Thursday
17 February 2005
4:30-5:30 pm
102 Fishery Sciences
(auditorium)
Social follows talk
Nancy RabalaisProfessor, Louisiana Universities Marine ConsortiumDead Zones: Causes and Consequences
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Many areas of the world’s coastal ocean now have recurring or persistent oxygen-depleted waters, commonly known as ‘Dead Zones’ where motile fish, shrimp and crabs vacate the area and less motile animals die or numbers diminish. A large zone of oxygen-depleted water extends across the Louisiana continental shelf and on to the Texas coast most summers. The Gulf of Mexico hypoxic zone (< 2 mg l-1 dissolved oxygen) is the second largest such zone in global coastal waters, reaching up to 22,000 km2 in mid-summer. Gulf hypoxia results from the stratification of marine waters due to Mississippi River freshwater inflow and eutrophication of the system resulting from enhanced primary production stimulated by Mississippi River nutrients. Severe oxygen depletion occurs over broad areas of the Louisiana shelf, coincident with habitat of commercially important species. Significant decreases in species richness, abundance and biomass of demersal and benthic organisms occur under severe hypoxia/anoxia. Effects at episodically-hypoxic sites are less severe or negligible, but masked by high variability consistent with pulses of biological productivity on a river-influenced shelf. The interactions of nutrient increases, altered nutrient ratios, and oxygen depletion in the lower water column result in shifts in phytoplankton, zooplankton, demersal and benthic community compositions. Trophic interactions are likely to change and affect energy transfer. While low-oxygen effects on certain species and communities are well-documented, others such as secondary and overall productivity of the system, including fisheries, in general are not known.
Nancy Rabalais is a Professor at the Louisiana Universities Marine Consortium. Dr. Rabalais' research interests include the dynamics of hypoxic environments, interactions of large rivers with the coastal ocean, estuarine and coastal eutrophication, benthic ecology, and environmental effects of habitat alterations and contaminants. Dr. Rabalais is an AAAS Fellow, an Aldo Leopold Leadership Program Fellow, a Past President of the Estuarine Research Federation, a National Associate of the National Academies of Science, a member of the Scientific Steering Committee of LOICZ/IGBP, and currently is Chair of the Ocean Studies Board of the National Research Council, National Academy of Science. She received the 2002 Bostwick H. Ketchum Award for coastal research from the Woods Hole Oceanographic Institution and was the Ian Morris Scholar in Residence at the University of Maryland Center for Environmental Studies in 2004. Her work on the causes and consequences of Gulf hypoxa have garnered several citationsthe Blasker award shared with R.E. Turner, and a NOAA Environmental Hero, Clean Water Act Hero, and Gulf Guardian award. She earned a Ph.D. in Zoology from the University of Texas at Austin in 1983, and her B.S and M.S. in Biology from Texas A&I University, Kingsville.