U.S. Environmental Protection Agency
EPA Science Advisory Board
Background Information


Document NameBenthic Communities in the Northern Gulf of Mexico Hypoxic Area: Potential Prey for Demersal Fish.
Document AuthorBaustian, M.M
Short DescriptionM.S. Thesis. Louisiana State University. http://etd.lsu.edu/docs/available/etd-07142005-082657/
CategorySubgroup 1: Characterization of the Cause(s) of Hypoxia
Publication Year2005
Text:

Abstract: Bottom-water hypoxia ( < 2 mg O2 l-1) usually occurs on an annual basis on the Louisiana/Texas continental shelf from mid-May through mid-September over a large area (up to 20,000 km2 in mid-summer). The effects of hypoxia on the benthic infauna (potential prey) for demersal fish were examined, because changes in optimal diet can lead to negative impacts on growth and reproduction. Benthic samples were taken in three areas (inshore and offshore out of hypoxia and in the hypoxic area) during August 2003. Samples were also taken monthly from September 2003 to October 2004 at a fixed station (C6B) where summer hypoxia occurs consistently. The mean abundance of the benthic infauna in the three summer areas were not significantly different indicating similar prey abundances found in the study area. Diverse infaunal communities exist offshore of the hypoxic zone with similar species composition compared to the inshore but different compared to the hypoxic area. An abundance of benthos at the surface was not found at the summer 2003 hypoxic stations; therefore there was not an abundance of available prey at the surface. However, benthos migrated toward the surface at station C6B in June and July 2004 during hypoxia, providing an increase of prey at the surface compared to other months. During the spring months, the infaunal community was more diverse and abundant compared to the post hypoxic months (August, September, and October), which suggests fewer and less diverse potential prey in the fall for demersal predators. The most abundant prey items for demersal fish in the study area were polychaetes and secondarily molluscs. The benthic community abundances during the summer 2003 and 2004 were not expected and may be due to the storm events in summer 2003 and shorter duration of hypoxia in summer 2004.