Defense Date

12-4-2023

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Tracey Sutton

Second Advisor

Tamara Frank

Third Advisor

Heather Bracken-Grissom

Keywords

Bioluminescence, cephalopods, crustaceans, gelatinous megaplankton, bathypelagic ecology, Gulf of Mexico, vertical distribution

Abstract

Bioluminescence is the phenomenon of light emission by living organisms. It occurs through a chemical reaction within an organism and serves various purposes. The diversity of bioluminescent capabilities and occurrence in unrelated taxa suggest that bioluminescence has evolved independently numerous times amongst taxa thriving in certain environments. One such environment is the deep ocean, where little to no sunlight penetrates the water column, specifically in the mesopelagic (200-1000 m depth) and bathypelagic (> 1000 m) zones. The mesopelagic and bathypelagic zones have been extensively sampled and well documented in the Gulf of Mexico (GoM), one of the few places globally where this has occurred. Currently, no detailed faunal inventory of bioluminescence for the deep-pelagic GoM exists. This study is the first to quantitatively characterize the prevalence (both taxonomic and numerical), faunal composition, and vertical distribution of bioluminescence among major taxonomic groups at intermediate trophic levels. This large cumulative dataset of fishes, crustaceans, and cephalopods (micronekton hereafter) provides the basis for the current study with the following aims: (1) create an inventory of the bioluminescent micronekton and net-caught gelatinous megaplankton in the “upper mile” (0-1500 m depth) of the northern and eastern GoM; (2) quantitatively assess the vertical partitioning of bioluminescence as a function of taxonomic composition and organismal abundance; and (3) investigate variability in the vertical partitioning of bioluminescence as a function of diel cycle. Additionally, these topics will provide insight for discussing the relationship between the distribution of bioluminescence and the overall vertical ecology of a low-latitude, oceanic ecosystem. Quantification of abundance amongst bioluminescent organisms within the GoM revealed that approximately 75.5% of all captured individuals were capable of bioluminescence. The expression of bioluminescence was found to be most prominent vertically between 200-1000 m, representing the upper and lower mesopelagic zones, with ~87% of all individuals capable of bioluminescence. The mesopelagic also contained the largest percentages of bioluminescent fishes in this study. In the upper mesopelagic (200 to 600 m) ~67% of fish taxa in this depth interval were bioluminescent during daytime, while at night time values decreased to approximately 54%. Day and nighttime percentages of bioluminescent individuals in this depth zone were very similar and very high (97-98%). The most numerically abundant bioluminescent taxon was fishes, notably the Order Stomiiformes (genus Cyclothone). Alone, Cyclothone comprised approximately 72% of all bioluminescent fishes. Regarding crustaceans, a vertical ‘gradient’ of bioluminescent was exhibited, reaching a maximum 93.4% in the 200-1600 m depth stratum. Below this depth, the percentage of bioluminescent individuals decreased. While pelagic cephalopods are characterized by rapid swimming speeds and avoidance behavior, making sampling quite difficult, this study found that approximate 94% of all individuals collected were bioluminescent, with these distributed evenly throughout the water column. Finally, as predicted, there was a profound shift in bioluminescent organisms from deeper zones towards the epipelagic zone at night, highlighting the tight connections between diel vertical migration and bioluminescence in Earth’s largest ecosystem type.

Additional Files
Bioluminescence of GoM Appendices.docx (252 kB)
Appendices of Bioluminescent Taxa
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