estuaries, which typically also contain high levels of dissolved and 

 particulate organic matter. Through the work of bacteria, organic 

 material in the water column is converted to dissolved and suspended 

 nutrients, a process requiring dissolved oxygen. Consumers in the water 

 column also regenerate nutrients (which can stimulate production) as 

 well as contribute directly to levels of suspended organic matter 

 through excretion and death (Figure 21). 



As with suspended solids, organic material in the water column 

 tends to sink to the bottom, where it is either burled, or in the 

 presence of oxygen, converted to nutrients by the work of bacteria and 

 other reducers. There is considerable flux in water versus sediment 

 levels of organic detrital materials and other suspended solids, 

 particularly near the bottom. The recycling and release of nutrients 

 and resuspension of organic materials are dependent upon current 

 turbulence and the ease with which bottom sediments can be resuspended. 



Primary productivity in the upper water column of the shelf usually 

 peaks in spring with a smaller peak in fall in conjunction with 

 freshwater runoff. Primary production apparently decreases from the 

 east to the west and southwest of the Texas-Louisiana shelf, and with 

 distance offshore (Fucik and El-Sayed 1979; Flint 1979). The decreases 

 in productivity along these gradients are correlated with salinity 

 increases, or conversely, with runoff. Apparent zooplankton production 

 in the water column lags slightly behind primary production but follows 

 a trend similar to that exhibited by the primary producers. The amount 

 of pelagic biomass supported by primary production is unknown, but based 

 upon the amount of zooplankton production would be expected to be small 

 over most of the shelf (Flint 1979). Gulf menhaden, however, are 

 commercially exploited in the eastern part of the Texas-Louisiana shelf. 

 Commercial landings of Gulf menhaden over the period 1 974-78 in the gulf 

 averaged 2,046.9 x 10 6 lb valued at 69.9 x 10 6 dollars. 



Based on studies performed in south Texas, Flint (1979) showed that 

 only approximately 20$ of the observed primary production would be 

 required to support the estimated zooplankton production in shelf 

 waters, leaving some 80$ available to support demersal communities. 

 Investigations of bottom waters during summer months showed that bottom 

 waters not only appeared to support greater amounts of primary producers 

 than surface waters, but also that they were characterized by the 

 presence of a prevalent nepheloid layer and peaks of nitrogen (ammonia) 

 in conjunction with the peak chlorophyll layers. Light transmission 

 exceeded 1$ and primary production was demonstrated. The high ammonia 

 concentrations were considered as evidence of a considerable amount of 

 nutrient regeneration. 



Based upon standing crop biomass and turnover rates, the annual 

 production of carbon was estimated for infaunal benthos, shrimp and 

 other epibenthic species. The annual production by infaunal benthos 

 (0.39 g C/m 2 /yr) was not believed adequate (assuming a 10$ transfer 



48 



