Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Marine Science

Major Professor

Ernst B. Peebles, Ph.D.

Committee Member

Jeffrey P. Chanton, Ph.D.

Committee Member

Greg S. Ellis, Ph.D.

Committee Member

David J. Hollander, Ph.D.

Committee Member

Steven A. Murawski, Ph.D.

Keywords

amino acid, carbon, isoscape, migration, nitrogen

Abstract

The present research examined the viability and utility of eye lenses as a source of lifetime stable-isotope records in fish. It is presented in three sections. The first section compared bulk isotopic variation (bulk analysis) within fish eye-lenses at two temporal resolutions and compared patterns obtained from left and right eyes. The first temporal resolution was lower in an attempt to expose broad-scale isotopic changes during life while reducing effort and cost. This approach did reveal lifetime patterns, but tended to miss certain life events, particularly during early life. The second resolution was higher and provided detail that was missed at the lower resolution. Isotopic trends in left and right eyes from the same individual were nearly identical for both δ13C and δ15N. It therefore appears unnecessary to process only the left or right eyes.

The second section tested the prospect of applying compound-specific isotope analysis (CSIA) to amino acids within individual eye-lens layers (laminae). CSIA of amino acids (CSIA-AA) allows trophic positions to be calculated at various life stages, thus enabling the reconstruction of trophic growth curves for individuals using the δ15N differences between trophic and source amino acids. The methods used were successful at measuring δ15N within ten intra-laminar amino acids. Of the ten amino acids, five were trophic, two were source, and three were neither trophic nor source. Lifetime variation was observed in all amino acids. While lifetime changes in trophic amino acids were expected because fish tend to increase their trophic positions during life, lifetime variation in source amino acids was also observed, indicating change in the baseline δ15N of primary producers at the base of the food web.

In the third section, bulk analysis and CSIA-AA were combined to isolate variation in geographic baseline from variation in trophic position; this approach was applied to 16 fish from three species: Red Snapper (Lutjanus campechanus), King Mackerel (Scomberomorus cavalla) and Greater Amberjack (Seriola dumerili). It was apparent that not all fish reached their trophic maximum in the same manner; lifetime trends in trophic position of individuals of the same species (Red Snapper) steadily increased along concave, convex, or linear pathways, whereas the lifetime trophic positions of King Mackerel fluctuated irregularly among multiple trophic positions instead of steadily increasing to similar trophic maxima, as in Red Snapper. These CSIA-AA-based trends in trophic position were subtracted from the bulk eye-lens trends for both δ15N and δ13C, mathematically isolating the geographic component within the lifetime isotope records. Three geographic trends, or migration paths, were revealed: resident, lifetime (one-way) migrator, and seasonal migrator. This combined bulk and CSIA-AA method is likely to have widespread application to fishes in general and is particularly likely to provide new information on life stages that are poorly understood.

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