Dalyan Beach Research Articles

Taxonomy and distribution of diatoms on the Turkish Mediterranean Coast, Dalyan (Muğla)

Diatoms are one of the components in the littoral zone and the most productive in terms of O2 production and primary production. Despite their importance in these coastal ecosystems, the diatoms of littoral zones of Turkish coastlines have been understudied. In this report, we document the littoral diatoms from Dalyan Iztuzu Beach at the southeast coasts of Aegean Sea. Samples were collected from 6 stations in Dalyan Beach between 2012 and 2016. We report here on the occurrence of 9 genera including, Catenula Mereschkowsky, Cymatosira Grunow, Dimeregramma Ralfs, Diplomenora Blazé, Eunotogramma Weisse, Meloneis Louvrou, Danielidis & Economou-Amilli, Neohuttonia Kuntze, Plagiogramma Greville and Tetramphora Mereschkowsky, as well as 40 taxa as newly-recorded from Turkey. The newly-recorded diatoms are characterized in terms of their morphology and illustrated with light micrographs. For each species, their habitat and geographic distribution along the coasts are discussed.

First observation of multiple paternity in loggerhead sea turtles, Caretta caretta, nesting on Dalyan Beach, Turkey

Sea turtles are promiscuous breeders with both males and females mating multiply. Due to this mating system, multiple paternity (MP) occurs in sea turtle clutches, and the frequency of MP varies greatly within and among species. In this study, the paternity of a population of loggerhead sea turtles (Caretta caretta) nesting on Dalyan Beach in Turkey was investigated using two highly polymorphic microsatellite markers (CcP2F11 and CcP7C06). Tissue samples collected from randomly selected hatchlings (a total of 522 hatchlings) from two to three successive clutches (a total of 25 clutches) of 10 nesting females were used for paternity analysis with an average sampling effort of 28.2% of offspring per clutch. Evidence of MP in seven out of 10 females (70%) was found, and it was detected that four out of these seven females mated with at least two males, whereas the remaining three females with at least three males. By analysing the successive clutches of females, it was detected that both the number and genotype of contributing sires was same in all clutches of a given female, possibly due to the lack of successful inter-nesting mating in this population. The high frequency of MP implies the possible high genetic diversity within this population. This study indicates that the density of individuals may be the reason of the high frequency of MP in this relatively small population because mating takes place mainly in a narrow area in Dalyan. The possible mating behaviours of the sea turtles and their population structures were discussed in light of the high frequency of MP within this population reported for the first time.

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.

Nest temperatures in a loggerhead nesting beach in Turkey is more determined by sea surface than air temperature

While climate change is now fully recognised as a reality, its impact on biodiversity is still not completely understood. To predict its impact, proxies coherent with the studied ecosystem or species are thus required. Marine turtles are threatened worldwide (though some populations are recovering) as they are particularly sensitive to temperature throughout their entire life cycle. This is especially true at the embryo stage when temperature affects both growth rates and sex determination. Nest temperature is thus of prime importance to understand the persistence of populations in the context of climate change. We analysed the nest temperature of 21 loggerheads (Caretta caretta) originating from Dalyan Beach in Turkey using day-lagged generalised mixed models with autocorrelation. Surprisingly, the selected model for nest temperature includes an effect for sea surface temperature 4-times higher than for air temperature. We also detected a very significant effect of metabolic heating during development compatible with what is already known about marine turtle nests. Our new methodology allows the prediction of marine turtle nest temperatures with good precision based on a combination of air temperature measured at beach level and sea surface temperature in front of the beach. These data are available in public databases for most of the beaches worldwide.

