dimensions as well as individual and specific tolerances. 

 Laboratory studies are generally concerned with the interrela- 

 tionships between biological response and multiple environ- 

 mental factors acting in concert. However, application of 

 laboratory methodology to ecological field studies is often quite 

 difficult (Alderdice 1972), especially when dealing with mobile 

 organisms such as fishes and decapods. The interpretation of 

 results concerning distribution of these organisms within the 

 Santee system is no exception to this difficulty. Nevertheless, it 

 is possible to make some interpretation of community stability 

 and specific distributional patterns based on the information 

 collected over the intensive 2-yr sampling period. 



The freshet in spring of 1975 appeared to have the most pro- 

 nounced singular effect on species composition and abundance. 

 The total number of species collected was lower at that time 

 than at any other during the sampling period. This was par- 

 ticularly noticeable at the upriver stations. Abundance of in- 

 dividual species such as Micropoganias undulatus, Anchoa 

 mitchilli, and Trinectes maculatus were also lower at these sta- 

 tions, which also may be attributable to flood effects. The ef- 

 fects on the decapod crustaceans and other numerically domi- 

 nant fishes were not obvious. Calder et al. (1977) also reported 

 alterations of species composition and density among benthic 

 organisms collected from the Santee system during 1975 and 

 1976; however, they noted that the flood most affected benthos 

 in the lower, usually more saline reaches of the river where an in- 

 crease in species normally associated with greater freshwater in- 

 trusion into the lower estuary occurred. Others (Andrews 1973; 

 Boesch et al. 1976) have noted that effects of lowered salinity 

 from floods are greatest among meso- or polyhaline species, but 

 the magnitudes of the effects differ for epifaunal, infaunal, and 

 highly motile organisms. The depressed species number ob- 

 served by us may reflect the tendency of fishes and decapods to 

 escape from areas whose salinity is drastically lowered by flood- 

 waters or, in the case of juveniles and small-bodied species, may 

 be attributed to their being flushed downstream and out of the 

 system. 



The positive correlation between salinity and number of 

 species in the Santee system agrees with results obtained by 

 Gunter (1961), who noted that the number of species increased 

 toward the lower reaches of estuaries where there occurred a 

 mixture of euryhaline and marine stenohaline species. Hoff and 

 Ibara (1977) found that in a New England estuary the number of 

 species was greatest at stations which had the greatest fluctua- 

 tion in salinity. Both species number and the community 

 assemblages defined by us for the Santee system reflect in- 

 creased diversity with proximity to the river mouth. Also, most 

 assemblages defined for the Santee system consisted partially of 

 euryhaline species. This is not an unusual occurrence within 

 estuaries. Pearse (1936) noted that the estuarine fauna consists 

 of marine or marine-derived species, and Weinstein (1979) 

 stressed how depauperate the shallow marsh estuarine fauna 

 would be if all transient marine species were removed. The 

 distribution of the endemic estuarine species appeared to be 

 more restricted than that of the marine transients. Nevertheless, 

 we observed no abrupt faunal changes along the salinity 

 gradient in the Santee system. Rather, the faunal assemblages 

 overlap and do not exist as sharply delineated groups. This no 

 doubt results from the different tolerances of juveniles and 

 adults; the effect of salinity, in concert with other factors, on 

 reproduction; and the highly compressed nature of salinity 

 regimes in South Carolina estuaries as compared with many 

 estuaries elsewhere. 



As indicated by Pearson product-moment correlations, 

 temperature, depth, and dissolved oxygen also affect com- 

 munity composition and abundance. The positive correlation of 

 number of species and number of individuals with temperature 

 is not at all surprising when one considers that species composi- 

 tion was most diverse during summer in both rivers. The huge 

 influx of Penaeus setiferns and, to a lesser extent, P. aztecus 

 into the estuary during summer and fall probably accounts for 

 this correlation. The association between depth and number of 

 species and individuals is more difficult to explain. All collec- 

 tions were made in the channel where depths ranged from 2 to 8 

 m in the North Santee River and from 1 to 5 m in the South 

 Santee River. Although the range in depths sampled is slight, 

 sufficient salinity stratification may exist in the Santee system so 

 that higher salinity water occurs in the deeper channel regions. 

 This may indeed be true for the South Santee River which 

 receives less freshwater input. Also, salinity stratification may be 

 greater on the floodtide, where samples were collected (Mathews 

 footnote 4.) Since there is a positive correlation of species 

 number and abundance, the correlation between depth and 

 species composition and abundance is most likely a secondary 

 effect. Similarly, the negative association between dissolved 

 oxygen and abundance which was noted only for the South 

 Santee River may be explained by lower dissolved oxygen values 

 in the deeper, more saline channel areas. We realize the correla- 

 tions are simplistic and that misinterpretation can result from 

 speculating about cause and effect relations in correlation 

 analysis (Sokal and Rohlf 1969). We are merely presenting this 

 information as untested hypotheses. 



Peaks of abundance for the numerically dominant species 

 were not generally consistent over the 2-yr sampling period, but 

 peaks of maximum richness (number of species) consistently oc- 

 curred in summer. This observation compares favorably with 

 those of Livingston et al. (1976) for fishes and invertebrates of 

 Apalachicola Bay, Fla. They noted a relatively stable ap- 

 pearance of organisms from year to year, but considerable 

 within-species variability in annual abundance. Temporal parti- 

 tioning by our dominant species was not as noticeable as that 

 described by Livingston et al. (1976). Dominant fishes were 

 present in the Santee system throughout the year and showed 

 fairly equitable abundances, although M. undulatus and A. 

 mitchilli dominated our catches in winter and spring. Penaeus 

 setiferus was much more regular in its pattern of appearance and 

 abundance. Although regular fluctuations in species composi- 

 tion over time may indicate that an estuary is not stressed (Liv- 

 ingston et al. 1976), we feel that the year-round presence of 

 stress-tolerant estuarine species better indicates temporal stability 

 than overall stability of the estuarine system. We relate such oc- 

 curance to a protracted spawning season in warm temperate areas 

 which enable some element of the population, probably juveniles, 

 to be present in the estuary year-round. 



As the length-frequency polygons for selected species showed, 

 the Santee system fish fauna captured during this study are 

 primarily composed of immature fishes. Some larger mature in- 

 dividuals were collected, but the Santee system functions 

 strongly as a juvenile fish habitat. The importance of estuaries 

 as nursery areas is well documented (Gunter 1961; Wallace and 

 Van der Elst 1975; Livingston et al. 1976; Weinstein 1979), and 

 the attraction of young fish to estuaries is attributed to 

 physiological suitability in terms of physiochemical features, an 

 abundance of food, and protection from predators (Gunter 

 1961; Van Engel and Joseph 1968'; Wallace and Van der Elst 

 1975). 



14 



