Pan-oceanic distribution of mercury (Hg) in sea turtles: a review

Abstract

With no known biological function, mercury (Hg) is highly toxic, bio-accumulates, and biomagnifies up the food web. Long-living marine animals, such as sea turtles, can be exposed to Hg in the oceans. The wide distributions of these reptiles and lifespans compatible with Hg residence time in ocean surface waters (approximately 30 yr) makes them reliable biological monitors of the long-term changes in Hg concentrations in the oceans. Taking this into consideration, we conducted a thorough review of studies to compare the concentrations of Hg in the 7 species of sea turtles distributed in different regions of the Atlantic, Pacific, and Indian Oceans and the Mediterranean Sea. Hg concentrations in muscle and scutes of Chelonia mydas were highest in the South Atlantic, whereas the highest concentrations found in Caretta caretta occurred in the Mediterranean Sea. The differences could be associated with the feeding habits of each species and the characteristics of the environment, such as the oligotrophic nature of the water and the lower productivity in the Mediterranean Sea. Unfortunately, few studies exist for the other 5 sea turtles (Dermochelys coriacea, Eretmochelys imbricata, Lepidochelys olivacea, L. kempii, and Natator depressus), which hampers a more detailed regional or ecological comparison among species. The results found in this review reveal information gaps that should be filled through more numerous studies focused on different oceanic regions and species.