Adaptation of sea turtles to climate warming: Will phenological responses be sufficient to counteract changes in reproductive output?

Sea turtles are vulnerable to climate change since their reproductive output is influenced by incubating temperatures, with warmer temperatures causing lower hatching success and increased feminization of embryos. Their ability to cope with projected increases in ambient temperatures will depend on their capacity to adapt to shifts in climatic regimes. Here, we assessed the extent to which phenological shifts could mitigate impacts from increases in ambient temperatures (from 1.5 to 3°C in air temperatures and from 1.4 to 2.3°C in sea surface temperatures by 2100 at our sites) on four species of sea turtles, under a "middle of the road" scenario (SSP2-4.5). Sand temperatures at sea turtle nesting sites are projected to increase from 0.58 to 4.17°C by 2100 and expected shifts in nesting of 26-43 days earlier will not be sufficient to maintain current incubation temperatures at 7 (29%) of our sites, hatching success rates at 10 (42%) of our sites, with current trends in hatchling sex ratio being able to be maintained at half of the sites. We also calculated the phenological shifts that would be required (both backward for an earlier shift in nesting and forward for a later shift) to keep up with present-day incubation temperatures, hatching success rates, and sex ratios. The required shifts backward in nesting for incubation temperatures ranged from -20 to -191 days, whereas the required shifts forward ranged from +54 to +180 days. However, for half of the sites, no matter the shift the median incubation temperature will always be warmer than the 75th percentile of current ranges. Given that phenological shifts will not be able to ameliorate predicted changes in temperature, hatching success and sex ratio at most sites, turtles may need to use other adaptive responses and/or there is the need to enhance sea turtle resilience to climate warming.

Priorities for Mediterranean marine turtle conservation and management in the face of climate change

As climate-related impacts threaten marine biodiversity globally, it is important to adjust conservation efforts to mitigate the effects of climate change. Translating scientific knowledge into practical management, however, is often complicated due to resource, economic and policy constraints, generating a knowledge-action gap. To develop potential solutions for marine turtle conservation, we explored the perceptions of key actors across 18 countries in the Mediterranean. These actors evaluated their perceived relative importance of 19 adaptation and mitigation measures that could safeguard marine turtles from climate change. Of importance, despite differences in expertise, experience and focal country, the perceptions of researchers and management practitioners largely converged with respect to prioritizing adaptation and mitigation measures. Climate change was considered to have the greatest impacts on offspring sex ratios and suitable nesting sites. The most viable adaptation/mitigation measures were considered to be reducing other pressures that act in parallel to climate change. Ecological effectiveness represented a key determinant for implementing proposed measures, followed by practical applicability, financial cost, and societal cost. This convergence in opinions across actors likely reflects long-standing initiatives in the Mediterranean region towards supporting knowledge exchange in marine turtle conservation. Our results provide important guidance on how to prioritize measures that incorporate climate change in decision-making processes related to the current and future management and protection of marine turtles at the ocean-basin scale, and could be used to guide decisions in other regions globally. Importantly, this study demonstrates a successful example of how interactive processes can be used to fill the knowledge-action gap between research and management.

Drivers of litter ingestion by sea turtles: Three decades of empirical data collected in Atlantic Europe and the Mediterranean

Sea turtles are considered as bio-indicators for monitoring the efficiency of restoration measures to reduce marine litter impacts on health. However, the lack of extended and standardised empirical data has prevented the accurate analysis of the factors influencing litter ingestion and the relationships with individual health. Historic data collected from 1988 and standard data collected from 2016 were harmonised to enable such analyses on necropsied loggerhead turtles (Caretta caretta) in eight Mediterranean and North-East Atlantic countries. Litter was found in 69.24 % of the 1121 individuals, mostly single-use and fishing-related plastics. Spatial location, sex and life history stage explained a minor part of litter ingestion. While no relationships with health could be detected, indicating that all individuals can be integrated as bio-indicators, the mechanistic models published in literature suggest that the high proportion of plastics in the digestive contents (38.77 % per individual) could have long-term repercussions on population dynamics.

