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There is an intense interest in long-term trends of species abundance that may reflect, for example, climate change or conservation actions. Less well studied are patterns in the magnitude of inter-annual variability in abundance across large spatial scales. We collated abundance time-series for 133 nesting sites across the globe of the seven sea turtle species. Inter-annual variability in nest numbers was lowest in loggerhead turtles (Caretta caretta), Kemp's ridley (Lepidochelys kempii) and flatback turtle (Natator depressus) and highest in green turtles (Chelonia mydas), likely reflecting their lower trophic position compared to other species and hence tighter coupling of food availability to environmental conditions each year. The annual number of nests in green turtles could vary by 60-fold between successive years. We identified regional patterns in the magnitude of inter-annual variability in green turtle nest numbers, variability being highest for nesting beaches around Australia and lowest in the western Indian Ocean and equatorial Atlantic. These regional patterns are likely linked to corresponding patterns of environmental variability with, for example, areas subjected environmental extremes as part of the El Nino Southern Oscillation (ENSO) showing high inter-annual variability in nest numbers. [ABSTRACT FROM AUTHOR]

While polyandry in sea turtles is indicated through multiple‐paternity analyses of offspring, confirmed observations of the same female mating with multiple males are extremely challenging to obtain. To contribute to this discussion, we analysed a long‐term photo‐identification database (>20 years) of adult male and female loggerhead sea turtles frequenting the breeding area of Zakynthos, Greece, Mediterranean. A total of 38 records of mating individuals within and across seasons were assimilated via field surveys and citizen science records between 2003 and 2020. For one female, we recorded it mating with two different males within a 5.5‐h interval on the same day in 2015. This observation constitutes the first direct evidence of polyandry in sea turtles, in addition to highlighting the potential for photo‐identification to contribute information on less well‐known aspects of sea turtle biology, such as validating outputs of genetic studies. [ABSTRACT FROM AUTHOR]

Delineating priority areas for highly mobile marine megafauna represents a major challenge for conservation biology. To manage such areas, one must understand both their spatial properties (i.e., location, number, extent), and the level of exposure to a number of given pressures. Here, we used a combination of ensemble distribution models, field-based validation methods and a cumulative effect assessment to illustrate key foraging sites and risk hotspots for adult loggerhead sea turtles, Caretta caretta, in the Mediterranean Sea. We found that foraging sites covered about 10% of the neritic zone of the Mediterranean basin. We identified sites which are well recognized by scientists, but also other areas for which our knowledge on the potential importance is limited. The patterns of the habitat use generated by field data validated the accuracy of the distribution model. About one fifth of the foraging areas hosted in the Mediterranean could be considered as hotspots of risk, characterized by high or very high exposure to cumulative pressures. Our results suggest that management and conservation efforts should continue to be held at key, well-known foraging grounds of adult sea turtles (e.g., Northern Adriatic Sea, Tunisian Plateau) but there are several more potential sites (e.g., parts of the Aegean Sea and the Western Mediterranean) which deserve our attention in order to ensure viable populations. [ABSTRACT FROM AUTHOR]

Conserving marine megafauna is a complex task, particularly due to the gaps in our knowledge regarding their distribution and susceptibility to human pressures. While the Ionian Sea, eastern Mediterranean, is renowned for hosting nesting sites for sea turtles and supporting diverse cetacean populations, identifying key marine habitats for elusive species remains a significant challenge in the region. This study offers insights drawn from 15 years of stranding data collected in the Ionian Sea, shedding light on the utilization of marine habitats by marine megafauna. Stranding records of loggerhead sea turtles (Caretta caretta), reported even beyond the breeding season, highlight the ecological significance of the area as a year-round foraging and developmental habitat. Stranding records have consistently revealed the presence of green sea turtles (Chelonia mydas) in the region, emphasizing the need for further research on their habitat utilization. The higher stranding frequencies observed during the spring/summer months can be attributed to factors such as increased individual abundance, heightened reporting rates, or intensified human activities at sea. While human-induced disturbances are evident in the reporting of stranded cetaceans in the region, the annual records of stranded Mediterranean monk seal (Monachus monachus) raise questions about the viability of the local population of this endangered species. This study provides substantial evidence suggesting the significance of the Ionian Sea as a potential hotspot for marine megafauna in the Mediterranean. Results highlight the need for policy measures aimed at safeguarding the marine habitats of these charismatic creatures. • 15 years of stranding data for marine megafauna in the Ionian Sea were examined. • The region features diverse megafauna species alongside human-induced pressures. • Year-round presence of sea turtle individuals was highlighted. • Results emphasize the need for a marine action plan to address human disturbances. [ABSTRACT FROM AUTHOR]

