One other factor that should be considered is that 

 other valuable species, such as furbearers, are not bene- 

 fited by impoundments. Other management practices 

 are carried out by landowners and refuge personnel 

 to benefit these species. 



4.8 AQUATIC HABITATS 



This section considers the broad physical, chemi- 

 cal, and biological characteristics of the Chenier Plain 

 aquatic system. This system comprises two habitats, 

 divided at the barrier beach where inland waters fiow 

 through tidal passes to the Gulf. All water bodies 

 landward of the beach and passes, including estuaries, 

 rivers, drainage ditches, navigation canals, tidal creeks' 

 bayous, lakes, and ponds collectively make up the 

 inland open water habitat. Waters seaward of the 

 beach and passes to a depth of 10 m (33 ft) constitute 

 the nearshore Gulf habitat. While these two habitats 

 differ descriptively and functionally, there is a strong 

 physical, chemical, and biological interaction between 

 them. For e.xample, important commercial species 

 (brown shrimp, white shrimp, blue crab. Gulf men- 

 haden, Atlantic croaker) and others spend some part 

 of their life histories in both habitats. 



4.8.1 A FUNCTIONAL OVERVIEW OF AQUATIC 

 HABITATS 



Functionally, the interrelationships between hy- 

 drodynamic features, primary and secondary pro- 

 ductivity, and food web interlinkages in the Chenier 

 Plain aquatic system are complex (fig. 4-27). Much of 

 this complexity is associated with the shallow waters. 

 The bottom and the water column together afford 

 many possibilities for specialization not found in 

 either alone. In addition to plants and animals which 

 occupy only the bottom (many invertebrates) or the 

 water column (zooplankton), many organisms (fishes) 

 use both parts of the system. 



Phytoplankton are the major producers in the 

 aquatic system. Benthic algae are important sea- 

 sonally, especially in winter when the water is often 

 clear. Little of the primary production is directly 

 grazed; most of it dies, settles to the bottom, and 

 becomes the base of a complex detrital food web. 

 Benthic consumers predominate, from small Crustacea 

 in the sediments to large demersal fish which eat 

 them. Birds feed in all areas along the shore, on 

 intertidal mudflats, and along fringing marshes. Most 

 nektonic species migrate between the nearshore 

 Gulf and inland open water habitats. 



Although productivity in the aquatic system is 

 dependent upon solar energy, its magnitude is con- 

 trolled by the hydrodynamic regime through nutrient 

 and pollutant transport, turbidity, and the density of 

 plankton. Indirectly, the production level and the 

 integrity of the overall system determine the useful- 

 ness of the system to man through commercial har- 

 vests and sportfishing. 



The Chenier Plain aquatic system model clearly 

 conveys the idea that alteration or loss of one type of 

 coastal aquatic habitat may directly or indirectly af- 

 fect the endemic living resources of the entire system. 

 The clear implication is that the nearshore Gulf, in- 

 land open waters, and wetlands must be maintained 

 as an integral biological unit if the natural resources 

 are to maintain their current characteristics. 



4.8.2 ROLE OF HYDROLOGY IN AQUATIC 

 HABITATS 



The hydrodynamic characteristics of coastal aqua- 

 tic habitats are a strong controlling factor affecting 

 basic productivity, energy transfer, and the composi- 

 tion, abundance, and distribution of living organisms. 



Figure 4-27. Conceptual model of energy flow and interrelationships between the inland open water and the near- 

 shore Gulf habitats of the Chenier Plain. 



195 



