distinct from land. This assumption has resulted in confusion, for example, about 

 whether some aquatic animals are actually wetland-dependent and, therefore, should be 

 included in estimates of wetland animal production, though they live primarily in the 

 open water. There is little dispute on this point if the animal lives, feeds, and reproduces 

 within wetlands. But what about the temporary resident, the migrating waterfowl 

 arriving in south Louisiana from Canada? What about the larval fish and shrimp, which 

 are spawned offshore and enter the estuary to live for only a tenth of their life cycle? 

 Fish, birds, and some invertebrates make long and involved migrations between feeding 

 ground and "nursery area". Penaeid shrimp spawn in deep oceanic zones, and may arrive 

 simultaneously with waterfowl in coastal wetlands to grow. River prawns of southeast 

 Asia move downstream to estuaries to spawn. In South America some fish move both 

 upstream and downstream to wetlands during their life cycle (Welcomme 1979). A 

 common denominator of these life history patterns is the considerable distance between 

 the habitat where the adults feed and the wetland where they began life or spent the 

 critical early stages of it. 



This nursery value of wetlands is a result of both the food found there and the 

 refuge value it affords prey. Wetland "edge" is an important locus for both functions. 

 The organic content of sediment adjacent to a natural marsh and that of sediment 

 separated from the marsh by a bulkhead, or levee are compared in Figure 4. The edge 

 next to the marsh has a much greater organic content than the edge without a marsh, and 

 this is typical. The same author found higher animal densities within the natural edge 

 than in the edge altered by a levee (Figure 5). 



Aquatic organisms suffer high predation when young. Wetland habitats limit the 

 access of larger predators simply because the zone is shallow. Prey species exploit the 

 micro-environment among the vegetation in order to avoid predators. Charnov et al. 

 (1976) conducted a simple experiment documenting this (Figure 6). When insect larvae 

 were placed in an aquarium together with a predator, they quickly hid in the darkened 

 corners. Wetlands are analogous to the corners of the aquarium: they provide both hiding 

 places and a source of food for larvae. Vince et al. (1976) documented a field example of 

 this for a temperate salt marsh. There the saltmarsh killifish, Fundulus heteroclitus , 

 preys upon two amphipods at the marsh/water interface. The dense, small stems provide 

 cover for the prey and reduce successful predation. As a consequence the size 

 distribution and abundance of the prey are directly dependent on the vegetation density. 



Because of these strong relationships between wetlands and coastal fisheries 

 species, it is possible to predict adult abundances if the environmental conditions during 

 juvenile life stages are known. Mortality is proportionally greatest while the species is 

 small; thus the available potential value of wetland habitat is modified by annual 

 climatic changes, e.g., temperature, flooding, and salinity (Condrey 1979; Barrett 1975; 

 Turner 1979). Wetlands are productive, and the fisheries couplings with wetlands are 

 known to exist. The mechanism of the couplings are not clear, however; the animal's life 

 history is an expression of the evolutionary adaptation to an exploitable habitat, be it 

 edge, food or both. 



CONSEQUENCES OF WETLANDS LOSS 



For management purposes it is a lot to know that wetlands areas, not water surface 

 area, limits commerical fishing yields. Based on the available information one can firmly 



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