spent power stroking throughout the trial, although mean maximum thrust was always significantly higher in green hatchlings, making them the most vigorous swimmers in our three-species comparison. Flatback hatchlings, however, were different from the other two species, with overall lower values in all three swimming variables. Their swimming effort dropped significantly during the first 2 h and kept decreasing significantly until the end of the trial at 18 h. These results support the hypothesis that ecological factors mould the swimming behaviour of hatchling sea turtles, with predator pressure being important in determining the strategy used to swim offshore. Loggerhead and green turtle hatchlings seem to adopt an intensely vigorous and energetically costly frenzy swim that would quickly take them offshore into the open ocean in order to reduce their exposure to near-shore aquatic predators. Flatback hatchlings, however, are restricted in geographic distribution and remain within the continental shelf region where predator pressure is probably relatively constant. For this reason, flatback hatchlings might use only part of their energy reserves during a less vigorous frenzy phase, with lower overall energy expenditure during the first day compared with loggerhead and green turtle hatchlings.

Measuring energy expenditure in sub-adult and hatchling sea turtles via accelerometry

Measuring the metabolic of sea turtles is fundamental to understanding their ecology yet the presently available methods are limited. Accelerometry is a relatively new technique for estimating metabolic rate that has shown promise with a number of species but its utility with air-breathing divers is not yet established. The present study undertakes laboratory experiments to investigate whether rate of oxygen uptake (VO2) at the surface in active sub-adult green turtles Chelonia mydas and hatchling loggerhead turtles Caretta caretta correlates with overall dynamic body acceleration (ODBA), a derivative of acceleration used as a proxy for metabolic rate. Six green turtles (25-44 kg) and two loggerhead turtles (20 g) were instrumented with tri-axial acceleration logging devices and placed singly into a respirometry chamber. The green turtles were able to submerge freely within a 1.5 m deep tank and the loggerhead turtles were tethered in water 16 cm deep so that they swam at the surface. A significant prediction equation for mean VO2 over an hour in a green turtle from measures of ODBA and mean flipper length (R(2) = 0.56) returned a mean estimate error across turtles of 8.0%. The range of temperatures used in the green turtle experiments (22-30 °C) had only a small effect on Vo₂. A VO2-ODBA equation for the loggerhead hatchling data was also significant (R(2) = 0.67). Together these data indicate the potential of the accelerometry technique for estimating energy expenditure in sea turtles, which may have important applications in sea turtle diving ecology, and also in conservation such as assessing turtle survival times when trapped underwater in fishing nets.

Determining optimal incubation temperature for a head-start program: the effect of incubation temperature on hatchling Burnett River snapping turtles (Elseya albagula)

This study monitored natural nest temperatures and examined the effect of incubation temperature on hatchling phenotype of the freshwater turtle Elseya albagula to determine the optimal temperature for a potential head-start program. Eggs were incubated at constant temperatures (26°C, 28°C and 30°C) to determine the influence of temperature on incubation period, hatchling morphology, swimming performance and post-hatching growth rate. Hatchlings incubated at 26°C had longer plastrons than hatchlings from 30°C and swam faster, three days after hatching, than did hatchlings incubated at either 28°C or 30°C. Incubation temperature also provided a source of variation in hatchling scute patterns. Clutch of origin influenced hatchling mass and size, growth at 184 days after hatching, and the swimming performance of 3-day and 75-day post-hatch hatchlings. Constant temperatures of 26°C and 28°C produced the highest hatching success and highest-quality hatchlings and are therefore recommended for incubation of eggs in a head-start program. In the field, unshaded nests experienced greater daily fluctuations in temperature and higher temperatures overall compared with shaded nests, such that unshaded nest temperatures approached the upper thermal limit to development.

Influence of the hydric environment on water exchange and hatchlings of rigid-shelled turtle eggs

To examine the possible influence of incubation substrate water potential on rigid-shelled chelonian eggs and hatchlings, rigid-shelled eggs from four clutches of Brisbane River turtle (Emydura signata) were incubated buried in vermiculite at water potentials of approximately -100, -350, and -850 kPa, and patterns of egg mass change and hatchling attributes were examined. All eggs hatched successfully, and there was no apparent effect of water potential on incubation period, fresh hatchling mass, hatchling water content, or hatchling size. Clutch of origin also had no apparent effect on these attributes when initial egg mass was used as a covariate. However, clutch of origin affected initial egg mass, and clutch of origin and incubation water potential influenced the amount of water exchanged between the eggs and their environment during incubation and the amount of residual yolk found in hatchlings. Substrate water potential has little effect on hatchling outcomes other than the proportion of yolk converted to hatchling tissue during incubation in the rigid-shelled eggs of E. signata. It would appear that in general, the substrate water potential during incubation affects the quality of chelonian hatchlings by influencing the amount of yolk converted to hatchling tissue during embryonic development and that this influence is stronger in flexible-shelled eggs than in rigid-shelled eggs.

