Concentrations of heavy metals in scute samples from nesting female olive Ridley, Lepidochelys olivacea, and Eastern Pacific rreen, Chelonia mydas agassizii, sea turtles in Costa Rica
Sea turtle populations are declining worldwide due to a number of anthropogenic factors: fishery bycatch, habitat destruction, illegal egg harvesting, and marine pollution. Marine pollution is the result of industrial processes or waste disposal that produce by-products that are either discharged into the atmosphere or directly into oceans. Sea turtles undertake extensive migrations; therefore, they can readily serve as biomonitors for the overall health of the aquatic ecosystem, especially for the evaluation of heavy metals that biomagnify across trophic levels. Heavy metals are known to have endocrine-disrupting properties, and at high concentrations, can be lethal. The objective of this study was to provide baseline toxicological information on heavy metal concentrations in nesting female sea turtles, specifically, the olive ridley (Lepidocheyls olivacea), a pelagic omnivore, and Eastern Pacific green ( Chelonia mydas agassizii), a herbivore, that migrate to Playa Grande and Playa Cabuyal in Guanacaste, Costa Rica. Tissue samples were collected along the posterior marginal scutes located on the carapace and analyzed for the following metals: Cd, Co, Cr, Mn, Ni, and Pb. Concentrations were analyzed using inductively-coupled plasma mass spectrometry (ICP-MS) at the level of parts per billion (ppb). Scute tissue was sampled as it has been shown to yield higher metal concentrations than blood and provides a more accurate estimation of long-term metal accumulation. Other studies have demonstrated that metals have a high affinity for keratin, which is the tissue that makes up the outer layer of a turtle scute. For this reason, sea turtle scutes serve as an accurate storehouse of exposure to marine metal exposure. Since green turtles are herbivorous and remain in neritic nearshore environments and olive ridley turtles are open-ocean pelagic omnivores these results should provide a good comparison of possible differences in exposure and accumulation in two distinct habitats and lifestyles. A total of 34 scute samples were collected from olive ridley (n=17) and Eastern Pacific green (n=17) nesting females. Olive ridleys were sampled from Playa Grande, while Eastern Pacific green samples were collected from Playa Cabuyal. Concentrations (mean ±SE) for olive ridleys and Eastern Pacific greens are reported in ppb, respectively: Cd – 26.9 ± 1.5; 30.9 ± 1.6, Co – 26.7 ± 8.0; 69.8 ± 6.8, Cr – 106.0 ± 6.6; 123.5 ± 6.9, Mn – 524.2 ± 52.0; 485.8 ± 68.7, Ni – 216.8 ± 75.8; 123.7 ± 20.2, Pb – 90.5 ± 25.1; 94.8 ± 25.1. Cd and Co were significantly different (p < 0.05) between the two species with Eastern Pacific green turtles having higher concentrations. Relative size comparison using curved carapace length, a rough estimate of turtle age, was not correlated with metal concentration within the sea turtles sampled (p > 0.05). The reported concentrations found in these two marine turtle species are lower than other studies that used scute tissue samples as indicators of heavy metal pollution. However, study site locations were associated with major industrialized areas whereas this study was along the somewhat undeveloped Central American Pacific coast where there may be differing concentrations of pollution which explain these differences. Furthermore, the results of this study suggest that Eastern Pacific green turtles, a neritic herbivore, may be at a higher risk of contamination by specific metals than a pelagic omnivore like the olive ridley. Sea grasses and red algae, the main staple of the Eastern Pacific green's diet, have unique uptake pathways where some metals are utilized in the plant's metabolic processes, while others accumulate as free ions. Accompanied with their inshore, neritic habitat utilization, the Eastern Pacific green turtle's risk of run-off and land-based contamination will increase if it happens to reside in a heavily polluted area. Determining a baseline for the amount of heavy metal contamination in ocean habitats using long-lived species like sea turtles from both pelagic and neritic environments is important for understanding anthropogenic influences on aquatic ecosystems. Sea turtle species spend the majority of their lives in the ocean, only coming ashore for brief periods during nesting events. During their lifetimes, they traverse waters with varying levels of pollution that can provide us with important insight into the health of the environment that they inhabit.
Paladino, Purdue University.
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