RAPID collaborative research: Historic freshwater input and hypoxia effects on zooplankton populations of the northern Gulf of Mexico

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Since 2003 the PIs have conducted 5 summer cruises in the northern Gulf of Mexico using high-resolution sampling to define the spatially-explicit relationships between physical structure, hypoxia and pelagic zooplankton distributions. After the Deepwater Horizon spill, the PIs received a NSF Rapid Response grant to measure zooplankton community composition and abundance in the same spatial domain as the previous 5 cruises. They now have one of the most comprehensive, synoptic data sets on temperature, salinity, oxygen, phytoplankton, zooplankton and fish in the northern Gulf of Mexico. Synthetic products from these efforts include biomass size spectrum models which have been used to assess anthropogenic effects on planktonic and fish food-webs; the species composition of phytoplankton, microzooplankton, mesozooplankton, and fish; fish diet data; and fish growth potential models to quantitatively assess fish habitat requirements based on food availability and physical conditions. For the past several months and continuing into summer 2011, the amount of freshwater delivery to the Gulf has been of historic proportions, creating the largest stratified and hypoxic water column seen in a century (http://www.cop.noaa.gov/gulf_hypoxia_forecast/). Earlier studies by the PIs in Chesapeake Bay suggest that vertical extent of hypoxia (% water column) may be the main factor causing shifts in both location and size distribution of zooplankton. Change in the vertical structure of zooplankton populations directly impacts trophic transfer to fish, since they are more tolerant of low oxygen than their zooplanktivorous predators. The PIs propose to take advantage of a planned survey cruise to collect and analyze zooplankton in the study area (LA-TX shelf) from 25 July to 2 August. Intellectual Merit: The impact of hypoxia on benthic organisms has been well-studied and the impacts are largely understood. Pelagic organisms, such as zooplankton, present a more difficult problem as they are able to use behavior to avoid hypoxic waters and this behavior is tightly related to the hypoxia tolerance of individual species. Hypoxia results in water columns that are biologically stratified, causing as yet unquantified impacts on trophic transfer. The PIs' prior work provides a high-resolution, spatially explicit database to compare with the anticipated hypoxia of 2011 and address specific hypotheses about these effects. Broader Impacts : Given the economic importance of the Gulf of Mexico commercial fisheries (about 20% of the U.S. total landings representing about $991 million) and recreational fishing (generating ~30% of the nation?s saltwater fishing expenditures and supporting nearly 25% of the nation?s recreational saltwater jobs). The Horn Point Laboratory is part of the National Science Foundation's Center for Ocean Sciences Education Excellence (NSF-COSEE) and Experience for Undergraduates (REU) programs. Where possible in this NSF RAPID response grant, the PIs will involve REU undergraduate students and teachers in their research. All data will be submitted to the BCO-DMO database in a timely manner so they will be available to the larger scientific community.