3 

 O 



o '= 



CL 

 _>» 

 O 



o 



ONDJ FMAMJ JAS 



Month 



Figure 23. Average seasonal variation in 

 daily phytoplankton productivity for the 

 Apalachicola estuary (taken from Estabrook 

 1973; Livingston et al. 1974). 



various bayous along the northeastern 

 margin of the bay (Livingston, unoublished 

 data). There is little or no submerqed 

 vegetation in St. Vincent Sound. Seagrass 

 beds in Apalachicola Bay and western St. 

 George Sound are restricted to shallow 

 lagoonal oortions of Hog Island and St. 

 George Island and are dominated by 

 Halodule wrighti i , Gracil aria spp., and 

 Syringodium f il iforme . Thus the 

 distribution of submerged vegetation 

 generally reflects previously described 

 depth characteristics, water-quality 

 features, drainage and current patterns, 

 and salinity distribution. 



Seagrass beds undergo regular sea- 

 sonal cycles of productivity and standing 

 croD. The ecology of the East Bav 

 Vallisneria beds has been well studied 

 (Livingston and Duncan 1'57Q; Purcell I'^ll; 



Sheri dan 



Livingston 



production 



q C m-^ 



species 



standing 



months. 



growth. 



1Q78, 1^70; 



1079, 1P83). 

 of Vallisneria 

 yr-1 to 3^0 g C 

 undergoes sharp 

 crop biomass 

 After a period 

 maximum leaf 

 maintained from May 

 August, considerable 

 plant standing crop occurs 

 by new growth during 



Sheridan and 



Net annual 



varies from 3?0 



m-2 yr-1. This 



reductions of 



durina winter 



of rapid sprinq 



development is 



through July. By 



degeneration of the 



and is followed 



September and 



October. Similar cycles of growth occur 

 in the Thai ass i a -domina ted qrassbeds in 

 areas of higher salinity (Bittaker 107S; 

 Livingston 10R?a; Zimmerman and Livingston 

 1976a, b, 1Q79). Net annual production 

 has been estimated to be 'iDO g C 

 fn-2 vr-1 (Iverson unpublished data). 

 Rapid growth occurs during soring and 

 early summer. Standing crop biomass 

 usually peaks during summer months with 

 rapid degeneration as water temperature 

 falls (November, December). Durina winter 

 months, productivity and standing croD are 

 relatively low in the various types of 

 seagrass beds in shallow coastal areas of 

 the northeast Gulf coast of Florida. 



Based on the productivity figures and 

 the seagrass distribution (Table 1), the 

 grassbeds in the East Bay-Apalachicola Bay 

 area produce 8,053 t C yr-1 (P,866 tons C 



-ll 



yr-J-). Grassbed production in the 



remaining portions of the Apalachicola Bay 

 system approximates 18,?60 t C yr-1 

 (?0,1?? tons r yr-1). Total production 

 for the entire system is ?7,?1'' t r y-1 

 (?Q,'^89 r. y-1). 



3.?. DETRITUS FLUX AND NUTRIENT DYNAMICS 



Availability of organic matter does 

 not explain the processes involved in 

 transformation of energy as it moves 

 through the complex food webs of the 

 ri ver-estuarv system. Since relatively 

 few organisms feed directly on living 

 macrophytes, the degradation processes, 

 which include mechanical fragmentation, 

 chemical leaching, autolysis, hydrolysis, 

 oxidation, and microbial activity, are 

 important in the dynamic transfer of 

 estuarine nutrients from available organic 

 matter. Input to the immediate estuarv 

 and the bay system as a whole is 

 seasonally timed to specific 

 meteoroloqical factors (Table o). Most of 

 the river input occurs during winter and 

 sprinq periods, while major phytoplankton 

 blooms take place in the spring and fall. 

 Input of organic matter from the seagrass 

 beds occurs during the summer and fall. 

 The transfer of organic materials from the 

 coastal marshes is not as well understood 

 as that of the other sources. In general, 

 the contribution of plant detritus to the 

 nutrient dynamics of the estuary is ex- 

 tremely complex in terms of timing and 



36 



