CHAPTER 11 



VALUE OF MANGROVE ECOSYSTEMS TO MAN 



Mangrove swamps are often hot, fetid, 

 mosquito-ridden, and almost impenetrable. 

 As a consequence, they are frequently held 

 in low regard. It is possible that more 

 acres of mangrove, worldwide, have been 

 obliterated by man in the name of "recla- 

 mation" than any other type of coastal 

 environment. Reclamation, according to 

 Webster's, means "to claim back, as of 

 wasteland". Mangrove swamps are anything 

 but wasteland, however, and it is impor- 

 tant to establish this fact before a 

 valuable resource is lost. We can think 

 of six major categories of mangrove values 

 to man; no doubt, there are more. 



11.1 SHORELINE STABILIZATION AND STORM 

 PROTECTION 



The ability of all three Florida 

 mangroves to trap, hold and, to some 

 extent, stabilize intertidal sediments has 

 been demonstrated repeatedly (reviewed by 

 Scoffin 1970; Carlton 1974). The contem- 

 porary view of mangroves is that they 

 function not as "land builders" as hypo- 

 thesized by Davis (1940) and others, but 

 as "stabilizers" of sediments that have 

 been deposited largely by geomorphological 

 processes (see section 3.2). 



Gill (1970), Savage (1972), Teas 

 (1977), and others have emphasized that 

 land stabilization by mangroves is pos- 

 sible only where conditions are relatively 

 quiescent and strong wave action and/or 

 currents do not occur. Unfortunately, no 

 one has devised a method to predict the 

 threshold of physical conditions above 

 which mangroves are unable to survive and 

 stabilize the sediments. Certainly, this 

 depends to some extent on substrate type; 

 mangroves appear to withstand wave energy 

 best on solid rock substrates with many 

 cracks and crevices for root penetration. 

 From our own experience, we suspect that 

 mangroves on sandy and muddy substrates 

 cannot tolerate any but the lowest wave 

 energies, tidal currents much above 25 

 cm/s, or heavy, regular boat wakes. 



The concept that the red mangrove is 

 the best land stabilizer has been ques- 



tioned by Savage (1972), Carlton (1974), 

 and Teas (1977). These authors argue that 

 the black mangrove (1) is easier to 

 transplant as a seedling, (2) establishes 

 its pneumatophore system more rapidly than 

 the red mangrove develops prop roots, (3) 

 has an underground root system that is 

 better adapted to holding sediments (Teas 

 1977), (4) is more cold-hardy, and (5) can 

 better tolerate "artificial" substrates 

 such as dredge-spoil, finger fills, and 

 causeways. Generally, the white mangrove 

 is regarded as the poorest land stabilizer 

 of the Florida mangroves (Hanlon et al. 

 1975). 



Although mangroves are susceptible to 

 hurricane damage (see section 12.1), they 

 provide considerable protection to areas 

 on their landward side. They cannot 

 prevent all flooding damage, but they do 

 mitigate the effects of waves and 

 breakers. The degree of this protection 

 is roughly proportional to the width of 

 the mangrove zone. Very narrow fringing 

 forests offer minimal protection while 

 extensive stands of mangroves not only 

 prevent wave damage, but reduce much of 

 the flooding damage by damping and holding 

 flood waters. Fosberg (1971) suggested 

 that the November 1970 typhoon and accom- 

 panying storm surge that claimed between 

 300,000 and 500,000 human lives in 

 Bangladesh might not have been so destruc- 

 tive if thousands of hectares of mangrove 

 swamps had not been replaced with rice 

 paddies. 



11.2 HABITAT VALUE TO WILDLIFE 



Florida mangrove ecosystems are 

 important habitat for a wide variety of 

 reptiles, amphibians, birds, and mammals 

 (see sections 8, 9, and 10). Some of 

 these animals are of commercial and sport 

 importance (e.g., white-tailed deer, sea 

 turtles, pink shrimp, spiny lobster, 

 snook, grey snapper). Many of these are 

 important to the south Florida tourist 

 industry including the wading birds (e.g., 

 egrets, wood stork, white ibis, herons) 

 which nest in the mangrove zone. 



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