1978, years with high levels of winter 

 recruitment were preceded by years of hiqh 

 population abundances; however, the 

 opposite was not true for winters of low 

 recruitments. 



Unlike the brief squid, there was no 

 significant linear relationships between 

 blue crab population parameters and 

 abiotic factors. Including 1-, ?-, and 

 3-month time lags of the abiotic variables 

 did not improve such linear relationships. 

 However, for a given year, there was a 

 significant inverse correlation between 

 winter recruitment and the following 

 summer recruitment (p < 0.1). In other 

 words, in any given year, above-average 

 winter recruitment was usually followed by 

 a sharp decrease in total population and 

 by low summer recruitment levels. 

 Conversely, relatively hiqh population 

 abundances and high levels of summer 

 recruitments followed winters of low 

 recruitment levels. Thus, long-term 

 population features of these dominant 

 invertebrate species (brief squid and blue 

 crabs) are dependent on different factors. 



Temporal variability is extremely 

 complex since, at any given instant, a 

 natural system represents a composite ot 

 different sequences of varyinq periods 

 superimposed over one another as the 

 result of an almost infinite number of 

 cause-and-effect reactions. Determining 

 causality is difficult because these 

 overlapping cycles may differ along 

 habitat gradients and at different levels 

 of biological organization. Consequently, 

 the term "backqround noise" has become a 

 euphemism for our inability to determine 

 the temporal or sequential cause and 

 effect relationships. Modeling efforts 

 often assume that systems are in a state 

 of equilibrium, without defininq the 

 actual extent of temporal variability. 

 Terms such as stability, resilience, and 

 diversity are used to give a theoretical 

 ^'ramework to what is essentially a lack of 

 consistent observations of organisms under 

 field conditions. 



Annual variability among dominant 

 fish populations in the Apalachicola 

 estuary was considerable (Figure 41). 

 Each species followed a distinct, long- 

 term pattern of abundance; no single 



aspect of the physical environment was 

 apparent as the controlling factor of the 

 long-term changes. Bay anchovies were 

 most dominant during periods of high 

 salinity. The sand seatrout population 

 tended to follow the anchovy pattern with 

 particularly low numbers during the vear 

 of peak flooding when anchovies were also 

 low (1973). The Atlantic croaker followed 

 no obvious pattern relative to temperature 

 or salinity. Spot showed the highest 

 year-to-year variability with relatively 

 high numbers taken during the winter- 

 spring months of 1981. The cold winters 

 of 1976-77 and 1977-78 did not appear to 

 affect any of the dominant fish 

 populations in the Apalachicola estuary. 

 It is clear that factors other than 

 temperature and salinity are important in 

 the control of long-term fluctuations of 

 these populations. 



Although generalized temperature and 

 salinity preferences are well established 

 for various estuarine species (Table 17), 

 most such organisms have a relatively wide 

 tolerance for these factors. Tolerance of 

 this kind could explain the lack of 

 importance of these factors in the 

 determination of long-term population 

 variability (Table 23). When viewed from 

 the aspect of relative (percentage) 

 abundance, a certain temporal regularity 

 of the appearance of the dominant fishes 

 and invertebrates becomes apparent 

 (Livingston et al. 1976b; Figure 42). For 

 example, relative occurrence of 

 Palaemonetes pugio is high during spring 

 while Penaeus setif erus was dominant 

 during late summer and fall. The blue 

 crab is abundant during winter periods. 

 Among the fishes, sand seatrout are 

 dominant during the spring and summer 

 while bay anchovies (after the first year 

 of sampling) predominate in the fall and 

 Atlantic croaker prevail during the late 

 winter and soring. When a comparison is 

 made among the dominant fishes for peaks 

 of abundance, such increases tend to be 

 evenly distributed over a 12-month period. 

 However, of the top invertebrates, most 

 abundance peaks occur during fall periods 

 (September-November) with secondary 

 concentrations of peaks during early 

 summer (May-June). The major dominants 

 for both fishes and invertebrates thus 



94 



