Utilizing stable isotopes δ13C and δ15N to analyze diet and role of mesopelagic fishes in the biological pump from the North Pacific Subtropical Gyre
Author
Easterling, Elise A
Abstract
Several studies have sought to quantify the contribution of mesopelagic fishes to the ocean carbon cycle and the biological pump. However, to determine fish-mediated carbon transport, it is necessary to understand the behavior and ecology of mesopelagic fishes, including their foraging ecology. In this study, stable isotope analysis (SIA) was used to gather insight into mesopelagic fishes’ contribution to marine food webs and their feeding behavior by interpreting δ13C and δ15N isotope signatures obtained from white muscle tissue. δ13C and δ15N represent the ratio of 13C/12C and 15N/14N isotopes relative to an international standard in a sample, in this case mesopelagic fish white muscle tissue. Mesopelagic fishes were sampled from the North Pacific Subtropical Gyre at station ALOHA. A MOCNESS net was used to sample mesopelagic fishes from depths of 0-1,000 m. From SIA results, I compared δ13C and δ15N isotope signatures based on fish migratory status (fishes who vertically migrate to feed or those that do not), time of day, depth sampled, variations in fish size (length/weight), and interspecific variation in isotope signatures. From this thesis, I sought to gather insight of fish dietary sources and trophic structure based on the studied parameters. In addition, how SIA results fluctuate with the chosen factors will help scientists learn how to properly interpret SIA results. The results of my study indicated that δ13C and δ15N isotope signatures are higher in fishes caught at deeper depths and in those classified as non-migrators in comparison to migratory fishes. In addition, δ13C was slightly higher for migratory fishes in shallower depths (<400 m) at day-time compared to other time and depth categories. An increase in δ15N at night at deeper depths (>400 m) for non-migratory fishes was found to be significant. I also observed a positive trend in δ13C and δ15N isotope signatures with increasing fish biomass (both length and weight) for migratory and non-migratory fishes. Variation in δ15N was observed amongst different species and genera of mesopelagic fishes; yet there was little fluctuation in δ13C between mesopelagic fish genera/species. Based upon δ15N isotope signatures, my data indicate that non-migratory fishes, who feed at deeper depths, likely feed from a detrital based food web and fishes who feed near the ocean surface feed from pelagic based food web. These sources of carbon are important to account for when quantifying fish mediated carbon contribution to the biological pump. The depth at which carbon is transported by physical or biological processes impacts the duration for which carbon is sequestered in the ocean. The deeper carbon is transported, the longer it remains sequestered and increases the chances of escaping bacterial remineralization and being released back into the atmosphere through wind and wave activity. In addition, biological factors such as fish size and their diet also impact how much carbon is injected into the ocean interior by functions such fecal pellet egestion, respiration, and mortality.
Date
2024-01-05
Citation:
APA:
Easterling, Elise A.
(January 2024).
Utilizing stable isotopes δ13C and δ15N to analyze diet and role of mesopelagic fishes in the biological pump from the North Pacific Subtropical Gyre
(Master's Thesis, East Carolina University). Retrieved from the Scholarship.
(http://hdl.handle.net/10342/13236.)
MLA:
Easterling, Elise A.
Utilizing stable isotopes δ13C and δ15N to analyze diet and role of mesopelagic fishes in the biological pump from the North Pacific Subtropical Gyre.
Master's Thesis. East Carolina University,
January 2024. The Scholarship.
http://hdl.handle.net/10342/13236.
May 15, 2024.
Chicago:
Easterling, Elise A,
“Utilizing stable isotopes δ13C and δ15N to analyze diet and role of mesopelagic fishes in the biological pump from the North Pacific Subtropical Gyre”
(Master's Thesis., East Carolina University,
January 2024).
AMA:
Easterling, Elise A.
Utilizing stable isotopes δ13C and δ15N to analyze diet and role of mesopelagic fishes in the biological pump from the North Pacific Subtropical Gyre
[Master's Thesis]. Greenville, NC: East Carolina University;
January 2024.
Collections
Publisher
East Carolina University
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