Phenological shifts are widely reported for different species as a response to climate change. Still, the efficiency of this mechanism is questioned because of the accelerated rate of change and the different change patterns of various climate parameters that may cause mismatches. Here, using loggerhead sea turtles (Caretta caretta) as model species, we examined whether phenological shifts could be an effective adaptive strategy over the critical period that determines reproductive output in the Mediterranean region. We compared the rate of temperature and precipitation change over the recent past (1971-2015) and future periods (2016-2060) along the 45 main nesting sites of the Mediterranean population, during the incubation period. Next, utilizing predictions of an earlier nesting season, we evaluated whether the timing of incubation will impact offspring survival on the Mediterranean population. To further assess species vulnerability, we investigated any potential relationship between hatching success and climate parameters at the largest Mediterranean nesting rookery (Zakynthos, Greece). We found that phenological changes would allow species to capture a thermal window similar to one they experience nowadays during the incubation period. Still, phenological shifts might be less adequate to follow precipitation changes, which however, were found to have a limited impact upon hatching success. Global adaptation management strategies should be directed towards (a) acquisition of long-term high-resolution temperature and precipitation series at nesting sites, (b) developing early warning systems to prevent negative impacts upon reproductive outputs, and (c) directly applying cooling of the nests when first altered climate signs are detected. [ABSTRACT FROM AUTHOR]

AC was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the "First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant" (Project Number: 2340). ADM acknowledges the European Union's Horizon 2020 research and innovation programme under grant agreements No 869300 (FutureMARES)." Correction to: Biodiversity and Conservation https://doi.org/10.1007/s10531-021-02326-0 In the original publication of the article, the last sentence of the funding statement was inadvertently missed to be included. [Extracted from the article]

Abstract: The sea surface temperature (SST) in loggerhead turtle breeding areas affects the species reproductive biology. Less is known about the effects of changes in SST in the species foraging grounds. We used nesting data for the Mediterranean loggerhead turtle population breeding on the Greek island of Zakynthos to study the effect of SST in the population foraging grounds upon the initiation of nesting and the number of clutches laid. We found that the climatic conditions (SST) in the foraging grounds affected the population nesting phenology in the short term (i.e. within the same year); warmer years triggered an earlier onset of nesting. However, the effect of foraging grounds SST upon nesting is comparatively less important than the local conditions at the nesting ground. Although nesting phenology seems to depend on current''s year foraging grounds SST the number of nests in our study rookery were negatively correlated with SSTs recorded 2 years prior nesting, with higher SST leading to fewer nests. From this point of view, climate change at the foraging grounds may influence the reproductive phenology of loggerheads. [Copyright &y& Elsevier]

Sea turtles are highly mobile species that use oceanic, neritic, and coastal habitats as nursery, foraging, wintering, breeding and migration areas at distant locations throughout their lifetime. Due to their highly migratory nature and large-scale habitat use, they are subjected to multiple threats across marine and coastal ecosystems that can impact every stage of their life cycle and result in increased mortality rates. Here, we present new data on stranding events across the eastern Ionian Sea (central Mediterranean). Our analysis on stranding data, collected over a 6-year period, provided clear evidence of continuing and increased mortality events in the region (n = 413, Caretta caretta : 79%, Chelonia mydas : 4%, and unknown: 17%). Based on the alarming results of increased mortality, and taking into account the limitations posed by the nature of stranding data, we further identified potential risk hotspots within critical marine and coastal sea turtle habitats. To do so, we performed a spatially explicit cumulative pressure assessment at different spatial scales in an effort to identify, map, quantify, and synthesize the multiple anthropogenic pressures that are recognized to potentially impact sea turtles. Our results clearly demonstrated that the Ionian Sea is subjected to intense pressures (i.e. fisheries, marine traffic, and underwater noise). We identified three main hotspots of very high risk related to critical foraging grounds, nesting sites, and migration corridors for sea turtles regardless of the spatial scale of the analysis. We found high sea turtle mortality associated with locations characterized as high and very high risk areas. This study offers key information on mortality and spatial risk for sea turtles that can facilitate their effective conservation. Thus, our findings can be used in the light of marine spatial planning, allowing planners to more realistically assess where conservation resources should be directed to control harmful activities and to mitigate impacts on sea turtles. • Cumulative pressures and mortality for Sea turtles are reported in a critical area. • Risk hotspots within critical habitats of the Mediterranean loggerheads and green turtles are identified. • Our findings support policy decisions and management plans in the region. [ABSTRACT FROM AUTHOR]

