reported by Dr. Seneca in these proceed- 

 ings, might protect such a shoreline. 

 Figure 8 shows red mangroves near 

 the Card Sound Bridge in Florida being 

 subjected to wave erosion. No new seed- 

 lings were becoming established in this 

 area. 



ROOT MAT AND SOIL HOLDING 



The relatively greater resistance 

 to wave erosion of the root systems of 

 the black and white mangroves in compar- 

 ison with red mangroves is an important 

 factor in shoreline stabilization and 

 mangrove swamp creation. The root system 

 of red mangroves (Figure 9) does not 

 form nearly as dense a mat as do roots 

 of white or black mangroves. Figure 10 

 shows the storm-washed (probably hurri- 

 cane) roots of a white mangrove. Black 

 mangroves have a dense root mat similar 

 to the whites. 



Black and white mangroves are found 

 in areas of higher wave energy than red 

 mangroves, especially on rocky shores. 

 Figure 11 shows black and white man- 

 groves, but no red, that have success- 

 fully colonized an exposed soil bank 

 along south Biscayne Bay, Florida. Also, 

 black or white mangroves are probably 

 better than reds for planting on rocky 

 sites. 



If rapid shoreline stabilization is 

 desired for protection against erosion, 

 black or white mangroves may be more 

 suitable than reds. Lewis and Dunstan 

 (1975) have suggested that rapid soil 

 stabilization might be achieved by 

 planting Spartina alterniflora , and then 

 planting mangroves in the Spartina . 

 Mangroves appear to compete successfully 

 in such a situation. Rapid shoreline 

 stabilization can be achieved by plant- 

 ing mangroves at greater density, then 

 allowing natural thinning to occur, or 

 thinning artificially, as suggested by 

 Pulver (1975). 



FLOTSAM AND JETSAM 



Another enemy of mangrove seedling 

 establishment is floating trash (flot- 

 sam) that can cover, break off, or up- 

 root seedlings. Even mats of the float- 

 ing seagrass or algae can sometimes up- 

 root an unprotected mangrove planting. 



It may be possible in some cases to con- 

 struct small breakwaters to divert the 

 floating trash from a planting site. 



SUBSTRATE AND MINERAL NUTRIENTS 



In a mangrove swamp, which is a 

 "climax" or "subclimax" forest, there is 

 probably a tight coupling of mineral nu- 

 trients. The mineral elements from man- 

 grove leaves, wood bark, and other de- 

 bris that reach the forest floor are 

 efficiently recycled by the trees. 



Atmospheric nitrogen is fixed by 

 microorganisms in the mangrove soils 

 (Kimball and Teas 1975). The amount of 

 fixation found, on the order of 5.6 to 

 16.8 kg/ha (5-15 lb/acres) per year, is 

 not spectacular by comparison with an 

 equal area in a field of soybeans. An 

 unknown factor in mangrove swamp nitro- 

 gen utilization is whether or not deni- 

 trification (nitrogen loss) occurs in 

 mangrove soils. As noted by Pomeroy 

 ("Nutrient Cycling in Coastal Ecosys- 

 tems" in this volume) rates of nitrogen 

 loss can offset nitrogen fixation in 

 some soils. 



In a mangrove forest, some of the 

 mineral nutrients in leaves, fruits and 

 propagules, wood and other debris are 

 lost from the system when carried out 

 with the tide. Along many mangrove 

 shores, mineral nutrients are gained 

 when seagrass, algae, and other plant 

 materials are washed into the forest, 

 decay, and release mineral nutrients. 



Some soils, such as broken coral 

 and nutrient-deficient leached soils, 

 provide poor substrates for mangrove de- 

 velopment (Macnae 1968). There is some 

 evidence that south Florida marl soils, 

 with their high pH and deficiencies of 

 certain mineral elements, may be a poor 

 soil for mangroves (Teas 1*974 ) . 



SPHAEROMA ROOT PARASITE 



The isopod parasite Sphaeroma tere- 

 brans , a pill bug-sized root borer, is a 

 serious problem for red mangroves in 

 some areas (Rehm and Humm 1973). Sphae- 

 roma is also known to attack black and 

 white mangroves (Rehm 1976). In an area 

 of heavy Sphaerom a infestation, para- 

 sites were found even in the timbers of 

 wooden derelict boats (H. J. Teas, 



72 



