Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
The northwest Gulf of Mexico (Gulf) shelf-edge banks both provide unique hard bottom habitat and support the northernmost coral reefs on the North American continental shelf in a region that is generally characterized by low relief, soft sediments. The habitat value of many of these banks has led to their designation as Habitat Areas of Particular Concern (HAPC) and the Flower Garden Banks National Marine Sanctuary (FGBNMS). However, little is known about the fisheries resources and dynamics of the banks outside the FGBNMS. This study had three main objectives: 1) define reef fish assemblages at northwestern Gulf shelf-edge banks and determine if assemblages were related to the varied benthic habitats present at these features, 2) define large-scale fish distributions at these same banks and determine the influence of habitat and environmental factors on distribution, and 3) examine the trophic ecology of red snapper (Lutjanus campechanus), a common and highly prized reef-associated fish, at these features. Assemblage definition and relation to habitat was based upon baited underwater video surveys conducted across a range of depths and habitats. Four distinct reef fish assemblages were resolved at the shelf-edge banks, the distribution of which corresponded to benthic habitat zonation. The specific habitat characteristics of mud substrate and live cover most strongly related to species distribution. Spatial distribution of fish biomass and density at the scale of individual banks was assessed using a mobile hydroacoustic approach. The highest fish biomass and density were observed directly adjacent to hard substrate, but showed high variability with regard to site, season, and habitat zone. Red snapper trophic ecology was assessed using stable isotope analyses to examine both relative trophic position and extent among bank sites. Results indicated a consistent carbon source, but differences in basal nitrogen between mid-shelf and shelf-edge locations. Differences in isotopic, and presumable trophic, variability between banks was attributed to different red snapper size distributions, with larger individuals displaying higher isotopic variability. Results of this study indicate the less studied northwest Gulf shelf-edge banks harbor predictable, habitat-related fish species assemblages that show variable large-scale distributions.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Langland, Todd, "Fish Assemblage Structure, Distribution, and Trophic Ecology at Northwestern Gulf of Mexico Banks" (2015). LSU Doctoral Dissertations. 392.
Cowan, James H., Jr.