New research emerging from the University of Georgia’s Odum School of Ecology, in collaboration with the Marine Extension and Georgia Sea Grant, has unveiled alarming evidence of elevated mercury concentrations in key aquatic ecosystems spanning Georgia and South Carolina. The study focuses on American alligators inhabiting three significant research sites: the Okefenokee Swamp, Jekyll Island, and the Yawkey Wildlife Center. The findings suggest that mercury contamination in these environments could have far-reaching ecological and public health implications, heightening concern over the persistence and bioaccumulation of this toxic heavy metal in sensitive food webs.
Mercury is a well-known neurotoxin, with trace quantities often introduced into aquatic systems through runoff and atmospheric deposition linked to industrial emissions. While prior investigations have documented mercury accumulation in smaller organisms inhabiting southeastern U.S. wetlands, this study breaks new ground by exploring mercury burdens in apex predators, such as the American alligator. These large reptiles occupy a high trophic position, making them particularly susceptible to biomagnification, which refers to the progressive concentration of contaminants in successive levels of a food web.
The research involved extensive fieldwork, during which over one hundred alligators across diverse habitats were examined. Blood samples were collected and analyzed to determine total mercury concentrations, while dietary information was meticulously assessed to unravel trophic relationships and sources of metal uptake. Striking disparities in mercury levels were observed among the different populations, with alligators dwelling within the Okefenokee Swamp exhibiting mercury burdens up to eight times greater than those found on Jekyll Island and the Yawkey Wildlife Center. This pronounced regional variation underscores the importance of site-specific factors influencing mercury bioavailability and accumulation.
The ecological ramifications of such elevated mercury concentrations are profound and multifaceted. As Jeb Byers, an Odum School professor and co-author of the study, articulates, mercury acts as a potent neurotoxin capable of devastating neurological function across a range of species. When contaminants like mercury accumulate in high apex predators, it signals a "perfect storm" scenario, indicative of pervasive contamination that can cascade through complex food webs with lethal consequences. This phenomenon calls attention not only to wildlife health but also to potential risks facing human populations reliant on these waters for subsistence fishing and recreational hunting.
Mercury enters aquatic ecosystems primarily through atmospheric deposition from fossil fuel combustion and industrial discharge, subsequently undergoing microbial transformation into methylmercury—the organic form most readily absorbed and retained in organisms. This methylation process enables mercury to bioaccumulate efficiently, becoming increasingly concentrated as it moves from prey species to their predators. Consequently, apex predators such as alligators serve as important sentinel species for monitoring ecosystem health and contaminant load.
The researchers further observed that the age and size of alligators played a significant role in mercury accumulation. Larger and older individuals consistently demonstrated higher mercury concentrations, which is indicative not only of bioaccumulation over time but also of trophic shifts in dietary habits toward larger and more contaminated prey. Benjamin Parrott, a co-author and associate professor at the Savannah River Ecology Laboratory, emphasizes the ontogenetic—age-related—nature of these findings, which illustrate how alligator growth stages correlate with increasing exposure to mercury via dietary pathways.
In addition to adult alligators, notable mercury burdens were detected in hatchlings, challenging assumptions about early-life exposure. The study suggests that mercury may be maternally transferred to offspring through contamination of egg yolks, a route of exposure that can have detrimental impacts on neonatal development and survival. This vertical transfer presents an additional dimension of ecological risk, potentially affecting population viability through sublethal effects on hatchling growth, behavior, and neurological function.
The spatial and ontogenetic patterns highlighted in this research underscore the urgent need to investigate the sources, pathways, and ecosystem-wide impacts of mercury contamination in southeastern U.S. wetlands. Kristen Zemaitis, lead author of the study, advocates for expanded research efforts to pinpoint specific mercury inputs and elucidate the broader effects on other fauna sharing these habitats. Such work is critical to inform conservation strategies, public health advisories, and regulatory policies aimed at mitigating mercury pollution.
The information is particularly salient given the hydrological connectivity between the Okefenokee Swamp and adjoining river systems, including the Suwannee and St. Marys rivers. This connectivity allows contaminated waters to disseminate downstream, potentially compromising aquatic species beyond the swamp itself. Communities relying on fish and game harvested from these waterways face uncertain risks, as mercury exposure poses neurological, reproductive, and developmental hazards that can manifest in humans as well as wildlife.
The methodological rigor of this study is noteworthy, combining blood mercury assays with dietary analysis over multiple months to achieve a comprehensive picture of mercury dynamics in alligator populations. Such interdisciplinary approaches are vital in unraveling the ecological complexities that govern contaminant fate and transport across landscape gradients and life history stages.
The research was supported by funding from the Jekyll Island Authority and the Okefenokee Swamp Park. Collaborative contributions included Thomas Rainwater, affiliated with the Tom Yawkey Wildlife Center and Clemson University; Yank Moore, associated with the Conservation for Jekyll Island Authority; and Kimberly Andrews, a coastal ecology specialist with UGA Marine Extension and Georgia Sea Grant. Their combined expertise strengthened the study’s capacity to address environmental toxicology within ecologically and socioeconomically important sites.
Looking forward, this work invites a deeper interrogation of mercury sources—both anthropogenic and natural—and encourages the use of apex predators such as alligators as bioindicators to assess ecosystem health. The implications extend beyond regional concerns, alerting scientists and policymakers worldwide to the persistent challenge posed by mercury and other heavy metals in aquatic ecosystems. Given the profound effects of mercury contamination on neurological health, biodiversity, and ecosystem integrity, coordinated efforts are imperative to curtail inputs and protect vulnerable species and human communities.
Subject of Research: Mercury contamination in American alligators and aquatic ecosystems of Georgia and South Carolina
Article Title: Site-specific ontogenetic drivers of mercury concentrations in American alligators
News Publication Date: 7-Mar-2025
Web References:
Image Credits: Jeb Byers
Keywords: Vertebrates, Transition metals, Water pollution
