4.2.5 THE IMPORTANCE OF THE MARSH EDGE 



The extensive interface between the marsh sur- 

 face and the open water, especially in salt marsh and 

 brackish marsh habitats, is a particularly important 

 area (fig. 4-15). High production and a large biomass 

 of many kinds of plants and animals are characteristic 

 of the water-wetland transition zone. This is illustrated 

 for plants (fig. 4-16) and macrofauna (fig. 4-17) in the 

 marsh. Two features of the interface are particularly 

 important for biota. Detritus carried off the marsh, 

 and nutrients and silt carried onto it by high waters 

 are concentrated near the interface. Thus, food and 

 nutrients are in highest supply there. In addition, the 

 irregular edge, thick plant growth, and eroded, ex- 

 posed roots all provide protection from predators for 

 many small animals. 



The nonnal branching pattern of sinuous streams 

 in tidal marshes maximizes the marsh edge/surface 

 area ratio and contributes to the productivity of the 

 marsh-estuarine system. In contrast, straight dredged 

 canals with spoil banks on each side have a low edge/ 

 surface ratio. The edge present does not function as a 

 normal marsh edge because the deep water on the 

 canal side and the high spoil bank on the landward 

 side prevent the nomial exchange of water and or- 

 ganisms. 



4.2.6 EXTENDED NURSERY FUNCTION OF WET- 

 LANDS 



One major characteristic of wetland habitats is 

 their degree of coupHng with other habitats. The 

 flooding waters provide a veliicle for passive transfer 

 of nutrients, silt, and organic detritus. In addition to 

 these passive transfers, active migrations of animals 

 occur across habitat boundaries. For some species 

 these movements are closely related to the seasons; 

 for others, to diurnal cycles or to periodic inundation. 

 Since many species are found in wetlands only during 

 their juvenile stages, this role is commonly termed the 

 "nursery function" of wetiands. In fact, use of wet- 

 lands by migrating species is much broader than the 

 temi "nursery function" indicates, as the following 

 discussion shows. 



For centuries man harvested fishes and shellfishes 

 from offsliore regions with little appreciation of the 

 nursery role of estuaries. Recently, the importance of 

 wetlands fringing these estuaries has been docu- 

 mented. These wetlands provide a more diverse 

 system than the estuarine areas alone. Flooding waters 

 encourage small fishes and sheUfishes to forage into 

 small marsh ponds andchannels. Wagner (1973) found 

 extremely liigh concentrations of small fishes in a 

 marsh pond, as compared to the adjacent open waters 



The Importance of the Marsh -Water Interface 



Figure 4-15. Important processes of the marsh-water interface. 



168 



