Mercury levels in Loggerhead and Green Sea turtle eggshells from nests along the southeastern Mediterranean coast

Sea turtles roam vast regions of the Mediterranean Sea throughout their lives, during which they accumulate mercury, primarily as a function of their tropic level and age. This study examined the spatial distribution of mercury in hatched eggshells of loggerhead sea turtles (caretta caretta, n=200) and green sea turtles (chelonia mydas, n=40) from nests along the Mediterranean coast of Israel. This was done to determine spatial trends of mercury exposure on a regional scale in nesting females, assuming that eggshell mercury levels are related to the mother’s mercury burden. Ten eggshells were sampled from each nest during the nesting seasons of 2022, and 2023 (n=22).

Some of the nests were transferred to protected enclosures after the eggs were laid. In general, mean mercury levels in each nest varied greatly between nests from the same enclosures and between different shores in both species. As expected, the mean mercury level in loggerhead eggshells was significantly higher than green sea turtle eggshells (8±1 and 1.0±0.5 ppb (mean±SE), respectively, p<0.0001). Furthermore, mercury in loggerhead eggshells decreased from the northern to the southern region of Israel from 10±1 ppb (n=100) to 5.4±0.3 ppb (n=80), respectively. Finally, mercury levels in loggerhead eggshells are substantially higher and more robust (much higher sample size of eggs and nests in this study) than previously reported values from other regions in the Mediterranean Sea and globally. This result suggests that eastern Levantine sea-turtles are more exposed to mercury pollution than other marine areas of the Mediterranean Sea and globally.