Red Blood Cell Morphology and Blood Biochemistry of Bufotes variabilis

To determine blood biochemistry and reassess and compare red blood cell morphology based on individuals’ gender, age and SVL (Snout-Vent Length), we studied 30 blood samples of Bufotes variabilis (15 males, 15 females) from Ornaz Valley, Denizli/Turkey. For age determination, bone samples were threated according to the skeletochronology procedure and a strong positive correlation between SVL and age structure (Pearson’s, n = 30, r2 = 0.937, p 0.001) was detected. Like all anurans, the shapes of the erythrocytes and their nuclei were ellipsoidal while their dimensions were bigger than expected when compared with those in the previous studies. Statistical evaluations of the red blood cells were made according to individuals’ gender, age and SVL and no significant differences were found amongst them. This is the first study about the blood biochemistry of B. variabilis which includes pH, blood gas, oximetry, electrolyte (potassium, sodium, calcium, chloride and bicarbonate ion concentrations) and metabolite [D-glucose and L(+)-lactate concentration] values. Biochemical data were statistically analysed according to gender, age and SVL to evaluate whether there are any relationships or differences between the studied individuals. Statistical analyses of the biochemical assessments showed that cCa values of females were significantly high (t-test: t = 2.30, df = 20, p 0.05), possibly due to the spawning period. The mean value of the individuals’ age was 7.77 ± 1.33 years with the mean SVL of 80.4 ± 1.2 mm. Pearson’s correlations of the biochemical data indicated a very significant relationship between cCl ion concentration and SVL as well as age. However, highly significant positive correlations were found between sO2 – pO2, FO2Hb – pO2, FO2Hb – sO2, FHHb – pCO2, cNa – pH, cNa – cK, cCa – cK, cCa – cNa, cHO3 – pCO2 and cLac – cGlu values while pO2 – pCO2, sO2 – pCO2, FHHb – pO2, FHHb – sO2, FHHb – FO2Hb, cK – pCO2 values showed a very significant negative correlation. These are the first biochemical data and evaluations about B. variabilis blood. In addition, according to the data obtained in our study, it is possible to say that age can be used as a substitute of SVL when it is not possible to procure the exact measurements of an individual for assessment.

Biodiversity of carapace epibiont diatoms in loggerhead sea turtles (Caretta caretta Linnaeus 1758) in the Aegean Sea Turkish coast

Background

The Aegean Sea coast of Turkey hosts one of the most important nesting grounds for loggerhead sea turtles (Caretta caretta) in the Mediterranean Sea. Previous studies have revealed that the sea turtle carapace provides favourable conditions for various epibiontic organisms. Epibionts occurring on the carapace have been examined from different locations in the oceans.

Methods

This is the first time such a high number (39) of samples collected from nesting turtles during such a long time period (extending from 2011 to 2018) has been used for the study of the diatom component of the microbiome on the turtle carapaces. A total of 33 samples were investigated in terms of light microscopy (LM) and scanning electron microscopy (SEM). Six unprocessed biofilm fragments were subject to SEM observations.

Results

A total of 457 epizoic diatom taxa belonging to 86 genera were identified. Epizoic forms, e.g., Achnanthes spp., Chelonicola spp. or Tripterion spp. (also identified by SEM observations of the undisturbed pieces of the microbiome) dominated in terms of relative abundance, but the highest numbers of taxa were ubiquitously represented by Navicula (79), Nitzschia (45), Amphora (40), Cocconeis (32), Diploneis (25) and Mastogloia (23). Navicula perminuta and Delphineis australis were the most frequent taxa, present in 65% of the samples, both with an average relative abundance of 10%. The results of our study revealed that diatoms are an essential component of the loggerhead sea turtles’ microbiome, in terms of high biodiversity and abundance. Although strict epibionts provide a signature of the turtle microbiome, the carapace as a solid substrate attracts numerous benthic diatom species which are considered opportunistic forms and can be found in the surrounding benthic habitats of the vast ocean littoral space.

