including mangroves in the Tampa Bay 

 estuary has been destroyed during the past 

 100 years. (4) Heald (unpublished MS.) 

 has estimated a loss of 2,000 acres (810 

 ha) of mangroves within the Florida Keys 

 (not considered by Birnhak and Crowder 

 1974). So while loss of mangrove ecosys- 

 tems throughout Florida is not over- 

 whelming, losses at specific locations 

 have been substantial. 



Diking, impounding, and long-term 

 flooding of mangroves with standing water 

 can cause mass mortality, especially when 

 prop roots and pneumatophores are covered 

 (Breen and Hill 1969; Odum and Johannes 

 1975; Patterson-Zucca 1978; Lugo 1981). 

 In south Florida, E. Heald (pers. comm.) 

 has observed that permanent impoundment by 

 diking which prevents any tidal exchange 

 and raises water levels significantly 

 during the wet season will kill all adult 

 red and black mangrove trees. If condi- 

 tions behind the dike remain relatively 

 dry, the mangroves may survive for many 

 years until replaced by terrestrial vege- 

 tation. 



Mangroves are unusually susceptible 

 to herbicides (Walsh et al. 1973). At 

 least 250,000 acres (100,000 ha) of man- 

 grove forests were defoliated and killed 

 in South Viet Nam by the U.S. military. 

 This widespread destruction has been docu- 

 mented by Tschirley (1969), Orians and 

 Pfeiffer (1970), Westing (1971), and a 

 committee of the U.S. Academy of Sciences 

 (Odum et al. 1974). In many cases these 

 forests were slow to regenerate; observa- 

 tions by de Sylva and Michel (1974) indi- 

 cated higher rates of siltation, greater 

 water turbidity, and possibly lower dis- 

 solved oxygen concentrations in swamps 

 which sustained the most damage. Teas and 

 Kelly (1975) reported that in Florida the 

 black mangrove is somewhat resistant to 

 most herbicides but the red mangrove is 

 extremely sensitive to herbicide damage. 

 He hypothesized that the vulnerability of 

 the red mangrove is related to the small 

 reserves of viable leaf buds in this tree. 

 Following his reasoning, the stress of a 

 single defoliation is sufficient to kill 

 the entire tree. 



Although mangroves commonly occur in 

 areas of rapid sedimentation, they cannot 

 survive heavy loads of fine, floculent 

 materials which coat the prop roots. The 

 instances of mangrove death from these 

 substances have been briefly reviewed by 

 Odum and Johannes (1975). Mangrove deaths 

 from fine muds and marl, ground bauxite 

 and other ore wastes, sugar cane wastes, 

 pulp mill effluent, sodium hydroxide 

 wastes from bauxite processing, and from 

 intrusion of large quantities of beach 

 sand have been documented from various 

 areas of the world. 



12.3 EFFECTS OF OIL SPILLS ON MANGROVES 



There is little doubt that petroleum 

 and petroleum byproducts can be extremely 

 harmful to mangroves. Damage from oil 

 spills has been reviewed by Odum and 

 Johannes (1975), Carlberg (1980), Ray (in 

 press), and de la Cruz (in press, b). 

 Over 100 references detailing the effects 

 of oil spills on mangroves and mangrove- 

 associated biota are included in these 

 reviews. 



Petroleum and its byproducts injure 

 and kill mangroves in a variety of ways. 

 Crude oil coats roots, rhizomes, and pneu- 

 matophores and disrupts oxygen transport 

 to underground roots (Baker 1971). 

 Various reports suggest that the critical 

 concentration for crude oil spills which 

 may cause extensive damage is between 100 

 and 200 ml/m of swamp surface (Odum and 

 Johannes 1975). Petroleum is readily 

 absorbed by lipophylic substances on sur- 

 faces of mangroves. This leads to severe 

 metabolic alterations such as displacement 

 of fatty molecules by oil hydrocarbons 

 leading to destruction of cellular permea- 

 bility and/or dissolution of hydrocarbons 

 in lipid components of chloroplasts (Baker 

 1971). 



As with other intertidal communities, 

 many of the invertebrates, fishes, and 

 plants associated with the mangrove com- 

 munity are highly susceptible to petroleum 

 products. Widespread destruction of 

 organisms such as attached algae, oysters, 

 tunicates, crabs, and gobies have been 

 reported in the literature (reviewed by de 



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