archives@tulane.edu / The goal of this dissertation was to identify the large scale effects that seasonal hypoxia has on the benthic community, with a particular focus on groundfish, in the Gulf of Mexico (GOMEX) while also examining ecological and physiological factors that could explain how hypoxia alters benthic communities. Seasonal hypoxia is a rapidly growing threat, not just in the GOMEX, but globally. Hypoxic conditions are known to impact marine organisms at the individual level by altering behavior and reproductive physiology while also impacting marine communities by disrupting predator prey interactions, community biomass, community composition, and community spatial dynamics. Research into hypoxia in the GOMEX has historically been localized, focusing on specific sub-regions with temporally limited sampling. While this approach has produced findings of the highest quality and importance, it has also shown that the impacts of hypoxia can be variable making the overall impact of hypoxia on GOMEX benthic communities difficult to discern. In taking both a geographically and temporally broad approach in comparing the abundances of marine organisms between hypoxic sites and normoxic (normal levels of dissolved oxygen, not hypoxic) sites I found that hypoxic sites had significantly lower biodiversity compared to normoxic sites and that 102 out of 465 examined species had significantly lower abundances in hypoxic areas compared to normoxic areas. When I compared the diets of common groundfish species from hypoxic areas to the diets of the same species from normoxic areas a few key differences were noted for some species, while the diets of other species remained relatively unchanged. After comparing the reproductive condition and presence/absence of ovarian masculinization between hypoxic areas and normoxic areas in three species of groundfish, I found evidence of ovarian masculinization in all three species, and evidence of reproductive impairment in two species. In this dissertation I showed that hypoxia in the GOMEX alters the community composition and biodiversity of the benthic community, additionally finding evidence that hypoxic conditions alter the diets and reproductive biology of several fishes / 1 / Michael Vincent Cyrana

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