Swimming for your life: locomotor effort and oxygen consumption during the green turtle (Chelonia mydas) hatchling frenzy

Swimming effort and oxygen consumption of newly emerged green turtle Chelonia mydas hatchlings was measured simultaneously and continuously for the first 18 h of swimming after hatchlings entered the water. Oxygen consumption was tightly correlated to swimming effort during the first 12 h of swimming indicating that swimming is powered predominantly by aerobic metabolism. The patterns of swimming effort and oxygen consumption could be divided into three distinct phases: (1) the rapid fatigue phase from 0 to 2 h when the mean swim thrust decreased from 45 to 30 mN and oxygen consumption decreased from 33 to 18 ml h(-1); (2) the slow fatigue phase from 2 to 12 h when the mean swim thrust decreased from 30 to 22 mN and oxygen consumption decreased from 18 to 10 ml h(-1); and (3) the sustained effort phase from 12 to 18 h when mean swim thrust averaged 22 mN and oxygen consumption averaged 10 ml h(-1). The decrease in mean swim thrust was caused by a combination of a decrease in front flipper stroke rate during a power stroking bout, a decrease in mean maximum thrust during a power stroking bout and a decrease in the proportion of time spent power stroking. Hence hatchlings maximise their swimming thrust as soon as they enter the water, a time when a fast swimming speed will maximise the chance of surviving the gauntlet of predators inhabiting the shallow fringing reef before reaching the relative safety of deeper water.

Temperature-dependent sex-biased embryo mortality in a bird

Sex ratios have important evolutionary consequences and are often biased by environmental factors. The effect of developmental temperature on offspring sex ratios has been widely documented across a diverse range of taxa but has rarely been investigated in birds and mammals. However, recent field observations and artificial incubation experiments have demonstrated that the hatching sex ratio of a megapode, the Australian brush-turkey (Alectura lathami), varied with incubation temperature; more females hatched at high incubation temperatures and more males hatched at low temperatures. Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.

Estimating the sex ratio of loggerhead turtle hatchlings at Mon Repos rookery (Australia) from nest temperatures

Sand temperatures and loggerhead turtle nest temperatures (Caretta caretta) at Mon Repos rookery (Australia) were monitored over the 2005–06 and 2006–07 nesting seasons and hatchling sex ratios of clutches were estimated using the Constant Temperature Equivalent method. Nest temperatures were positively correlated with the sand temperature and air temperature in both seasons. Both seasons produced a female-biased sex ratio, especially the 2005–06 season, when almost all hatchlings were predicted to be female. Hatch success rate was not affected by nest temperature and averaged 85%, but hot nests from 2005–06 had a reduced emergence success compared with other nests. Daily cyclic temperature fluctuations of 0.5–1.5°C were a feature of nests, with a tendency for greater daily amplitude in the 2005–06 season when the average daily temperature was hotter. These daily temperature fluctuations increased the constant temperature equivalent temperature by 0.1–0.5°C above mean nest temperature during the sex-determining period and resulted in an increased female bias in the estimated hatchling sex ratio.

Temperature and the energetics of development in the house cricket (Acheta domesticus)

The influence of rearing temperature on the energetics of development was investigated in house crickets (Acheta domesticus). Crickets raised at 25 degrees C grew slower (0.51 mg d(-1), dry mass basis) and took longer to develop (119 d) but obtained a greater adult body mass (61 mg, dry mass) than crickets reared at 28 degrees C (0.99 mg d(-1), 49 d, 48 mg). Total metabolic energy consumed during development at 25 degrees C (1351 J) was twice that at 28 degrees C (580 J) primarily because of the longer development period, and as a consequence the specific net cost of growth was much greater for crickets reared at 25 degrees C (22.1 kJ g(-1)) than 28 degrees C (11.9 kJ g(-1)).

Temperature-dependent sex ratio in a bird

To our knowledge, there is, so far, no evidence that incubation temperature can affect sex ratios in birds, although this is common in reptiles. Here, we show that incubation temperature does affect sex ratios in megapodes, which are exceptional among birds because they use environmental heat sources for incubation. In the Australian brush-turkey Alectura lathami, a mound-building megapode, more males hatch at low incubation temperatures and more females hatch at high temperatures, whereas the proportion is 1:1 at the average temperature found in natural mounds. Chicks from lower temperatures weigh less, which probably affects offspring survival, but are not smaller. Megapodes possess heteromorphic sex chromosomes like other birds, which eliminates temperature-dependent sex determination, as described for reptiles, as the mechanism behind the skewed sex ratios at high and low temperatures. Instead, our data suggest a sex-biased temperature-sensitive embryo mortality because mortality was greater at the lower and higher temperatures, and minimal at the middle temperature where the sex ratio was 1:1.