Hypoxia in the Northern Gulf of Mexico (EPA-SAB-08-003)

Hypoxic conditions in estuaries are one of the major factors responsible for declines inhabitat quality. Previous studies examining the effects of hypoxia on crustacea have focused onindividual/population-level, physiological or molecular responses but have not considered morethan one type of response in the same study. The objective of this study was to integratedisciplines by examining the responses of grass shrimp to chronic hypoxia both at the molecularand whole animal level. Hypoxia-induced alterations in gene expression were screened usingcustom cDNA macroarrays containing 78 clones from a hypoxia-responsive suppressionsubtractive hybridization (SSH) cDNA library. Grass shrimp respond differently to moderate (2.5ppm DO) versus severe (1.5 ppm DO) chronic hypoxia. The initial response to moderate hypoxiawas down-regulation of genes coding for ribosomal proteins, HSP 70 and MnSOD. The initialresponse after short-term (3 d) exposure to severe hypoxia was upregulation of genes involved inoxygen uptake/transport and energy production, such as hemocyanin and ATP synthases. Themajor response by day 7 was an increase of transcription of genes present in the mitochondrialgenome, together with upregulation of a putative heme binding protein and the iron storageprotein, ferritin. By day 14 a dramatic reversal was seen, with a significant downregulation oftranscription of genes in the mitochondrial genome. Both ferritin and the heme binding proteinwere downregulated as well. Levels of Hypoxia Inducible Factor (HIF1-alpha) remainedunchanged. The macroarray data were validated using real-time qPCR. Changes in mitochondrialproteins were examined by separating proteins in 2 dimensions (IEF and reverse phase) followedby MS. At the organismal level, hypoxia exposure resulted in marked effects on shrimp eggproduction and larval survival, suggesting population-level implications of long-term hypoxia. Baltz, Donald M., Hiram W. Li, Philippe A. Rossignol, Edward J. Chesney andTheodore S. Switzer, 2006. “A Qualitative Assessment of the Relative Effects ofBycatch Reduction,Fisheries and Hypoxia on Coastal Nekton Communities in the Gulf ofMexico”, Presentation at “Hypoxia Effects on Living Resource in the Gulf of Mexico”NOAA Center for Sponsored Coastal Ocean Research, Tulane University, New Orleans,LA. September 25 – 26, 2006. Abstract: We applied qualitative mathematical models to develop an understanding of linkagesthat influence shrimp, fishes, and fisheries in coastal Louisiana where biotic communities facemany natural and anthropogenic stressors, one of which is fishing activities related to the harvestof shrimp. Shrimp trawling ranks high in terms of impact on nekton and their habitats, and likemost fishing gears catches non-target species or sizes that are not marketed. These individuals,termed 'bycatch', are often returned to the water in dead or dying condition. Numerous other We applied qualitative mathematical models to develop an understanding of linkagesthat influence shrimp, fishes, and fisheries in coastal Louisiana where biotic communities facemany natural and anthropogenic stressors, one of which is fishing activities related to the harvestof shrimp. Shrimp trawling ranks high in terms of impact on nekton and their habitats, and likemost fishing gears catches non-target species or sizes that are not marketed. These individuals,termed 'bycatch', are often returned to the water in dead or dying condition. Numerous other