RESUMEN

Freshwater ecosystems are among the most important ecosystems worldwide, however, over the last centuries, anthropogenic pressures have had catastrophic effects on them. Mercury (Hg) is one of the main environmental contaminants which globally affect ecosystems and particularly freshwater wildlife. While Hg originates from natural sources, anthropogenic activities such as agriculture, biomass combustion, and gold mining increase its concentrations. Gold mining activities are the main drivers of Hg emission in tropical ecosystems and are responsible for up to 38% of global emissions. Once in its methylated form (MeHg), mercury biomagnifies through the trophic chain and accumulates in top predators. Due to the toxicity of MeHg, long-lived predators are even more subjected to chronic effects as they accumulate Hg over time. In the present study we quantified Hg contamination in two top predators, the Black caiman Melanosuchus niger and the Agami heron Agamia agami, and in their prey in the Kaw-Roura Nature Reserve in French Guiana and evaluated the biomagnification rate in the trophic chain. Our results show that despite a TMF in the range of others in the region (4.38 in our study), top predators of the ecosystem present elevated concentrations of Hg. We have found elevated Hg concentrations in the blood of adult Black caiman (2.10 ± 0.652 µg g-1 dw) and chicks of Agami heron (1.089 ± 0.406 µg g-1 dw). These findings highlight the need to better evaluate the potential impact of Hg in freshwater top predators, especially regarding reprotoxic effects.

RESUMEN

Trace elements in the blood of crocodilians and the factors that influence their concentrations are overall poorly documented. However, determination of influencing factors is crucial to assess the relevance of caimans as bioindicators of environmental contamination, and potential toxicological impact of trace elements on these reptiles. In the present study, we determined the concentrations of 14 trace elements (Ag, As, Cd, Cr, Co, Cu, Fe, Hg, Pb, Mn, Ni, Se, V, and Zn) in the blood of four French Guiana caiman species (the Spectacled Caiman Caiman crocodilus [n = 34], the Black Caiman Melanosuchus niger [n = 25], the Dwarf Caiman Paleosuchus palpebrosus [n = 5] and the Smooth-fronted Caiman Paleosuchus trigonatus [n = 20]) from 8 different sites, and further investigated the influence of individual body size and stable isotopes as proxies of foraging habitat and trophic position on trace element concentrations. Trophic position was identified to be an important factor influencing trace element concentrations in the four caiman species and explained interspecific variations. These findings highlight the need to consider trophic ecology when crocodilians are used as bioindicators of trace element contamination in environmental studies.

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RESUMEN

Mercury (Hg) is a contaminant that is impacting ecosystems worldwide. Its toxicity is threatening wildlife and human populations, leading to the necessity of identifying the most affected ecosystems. Therefore, it is essential to identify pertinent bioindicator organisms to monitor Hg contamination. In this study, we determined the stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in the red blood cells (RBCs), and the total Hg concentration in total blood of 72 Melanosuchus niger in French Guiana. The goals of our study were to assess the level of Hg contamination in total blood of Black caimans and to further investigate the influence of individual traits (i.e., sex, size/age, diet) on Hg concentrations. Mercury concentration in total blood of Black caimans ranged from 0.572 to 3.408 µg g-1 dw (mean ± SD is 1.284 ± 0.672 µg g-1 dw) and was positively correlated to individual body size and trophic position (δ15N). We did not find any sexual or seasonal effects on Hg concentrations in the blood. The use of blood of M. niger is relevant to determine Hg concentrations within the population and suggests that this species can be used as a bioindicator for environmental contamination. In addition, our results emphasize trophic position as a major source of Hg variation and further suggest that it is essential to take trophic position (δ15N) into account for future studies.

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RESUMEN

The black caiman is one of the largest neotropical top predators, which means that it could play a structuring role within swamp ecosystems. However, because of the difficulties inherent to studying black caimans, data are sorely lacking on many aspects of their general biology, natural history, and ecology, especially in French Guiana. We conducted a detailed study of the Agami Pond black caiman population using a multidisciplinary approach. The aim was to better understand the species' dietary ecology and movements in the pond, and thus its functional role in pond system. We gathered natural history data, tracked caiman movements using satellite transmitters, and characterized feeding ecology via stable isotope analysis. Our study was carried out over three sampling periods and spanned both wet and dry seasons, which differ in their hydrological and ecological conditions. Our results show that black caiman abundance and age demographics differed between seasons in Agami Pond. In the dry season, Agami Pond is one of the only areas within the marsh to hold water. It thus contains large quantities of different fish species, which form the basis of the black caiman's diet. Caiman body size, a proxy for age class, was around 1.5 meters. During the wet season, which corresponds to the breeding period for migratory birds (e.g., Agami herons), adult black caimans are present in Agami Pond. Adults were most abundant in the inundated forest. There, most individuals measured up to 2 meters. They also exhibited a particular "predatory" behavior near bird nests, preying on fallen chicks and adults. Juveniles and subadults were present during both seasons in the pond's open waters. These behavioral observations were backed up by stable isotope analysis, which revealed ontogenetic variation in the caiman's isotopic values. This isotopic variation reflected variation in diet that likely reduced intraspecific competition between adults and young. The telemetry and microchip data show that different age classes had different movement patterns and that seasonal variation in the pond may influence caiman prey availability and reproductive behavior. The new information gathered should help predict this species' responses to potential ecosystem disturbance (e.g., water pollution, habitat destruction) and inform the development of an effective conservation plan that involves locals and wildlife officials.

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