Mercury (Hg) in the environment has deleterious ecological and health affects for humans and wildlife and is primarily
transferred to humans through the consumption of marine biota (USEPA, 2001). These ecological and health concerns are exacerbated by the
production of methylmercury (CH3Hg+; MMHg) in aquatic ecosystems. Sulfur isotopes (δ34S) are an indicator of the strength of sulfate
reduction associated with MMHg production. In chapter 1, we assessed the relationship between MMHg concentrations and reduced-sulfur
stable isotope δ34S signals in four coastal consumer organisms (length = 26–75 mm) from Florida's Big Bend seagrass meadows: pinfish
(Lagodon rhomboides); pigfish (Orthopristis chrysopter); black sea bass (Centropristis striata melana); and shrimp (Tozeuma carolinense
and T. serratum). We found a significant correlation between depleted δ34S signatures in fauna tissue (R2 = 0.27; p < 0.001; total n =
179) with higher MMHg concentrations. A correlation was observed in lower δ34S isotopic signatures and higher MMHg concentrations of
consumers from the southern region of the study area indicating a "hotspot" of net mercury methylation in the sediments near Tampa Bay,
Florida. To better understand the sources of Hg to coastal pinfish and to assess the contribution of pinfish annual egress to offshore
food webs, chapter 2 applies isotopic tracing (C, N, S) combined with mercury (Hg) concentrations and isotope ratios in sediments,
juvenile pinfish, juvenile gag grouper (Mycteropera microlepis), and adult gag grouper and pinfish to assess exposure pathways of MMHg in
the northeastern Gulf of Mexico. We found that pinfish from the northern and southern Big Bend regions had distinct Hg sources. Southern
pinfish had enriched δ202Hg and, when combined with lower pinfish δ34S values and lower sediment δ202Hg values, suggested elevated
microbial methylation/demethylation in the southern region. The southern, coastal pinfish exhibited similar Δ199Hg as offshore gag grouper
suggesting pinfish from this region represent an important Hg source to offshore reef fish species and/or these two cohorts are exposed to
the same Hg source. Results suggested that estuaries can be an important source of MMHg to adjacent, offshore commercially important reef
species and confirmed the utility of Hg isotope analysis to identify multiple marine Hg sources and inform our understanding of the
pathways of MMHg bioaccumulation in estuarine food webs. In the northern Gulf of Mexico (nGOM), the Hg cycle is further complicated by the
influence of the Mississippi River (MR) and potentially confounded, since April 2010, by the Deepwater Horizon (DWH) oil spill.
Approximately 3.0-4.9% of oil-derived carbon released during the Deepwater Horizon oil spill was deposited on the seafloor (Chanton et
al., 2014; Valentine et al., 2014) causing local, but persistent, oxygen depletion (Kessler et al., 2011). In these low-oxygen
environments, the formation of monomethylmercury (MMHg) is promoted and may have led to higher MMHg concentrations in commercially
important reef fish species. Expanding our research to include the entire nGOM shelf, slope, and the far-reaches of the deep Gulf canyons,
chapter 3 explores Hg cycling using benthic and pelagic fishes as indicator-samples. Fish in the western study region appeared to rely
more on benthic feeding, as indicated by enriched δ13C values and depleted δ34S values. Fish species closer to the MR plume had enriched
δ15N and depleted δ202Hg and Δ199Hg values suggesting the MR influenced the nutrient and Hg cycle in the northeastern GOM. Cutthroat eels
(~1,000 m) had higher MIF signatures than slope snake eels (~250 M) and, when combined with decreasing δ13C values with depth, suggested
the presence of near-surface derived Hg in the deep DeSoto Canyon. Our results highlighted the importance of the deposition of Hg
associated upper water column OM such as the marine snow pelagic carbon. Chapter 4 investigates whether more reducing conditions cause by
DWH led to higher levels of mercury in commercially important reef associated organisms. We compared pre-spill (collected 2007-09) and
post-spill (collected 2012) fish species of similar length from hard-bottom reefs on the West Florida Shelf. Light stable isotope analyses
of carbon, nitrogen, and sulfur was employed to assess feeding ecologies of those species exhibiting higher MMHg concentrations following
the oil spill. Some species, like porgy, showed significant increase in Hg concentration. This increase may have been associated with a
shift to a more pelagic, higher trophic feeding regime. The significance of this study is that it shows that the oil spill had an effect
on the mercury cycling but that the effect is not uniform for each fish species. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial
fulfillment of the Doctor of Philosophy. / Spring Semester 2016. / January 11, 2016. / Bioaccumulation, Deepwater Horizon oil spill, Florida Big Bend, Isotope, Mercury, Pinfish / Includes bibliographical references. / Jeffery Chanton, Professor Co-Directing Dissertation; William Landing, Professor Co-Directing
Dissertation; Xiaojun Yang, University Representative; Yang Wang, Committee Member; Dean Grubbs, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_360514 |
| Contributors | Harper, Alexandra Rose (authoraut), Chanton, Jeffrey P. (professor co-directing dissertation), Landing, William M. (professor co-directing dissertation), Yang, Xiaojun (university representative), Wang, Yang (committee member), Grubbs, R. Dean (Ralph Dean) (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (191 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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