LONG-TERM FLUCTUATIONS OF 

 EPIBENTHIC FISH AND INVERTEBRATE POPULATIONS IN 



APALACHICOLA BAY, FLORIDA 



Robert J. Livingston, Gerard J. Kobylinski, Frank G. Lewis, HI, and Peter F. Sheridan^ 



ABSTRACT 



A 3-yr study was made concerning seasonal changes in the biota of Apalachicola Bay. The 

 Apalachicola River causes a temporal progression of changes of various environmental parameters in 

 the bay such as salinity, turbidity, nutrients, and detritus levels. Fishes were more widespread 

 in their distribution throughout the bay than invertebrates. This was thought to be related to 

 trophic response and habitat preference. High levels of relative dominance prevailed for both groups 

 with the top three species of each group accoiuiting for more than 80% of the total number of 

 individuals taken. 



Peak levels of monthly abundance of various dominant fish species tended not to overlap through a 

 given 12-mo period. Invertebrate species abundance usually reached peak levels during summer and 

 fall periods. The seasonal appearance and distribution of organisms in the Apalachicola Bay system 

 was comparable to that found in other estuaries in the northern Gulf of Mexico. The temporal and 

 spatial distribution of estuarine fishes and invertebrates was associated with species-specific 

 reproductive cycles, trophic relationships, and habitat preferences. The Apalachicola estuary was 

 viewed as a seasonally stable system, with regular temporal fluctuations of the biota through each 

 annual cycle. 



There is a rapidly growing literature concerning 

 fluctuations of populations of epibenthic es- 

 tuarine organisms (Dahlberg and Odum 1970; 

 Bechtel and Copeland 1970; Copeland and 

 Bechtel 1971; McErlean et al. 1973; Oviatt and 

 Nixon 1973; Copeland and Bechtel 1974; Calla- 

 way and Strawn 1974; Livingston 1975). Haed- 

 rich and Haedrich (1974) noted that seasonal 

 changes of fish populations in a Massachusetts 

 estuary allow more species to utilize the estuary 

 than if there were constant direct competition. 

 Staggered reproductive cycles were postulated as 

 a partial explanation for this "dynamic situa- 

 tion." Trophic variability was also considered a 

 mechanism for reduced competition. Copeland 

 and Bechtel (1974) identified key environmental 

 requirements for six Gulf coast species, and con- 

 sidered such limits as potential criteria for es- 

 tuarine management programs. Oviatt and 

 Nixon (1973) noted that although fish biomass 

 remained constant throughout the year, indi- 

 vidual species abundance varied seasonally. They 

 found that biomass and numbers of individuals 

 could not be accounted for on the basis of physical 



^Department of Biological Science, Florida State University, 

 Tallahassee, FL 32306. 



parameters alone, and it was considered that 

 biological functions such as competition and pre- 

 dation could be more important determinants of 

 species distribution in estuarine systems. 



The present study is part of a comprehensive 

 field program in Apalachicola Bay, Fla. (Liv- 

 ingston et al. 1974). This is a relatively un- 

 polluted, shallow coastal estuary bounded by 

 barrier islands. The bay is physically dominated 

 by the Apalachicola River (Estabrook 1973; 

 Livingston et al. 1974). This paper is concerned 

 with long-term, seasonal fluctuations of epiben- 

 thic fish and invertebrate populations, and the 

 possible interrelationships of the physicochemical 

 and biological elements of the Apalachicola Bay 

 system. 



MATERIALS AND METHODS 



Field Operations 



A detailed description of the sampling meth- 

 odology is already available (Estabrook 1973; 

 Livingston et al. 1974). Physicochemical and 

 biological samples were taken monthly from 

 March 1972 to February 1975 at a series of sta- 

 tions in East Bay and Apalachicola Bay (Figure 

 1). Water samples were taken at the surface and 



Manuscript accepted December 1975. 

 FISHERY BULLETIN: VOL, 74, NO. 2, 1976. 



311 



