Hagfishes (Myxinidae) are common in deep waters of the Gulf of Mexico (GOM). Two of the species found in the GOM are endemic to
the area and potentially provide key ecosystem services (e.g. generate substrate turnover and recycling of organic matter by consuming
carrion falls) to the deep environments of the Gulf. Yet, very little is known about hagfish life histories and ecology. I investigated
inter and intraspecific variations in trophic structure of Eptatretus springeri, Eptatretus minor, Myxine mcmillanae, including variations
along relevant environmental gradients. At the time of this study, the Gulf of Mexico had recently experienced an environmental disaster
with the Deep Water Horizon (DWH) oil spill. As a result, I also investigated the potential effects of the DWH oil spill on hagfish
trophic structure, and the potential for higher bioaccumulation of mercury (Hg) in their muscle tissue. Feeding ecology and trophic
structure were investigated using nitrogen (δ15N), carbon (δ13C) and sulfur (δ34S) stable isotopes and variability in the lipid content
(Δδ13C) of each species was used as an indicator of periods of feeding and fasting. I was able to differentiate the isotopic niche of each
of the species and determine the different feeding ecologies of E. springeri and M. mcmillanae. The isotopic niche of E. minor overlaps
with that of E. springeri and M. mcmillanae. The most depleted mean δ15N values were observed in E. springeri (12.8‰), followed by E.
minor (13.9 ‰) and M. mcmillanae (14.9‰). Eptatretus springeri had the highest (Δδ13C), lowest trophic level (δ15N) and exhibited the most
isotopic variation with depth. This could suggest this species is an active predator that feeds regularly, and potentially relies on
scavenging only to supplement its diet. Eptatretus minor had slightly higher Δδ13C, intermediate but depleted δ15N, and higher δ15N
isotopic diversity. These characteristics suggest a more opportunistic foraging behavior for this species, potentially feeding on prey
items from several trophic levels. Myxine mcmillanae had the highest δ15N but lowest Δδ13C, and no variation in δ15N with depth. These
trends indicate this species could be experiencing irregular feeding with periods of fasting, potentially due to a mostly scavenging
behavior and occasionally feeding on larger but infrequently available carrion falls of large animals. Spatial analysis showed all hagfish
species displayed enriched δ15N and δ13C, and depleted δ34S values on the continental slope off Louisiana than along the North Florida
Slope and in DeSoto Canyon. These shifts in isotopic signatures could be attributed to influx from riverine sources from the Mississippi
River. Temporal variations were also correlated to the seasonality of nutrient discharge from the river. Isotopic shifts seemed to be a
consequence of riverine inputs rather than as a result of changing environmental conditions from the DWH oil spill. This study also
determined Total Hg (THg) and Hg species (Methyl-Mercury-MeHg, inorganic Hg-IHg) concentrations in hafish muscle tissue. There was
significant intra and interspecific variation in THg concentrations of all three hagfish species. Enriched δ15N and much higher THg
concentrations were observed in M. mcmillanae (11.9 ppm) when compared to E. minor (2.1 ppm) and E. springeri (1.1 ppm). Mean MeHg
concentrations were highest in M. mcmillanae (10.9 ppm), followed by E. minor (1.4 ppm) and E. springeri (0.8 ppm), while mean IHg
concentrations were 1.3 ppm, 0.7 ppm, and 0.4 ppm , respectively. However, Hg species displayed a wide range of variation, with IHg
concentrations in muscle tissue accounting for up to 75% to 95% of the THg content for some individuals. THg concentrations were studied
in relation to several biological and environmental factors (stable isotopes, depth, total, length, body weight and lipid content, spatial
and temporal variations) but most of these relationships were not significant for one or more species, which suggests that more than one
uptake and depuration pathway or factors could contribute to the bioaccumulation of Hg in hagfishes. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment
of the Master of Science. / Spring Semester 2016. / April 11, 2016. / Bioaccumulation, Diet, Hagfish, Mercury, Stable Isotopes, Trophic Ecology / Includes bibliographical references. / Jeffrey P. Chanton, Professor Co-Directing Thesis; William M. Landing, Committee
Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_360408 |
| Contributors | Mickle, Alejandra (authoraut), Chanton, Jeffrey P. (professor co-directing thesis), Landing, William M. (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 (96 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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