changes between 1974 and 1979 as il- 

 lustrated in Figure 2. Salinity ex- 

 hibited a great deal of variation 

 over the study period, which is typ- 

 ical for an estuarine habitat. There 

 was a dramatic decrease in salinity, 

 however, in November and December of 

 1976 (Figure 2). This particular de- 

 crease in salinity was followed by a 

 jump in the number of infaunal spe- 

 cies for all the shallow stations, 

 representing the highest number ob- 

 served during the entire study peri- 

 od. The most dramatic change, how- 

 ever, was the tremendous increase in 

 infaunal density for the shallow sta- 

 tions (Transect 2) following the drop 

 in salinity of 1976 (Figure 2). In 

 addition to this obvious trend, 

 there was another period of low sali- 

 nity observations during the initial 

 stages of the study, November-Decem- 

 ber 1974 (Figure 2) . The number of 

 infaunal species did not peak as in 

 1976 but the infaunal total densities 

 again exhibited a large increase. 



These historical patterns sug- 

 gested to us that the intense rain- 

 fall that occurred in September 1979 

 with the resulting dramatic de- 

 creases in salinities in Corpus 

 Christi Bay had a significant effect 

 on the ecosystem, which was reflect- 

 ed by changes in benthic infaunal 

 patterns. Therefore, we continued 

 our study on the premise that any 

 changes observed would provide valu- 

 able information concerning the over- 

 all functioning of this ecosystem, 

 including effects on the important 

 fisheries it contained. 



POST-EVENT TPvENDS 



The salinity changes are in direct 

 contrast to salinity records for the 

 same seasonal period of 1977 and 

 1978. As mentioned earlier, estua- 

 rine salinities remained low for more 

 than a month in the fall of 1979. 



Also illustrated in Figure 3 are 

 some of the more immediate responses 

 in benthic infaunal populations that 

 were observed after the inflow event. 

 Three polychaetes (Tharyx setigera , 

 and Streblospio benedicti) and one 

 bivalve (Lucina multilineata) showed 

 density increases that were not 

 observed during the same time period 

 in either 1977 or 1978 (Figure 3). In 

 fact the densities for all species 

 but Mediomastus californiensis were 

 more than doubled in October-November 

 1979 as contrasted with previous 

 years, and July-August of the same 

 year. 



Above we highlighted several in- 

 stances in the historical data (pre- 

 event) in which the number of infau- 

 nal species and total density showed 

 significant correlations with sali- 

 nity changes. As exhibited in Fig- 

 ure 4, however, these previous trends 

 were small in contrast to the changes 

 observed for these two benthic com- 

 munity variables after the freshwater 

 inflow event of September 1979. Both 

 variables reached peaks never ob- 

 served before for this area of Cor- 

 pus Christi Bay. It is reasonable 

 to conclude that there was probably 

 a cause and effect relationship be- 

 tween the inflow event and the in- 

 creases in these two benthic infau- 

 nal variables. 



The actual change in salinity 

 following the intensive rainfall of 

 September 1979 for Corpus Christi 

 Bay is illustrated in the 1979 

 (third) salinity plot of Figure 3. 



Figure 5, which is a plot of 

 equitability , the measure of even- 

 ness of the different infaunal pop- 

 ulation densities in the community, 



493 



