Total mercury levels in Loggerhead and Green sea turtle hatched eggshells from nests along the southeastern Mediterranean coast

Abstract

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, age and exposure. This study examined the spatial distribution of mercury in hatched eggshells of Loggerhead Sea turtles (Caretta caretta, n = 180) 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 gravid female's mercury burden. In this study, mercury levels were measured in ten hatched eggshells, sampled from 22 nests (18 Loggerhead and 14 Green Sea turtle nests) in four hatcheries along the Mediterranean coast of Israel, during the nesting seasons of 2022, and 2023. The mean mercury level in Loggerhead eggshells was significantly higher than Green Sea turtle eggshells (7.8 ± 0.5 and 1.3 ± 0.2 ng g DW^-1 (mean ± standard error), respectively, Students t-test, p < 0.0001), possibly reflecting the differences in maternal trophic levels. Furthermore, mercury in Loggerhead eggshells decreased from the northern to the southern region of Israel, from 9.7 ± 0.8 ng g DW^-1 (n = 100) to 5.4 ± 0.3 ng g DW^-1 (n = 80), respectively. Finally, mercury levels in Loggerhead eggshells are substantially higher than previously reported values from other regions in the Mediterranean Sea and globally, suggesting that eastern Levantine female Sea turtles are more exposed to mercury pollution than other marine areas of the Mediterranean Sea and globally.