input to Rookery Bay. In very large sys- 

 tems, such as Biscayne Bay near Miami, 

 Florida, mangroves are clearly less impor- 

 tant than any other sources such as algae 

 and sea grasses, although mangrove carbon 

 may be important in localized situations 

 such as the immediate vicinity of fringing 

 and overwash forests. The magnitude of 

 mangrove carbon export to unenclosed 

 coastal waters and offshore remains a 

 mystery. 



3.6 ENERGY FLOW 



At least seven sources of organic 

 carbon may serve as energy inputs for 

 consumers in mangrove ecosystems (Figure 

 8). The pathways by which this energy 

 containing material is processed and made 

 available to each consumer species is 

 indeed complex. Not surprisingly, current 

 understanding of energy flow in Florida 

 mangrove ecosystems exists largely in a 

 qualitative sense; quantitative data are 

 scarce and piecemeal. A variety of inves- 

 tigators have contributed information over 

 the past decade including, but not limited 

 to, Heald (1969), Odum (1970), Odum and 

 Heald (1972), Carter et al. (1973), 

 Snedaker and Lugo (1973), Heald et al. 

 (1974), Lugo and Snedaker (1974, 1975), 

 Odum and Heald (1975a, b), and Pool et al. 

 (1977). Probably, the most complete study 

 to date is the investigation of energy 

 flow in the black mangrove zone of Rookery 

 Bay by Lugo et al. (1980). 



It is possible at this time to pre- 

 sent a series of hypotheses concerning the 

 relative importance of these energy 

 sources. First, the relative importance 

 of each source can vary from one location 

 to the next. As will be shown in the 

 following discussion, the consumers in 

 certain mangrove forests appear to depend 

 primarily upon mangrove-derived carbon 

 while in other locations inputs from phy- 

 toplankton and attached algae are probably 

 more important. 



Our second hypothesis is that energy 

 flow based upon phytopl ankton is most 

 important in overwash mangrove forests and 

 other locations associated with large 



bodies of clear, relatively deep water. 

 Conversely, phytoplankton are hypothesized 

 to be relatively unimportant to the energy 

 budgets of the large riverine forest com- 

 munities along the southwest coast of 

 Florida. It should be remembered, how- 

 ever, that even where phytoplankton are 

 quantitatively unimportant, they poten- 

 tially perform an important function as 

 the basis of phytopl ankton-zoopl ankton- 

 larval fish food webs (Odum 1970). 



As a third hypothesis, Iver Brook 

 (Rosensteil School of Marine and Atmos- 

 pheric Sciences, Rickenbacker Causeway, 

 Miami, Fla.; personal communication 1979) 

 has suggested that both sea grasses and 

 benthic algae serve as an important energy 

 source for fringing mangrove communities 

 adjacent to large bodies of water such as 

 Biscayne Bay and Whitewater Bay. Although 

 little evidence exists to test this hypo- 

 thesis, observations of extensive deposits 

 of sea grass and macroalgal detritus with- 

 in mangrove forests suggest intuitively 

 that Brook's hypothesis may be correct. 



In regions where mangrove shading of 

 the prop roots is not severe, our fourth 

 hypothesis suggests that carbon origina- 

 ting from prop root epiphytes may be sig- 

 nificant to community energy budgets. 

 Lugo et al. (1975) have measured net pro- 

 duction of periphyton in mangroves 

 fringing Rookery Ba^ and found average 

 values of 1.1 gC/m /day. Hoffman and 

 Dawes (1980) found a lower value of 0.14 

 gC/mVday. Because these values are 

 roughly comparable to average exports of 

 mangrove leaf carbon (section 3.5), its 

 potential importance is obvious. 



The fifth hypothesis states that 

 mangrove organic matter, particularly leaf 

 material, is an important energy source 

 for aquatic consumers. This hypothesis 

 was first espoused by Heald (1969) and 

 Odum (1970), who worked together in the 

 riverine mangrove communities between the 

 Everglades and Whitewater Bay. Clearly, 

 mangrove carbon is of great importance 

 within the riverine and basin communities 

 all along the southwest coast of Florida 

 (Odum and Heald 1975b); Carter et al . 

 (1973) and Snedaker and Lugo (1973) 



36 



