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Trophic Transfer of Mercury in a Subtropical Coral Reef Food Web
Title
Trophic Transfer of Mercury in a Subtropical Coral Reef Food Web.
Creator
Lienhardt, Christopher Tyler
Abstract / Description
Mercury is a widespread and damaging toxic metal that is trophically transferred through food webs. Coral reefs present an interesting dynamic in that they are comprised of complex food webs containing a high number of lateral or horizontal links that do not always end in top predators, thus possibly reducing trophic transfer. Therefore, the objective of the study was to assess the efficiency of trophic transfer in a coral reef food web, using mercury as the tracer. Concentrations of mercury...
Show moreMercury is a widespread and damaging toxic metal that is trophically transferred through food webs. Coral reefs present an interesting dynamic in that they are comprised of complex food webs containing a high number of lateral or horizontal links that do not always end in top predators, thus possibly reducing trophic transfer. Therefore, the objective of the study was to assess the efficiency of trophic transfer in a coral reef food web, using mercury as the tracer. Concentrations of mercury and stable isotopes of nitrogen (δ15N) and carbon (δ13C) were measured in fish from two sites near the coastal waters of Long Key, Florida. The relationship between mercury and δ15N can be used to estimate biomagnification across the food web (i.e., trophic magnification slope, food web magnification factor). Using mercury and stable isotopes of nitrogen and carbon as tracers assisted in quantifying the efficiency at which coral reef ecosystems transfer these and other bioaccumulative toxins (e.g., ciguatoxins, etc.) through the food web, while also increasing our understanding of the associated flow of energy in the system. A total of 242 samples were collected from April 2012 through December 2013 using spear guns, hook and line, and hand collection techniques. Individual Hg concentrations ranged from 17.33 µg/kg in a gray angelfish (Pomacanthus arcuatus) to 3,317 µg/kg in a great barracuda (Sphyraena barracuda) at Long Key Hard Bottom, and 19.01 µg/kg in a rock beauty angelfish (Holacanthus tricolor) to 6,842 µg/kg in a porkfish (Anisotremus virginicus) at Tennessee Reef. Variability in both fish size and δ15N increased the variance in tissue Hg concentration both intra- and inter-specifically. As observed in other systems, the log transformed Hg concentrations in the food web, pooled across species, were significantly related to δ15N. The trophic magnification slope (i.e., slope of Log [Hg] regressed on δ15N), as an estimate of the biomagnification rate of Hg in the subtropical coral reef food web was 0.23 ± 0.03 (±95% confidence interval) at Tennessee Reef and 0.16 ± 0.04 for Long Key Hard Bottom. When δ15N was translated to trophic level, the food web magnification factor (calculated from slope of Log [Hg] regressed on trophic level) were 7.8 and 3.4 for Tennessee Reef and Long Key Hard Bottom, respectively. Although there was some evidence to support significant differences between the two sites (which could have been due to differences in water quality), this difference in slopes could also be a result of unbalanced sampling design. Nonetheless, these results clearly demonstrate that Hg is biomagnified through subtropical coral reef ecosystems and that the transfer efficiency (i.e., slopes) were consistent with previous reports for marine ecosystems.
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Date Issued
2015
Identifier
Lienhardt_fgcu_1743_10140
Format
Document (PDF)
The Hematological and Histological Effects of Maternal Offloading of Mercury in Neonatal and Juvenile Blacktip Sharks (Carcharhinus limbatus)
Title
The Hematological and Histological Effects of Maternal Offloading of Mercury in Neonatal and Juvenile Blacktip Sharks (Carcharhinus limbatus).
Creator
Bridenbaugh, Sarah
Abstract / Description
The biomagnification of methylmercury (MeHg) through the world’s oceans begins with absorption at the primary producer level and culminates in the highest mercury (Hg) burdens in apex predators and humans. The health concerns associated with excessive Hg consumption and accompanying toxicity are detrimental to both fish and humans. As apex predators, blacktip sharks (Carcharhinus limbatus) are highly susceptible to biomagnified Hg particularly in the Gulf of Mexico (GOM), which is known to...
Show moreThe biomagnification of methylmercury (MeHg) through the world’s oceans begins with absorption at the primary producer level and culminates in the highest mercury (Hg) burdens in apex predators and humans. The health concerns associated with excessive Hg consumption and accompanying toxicity are detrimental to both fish and humans. As apex predators, blacktip sharks (Carcharhinus limbatus) are highly susceptible to biomagnified Hg particularly in the Gulf of Mexico (GOM), which is known to contain fishes and invertebrates with elevated Hg levels. Blacktips occur in the GOM year-round and are a heavily fished species both commercially and recreationally, but little is known about how Hg affects the species. High Hg burdens can be mobilized by females during reproduction and transferred to the blood and tissues of developing embryos and eggs—a phenomenon referred to as maternal offloading. In this study, blood, muscle, liver, and kidney samples were collected from neonatal (n=57) and juvenile (n=13) blacktip sharks gillnetted in Pine Island Sound, Florida. Combined Hg concentrations ([Hg]) in neonates and juveniles were found to be elevated in muscle (0.588 ± 0.23 mg kg-1), liver (0.385 ± 0.29 mg kg-1), kidney (0.558 ± 0.25 mg kg-1), and blood (0.0594 ± 0.041 mg kg-1) compared to other species and conspecifics from other areas. Blood plasma chemistry, hematology, and liver histology were evaluated to assess the relationship between maternal offloading of Hg and tissue damage. Plasma chemistry parameters alanine aminotransferase (ALT) and phosphorous (PHOS) were not correlated with tissue [Hg] or liver condition index. Hematological effects (e.g., displaced erythrocyte nuclei and vacuolization of erythrocytes) were not correlated with tissue [Hg]. Several types of histopathologies were observed, but only three were statistically related to [Hg]: melanomacrophage presence x juvenile liver [Hg] (p=0.0201), melanomacrophage presence x juvenile [ALT] (p=0.0201), and adipose deposition x neonate liver [Hg] (p=0.0025). These results suggest that Hg exposure may have had some limited effects in the blacktips but that they may also be responding to other stressors.
