these events, the Nueces Delta is one of the most 

 important sources of nutrient material for the entire 

 estuary system (Texas Department of Water Resources 

 1981). 



ECOLOGY OF THE NUECES 

 ESTUARY AND DELTA 



Montagna et al. (1996) has described eight different 

 t)^es of habitat subsystems occurring in the Nueces 

 Estuary: salt marshes, beaches, the water column, 

 muddy bottoms, sandy bottoms, oyster reefs, seagrass 

 beds and algal mats. Although each subsystem is 

 described separately, it is noted that there are many 

 interconnections among them, as water cxirrents, waves 

 and tides transport organic matter, energy and even 

 animals pass between habitats (Montagna et al. 1996). 



According to a conceptual ecosystem model developed 

 for the Nueces Estuary (Montagna et al. 1996), these 

 eight habitat subsystems may be organized by their 

 relative relation to the tidal water level. Intertidal 

 habitats (those within the range of high and low tides) 

 include salt marshes and beaches. Salt marshes are 

 important sources of organic matter for the estuary, 

 serve to buffer shorelines and provide habitat for 

 important fish and wildlife species. Beaches support a 

 low diversity of species because they experience high 

 energy from waves, wind and currents which mix and 

 transport detrital matter (plant and animal tissue) from 

 the estuarine and marine environments. 



Subtidal habitats (those below the average low tide 

 level) include the water column, muddy bottoms, sandy 

 bottoms, oyster reefs and seagrass beds. The water 

 column {i.e., the vertical portion of open water areas) 

 supports a complex and productive food-web 

 comprised of small, often single-celled organisms 

 (plankton) that move with currents, and their 

 predators, which are larger organisms (nekton), like 

 fish. Beneath the water column, the substrate of the 

 estuarine floor may be muddy or sandy. Muddy 

 bottoms are more common in the estuary and support 

 shrimp and other commercially important species, 

 while sandy bottoms, which occur near the shoreline, 

 are less common and support a number of large 



animals. Oyster reefs are associated with high diversity 

 because they provide substrate, shelter and foraging 

 opportumries for many different species. Seagrass 

 beds are very diverse and productive, and serve as an 

 important nursery ground for larval crustaceans, fish 

 and invertebrates. 



Supratidal habitats (those above the average high tide 

 level) include algal mats. Algal mats occur in isolated 

 pools only periodically inundated by tide or rainfall and 

 are comprised of nitrogen-fixing mats of filamentous 

 blue-green algae living in colonies on the sediment 

 surface. These habitats provide nutrients to shoreline 

 environments and foraging habitats for wading birds. 



Estuarine Habitats in the Nueces 

 Delta 



The most predominant estuarine habitat subsystems in 

 the Nueces Delta are salt marshes, the water column, 

 muddy bottoms and algal mats. The following more 

 detailed description of these habitat types were 

 primarily derived from Montagna et al (1996), except 

 where noted. 



Salt Marsh 



Salt marshes are located in the shallow or intertidal 

 regions of the estuary and delta, often near a source of 

 freshwater input (e.g., river mouths and secondary 

 bays), and are dominated by marsh grasses and other 

 plants (Figure 2-7). The salt marsh of the Nueces 

 Delta is the most extensive within the Nueces Estuary. 

 Salt marshes trap soft sediment and organic material 

 from the water column between individual plants. 

 Beneath the plants are strong reducing conditions, and 

 often low oxygen levels due to decomposition of 

 organic matter. Areas with a higher frequency of 

 freshwater inflow have higher diversity, higher rates of 

 primary production and higher net community 

 production. The biomass of producer and consumer 

 organisms can also be high, but species diversity can be 

 low because of fluctuating salinity. 



2-8 ♦ Study Area 



