Identifier

etd-04072015-181424

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Nearshore Louisiana has experienced substantial changes within the last half-century, including the annual formation of the world’s second largest hypoxic zone and the construction of thousands of oil and gas platforms (rigs). Ship Shoal and its rigs may provide important substrate in nearshore Louisiana because rigs act as de facto artificial reefs and the shoal’s bottom waters were well oxygenated on 43% of days when surrounding areas were hypoxic. From July to September of 2014, fish assemblages and hydrography were compared at shoal rigs, rigs inshore of the shoal, and rigs offshore of the shoal, and stone crab populations were compared at rigs on and off the shoal. A camera array and YSI sonde were used to characterize fish assemblages and hydrography at shoal rigs, rigs inshore, and offshore of the shoal. Stone crab densities were estimated with visual counts, and their life history was characterized by removing a subsample of stone crabs for identification and measurements. Fish assemblage composition was significantly different between shoal rigs, rigs inshore, and rigs offshore of the shoal (P<0.05). The most notable difference between assemblages was greater contribution of demersal fishes at shoal rigs than rigs inshore and offshore of the shoal. Hypoxia was intermittent at shoal rigs and persistent at rigs inshore and offshore of the shoal. Mean hypoxia thickness (meters of hypoxic water) was significantly greater (P<0.05) at rigs inshore (2.6 m) and offshore of the shoal (3.1 m) than it was at shoal rigs (0.6 m). Crab densities were roughly twice as high on as they were off the shoal (mean 4.0 vs. 1.8 stone crabs/m2; P<0.05), and the carapace width where 50% of females were ovigerous was 26.4 mm smaller for females off than on the shoal (P=0.057). Shoal rigs and rigs in surrounding waters provide important substrate for reef- associated organisms, although higher contribution of demersal fishes and densities of SCs at shoal rigs than rigs in surrounding waters suggest that shoal rigs are of higher relative importance. These findings suggest that further mining of Ship Shoal and removal of rigs may be detrimental to reef-associated organisms in nearshore Louisiana.

Date

2015

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Baltz, Donald

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