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Date Issued
2017
Identifier
Bridenbaugh_fgcu_1743_10248
Format
Document (PDF)
Kinetics of Mercury Uptake by Juvenile Fish
Title
Kinetics of Mercury Uptake by Juvenile Fish.
Creator
Godwin, Jessica Ann
Abstract / Description
Increased mercury (Hg) emissions have become a widespread issue in the environment due to its long atmospheric residence time and potential for methylation in aquatic environments following deposition. Animals in aquatic environments are particularly vulnerable to toxicity due to high deposition and the capability of Hg to easily biomagnify through trophic levels. Diet is the primary pathway of Hg exposure as compared to water; leaving piscivorous species at higher risk of exposure and...
Show moreIncreased mercury (Hg) emissions have become a widespread issue in the environment due to its long atmospheric residence time and potential for methylation in aquatic environments following deposition. Animals in aquatic environments are particularly vulnerable to toxicity due to high deposition and the capability of Hg to easily biomagnify through trophic levels. Diet is the primary pathway of Hg exposure as compared to water; leaving piscivorous species at higher risk of exposure and toxicity. To examine kinetics of Hg uptake and subsequent distribution among tissue, a model fish was fed tissues from wild-caught higher trophic level fish with naturally incorporated Hg. Unexpectedly, the model redfish began dying early in the experiment. However, the mortality was not dose dependent and, thus, did not appear to be due to Hg. While other factors such as poor water quality, lack of nutrients in the experimental diet, and various toxins (e.g., ciguatoxins, brevetoxins, and composite cytotoxicity) were also ruled out, the cause of the mortality remains unknown. Although mortality was a source of uncertainty over the course of the exposure, Hg accumulated in the redfish in a dose-dependent manner. Potential steady-state of the redfish whole-body Hg concentration was assessed using a model derived from published literature. The model was effective in its ability to predict steady-state Hg concentrations that corresponded to the observed levels in the model redfish. Uptake kinetics was further studied by analyzing Hg distribution in the redfish. Mercury in ingested food was assumed to be taken up by the redfish intestinal tissue and distributed to the rest of the body in stages, as seen by the various Hg concentrations measured in the tissues over time. During periods of high exposure, Hg accumulated in the Liver>Muscle>Brain>Eyes, and Muscle>Liver>Brain>Eyes during low Hg exposure. The agreement between these results and the published literature suggests that the high mortality of redfish early in the experiment did not have a large effect on the Hg kinetics and assessment of the steady-state model.
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Date Issued
2018-07-16
Identifier
fgcu_ETD_0246
Format
Document (PDF)
Mercury Accumulation in Bonnethead (Sphyrna tiburo) and Bull Sharks (Carcharhinus leucas) in the Ten Thousand Islands National Wildlife Refuge
Title
Mercury Accumulation in Bonnethead (Sphyrna tiburo) and Bull Sharks (Carcharhinus leucas) in the Ten Thousand Islands National Wildlife Refuge.
Creator
Miller, Veronica
Abstract / Description
As apex, long-lived predators, sharks are susceptible to methylmercury (MeHg) exposure through biomagnification from prey items. Accordingly, tissue biopsy samples were collected from bonnethead (Sphyrna tiburo) and bull sharks (Carcharhinus leucas) from three estuaries within the Ten Thousand Islands National Wildlife Refuge (TTINWR) located in southwest Florida for determination of total mercury (THg). Muscle THg concentrations in bonnethead and bull sharks ranged up to 1.40 mg kg-1 and 2...
Show moreAs apex, long-lived predators, sharks are susceptible to methylmercury (MeHg) exposure through biomagnification from prey items. Accordingly, tissue biopsy samples were collected from bonnethead (Sphyrna tiburo) and bull sharks (Carcharhinus leucas) from three estuaries within the Ten Thousand Islands National Wildlife Refuge (TTINWR) located in southwest Florida for determination of total mercury (THg). Muscle THg concentrations in bonnethead and bull sharks ranged up to 1.40 mg kg-1 and 2.60 mg kg-1 (wet-weight basis), respectively. Concentration of THg generally increased with shark size, a proxy of its age, which explained much of the intraspecific variation. Interspecific variation in THg concentrations was evident, with bull sharks accumulating higher concentrations than bonnethead sharks, despite being younger and faster growing. The higher tissue concentration was likely due to greater maternal offloading of Hg to bull shark pups, as well as differences in diet among the two species. Baseline levels of MeHg entering the food web were assessed by examining THg concentrations in oysters (Crassostrea virginica), as primary consumers within each estuary. Concentrations of THg ranged up to 0.04 in oysters and differed among bays. These results confirm continued high Hg levels in sharks of the TTINWR as compared to conspecifics from other areas in Florida. Concentrations of THg observed in these sharks may pose a threat to the health and fitness of both shark and human populations.
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Date Issued
2018-07-26
Identifier
fgcu_ETD_0248
Format
Document (PDF)