Abstract: Global climate change is likely to have an important influence on the phenology, behaviour and population dynamics of many species. We investigate climatic related changes in the breeding phenology of Mediterranean loggerhead marine turtles Caretta caretta over a 19 year period and the potential relationship between these changes and reproductive success and performance. We found that the studied population has experienced fluctuating sea surface temperatures (SST) with an increasing trend during the last century. With increasing spring SST there is a trend towards earlier nesting. However, there is no significant relationship between SST and nesting season, defined as the duration between the first recorded emergence and the last nest laid. Our analyses indicate that marine turtles display phenological changes, and thus maintain favorable thermal conditions at the nesting sites. Furthermore, increasing spring SST was correlated with decreasing clutch size and increasing hatching success that resulted in an apparent lack of correlation between SST and hatchling production. This apparent independence might be misleading since it only holds for a limited range of SST values. Thus, if we estimate the effect of climate change on loggerhead population growth as neutral, based on the apparent independence between SST and total number of hatchlings, we will be underestimating the population extinction risk. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Marine turtle species have a complex life history characterized by interannual variability in reproductive performance and a long life span. These ecological features in combination with the animals’ highly migratory nature create numerous difficulties when trying to assess population dynamics. This study attempts to couple existing information on species demographics and behavioral strategies with simple energetic rules in a theoretical framework. We study sea turtle population dynamics using an individual-based model that incorporates known behavioral-ecological characteristics of the species. Methodology used to design the model was based on the superindividual approach (Scheffer et al. Ecol Model 80:161–170, ). We constructed our simulation experiment on a virtual sea turtle population, which was parameterized by using recent literature reviews with emphasis on reproductive parameters of the Mediterranean loggerhead sea turtle population. Switching rules describing critical processes of reproductive performances were established as theoretical functions of efficiency of energy transfer. In order to explore the significance of variable reproductive patterns upon population dynamics and persistence, a series of simulations was performed. The model was also run under fluctuated demographic variables to perform a sensitivity analysis of critical parameters and life-history stages. Based on the specific model parameterization, simulation results show that population persistence was most sensitive to fecundity and to survival at the pelagic juvenile stage. Additionally a surprising finding is the relatively high importance of egg survival in terms of both hatching and hatchling success. We conclude that enhancing the population with new individuals by increasing survival in the early life stages could compensate for additional losses in other age classes. The need for further research regarding biological and behavioral features as well as basic demographic insights into the endangered loggerhead sea turtle is also highlighted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nest incubation temperatures were higher for green turtles than for loggerhead turtles. • The nests in Cape Verde had higher temperatures than the ones in Greece. • Exceeding the nest temperature of 31 °C and 32 °C resulted in a reduction in hatching success. • Future warming incubation temperature of nests might pose a threat to sea turtles. Rising temperatures due to global warming over the last decades pose threats to marine biodiversity. Sea turtles are ectothermic species, and their embryonic development depends on nest conditions, particularly temperature. Here, we explore how increasing and extreme temperatures within the 558 nests can impact the hatching success of two sea turtle species, the green turtle (Chelonia mydas) and the loggerhead turtle (Caretta caretta), at two tropical locations, Cape Verde and Australia, and at temperate nesting sites, Turkey and Greece. Mean nest temperatures were higher for green turtles (30.84 °C) than for loggerhead turtles (29.42 °C) and significantly increased in all locations as the air temperature increased. However, nests from temperate locations, such as green turtles in Turkey and loggerhead turtles in Cape Verde, experienced higher temperatures than the nests in Australia and Greece, reaching lethal temperatures at extreme temperature peaks. Thus, temperate populations might be at risk as global warming continues because it is uncertain whether these higher latitudes can provide beach habitats cool enough for successful sea turtle nesting given the projected more frequent extreme temperatures in the future. [ABSTRACT FROM AUTHOR]

Increased temperatures caused by anthropogenic climate change are becoming a major challenge for species. In particular, species that migrate over long distances are affected by altered climatic conditions at the various sites they frequent and en route. Here, we investigated whether climatic conditions experienced by sea turtles during their migration would change in the future. We focused on the post-nesting migrations of female loggerhead sea turtles (Caretta caretta) in the Mediterranean region, to explore climatic variability along four main migration corridors and their surrounding environment. We also modeled the impact of earlier onset of migration, as a potential adaptive behavioral response of Mediterranean loggerheads. We found that over the next 80 years, sea turtles will be exposed to significant increases in sea surface temperatures (SSTs) along their key migration corridors and the surrounding area (mean rate of 0.24 °C increase per decade). The projected increase in SST falls outside the range of SSTs currently reported within the examined corridors, but falls below the threshold defined as the upper thermal limit for this species. A highly variable climatic mosaic was identified within the distinct segments of the corridors. We found no evidence to support that phenological shifts might result in turtles being exposed to climatic conditions that are similar to current levels, in the future. Our outputs offer the first comprehensive spatial assessment of climatic patterns along extended areas used for the migration of sea turtles and highlight the need to quantify the relationship between altered conditions and species physiological and energetic status. This regional analysis could provide a background methodological framework for mapping and assessing spatiotemporal patterns of climatic variability along migratory areas of marine megafauna. • We developed an approach to examine climatic conditions for migrating loggerheads. • We investigated species exposure and adaptive capacity to climate change. • Mediterranean loggerheads might confront increasing temperatures during migration. • The efficiency of phenology, as adaptive mechanism for migration, is questionable. [ABSTRACT FROM AUTHOR]

