110 



if predation or food supply may regulate benthic community structure on this shelf, since the 

 interpretation of the impacts of drilling muds, for example, may differ if a top predator, rather than key 

 food supply, are stressed. 



Approach : A mix of descriptive and experimental studies focused on control sites, measurements of 

 changes in food supply (sediment traps, phytoplankton productivity), mapping (time series) of growth 

 rates of important benthic animals, experiments on the effect of disturbance from trawls, storms, and 

 drilling muds/effluents, and on predation, especially from shrimp and other abundant epibenthos. 

 Separate studies are needed on the effects of resuspension and nepheloid layers. Previous studies 

 indicate that abundant or ubiquitous benthic organisms should be used as indicators in these studies. 



Question #4: Identification of Contaminants - What are the hydrocarbon and trace metals contaminants 

 (e.g., PAH, PCB, Hg) accumulating in TEXLA food webs? In which animals, trophic levels, and 

 oceanographic areas are these accumulated? 



Background : This is basic information required to address impacts. 



Approach : Trace the fate of petroleum products in food chains using standard fingerprinting techniques, 

 including stable isotope analyses. Synthesize target compounds with 14 C label and conduct uptake 

 experiments at platform sites. Focus monitoring program on detecting dispersal. Complete a general 

 survey of the shelf, but particularly at frequently-sampled stations. 



Question #5: General Variation and Covariance of System Components - What part of the biological 

 variability is driven by natural (i.e., environmental) processes on the TEXLA shelf? 



Background : There is great variability in the primary production and hence secondary production on 

 this shelf, but the reasons for it are not well known. Are variations in primary productivity of the 

 phytoplankton, which arise in response to variations in nitrogen input, driving the biological variability 

 of the entire marine ecosystem? 



Approach : Consider four mesoscale physical forcing functions and estimate their relative significance 

 for (1) nutrient inputs from the Mississippi-Atchafalaya River plume and coastal boundary current; (2) 

 upwelling of "new" nitrogen from interaction of Loop current eddies with shelf-upper slope topography; 

 (3) upwelling of "new" nitrogen at other thermohaline surface fronts/mixing zones (e.g., bottom layers); 

 and, (4) response to storms. Begin phytoplankton studies with the following caveats: (a) environmental 

 measurements within each region of high and variable phytoplankton productivity must be of adequate 

 resolution in time and space to create gradients as well as describe mean fields; (b) mesoscale physical 

 features evolve through time, on a scale of days to weeks, so that plumes and/or eddies must be mapped 

 synoptically; (c) the largest horizontal environmental gradients are at the mesoscale physical features and 

 these should be mapped at time-space scales of days and kilometers. 



Question #6: Variation Due to Regional Hypoxia - Are there observed changes in the species 

 abundance and individual numbers due to hypoxia? When does hypoxia start, how long does it last, what 

 are the seasonal variations, can it be predicted in time and space, and is it disrupted by storms? Will 

 it return after a tropical cyclone, and which species return first? What species survive hypoxia? 



Background : Hypoxia on the TEXLA shelf is widespread, intensive, and persistent with demonstrated 

 and catastrophic consequences to the biota. While much descriptive data has been collected and 

 experimental work is presently underway, large gaps in our understanding remain. The extent to which 

 oil and gas activities are influenced by or trivialized by hypoxic events is largely unexplored. 



Approach : Supplement existing efforts at the necessary scale and initiate new ones. Construct an oxygen 

 budget. Determine the vertical exchange coefficient across water column layers of different degrees of 

 stratification. Complete a total carbon budget. Primary production measurements, sediment trapping, 

 respiration rate measurements (water column and benthos) should be conducted concurrently. This 

 should be a seasonal study for one year at one location (transect) near the Mississippi River, and then 



