FISHERY BULLETIN: VOL. 74, NO. 2 



and plant material, mollusks, polychaetes, crus- 

 taceans, and fishes (Darnell 1959; Tagatz 1968; 

 Odum and Heald 1972). Penaeid shrimp are also 

 omnivores, feeding on similar forms (Williams 

 1965; Darnell 1958; Eldred et al. 1961; Odum and 

 Heald 1972). Palaemonetes pugio feeds primarily 

 on detritus (Adams and Angelovic 1970; Oviatt 

 and Nixon 1973; Welch 1975). Qualitative obser- 

 vations indicate that Lolliguncula brevis is a 

 planktivore (Dragovitch and Kelly 1967). Thus, 

 most of the epibenthic invertebrates utilize de- 

 tritus and are more closely associated w^ith sedi- 

 ment type, benthic macrophyte distribution, and 

 placement of allochthonous forms of detritus than 

 the planktivorous fishes; this, together with cer- 

 tain (species-specific) temperature and salinity 

 tolerances, could provide a partial explanation for 

 the observed differences in the spatial distribu- 

 tion of the fishes and invertebrates. 



Another important evolutionary mechanism 

 for the partitioning of the energy resources of an 

 estuary is the temporal succession of species over 

 an annual cycle. Abundance interrelationships 

 expressed as percentage of total catch are shown 

 in Figure 6. There was a certain regularity of 

 percent representation of dominant species of 

 fishes and invertebrates in the Apalachicola sys- 

 tem. For example, relative occurrence of P. pugio 

 was high during spring months while Penaeus 

 setiferus was dominant during late summer and 

 fall. The blue crab was abundant during winter 

 periods. Among the fishes, C. arenarius was dom- 

 inant during the spring and summer while A. 

 mitchilli (after the first year of sampling) pre- 

 dominated in the fall andM. undulatus prevailed 

 during the late winter and spring. When a com- 

 parison was made among the 10 most dominant 

 species of fishes for peaks of abundance, such in- 

 creases were evenly distributed over a 12-mo 

 period. However, of the top 10 species of inverte- 

 brates, most peaks of abundance occurred during 

 fall periods (September-November) with second- 

 ary concentrations of peaks during early summer 

 (May-June). Livingston (in press), describing pat- 

 terns of species richness and diversity in 

 Apalachicola Bay, noted that there was an an- 

 nual double peak in fish and invertebrate diver- 

 sity although there was far more seasonal varia- 

 bility mN (numbers of individuals) and S (num- 

 bers of species) among fishes than invertebrates. 

 These data would tend to corroborate and eluci- 

 date such findings. Thus, although the top domi- 

 nants in both groups showed distinct temporal 



sequences in relative peak abundance, there was 

 a tendency for increased numbers of invertebrate 

 species during summer and fall periods whereas 

 peaks of A'^ and S for fishes were more contin- 

 uously distributed throughout the year. Major dom- 

 inants for both fishes and invertebrates thus 

 showed temporal partitioning through an annual 

 cycle. The noted differences in temporal distribu- 

 tional patterns of fishes and invertebrates could 

 be related to trophic response, with the plank- 

 tivorous fishes competing for a more limited 

 resource than the omnivorous (detritovore and om- 

 nivore) invertebrate species. 



Several conclusions can be made with regard to 

 the biotic component in the Apalachicola estuary. 

 Various independent ecological factors operate to 

 determine the spatial and temporal distributions 

 of such organisms. Biological functions, as adap- 

 tive responses to the physical and trophic environ- 

 ment, determine such distributional patterns, 

 allowing a somewhat orderly temporal succession 

 of dominant forms within certain broad trophic 

 spectra. Patterns of reproduction of various dom- 

 inant estuarine species have evolved in such a 

 way as to permit such long-term partitioning of 

 the estuarine environment. Superimposed on this 

 are certain in situ mechanisms whereby further 

 resource division occurs due to vertical and hori- 

 zontal distribution of the component species. This 

 is largely determined by various microhabitat 

 phenomena such as salinity, bottom type, cur- 

 rents, availability of detritus, etc. In addition, 

 biological determinants such as intraspecific 

 competition and predation further modify the in- 

 dividual component populations. Thus, no single 

 parameter prevails in the determination of the 

 community structure of an estuary which under- 

 goes predictable seasonal changes even though it 

 is a physically forced system. Although there is 

 considerable short-term fluctuation in the num- 

 bers of individuals of various populations, the 

 system maintains a certain temporal constancy 

 which, according to a traditional view of such 

 phenomena, could be termed stability. This does 

 not mean that such a system is not in a constantly 

 transient state; on the contrary, through various 

 natural and unnatural mechanisms such as 

 habitat alteration and destruction, hurricanes, 

 etc., the various population equilibria can be 

 shifted so that the system is no longer charac- 

 terized by a stable temporal succession of energy 

 utilization. Each population fluctuates around a 

 certain point of equilibrium; such fluctuations are 



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