(3) that downstream export of carbon 

 affects primary productivity of aquatic 

 habitats. Direct measurements of organic 

 carbon export have been collected from 

 Lac des Alleraands to Lake Salvador (Day 

 et al 1977) and from Barataria Bay to 

 the Gulf of Mexico (Happ et al 1977). 



Research in both the Barataria 

 basin and in Lake Pontchartrain show 

 that bayous, canals, and lake edges that 

 are contiguous with wetlands are more 

 enriched than open water areas (Cramer 

 1978, Seaton 1979, Witzig and Day 1982). 



THE ROLE OF MARSHES AND ESTUARIES 

 IN FISHERIES PRODUCTION 



Louisiana has the greatest area of 

 coastal wetlands (Turner and Gosselink 

 1975) and the largest commercial fishery 

 in the United States (NOAA 1980). It is 

 a commonly held belief that the region's 

 coastal wetlands play an important role 

 in supporting the fisheries (Lindall and 

 Saloman 1977; Bahr et al. 1982). There 

 is strong evidence for coupling between 

 fisheries production and the marsh 

 estuarine system. 



Many nektonic species spend a part 

 of their life cycle in estuaries, using 

 them in predictable ways. Evidence 

 suggests that larval and juvenile forms 

 of many species seek out marsh ponds, 

 tidal creeks, and marsh edges adjacent 

 to wetlands. Nekton biomass in Bara- 

 taria basin and Lake Pontchartrain is 7 

 to 12 times higher in shallow water 

 marsh areas than in open waters (Table 

 20). This is also true for the emerging 

 wetlands of the new Atchafalaya Delta 

 (B. Thompson, Louisiana State Univer- 

 sity, Center for Wetland Resources, 

 Baton Rouge, La.; pers. comm.). Studies 

 on the east coast have shown that shal- 

 low tidal creeks and marsh shoals harbor 

 dense populations of juvenile marine 



species (Shenker and Dean 1979, 

 Weinstein 1979; Bozeman and Dean 1980). 



Nekton community composition, bio- 

 mass distribution, and migration have 

 been studied in the MDPR (Thompson and 

 Verret 1980). Eight species comprise 

 80% to 95% of the total numbers and 

 biomass (see the Barataria hydrologic 

 unit description). Of these species, 

 anchovies ( Anchoa mitchilli ) and sil- 

 versides ( Menidia beryllina ) spend their 

 entire life cycle in estuaries. Croaker 

 ( Micropogionas undulatus ) and menhaden 

 ( Brevoortia patronus ) spawn offshore and 

 use estuaries and marsh creeks as post 

 larvae and juveniles. Croaker and men- 

 haden are also important commercial 

 species . 



Correlations have been made between 

 the presence of estuarine wetlands and 

 commercial fisheries. Turner (1977) 

 correlated shrimp yield (kg/ha) and 

 intertidal wetland areas on a worldwide 

 basis. In the northern Gulf of Mexico, 

 he found that inshore shrimp yields were 

 directly related to the area of estua- 

 rine emergent vegetation; but not 

 related to the area, average depth, or 

 volume of estuarine open water. Moore 

 et al. (1970) presented data on the 

 distribution of offshore demersal fish 

 in Louisiana and Texas indicating that 

 the greatest fish populations occurred 

 adjacent to areas with freshwater runoff 

 and extensive wetlands areas. 



The evidence from the MDPR suggests 

 that wetlands enhance fisheries produc- 

 tivity. The question of absolute 

 dependence of nekton species on estua- 

 ries, particularly wetlands, is still 

 open to debate. The available data 

 indicate specific ways that commercially 

 important nekton species use wetlands. 

 It is highly probable that many nektonic 

 species have evolved behavioral patterns 

 that allow them to exploit wetlands for 

 both food sources and habitat. 



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