100 



liJ 



Q-co 80 

 SZ 



I*" 

 c/)0 60 



i< 



8^20 



UJ< 



10 20 30 40 50 



PERCENT SALINE PLANT COVER 



IN EACH HYDROLOGICALUNIT 



Figure 3. The relationship between the percent of brown shrimp caught in 

 Louisiana's coastal hydrologic units and the type of vegetation in that 

 unit (adapted from Turner 1977). 



prevalent where saline wetland vegetation is proportionally high (Figure 3). In summary, 

 then, a coastal fisheries species whose life cycle involves use of the estuary for the 

 juveniles is considered estuarine-dependent; in Louisiana this amounts to essentially all 

 of the landings (McHugh 1966; Chambers 1980). The area of wetlands, not that of open 

 water, seems to be the factor limiting the local species abundance. 



Coastal wetlands are very productive ecosystems as a result of abundant water, 

 nutrient supplies, and tidal flushing. In comparing animal production in various 

 ecosystems, where plant production is high, animal production is generally also high 

 (Table I). The greater grazing efficiency in aquatic ecosystems further increases animal 

 production relative to plant production. In wetlands, the percent consumption of plant 

 matter by animals averages 8% and is similar to that of animals in most terrestrial 

 systems. The renewal of animal biomass is twice annually. The net result is that 

 wetlands are excellent natural protein "factories" (Turner 1982). 



Attempts to distinguish between animal production in "wet" land and that in the 

 overlying water are problematical, since wetlands are, by definition, dependent on the 

 hydrological regime for the maintenance of ecosystem integrity. Sediments, nutrients, 

 and gases move from wetland to water and back again in very complex ways, which we 

 are only now beginning to describe in detail (e.g. Pomeroy and Wiegert 1981). Our 

 terrestrial experience in desert, forest, and grassland ecosystems has often led us to 

 assume conveniently (and erroneously) that, in wetlands, water is also functionally 



114 



