Defense Date

7-24-2026

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Tracey Sutton, Ph.D.

Second Advisor

Rosanna Milligan, Ph.D.

Third Advisor

David Kerstetter, Ph.D.

Keywords

continental slope, faunal composition, micronekton, multivariate, pelagic

Abstract

The Gulf of Mexico harbors a unique pelagic ecoregion, recognized for its diverse assemblages of mesopelagic fishes (200 – 1000 m depth distribution during daytime), which play a crucial role in deep-ocean food web dynamics. While mesopelagic fishes are well documented in the Gulf, little is known about how assemblage distribution patterns change where the oceanic domain meets the continental slope domain, a region dubbed the ‘oceanic rim.’ In the northern and eastern Gulf, a spatially extensive pelagic sampling and analysis program provides an opportunity to investigate onshore-offshore gradients in oceanic fish distributions. This thesis examined the nature of surficial and mesopelagic fish assemblage distribution patterns, and whether these patterns appear related to the continental slope. Analyses of a large biotic dataset revealed that lower-slope and offshore regions relative to the 2000-m isobath did not differ in assemblage structure. However, faunal composition varied strongly among cruises, possibly reflecting behavioral or seasonal drivers captured within sampling periods. Environmental variables accounted for only a limited proportion of the total variation, suggesting that behavioral processes likely drive the observed assemblage structure patterns in the oceanic Gulf. Together, these results indicate that deep-pelagic micronektonic (2 – 20 cm in length) fishes of the oceanic Gulf comprise a single, mixed community and should be considered as such in management decisions affecting their ecological role in food-web connectivity.

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