MANGROVES 



The three common mangroves in the order of 

 their abundance are the red mangrove (Rhizo- 

 phora mangle), the black mangrove (Avicennia 

 nitida), and the buttonwood (Conocarpus erec- 

 ta) , and their zonation landward is in this same 

 order (Fig. 25A). A fourth and less abundant 

 species, the white mangrove (Laguncularia 

 racemosa) , generally grows landward of the 

 black mangrove. Their distribution is world- 

 wide on tropical and subtropical shores of oceans 

 and estuaries. 



Mangroves grow on peat, muck, marl, sand, or 

 rock; thus, such environmental factors as killing 

 frost and land elevation control their distribu- 

 tion. Their "viviparous" seedlings germinate 

 while attached to the parent tree; seedlings de- 

 tach and float vertically in salt water, where 

 they remain alive several months, so they can be 

 carried long distances by currents. The red man- 

 grove grows inland along stream banks to fresh 

 water but attains its maximum 83-ft (25-m) 

 height and 6.6-ft (2-m) circumference in brack- 

 ish water of the Shark River (Davis, 1940). 



Heald (1969)' found that a mangrove forest 

 of southwest Florida produced 876 grams of dry 

 organic matter per square meter per year (7,779 

 lb/acre yr) in the form of leaves and twigs, 

 which together with attached microflora and 

 microfauna become available as food for estuar- 

 ine organisms. 



TIDAL MARSHES 



Tidal marshes extend northward the full 

 length of the coast, first as a transition zone be- 

 tween mangroves and freshwater marshes, then 

 as the predominant plant community of the 

 shore north of Tampa Bay. Juncus roemarianus 

 predominates, but several species are locally 

 abundant, among them Spartina alterniflora, 

 Spartina patens, Distichlis spicata, Salicornia 

 perennias, Borrichia frutescens, Batis marina 

 and Limonium carolinianum. Three useful 

 sources of taxonomic information are Small 

 (1933), Eyles and Robertson (1944), and West 

 and Arnold (1946). 



A few inches or centimeters of vertical eleva- 

 tion determine the suitability of habitat for a 



' Heald, Eric James. 1969. The production of organic 

 detritus in a south Florida estuary. Ph. D. dissertation, 

 Univ. of Miami, Coral Gables, Fla., ix + 110 p. 



given species or community as indicated in Fig- 

 ure 25B and C. Four major ecological zones are 

 discernible: Spartina alterniflora, Juncus 

 marsh, salt flats, and barrens (Martin et al., 

 1953; Thorne, 1954; Kurz and Wagner, 1957). 



The Spartina alterniflora zone typically 

 fringes tidal creeks, channels, inlets, and some- 

 times the outer side of barrier islands. A small 

 landward increase in elevation permits develop- 

 ment of the lush Juncus marsh that is by far the 

 most extensive and conspicuous feature of the 

 tidal marshes. Its plants grow to 6 or 7 ft (about 

 2 m) while at the edge of the marsh near the 

 flatwoods their height drops abruptly by one- 

 half or more and they merge with the third eco- 

 logical zone, the salt flats. Stunted specimens 

 of several genera typify the flats, especially 

 Spartina patens, Distichlis, Salicornia, Batis, 

 Borrichia, Aster, and Limonium. The fourth 

 zone, the barrens, consists of bare ground flooded 

 by high tides for brief periods of time. The tidal 

 inundation alternating with long exposure to 

 sunlight result in such high salt content of the 

 soil that seed plants are excluded. However, 

 diatoms and blue-green algae abound in prodigi- 

 ous quantities. For details see Jackson (1952) 

 and Kurz and Wagner (1957). 



Annual production of dry organic matter by 

 marsh plants is very large, probably about 2,000 

 g/m 2 (roughly 20,000 lb/acre) (Odum, 1961; 

 Teal, 1962). 



SUBMERGED VEGETATION 



The distribution of algae is far more interes- 

 ting and complex than Taylor (1954) believed it 

 to be. Taylor concluded correctly that the algal 

 flora of the Keys is more diverse and spectacular 

 than the flora to the north, but he was unaware of 

 two important facts: the remarkable variety 

 of perennial and annual subtropical and tropical 

 species on the inner continental shelf and the 

 seasonal appearance of temperate forms in win- 

 ter and spring (Phillips and Springer, 1960a; 

 Humm and Taylor, 1961; Dawes, Earle, and 

 Croley, 1967; Dawes and Van Breedveld, 1969; 

 Earle, 1969) . The distribution of the temperate 

 flora is disjunct on either side of the northern 

 Florida peninsula, probably the result of the 

 formation of a strait periodically between the 

 Gulf and the Atlantic Ocean in the Pleistocene 

 (Earle, 1969). 



48 