A model to predict the thermal reaction norm for the embryo growth rate from field data

The incubation of eggs is strongly influenced by temperature as observed in all species studied to date. For example, incubation duration, sexual phenotype, growth, and performances in many vertebrate hatchlings are affected by incubation temperature. Yet it is very difficult to predict temperature effect based on the temperature within a field nest, as temperature varies throughout incubation. Previous works used egg incubation at constant temperatures in the laboratory to evaluate the dependency of growtProd. Type: FTPh rate on temperature. However, generating such data is time consuming and not always feasible due to logistical and legislative constraints. This paper therefore presents a methodology to extract the thermal reaction norm for the embryo growth rate directly from a time series of incubation temperatures recorded within natural nests. This methodology was successfully applied to the nests of the marine turtle Caretta caretta incubated on Dalyan Beach in Turkey, although it can also be used for any egg-laying species, with some of its limitations being discussed in the paper. Knowledge about embryo growth patterns is also important when determining the thermosensitive period for species with temperature-dependent sex determination. Indeed, in this case, sexual phenotype is sensitive to temperature only during this window of embryonic development.

Reproductive Biology of the Loggerhead Sea Turtle, Caretta Caretta, in Dalyan Beach, Turkey, 2009

The reproductive biology of loggerhead turtles, Caretta caretta, was studied at Dalyan, Turkey in 2009. This study was conducted between 18 June and 15 September 2009. During the breeding season, the night and morning patrols on the beach were performed. During night patrols, they were tagged and after that body measurements were taken. During morning patrols, the shape and pattern of tracks were noted and those tracks that resulted in nests were marked. During the hatchling emergence season, the numbers of hatchling tracks coming from each nest were counted daily, and the numbers of hatchlings reaching the sea were determined by following the tracks. A total of 1154 emergences were recorded with 330 (29%) resulting in nests. Of these nests, 5% occurred in May, 57% in June, 36% in July and 2% in August. The nest density of C. caretta at Dalyan was 70.2 nests/km. The mean clutch size at Dalyan during 2009 breeding season was 68.3 eggs (range 25-138, n = 123). The incubation period was on average 50.2 days (range 40-63, n = 123). All eggs were predated in 177 nests (53%), and some eggs were predated in 51 nests (15%) by foxes (Vulpes vulpes) and badgers. A total of 102 nests (31%) were completely protected so that no eggs were predated. The hatching success was 31.9%. While 5398 hatchlings (85.3% of the total number of hatchlings) were able to reach the sea, 175 hatchlings (2.8%) died inside the nest, 695 (11%) were predated by foxes, and 59 (1%) were predated by crabs. Nests that were threatened by the tide or human activities were transplanted to safe areas of the beach. Furthermore, metal gratings were placed on the nests to prevent fox predation.

The effect of nest relocation on embryonic mortality and sex ratio of Loggerhead Turtles, Caretta caretta (Reptilia: Cheloniidae), at Dalyan Beach, Turkey

Marine turtles are globally endangered and one important conservation technique is nest relocation. This study assesses the relationship between nest site factors (wet nest depth, dry nest depth, total nest depth, nest diameter, distance to sea, moisture, clutch size and incubation duration) and embryonic mortality of natural and relocated nests at Dalyan beach, Turkey. Principal component analyses (PCA) revealed a three-factor structure for the natural nests and a four-factor structure for the relocated nests. The clutches in natural and relocated nests had a total of mortality ratio of 21% and 12%, incubation duration of 52 and 50 days, and estimated female ratio of 80% and 88%, respectively. Thus, mortality was lower and incubation faster in the relocated nests, but the proportion of females was higher. Hatching success in relocated nests (84.4%) was significantly higher than in natural nests (72.7%).

Loggerhead Turtles, Caretta caretta, at Dalyan Beach, Turkey: Nesting Activity (2004–2005) and 19-year Abundance Trend (1987–2005)

