Project: Historic freshwater input and hypoxia effects on zooplankton populations of the northern Gulf of Mexico

(Extracted from the NSF award abstract)
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.