Date of Award

Fall 12-2011

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Marine Science

Committee Chair

Charlotte A. Brunner

Committee Chair Department

Marine Science

Committee Member 2

Kevin B. Briggs

Committee Member 2 Department

Marine Science

Committee Member 3

Steven E. Lohrenz

Committee Member 3 Department

Marine Science

Abstract

Over the past 60 years, seasonal hypoxia in the northern Gulf of Mexico has occurred with increased severity and over a greater area. To determine if biogenic structures in the northern Gulf of Mexico vary in response to hypoxic stress, the seafloor on the continental shelf of Louisiana was analyzed during the spring and fall of 2009 at four provinces of similar sediment type that differ in recent history of bottom water oxygen concentration. Subcores were analyzed by computed tomography (CT) to determine the number, diameter, length, volume, surface area, and depth of biogenic burrow structures in sediments where biogenic mixing rates, sedimentation rates, mixing depth, and invertebrate macrofauna abundance were known. Because benthic community composition and density determine what types of biogenic structures are present and at what rate bioturbation occurs in sediments, the quantification of mixing rates and various physical parameters of biogenic structures reveals potentially important information about the effects of hypoxia on the macrobenthic community. Results show that macrobenthic burrows were the most numerous at province NO, which had not experienced hypoxia in the past ten years. However, at the province most recently affected by hypoxia (FH), burrow abundance was the second highest out of all four provinces. The proximity of province FH to the mouth of the Mississippi River coupled with a high sedimentation rate and high deposition of organic matter at this site could increase bioturbation activities and lead to increased burrow abundances. The CT subcore taken from the province that had experienced hypoxia one year previous to the study (HO) contained significantly longer burrows with greater median volumes, surface areas, and diameters than burrows at the other three provinces. Province HO also had high abundances of macrofaunal organisms and high rates of bioturbation. This could indicate that the macrofaunal community at province HO is in an active phase of recovery from hypoxia. In conclusion, computed tomography is a non-invasive, high resolution imaging technique that provides a means to accurately quantify the effects of hypoxia on macrobenthic bioturbation structures in marine sediments.

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