TIME 



Figure 52. 



Diagramatic repre- 

 sentation of protein 

 enrichment of mangrove 

 detritus during degra- 

 dation (adapted from 

 Heald 1971). 



Mangroves are basically freshwater 

 plants with a remarkable ability to 

 tolerate saltwater. This is believed 

 to be the major reason for their 

 success in the oscillating salinity 

 environment. Normal coastal salini- 

 ty regimes prevent invasion by (and 

 competition from) freshwater spe- 

 cies, thus allowing mangroves to 

 dominate. 



Snedaker and Brown (1982) sug- 

 gest that in addition to physical/ 

 chemical conditions such as moderate 

 flushing and adequate freshwater, at 

 least two water quality constituents 

 contribute significantly to under- 

 standing mangrove ecosystem dyna- 

 mics. Nitrate is important because 

 it serves as an oxidant in the 

 anaerobic decomposition of reduced 

 organic matter accompanied by the 

 release of nutrients in the rhizo- 

 sphere. Likewise, sulfate may be 

 highly important as an oxidant in 

 the anaerobic decomposition and the 

 formation of sulfides. The latter 



may combine with heavy metals and 

 render them unavailable for uptake. 



The metals copper, chromium, 

 iron, lead, manganese, and zinc are 

 consistently more concentrated in 

 the sediments of mangrove forests 

 than in the surface waters. Differ- 

 ences of several orders of magnitude 

 are typical. The generally nonclas- 

 tic sediments of south Florida do 

 not contribute an excessive back- 

 ground load of heavy metals to the 

 coastal environment. However, 



agricultural pesticides and cultural 

 sources of heavy metals have been 

 found to enrich the background envi- 

 ronment (Horvath 1973, Mathis 1973, 

 Manker 1975). More importantly, 

 mangrove tissues consistently exhi- 

 bit heavy metal concentrations 6 to 

 7 orders of magnitude greater than 

 sediments. It is currently unknown 

 whether uptake occurs via sediment 

 or water transfer, or both. On the 

 other end of the seasonal cycle, 

 Mathis (1973) reports a 3 to 200 

 fold enrichment of Fe, Mn, Cu, and 

 Cd in various decomposition stages 

 of red mangrove leaves, compared 

 with living leaves. Considering the 

 extreme dependance of nearby estu- 

 aries on mangrove detritus, this 

 could be an important pathway of 

 heavy metal enrichment in fish and 

 wildlife. 



Much information exists on 

 structural aspects of mangrove bio- 

 geochemistry (i.e., chemical concen- 

 trations in various components of 

 tissues, soils, and so forth), but 

 very little information exists on 

 dynamic aspects such as transfer 

 functions and uptake rates between 

 major components of the mangrove 

 system (Snedaker and Brown 1982). 



Trophic relations among terres- 

 trial and wetland consumers have 

 not been studied extensively. Thus 

 they are portrayed in Figure 51 in a 



153 



