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- Title
- The Hematological and Histological Effects of Maternal Offloading of Mercury in Neonatal and Juvenile Blacktip Sharks (Carcharhinus limbatus).
- Creator
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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.
Show less - Date Issued
- 2017
- Identifier
- Bridenbaugh_fgcu_1743_10248
- Format
- Document (PDF)
- 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.
Show less - Date Issued
- 2015
- Identifier
- Lienhardt_fgcu_1743_10140
- Format
- Document (PDF)
