provided subsequent supportive data. What 

 is not clear, is the relative importance 

 of mangrove carbon to consumers within 

 fringing, overwash, and more isolated 

 manqrove communities. 



Our sixth hypothesis involves the 

 assemblage of organisms that graze man- 

 grove leaves directly. A variety of in- 

 sects (see section 6) and the mangrove 

 tree crab, Aratus pi soni i , (Beever et al. 

 1979) obtain much of their energy directly 

 from living mangrove leaves, even though 

 grazing rarely exceeds 10% of net primary 

 production (Odum and Heald 1975b). 



As a seventh hypothesis we suggest 

 that anaerobic decomposition of mangrove 

 tissue, particularly root material, may 

 support an extensive food web based on 

 bacteria associated with methanogenesis or 

 the processing of reduced sulfur com- 

 pounds. Our suggestion of the importance 

 of reduced sulfur comes directly from 

 Howarth and Teal's (1980) discovery of 

 this potentially important energy pathway 

 in temperate Spartina (cordgrass) marshes. 

 They found that anaerobic decomposition is 

 such an incomplete process that if sul- 

 fates are available (from sea water) as 

 much as 75% of the original energy in 

 plant tissues may be converted by sulfur 

 reducing bacteria to reduced sulfur com- 

 pounds such as hydrogen sulfide and py- 

 rite. Subsequently, if these reduced 

 sulfur compounds are moved hydrologically 

 to an oxidized environment (sediment sur- 

 face or creek bank) sulfur -oxidizing bac- 

 teria (e.g., Thiobacillus spp.) may convert 

 the chemically stored energy to bacterial - 

 ly stored energy with an efficiency as 

 great as 50% (Payne 1970). Presumably, 

 deposit-feeding organisms such as grass 

 shrimp ( Pal aemonetes ) and mullet ( Mugil ) 

 are capable of grazing these sulfur- 

 oxidizing bacteria from the sediment 

 surface. If this hypothetical trophic 

 exchange does exist, it may be of con- 

 siderable magnitude and may cause us to 

 reexamine current concepts of energy pro- 

 cessing and export from mangrove 

 ecosystems. Since freshwater contains 

 remarkably little sulfate in comparison to 

 seawater, this energy pathway is probably 

 of little importance in mangrove forests 



of very low salinity. 



Carbon inputs from terrestrial 

 sources may be important to certain man- 

 grove communities. Carter et al. (1973) 

 have shown that terrestrial carbon can 

 reach coastal ecosystems particularly 

 where man has cut deep channels inland for 

 navigation or drainage purposes. The 

 magnitude of this influx has not been 

 adequately measured although Carter et al. 

 did find that mainland forests (including 

 mangroves) contributed approximately 2,100 

 metric tons of carbon per year to 

 Fahkahatchee Bay. 



Atmospheric inputs from rainfall 

 appear to be minimal in all cases. Lugo 

 et al. (1980) measured throughfall (preci- 

 pitation passing through the tree canopy) 

 in Rookery Bay mangrove forests of 15 to 

 17 gC/m /year. This would be an overesti- 

 mate of atmospheric input since it con- 

 tains carbon leached from mangrove leaves. 

 The best guess of atmospheric input is 

 between 3 to 5 gC/m /year for south 

 Florida mangrove ecosystems. 



Subsequent stages of energy transfer 

 in mangrove community food webs remain 

 largely hypothetical. Odum (1970) and 

 Odum and Heald (1975b) have outlined 

 several pathways whereby mangrove carbon 

 and energy are processed by a variety of 

 organisms (see Figure 8). Apparently, the 

 most important pathway follows the se- 

 quence: mangrove-leaf detritus substrate- 

 microbe-detritus consumer-higher consu- 

 mers. The critical links are provided by 

 the microbes such as bacteria and fungi 

 (see Fell et al. 1975) and by the detritus 

 consumers. The latter group was studied 

 by Odum (1970) and Odum and Heald (1975b) 

 and found to consist of a variety of 

 invertebrates (e.g., caridean shrimp, 

 crabs, mollusks, insect larvae, amphipods) 

 and a few fishes. 



Stable carbon studies such as those 

 done by Haines (1976) in Spartina 

 (cordgrass) marshes have not been per- 

 formed in mangrove ecosystems. Mangroves 

 are C3 plants and have 6 13 values in the 

 range of minus 25 to minus 26 (Macko 

 1981). According to the same author, 



38 



