Table 73. Results of a stepwise regression analysis of various independent parameters 

 and species (numerical abundance) in the Apalachicola estuary from March 1972 to 

 February 1^75. Independent variables are listed bv order of importance with R- 

 expressed as a cumulative function of the given parameters (from Livingston et al. 

 1976b). Independent variables were run with and without lag periods of 1-:^ months. 



Species 



Independent variables 



R? 



Anchoa mitchil li 



Micropogonias undulatus 

 Cynoscion arenanus 



Polydactylu 

 Arius felis 



s octonemus 



Leiostomus xanthurus 

 Chloroscombrus chrysurus 

 Menticirrhus americanus 

 Symphurus plagiusa 

 Bairdiella chrysura 

 Penaeus setif erus 

 Palaemonetes pugio 

 Callinectes sapidus 

 Penaeus duorarum 

 Lolliguncula br?yis 

 Portunus gibbesii 

 Palaemonetes vuTgaris 

 Rhithropanopeus harrisi i 

 Callinectes similis 



ChloroDhyll a, Secchi 



River flow (Tag), Secchi (lag) 



Chlorophyll _a, wind, Secchi (lag) temp. 



Chlorophyll _a (lag), salinity, Secchi 



Temp., wind 



Turbidity (lag), Secchi, salinity, temp. 



Temp, (lag), temp., salinity 



Temp, (lag) 



Color (laa), color, Secchi 



Wind, temp., color 



Wind, chlorophyll _a, incoming tide, color 



Turbidity 



Secchi, incoming tide 



Chlorophyl 1 a_, Secchi 



a (lag), temp. 



a (lag), Secchi 



Chlorophyl 1 

 Chlorophyll 

 Turbidity 

 Wind 

 Chlorophyl 1 



a, temp. 



0.38 

 0.46 

 0.83 

 0.=^8 

 0.30 

 0.85 

 0.44 

 0.19 

 0.63 

 0.40 

 0.48 

 0.40 

 0.43 

 0.41 

 0.43 

 0.39 

 0.32 

 0.18 

 0.34 



are also benthic omnivores, consume poly- 

 chaetes, harpacticoid copepods, bivalves, 

 and nematodes. Spot have a more diverse 

 diet than croaker and do not concentrate 

 on single prey types. Trends across size 

 classes are not as clearcut, although 

 there is decreased specialization with 

 growth. The sand seatrout is a water- 

 column predator of fishes and mysid shrimp 

 ( Mysidopsis bahia ). Small trout (SL 10-29 

 mm) tend to eat mysids and calanoid 

 copepods, while larger fish (SL 30-8° mm) 

 consume more juvenile fishes. Anchovies 

 ( Anchoa mitchil li ) comprise 70^ of all 

 fishes taken. 



Fishes regularly undergo ontoqenetic 

 dietary shifts encompassing planktivory, 

 carnivory, omnivory, and herbivory within 

 the same species (Sheridan 1978; Sheridan 

 and Livingston 1979; Livingston 1'379, 

 1982). Sheridan and Livingston (1979) 

 indicated that temporal differences in 

 feeding progressions were a major factor 

 in the lack of overlap in food types among 

 species. Laughlin (1979) found that blue 



crabs also undergo trophic progressions. 

 Juveniles, abundant during winter months, 

 feed largely on plant matter, detritus, 

 and bivalve mollusks such as Rangia 

 cuneata , Brachidontes exustus , and 

 Crassost r ea virginica . As the crab grows, 

 bivalves and fishes become progressively 

 more important in the diet. Larger blue 

 crabs feed primarily on bivalves, fishes, 

 and crabs (i.e., blue crabs, mud crabs 

 such as rhithropanopeus harrisi , and 

 xanthid crabs of the genus Neopanope ) . 

 Cannibalism is a significant mode of 

 foraqing in the older blue crabs. Diet 

 generally reflects seasonal shifts of prey 

 abundance. 



Although the distinctive nutrient 

 sources for the estuary have been 

 identified, the rate functions of energy 

 movement through the system are little 

 understood. The periodic inputs of 

 nutrients and detritus into the estuary 

 are transformed into biological matter. 

 Such integrative processes continuously 

 smooth out the episodic nature of energy 



84 