Data Collection on Marine Litter Ingestion in Sea Turtles and Thresholds for Good Environmental Status

The following protocol is intended to respond to the requirements set by the European Union's Marine Strategy Framework Directives (MSFD) for the D10C3 Criteria reported in the Commission Decision (EU), related to the amount of litter ingested by marine animals. Standardized methodologies for extracting litter items ingested from dead sea turtles along with guidelines on data analysis are provided. The protocol starts with the collection of dead sea turtles and classification of samples according to the decomposition status. Turtle necropsy must be performed in authorized centers and the protocol described here explains the best procedure for gastrointestinal (GI) tract isolation. The three parts of the GI (esophagus, stomach, intestine) should be separated, opened lengthways and contents filtered using a 1 mm mesh sieve. The article describes the classification and quantification of ingested litter, classifying GI contents into seven different categories of marine litter and two categories of natural remains. The quantity of ingested litter should be reported as total dry mass (weight in grams, with two decimal places) and abundance (number of items). The protocol proposes two possible scenarios to achieve the Good Environmental Status (GES). First: "There should be less than X% of sea turtles having Y g or more plastic in the GI in samples of 50-100 dead turtles from each sub-region", where Y is the average weight of plastic ingested and X% is the percentage of sea turtles with more weight (in grams) of plastic than Y. The second one, which considers the food remain versus plastic as a proxy of individual health, is: "There should be less than X% of sea turtles having more weight of plastic (in grams) than food remains in the GI in samples of 50-100 dead turtles from each sub-region".

Loggerhead sea turtle hatchling sex ratio differences between two nesting beaches in Turkey

Hatchling sex ratios of loggerhead sea turtles (Caretta caretta) were estimated on two main nesting beaches (Dalyan Beach and Göksu Delta) in Turkey using three methods: nest temperature, incubation period and gonad histology. The electronic temperature recorders were placed in 35 selected nests. The mean nest temperature in the middle third of the incubation period was calculated as 29.5 °C on Dalyan Beach and as 31 °C on Göksu Delta. Incubation periods on Dalyan Beach and Göksu Delta were found as 52.9 days and 50.4 days, respectively. Gonad histology method was used only on Dalyan Beach and it was determined that 235 (55.6%) hatchlings were female out of 423 histologically examined hatchlings. Using nest temperatures and incubation periods, sex ratios on Dalyan Beach were estimated as 61% and 69.3%, and on Göksu Delta as 81% and 73.1%, respectively. In light of our sex ratio results, Dalyan Beach has a relatively high proportion of male hatchlings possibly due to its relatively western location. Our findings indicate that Dalyan Beach is an important nesting beach for loggerhead sea turtles in the eastern Mediterranean not only in terms of nest numbers and hatching success but also for its high proportion of male hatchlings. As for the methods used in this study, for further studies, we can suggest that nest temperature method provides the most accurate sex ratio result compared with incubation period and gonad histology methods, if temperature-recorded nests are selected in a manner of representing temporal distribution of the total nests on study beach.

An assessment of initial body size in loggerhead sea turtle (Caretta caretta) hatchlings in Turkey

Eggs, hatchlings, and adult loggerhead turtles, and incubation durations of clutches, were measured on three Turkish beaches (Dalyan, Fethiye and Göksu Delta), and some physical features of nests were compared. These features were not statistically different among the beaches, except for nest depth and distance to the high water mark. There was a positive relationship between hatchling mass and egg size. The carapace length of hatchlings was correlated with both egg diameter and incubation duration. The duration of asynchronous emergence of hatchlings on Fethiye beach was slightly longer than on the other two beaches, and the size of hatchlings decreased as asynchronous emergence proceeded. Of the hatchlings that emerged first, those that died were significantly smaller in SCL and mass than those that lived. These results suggest that smaller hatchlings may not be vigorous enough to emerge earlier from nests, and that they may be less fit.