• Sea currents could facilitate species migration by reducing movement energetic cost. • We projected optimal migration routes for loggerhead sea turtles. • Real migration tracks had higher energetic cost than projected ones. • Loggerhead sea turtles do not adjust their migration routes according to currents. • Climate changes on sea currents are not expected to alter migration routes. For marine species, traveling with the current potentially reduces energetic costs. Still, the extent to which organisms adjust routes to follow current flow remains an open question. Moreover, the extent to which climate change is altering sea currents, and in turn species migration routes, remains unknown, representing a major challenge to spatial ecology and conservation efforts. We developed an approach to assess the extent to which projected optimal paths and corridors overlap with the observed migration routes of loggerhead sea turtles (Caretta caretta), minimizing exposure to opposing sea currents. To illustrate this approach, we used migratory tracks of the species traveling between breeding and foraging areas in the Mediterranean Sea. We calculated the energetic costs to sea turtles based on actual tracks and corresponding optimal paths. We also explored whether projected changes in ocean currents, driven by climate change, would alter the spatial patterns of optimal routes. The energetic cost of observed tracks was, on average, 1.25 times higher than that of corresponding optimal paths. While optimal corridors differed spatially to observed corridors used by loggerheads, some positive correlations still existed for three cases (r s = 0.43, 0.42, 0.30). Climate change projections showed no significant change to the migratory movement of sea turtles, as corridors for different climatic conditions overlapped by at least 70%. Our results show that loggerheads do not explicitly take advantage of ocean currents to facilitate long distance migrations and reduce energetic demands. The contemporary and future migration routes are characterized by similar energetic demands and together with their strong spatial overlap suggest that climate change is expected to minimally alter the species migration routes in the future. The approach presented here could be applied to different spatial scales and marine taxa, allowing possible mechanisms between sea currents (or other environmental characteristics) and species movements to be elucidated. [ABSTRACT FROM AUTHOR]

• Loggerhead sea turtle nests offer an ephemeral habitat for the decomposer food web. • Opportunistic bacterivorous nematodes are favored in the nests after egg hatching. • The nematode Metabolic footprint is associated to dead loggerhead turtle hatchlings. • High nematode diversity is associated to increased hatching success. • Nematode community characteristics can help to assess and monitor sea turtle nests. Nematodes represent an important group of animals in the decomposer food web, because of high diversities, abundances and functional roles supporting ecological processes, such as decomposition. They have been relatively well studied in numerous ecosystems, but have rather skipped attention in sea turtle nests at sandy shores, where a massive supply of nutrients is taking place after turtle egg hatching. Being excellent indicators of ecological functioning, we hypothesized that nematode community characteristics could be indicative of the ecological/functional state of sea turtle nests as affected by hatching characteristics (e.g. number of eggs, hatching success rate etc.). In our study, conducted in Zakynthos (Greece), we perform a pioneer in-depth analyses of nematode communities in Caretta caretta nests after egg hatching. We further explore whether turtle reproductive success, measured through a number of metrics reflecting stages and portion of alive/dead hatchlings, are linked to nematode community characteristics. We found 14 different nematode genera in total. Our analyses demonstrate that nematodes play a critical role in functionality and energy flow in sandy shore ecosystems and that sea turtle nests present an ephemeral micro-habitat hosting communities with specific characteristics. These include rather high nematode abundances and communities in early successional stages with a simple trophic structure, almost exclusively dominated by bacterivore nematodes (mostly opportunistic/c-p 1) and without top-down control. Variables either showing success or failure of hatching explained a large amount of variability of nematode community characteristics, supporting our hypothesis. The nematode Metabolic Footprint was strongly associated with the amount of dead hatchlings concentrated in the turtle nest. Nematode taxonomic diversity and richness were closely associated with an increased hatching success rate at nest level. Our findings can offer a base for developing a framework for comprehensive and standardized assessments of sea turtle nests that could ensure comparability of results over spatial or temporal scales in monitoring projects. Further research might show how increased diversity of nematode communities could be achieved so to improve reproduction output and success of loggerhead sea turtles. [ABSTRACT FROM AUTHOR]