Figure 5-9: Steblospio benedicti. This benthic organism 

 is approximately 1 cm long. 



Photo courtesy of the University of Texas Marine Science 

 Institute. 



Other than the four dominant species, all other species 

 were rare. The rare species were responsible for 

 regional and station clustering along the PC2 axis. 

 Presence oi Assiminea sucdnea (As) at Stations A and B 

 and oi Mediomastus amhiseta (Ma) at Stations E and F 

 were primarily responsible for separating stations. 

 Stations A and B also had a higher incidence of insect 

 larvae like Chironomid larvae (Ch) , Berosus sp. (Be), 

 Ceratopogonid larvae (Ce) and Damselfly nymphs 

 (Da). The three clusters (A and B, C and D, E and F) 

 indicated the communities within the treatments were 

 slighdy distinct from one another. The stations within 

 a treatment site {i.e., upper and central Rincon Bayou) 

 were more similar than the treatment sites themselves 

 (Figure 5- 10b). The community structure data 

 presented in the PCA plots were the only macrofauna 

 data that showed a strong treatment-site trend. 



The six most dominant species (Table 5-5) were found 

 continuously throughout the study, except when 

 salinity concentrations were high (> 35 ppt) 

 (Table 5-6). Rare species generally occurred during low 

 salinity periods only. The only species to occur 

 consistentiy during hyper-saline conditions was the 

 insect, Triio corixa (SP 371), but it was also found when 

 salinity values were brackish, so it was not considered 

 an indicator species of freshwater inflow. Each 



drought period {e.g., the summers of 1995, 1996 and 

 1998) appeared to be characterized by different species 

 (Table 5-6). 



Meiofauna 



The meiofauna community was composed of 

 Nematoda, Copepoda (primarily Harpacticoida) and 

 16 other taxa. Nematodes comprised 71% of all 

 organisms on average, and copepods comprised 9% 

 (Table 5-7). Insect larvae comprised only 0.02% of the 

 organisms found. The other metazoan taxa comprised 

 only 4% of all other organisms found and included 

 permanent meiofauna (Turbellaria, Gastrotricha, 

 Tardigrada, Cnidaria, Rotifera and Kinorhyncha) and 

 temporary meiofauna (Polychaeta, OUgochaeta, 

 Gastropoda, Bivalvia, Ostracoda and Amphipoda). In 

 addition, two groups of protozoans were found among 

 the meiofauna, Ciliata and Foraminifera, which 

 comprised about 1 5% of all meiofauna found. 



The average total number of meiofauna was 908,000 

 individuals per m^ (Table 5-2). There was a significant 

 interaction between stations and dates (P = 0.0001). In 

 contrast to macrofauna, meiofauna abundance 

 exhibited differences among treatments (Table 5-2, 

 Figure 5-1 la). Stations A and B always had the lowest 

 abundances. In fact, the average abundance at Stations 

 A and B was almost three times lower than the average 

 at Stations C and D, and four times lower than the 

 average at Stations E and F. 



The average abundance of meiofauna among all 

 stations at each sampling period changed with 

 changing salinity conditions (Figure 5-1 lb). 

 Abundances were lowest when salinity concentrations 

 were highest, and recovered after periods of low 

 salinity. In general, the pattern was similar to the 

 pattern for macrofauna abundances. The lowest 

 abundances were recorded during the dry periods of 

 1996. After significant freshwater inflow in 1997 

 (Events 16, 17 and 18), which lowered salinity, 

 abundances recovered and reached the highest level in 

 January 1998. 



Chapter Five 



5-17 



