Master of Science (MS)
Reef-dependent and reef-associated communities found on oil and gas platforms in the Gulf of Mexico occur in high densities and are species rich. Platforms may impact nearby communities through the introduction of benthic primary producers and by altering biological and environmental factors that may create influential gradients associated with these structures. To quantify the presence and effective distance exerted by such gradients, reef-dependent and reef-associated communities were analyzed in two ways: (1) community patterns of abundance and diversity were compared near and far from platforms; and (2) a food-web tracer was used to indentify basal resources from platforms used by consumers. Demersal and benthic communities, along with environmental gradients, were sampled 0.25 and 1.5 km from four operational platforms in the Gulf of Mexico. No distance effects were observed in demersal or benthic communities, metals concentration, organic carbon content of the sediment, or sediment particle size. A distance effect was detected in the abundance of Micropogonius undulatus (Atlantic croaker) and Centropristis philidelphica (rock sea bass). Prey depletion near platforms (i.e., a foraging halo) was not observed for potential demersal prey items of Lutjanus campechanus (red snapper) or in the benthic community. Reef-dependent communities at two platforms were sampled via SCUBA and analyzed using stable isotopes to determine the role of benthic algae from platforms in the diets of reef-dependent and reef-associated communities. Partial contributions of red algae endemic to platforms were observed in the crabs Pseudomedaeus agassizii, Teleophrys pococki, Micropanope nuttingi, stenothoid amphipods, and harpacticoid copepods as well as in the gut contents of L. campechanus and Balistes capriscus (grey triggerfish); however, phytoplankton is likely the dominant basal resource in both reef-associated and reef-dependent communities, contributing to over 78% of the diet of reef-dependent suspension-feeders. Dense suspension feeding communities may capture and process phytoplankton making secondary production and egestia available to reef-dependent and reef-associated consumers. No distance effects of stable isotopes were observed within reef-associated organisms or bulk sediment. Overall, the effects of platforms (both on community structure and food webs) are generally localized to < 250 m with species-specific effects on abundance, diversity, and diet extending to this distance.
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Daigle, Sara Terrebonne, "What is the importance of oil and gas platforms in the community structure and diet of benthic and demersal communities in the Gulf of Mexico?" (2011). LSU Master's Theses. 3793.
Fleeger, John W.