Inorganic elements in marine turtles (Lepidochelys olivacea) from La escobilla beach (Mexico) and biomarkers related to heavy metal pollutants)

Abstract

The principal objective of this Doctoral Thesis was the evaluation of Lepidochelys olivacea marine turtles regarding the presence and possible effects of inorganic elements (including heavy metals), in a population from Southern Pacific Mexican coast. The specific objectives were: (1) Study the current situation about heavy metals and other inorganic elements in blood and tissues of Olive Ridley turtle (Lepidochelys olivacea) around the world. (2) Biomonitoring inorganic element concentrations in blood from live and different tissues from death turtles from La Escobilla beach (Oaxaca, Mexico), during 3 years (2012 to 2014). (3) Assess biochemical and molecular biomarkers related to inorganic elements. (4) Assess a possible morphological biomarker using the carapace of the turtles. The first part (introduction) offers both an overview of the topic addressed in the thesis, and a complete insight of the study area and targeted species. It includes an oceanographic and geomorphological description of the natural sanctuary of La Escobilla beach (Mexico), as well as important aspects of the biology and ecology of the targeted species Lepidochelys olivacea. Chapter I is an in-deep review of metal pollution in the existing seven species of sea turtles. It offers a background information for ongoing and future biomonitoring programs and for the conservation of these species. Chapters II and III are biomonitoring studies of metal contamination in the endangered turtle L. olivacea from the Pacific coast of Mexico along the period 2012-2014. In these chapters, the largest number of individuals ever analyzed in a single population of marine turtles were studied, including live and dead animals. This allowed to analyze a high number of organs and animal tissues such as blood, liver, kidney, bone, muscle, brain and egg components. Another highlight is the wide set of essential and non-essential inorganic elements analyzed, including emergent and under-studied elements in marine turtles. The analysis of metal accumulation in turtle tissues is combined with molecular, biochemical and morphological analyses to assess the effects on turtles' health (Chapters IV, V and VI). The antioxidant defense system of the sampled turtles was studied at the molecular and biochemical levels by analyzing the level of expression of antioxidant related genes as well as the activity of the associated antioxidant enzymes (Chapter IV). Biochemical indicators and their correlation with the metal content in different animal tissues are included in Chapters V and VI. These integrative approaches offer novel and valuable insights about the level of stress produced by the accumulation of metals and metalloids on L. olivacea, and provide a useful tool for improving diagnosis and care of recued turtles. Finally, Chapter VII proposes a new marine biomarker of pollution based in the asymmetry of the turtles' carapace, the developmental instability index. It was conducted on the basis of photographs, being therefore non-invasive, and allowing for the characterization of large number of individuals due to the low cost of the technique. Although the proposed index still needs validation, the results issued in this chapter are quite promising. In summary, Lepidochelys olivacea from La Escobilla beach seem to be very highly contaminated with certain inorganic elements. In particular, the very high Cd concentrations require special attention and follow up studies. Several significant relationships were also detected relating different biomarkers with some elements. These results demonstrated which tissues are preferable in the measurement of different biochemical or molecular markers. This thesis also provided very complete databases for biochemical and molecular parameters and inorganic elements for future research and for assessing the health of rescue individuals in this area. Additionally, we developed a new tool to assess the asymmetry of the carapace of the individuals using just a single photo, an option which greatly simplifies fieldwork in this area.