Sex ratio estimations of loggerhead sea turtle hatchlings by histological examination and nest temperatures at Fethiye beach, Turkey

Hatchling sex ratios in the loggerhead turtle (Caretta caretta) were estimated by placing electronic temperature recorders in 21 nests at Fethiye beach during 2000-2002. Over the seasons, the mean temperature in the middle third of the incubation period ranged from 26.7 to 32.1 degrees C, and incubation periods ranged from 49 to 67 days. Based on the mean temperatures during the middle third of the incubation period, and on histologically sexed dead hatchlings, the sex ratios of hatchlings at Fethiye beach were roughly equal, i.e. 60-65% of the hatchlings were females. This contrasts with the highly female-skewed sex ratios in loggerhead turtles elsewhere; Fethiye has a relatively high proportion of male hatchlings. For endangered sea turtles, the knowledge of hatchling sex ratios at different beaches, coupled with appropriate conservation measures, can make an important contribution to their survival.

Determining the heavy metal pollution in Denizli (Turkey) by using Robinio pseudo-acacia L

The leaves of Robinia pseudo-acacia L. (Fabaceae) were evaluated as a biomonitors of heavy metal contamination in Denizli city, Turkey. Concentrations of Fe, Zn, Pb, Cu, Mn and Cd were determined in washed and unwashed leaves and soils collected from a wide range of sites with different degrees of metal pollution (industry, urban roadside, suburban) and from a rural (control) site by atomic absorption spectrometry. All the elements that measured were found to be at high levels in samples collected at industrial sites, except for lead and copper which were found at high levels in samples collected from urban roadsides that associated with the road traffic. The strong correlation between the degree of contamination and concentrations in all plant leaves assessed display that the leaves of R. pseudo-acacia reflect the environmental changes accurately, and that they seem as an effective biomonitor of environmental quality in areas subjected to industrial and traffic pollutions.

Nest temperatures and sex-ratio estimates of loggerhead turtles at Patara beach on the southwestern coast of Turkey

During the nesting period in 2000 and 2001 on Patara beach, total emergence and non-nesting emergence of loggerhead turtles (Caretta caretta), nest distribution, and nest distance from the sea were recorded . The main nesting seasons for sea turtles (family Cheloniidae) were during June and July. Loggerhead turtles comprised the majority of sea turtle emergence records; only two green turtle (Chelonia mydas) emergences were recorded. The small nesting population (52 and 53 nests in 2000 and 2001, respectively) of sea turtles on Patara beach was due to low hatching success resulting from a rise in seawater levels, owing to beach erosion, and the subsequent inundation of most nests. The temperatures of four nests and sand at different distances from the sea were measured with electronic temperature loggers, which recorded mean nest temperatures of 28.8–30.7 °C, with the mean temperature in the middle third of the incubation period from 28.5 to 31.0 °C. The mean temperatures, incubation periods, temperature during the middle third of the incubation period, and percentage of hatchling sexes were evaluated with respect to sand and nest temperatures. The results showed a female-dominated sex ratio, which was probably the result of predation of nests far from the sea and the seawater inundation of nests close to the sea, as the sand temperature was different at sites close and far from the sea.

Natural temperature regimes for loggerhead and green turtle nests in the eastern Mediterranean

Temperatures of green turtle (Chelonia mydas) and loggerhead turtle (Caretta caretta) nests on the beaches of northern Cyprus and Turkey were examined. Electronic continuous-temperature recorders programmed by computer were placed at the top, middle, and bottom of the nests. The sex of 3-7 hatchlings from each level was determined from gonadal histology. The maximum temperature increase during the incubation period was 9.6oC for both species. The mean temperature during the middle third of the incubation period is a good indicator of the sex ratio of the clutch. The percentage of female embryos increased with temperature, 50% being female at 29°C. The mean temperature over the entire incubation period is not a good indicator of sex ratio but can be used to predict the duration of incubation period. The temperature differences within the clutch were larger in loggerhead than in green turtle nests. Eggs at the top of the nest experienced generally warmer (up to 1.4°C) conditions than eggs at the bottom of the same nest, and this caused variation in sex ratio within nests. Over all nests, the sex ratio (percent female) of hatchlings was 91% at the top, 83% at the middle, and 69% at the bottom. There was considerable interbeach thermal variation. Marked diel cycles of up to 1.5°C were detected in loggerhead turtle nests but not in the deeper nests of green turtles.