The nesting biology of loggerhead turtles, Caretta caretta, on Dalyan beach, Turkey, was studied during the 2004 and 2005 nesting seasons. In addition, we analyzed nesting trends over 19 consecutive years, from 1987 to 2005. A total of 711 emergences occurred in 2004 and 605 emergences in 2005, of which 223 (31.4%) and 221 (36.5%) nests were deposited, respectively. Mean nesting densities were 47.5 nests km−1 and 47 nests km−1 in 2004 and 2005, respectively. Of the overall nests, 424 (95%) were excavated and 32,339 eggs were counted. Of these eggs, 19,947 (61.7%) hatchlings had come out and 18,607 (93.3% of hatchlings) of them were able to reach the sea. We recorded a total of 3688 nests on Dalyan beach during 19 consecutive years with a mean of 194 nests per year. There were also strong annual fluctuations in the number of nests, which ranged from a minimum of 57 nests (in 1990) to a maximum of 286 (in 2002). No trend in the number of nests over the 19-year period was seen (95% CI −2.7% to 6.7% change per year). The lack of increase was a surprising result when considering the long-term conservation efforts on the beach; although, a similar case was reported in Laganas Bay, Greece. High interannual fluctuations could obscure trends as stated in previous studies.

SEA TURTLE NEST CONSERVATION TECHNIQUES ON SOUTHWESTERN BEACHES IN TURKEY

Loggerhead turtle nests at risk from tidal inundation and predation were either relocated, screened against predation, or fenced in areas of heavy human activity on Fethiye, Dalyan, and Dalaman beaches during the nesting seasons of 2000-2002. Relocation, screening, and fencing clearly increased the hatching success rate and provided effective protection of sea turtle nests against inundation and predation. The emergence pattern and sex ratios of hatchlings, incubation periods, and distances of nests from the water line were analyzed. Incubation temperatures leading to a high female-biased sex ratio were found on Dalyan Beach. Sand and nest temperatures of the relocated nests at the hatchery site influenced the sex ratios, as seen from histological sexing of dead hatchlings from both in situ and relocated nests.

Reproduction biology of the marine turtle populations in Northern Karpaz (Cyprus) and Dalyan (Turkey)

The reproduction biology of Green Turtles, Chelonia mydas, and Loggerhead Turtles, Caretta caretta, was studied at Northern Karpaz, northern Cyprus, and Dalyan, Turkey, in 1996–1997. A total of 22 C. mydas and 7 C. caretta nests were recorded at Northern Karpaz in 1996, and 135 Loggerhead Turtle nests at Dalyan in 1997. The Green Turtle nesting density was 9.2 nests/km, the Loggerhead Turtle density 2.9 nests/km at Northern Karpaz and 28.7 nests/km at Dalyan. For Green Turtles, 78.9% of the hatchlings were able to reach the sea. The corresponding values for Loggerheads are 55.5% at Northern Karpaz and 87.1% for Dalyan. The mean incubation period for C. mydas was 58.0 days at Northern Karpaz and for C. caretta this period was 52.4 days on Dalyan Beach. Nests which were threatened by the tide or human activities were transplanted to safe areas of the beach. The hatching success of transplanted nests (72.8%) was significantly higher than nests left under natural conditions (55%).

Mesh grids protect loggerhead turtle Caretta caretta nests from red fox Vulpes vulpes predation

The efficacy of protecting loggerhead Caretta caretta turtle nests from red fox Vulpes vulpes predation was examined at Dalyan beach, Turkey. Twenty-five nests were protected using individual wire mesh grids. Predation occurred at 63% of the 88 unprotected control nests. In contrast, no protected nests were predated. As a consequence, hatching success was significantly higher at protected nests than at control nests. The feasibility of adopting wire mesh grids as a routine method for turtle nest conservation is evaluated.

Nesting biology of loggerhead turtles Caretta caretta L. on Dalyan Beach, Mugla-Turkey

The nesting biology of loggerhead turtles Caretta caretta was studied on a 3-km beach on the west coast of Turkey. Female turtles were recorded making 912 visits at night between 7 May and 18 August 1989, which resulted in 235 nests. The peak nesting period was the middle of June, and the mean incubation period for eggs 59 days. However, only 51 nests were successful in producing hatchlings that reached the sea. Out of an estimated total 17 254 eggs laid on the beach, predation by foxes and sand crabs accounted respectively for 12 078 and 1 725 of eggs and newly emerged hatchlings. These results are compared with 1988 data, and recommendations made for reducing predation.