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3.1.4 Important Questions and Approaches 



The actual design of the TEXLA study should be such as to answer seven key questions. These questions are 

 detailed below along with the approaches that a final design might embrace. It is important to note that these 

 questions are phrased so as to give high priority to traditional MMS needs concerning benthic populations and 

 variation. 



• Question #1: Physical - Biological Linkages - How does the physical oceanographic circulation affect 

 the structure and function of the biological communities on the TEXLA shelf? 



Background : The central TEXLA shelf is an area of high fisheries productivity, moderate phytoplankton 

 production, and freshwater discharge of the largest river in the U.S. Natural variation in the shelf 

 ecosystem in time and in space (horizontal and vertical) is anticipated to be driven by variations in river 

 flow, wind, currents, estuarine exchange, and eddies. These relationships are unqualified and should 

 be described, if not understood, in order to comprehend the biological system and how oil and gas 

 recovery activities affect the biological system. However, it is impossible to clone this system for 

 experimental treatments and so studies must make use of the natural variations to derive conclusions 

 regarding their influence. 



Approach : Recognize four oceanographic provinces (plume, coastal boundary currents, outer shelf and 

 gyres, mid-shelf) and develop information on ecosystem processes and structure for corresponding 

 biological components while simultaneously deriving physical oceanographic measurements. These 

 physical measurements need not be as comprehensive as in the MMS Physical Oceanography Program. 

 Build a data base for primary productivity and benthic community structure, especially on the Louisiana 

 shelf, and use natural gradients, storms and disturbances, and temporal salinity development of gyres 

 as experimental treatments in testing for the effects of circulation on biological processes. The role of 

 the river plume, wind-induced sediment resuspension, and upwelling as sources of nutrients and fixed 

 C and N needs to be evaluated. How much is imported from the coastal boundary layer? Are food 

 webs especially compact and efficient in this area? The physical measurements of flux may then be 

 compared to uptake rates to evaluate their relative importance. 



Question #2: Identification of Trophic Links - What is the food web structure of the continental shelf 

 ecosystem? 



Background : Information is lacking on food web structure of this continental shelf community and 

 cannot be adequately reconstructed synthetically using data/analyses from other continental shelves. We 

 need to know if predation is an important determinant of community structure in benthic TEXLA 

 communities, whether the food web is controlled by a "top down" or "bottom up" predation, or if it is 

 dominated by productivity controls on population size and the resulting cascading trophic interactions. 



Approach : Control sites should be first studied, and then compared to probable locations of OCS 

 impacts. Needed is background information on contamination accumulation (not intensive), growth rates 

 of ubiquitous and/or abundant key species, how close community metabolism is coupled to organic input 

 (cohort analysis; role of disturbance), and experimental studies on the effect of predation on structuring 

 community production and biomass. Stable isotope analysis is one promising approach, but should not 

 be used to the exclusion of experimental benthic studies (for example) with exclosure/inclosures, ship 

 board experimentation, and various new microbial studies (e.g., dilution experiments, chemical inhibitors, 

 isotope tracers, etc.). 



• Question #3: Identification of Controlling Factors - What controls benthic community structure and 

 function on the TEXLA shelf? 



Background : Benthic studies are important in MMS monitoring schemes but there are significant gaps 

 in our knowledge of benthic community structure, especially on the TEXLA shelf. Needed are a mix 

 of descriptive and experimental studies focused on the control of food supply, variations in growth rates, 

 and the effects of disturbance by trawling, storms, and drilling muds/effluents. It is important to know 



