further exhibited some of the dyna- 

 mics that were occurring in the ben- 

 thos after the inflow event. Equi- 

 tability of the infauna varied tre- 

 mendously over the entire study du- 

 ration (1974 to 1979). A distinc- 

 tive decrease in this community mea- 

 sure was observed, however, a short 

 time after the intense freshwater in- 

 flow event, with equitabilities for 

 the two observation stations reflect- 

 ing their lowest values for the en- 

 tire six years of study. This pat- 

 tern suggested that although there 

 was an increase in number of infau- 

 nal species (Figure 4) after the in- 

 flow event, the corresponding in- 

 crease in total infaunal density was 

 due to increases in a few populations 

 which then dominated the community 

 structure. The dominance by a few 

 species in respect to density, caused 

 the evenness of species distribution 

 to drop significantly (Figure 5). 



Evaluation of infaunal commun- 

 ity structure using the numerical 

 classification technique of cluster 

 analysis further documented the dra- 

 matic changes that occurred in the 

 Corpus Christi Bay benthos follow- 

 ing the freshwater inflow event in 

 September 1979. An examination of 

 the similarity in community struc- 

 ture between all collection periods 

 for station 1, between 1974 and 1980, 

 with the exception of the early sum- 

 mer months, showed a very striking 

 pattern (Figure 6). The period of 

 January to April 1980 exhibited a 

 dissimilarity with all other col- 

 lection periods at a level greater 

 than 65 percent. The dissimilarity 

 in benthic community structure be- 

 tween this period and all others was 

 strong enough to override any natural 

 seasonal patterns that may have ex- 

 isted in the data. The same pattern 

 was observed for station "4 benthic 

 community structure. 



A closer evaluation of speci- 

 fic time periods during the total 

 study period served to emphasize the 

 effect that the freshwater inflow 

 event had on the benthos. Figure 7 

 compares the early fall periods 

 (July to October) and the winter pe- 

 riods (December to March) for all 

 collection years at stations 1 and 

 4. The highest dissimilarities ob- 

 served for any collection periods 

 for the fall were slightly over 40 

 percent with no significant separa- 

 tion for the 1979 collection periods. 

 In contrast, the winter dendrograms 

 exhibited highest dissimilarities 

 around 60 percent with a distinct 

 separation of the winter 1980 col- 

 lection periods. This ability of the 

 cluster analysis technique to sepa- 

 rate benthic community structure 

 characteristics of winter 1980 from 

 all other winter periods while not 

 being able to also separate charac- 

 teristics for fall 1979 in respect 

 to previous fall periods further 

 indicates that the benthos was def- 

 initely changed by the freshwater 

 inflow. Furthermore, there appeared 

 to be a slight lag in the overall 

 response of the benthic infauna to 

 this natural disturbance of the 

 estuarine ecosystem. Although the 

 intensive inflow event occurred in 

 September and salinities remained 

 low well into October, the benthos 

 did not reflect the dramtic increase 

 discussed so far until December 

 January. 



A very good example of these 

 changes is derived by focusing on 

 one of the dominant populations in 

 the study area. Figure 8 illus- 

 trates the size class distribution 

 for the bivalve Abra aequalis during 

 February and March of 1979, prior to 

 the inflow event and during February 

 and March 1980, after the inflow 

 event. Several trends are apparent. 



498 



