Nearshore gulf is the sixth largest 

 habitat in the MDPR, containing 116,569 

 ha (288,000 acres) in 1978, or 3.4% of 

 the total land and water area (Table 5) . 

 Of this area, 65% is found in hydrologic 

 unit II (Pontchartrain) . 



Ecological studies of this habitat 

 are sparse. One of the main sources of 

 data is a study by Franks and Associates 

 (Franks et al. 1972) in which nutrient 

 chemistry, benthic fauna, and nekton 

 were investigated. Two of their six 

 sampling stations were in the nearshore 

 gulf. 



Surface concentrations of nitrate 

 in the nearshore gulf average 0.68 

 microgram atoms per liter (ug-at/1) , 

 with bottom concentrations of 0.38 

 ug-at/1. Nitrite was not detected in 

 these waters. Total phosphate concen- 

 trations in surface and bottom waters 

 averaged 1.75 and 1.78 ug-at/1, respec- 

 tively. Bottom sediments at these sites 

 were silty, containing much organic 

 matter. 



Turner and Allen (1982) examined 

 oxygen concentrations of nearshore bot- 

 tom waters and found that they were 

 usually below saturation. Oxygen levels 

 in summer months were especially low, 

 and the deficit was most obvious in the 

 shallower depths. Onshore transport of 

 the oxygen minimum layer and oxidation 

 of suspended organics were not believed 

 to be responsible for these low concen- 

 trations. Rather, Turner and Allen pro- 

 posed that stratification of the water 

 column, respiration by the benthic com- 

 munity, and/or sinking plankton led to 

 low oxygen levels. Respiration values 

 of 1 mg oxygen/m /hr, coupled with ob- 

 served stratification, could cause low 

 oxygen values. 



The major primary producers in the 

 nearshore gulf are benthic algae, sea- 

 grasses, and sargassum (Earle 1972). 

 The majority of the net phytoplankton 

 found are diatoms (Franks et al. 1972). 

 Most water column primary production is 

 diverted to the benthic community; and 

 most of the energy flow that character- 

 izes the nearshore and inner shelf gulf 

 food web passes through the benthic com- 

 munity to demersal fishes (Flint 1980). 



Common marine invertebrates found 

 in this area are the sea pansy ( Renilla 

 mulleri ) , brown shrimp ( Penaeus aztecus ) , 

 squid ( Lollinguncula brevis ), and mantis 

 shrimp ( Squil la empusa ) . Copepods make 

 up the majority of net zooplankters 

 found in the nearshore habitat. Other 

 invertebrates studied in this area are 

 amphipods (Stuck et al . 1980), and 

 cnidarians (Burke 1975, 1976). The most 

 abundant fish in the nearshore habitat 

 are croaker ( Micropogon ias undulatus ) , 

 longspined porgy ( Stenotomus caprinus ) , 

 spot ( Leiostomus xanthurus ) , and white 

 trout ( Cynoscion arenarius ) (Franks et 

 al. 1972). The nearshore gulf is also 

 used by menhaden for spawning (Christmas 

 and Waller 1975). Modde (1980) reported 

 70 migrant species and 6 resident spe- 

 cies of (primarily) postlarval fishes 

 utilizing the shallow surf zone off of 

 Home Island, Mississippi. The resident 

 species; including Harenguls sp . , Tra- 

 chinotus sp . , Astroscopus sp . , and Men- 

 ticirrhus sp., made up the dominant 

 component of Modde's sample, repre- 

 senting 42% of the total number of 

 fishes caught. Most numerous among the 

 migrant species were Anchoa sp., and 

 Brevoortia sp . 



RIVER, STREAM, AND BAYOU (14) 



Historically, the Mississippi River 

 and its distributaries dominated the 

 geology and ecology of MDPR wetland 

 habitats. Currently, artificial levees 

 prevent annual overbank flooding in all 

 but a few areas, such as the lower 

 modern delta area, and limit the direct 

 contact of river water with the wet- 

 lands. Now the Mississippi River and 

 its major distributary, the Atchafalaya 

 River, act primarily as transporters of 

 moving water, sediment, organic matter, 

 nutrients, and pollutants from the con- 

 tinent to the MDPR's estuarine open 

 water areas (Figure 31). 



Waters classified as rivers, 

 streams, and bayous in the MDPR include 

 swamp bayous, streams in freshwater 

 marshes, and upland streams north of 

 Lake Pontchartrain and in the State of 

 Mississippi. These habitats covered 

 37,503 ha (92,634 acres) in 1978 (Table 

 5). 



64 



