levels were highest. In contrast, during summer when 

 salinity values were highest and water levels were 

 lowest, biomass was always lowest (Figure 5-7). Inflow 

 events triggered bursts of productivity as indicated by 

 increased abundance and biomass following periods of 

 lower salinity concentrations. Biodiversity increases 

 just after inflow events and as salinity was rising again 

 indicated more species were utilizing the marsh habitat 

 as a result of increased inflow events, although 

 different species appeared after each inflow event 

 (Table 5-6). The responses to inflow were found by 

 following changes after inflow events that filled Rincon 

 Bayou with fresh water. 



Interestingly, prior to overflow channel construction, 

 brackish conditions in April 1995 resulted in decreased 

 diversity. In contrast, after the Nueces Overflow 

 Channel was excavated, brackish conditions in April 

 (1997 to 1999) resulted in increased diversity 

 (Table 5-6). The responses of increased abundance to 

 inflow by macrofauna and meiofauna were similar 

 (Figure 5-12), indicating that both trophic levels of 

 benthos were responding to inflow events through the 

 overflow channel. 



The mechanisms of infaunal response to inflow were 

 likely trophic as well as physiological. The physio- 

 logical responses were controlled by increased 

 survivability and tolerance to specific salinity ranges 

 caused by inflow events. Trophic responses were 

 indirect and related to responses by potential food 

 items. When primary producers responded to inflow 

 by increased biomass, then increased food levels led to 

 increased secondary production. Therefore, the 

 trophic link between primary producers and secondary 

 consumers was demonstrated by correlated, or lagged, 

 abundance patterns. 



Standing stocks of macrofauna and chlorophyll were 

 somewhat concordant. Peaks of macrofauna biomass 

 followed periods of increasing chlorophyll 

 (Figure 5- 13a). The only exception was in summer 

 1997, when meiofauna abundance was more 

 concordant with chlorophyll biomass (Figure 5- 13b). 

 Peaks of meiofauna abundance followed periods with 

 high concentrations of chlorophyll in the overlying 

 water. Meiofauna are known to be grazers and to 



favorably respond to the presence of chlorophyll 

 (Montagna 1995; Montagna et al. 1995). In 

 San Antonio Bay, meiofauna respond to freshwater 

 inflow and increased chlorophyll with increased grazing 

 rates (Montagna and Yoon 1991). 



Trophic Links 



There was evidence (Riera et al. 2000) that the 

 demonstration project also restored the function of the 

 Nueces marsh as a nursery habitat for development of 

 juvenile brown shrimp, Penaeus a^ecus. Brown shrimp 

 spawn offshore in the Gulf of Mexico. Post-lar%'ae are 

 carried by on-shore water movement and enter bays, 

 ultimately finding productive shallow estuarine waters 

 protected from storms and predators (Day et al. 1989). 

 Most of the larval brown shrimp enter marine bays 

 from late winter through early spring, spend about 

 three to four months in estuarine nursery grounds and 

 return to the offshore Gulf of Mexico in early summer 

 (Moffett 1970). 



As a sub-component to this benthic analysis, the 

 trophic dynamic links and migratory behavior of 

 juvenile brown shrimp were investigated from Aransas 

 Pass to Corpus Christi Bay to Nueces Bay and to the 

 Nueces Delta (Riera et al 2000). Stable isotopes ratios 

 of carbon and nitrogen (6"C and 6'^N) of shrimps 

 and their potential food sources were measured 

 between December 1995 and July 1996. Stable 

 isotopes of carbon and nitrogen change as a function 

 of the food an organism eats (DeNiro and Epstein 

 1978; Fry and Parker 1979). Because food sources 

 change in different habitats, stable isotopes can also be 

 used to assess migration of shrimp (Fry 1981). 



During the study, shrimp lengths increased from 10 to 

 1 1 mm when the animals entered Corpus Chnsti Bay 

 as larvae, to 80 to 90 mm when they returned to the 

 Gulf of Mexico as subadults. Brown shrimp exhibited 

 spatial and temporal 6"C variation (from -25.2 to 

 12.5%o), indicating a high diversity of food sources 

 throughout their migration. From examination of the 

 6''C values, it appears the main food sources used by 

 juvenile brown shrimp in Rincon Bayou were Spartina 

 altemiflora, Spartina spartinae, detritus and benthic 



5-22 ^* Benthic Communities 



