ancient coral known as Key Largo 1 lime- 

 stone, whereas the lower keys from Biq 

 Pine west are composed of oolitic facies 

 of the Miami linestone. (A note to boaters 

 and researchers in these shallow waters: 

 the limestone of the lower keys is much 

 harder than in the upper keys, and occa- 

 sional brushes with the bottom, which 

 would be minor in the upper keys, will 

 mangle or destroy outboard propellers and 

 lower drive units. ) 



The Florida reef tract is a shallow 

 barrier-type reef and lagoon extending 

 east and south of the Florida Keys. It 

 averages 5 to 7 km (4 to 4.4 mi) in width 

 with an irregular surface and depths vary- 

 ing fro-^ to 17 m (56 ft). The outer 

 reef tract is not continuous, but consists 

 of various reefs, often with wide gaps be- 

 tween them. The development is greatest 

 in the upper keys. The patch reefs are 

 irregular knolls rising from the limestone 

 platform in the area between the outer 

 reef and the keys. Behind the outer reef, 

 the back reef zone or lagoonal area is a 

 mosaic of oatchreefs, limestone bedrock, 

 and grass-covered sedimented areas. 



Florida Ray is a triangular region 

 lying west of the upper keys and south of 

 the Everglades. This large (226,000 ha or 

 558,220 acres), extremely 



reaches a maximum depth of 

 (7 to 10 ft), but averages 

 (3.3 ft) over a great area, 

 ments of fine carbonate mud 

 inq, anastomosing 

 filled "lakes" or 

 islands. 



shallow basin 

 only 2 to 3 m 

 less than 1 m 

 Surface sedi- 

 occjr in wind- 

 mud banks, seagrass- 

 basins, and mangrove 



1.4 REGIONAL SEAGRASS DISTRIBUTION 



this ,ir(;d (Bittaker and Iverson, in 

 press). In an inventory of the estuaries 

 of the gulf coast of Florida, McNulty 

 et al . (1972) estimated that over 45% of 

 the total area in the region of Florida 

 Bay v^est of the Keys and landward to the 

 freshwater line to Cape Sable was sub- 

 merged vegetation. By comparison, man- 

 grove vegetation comprised less than 7% of 

 the araa. 



The amount of seagrass coverage drops 

 off rapidly to the north of this area on 

 both coasts. On the Atlantic coast, the 

 shifting sand beaches signal a change to a 

 high-energy coast that is unprotected from 

 v/aves and has a relatively unstable sub- 

 strate, coupled with the littoral drift of 

 sand from the north. Throughout this area 

 seagrasses are usually found only in small 

 pockets in protected inlets and lagoons. 

 On the Gulf of f^exico coast north of Cape 

 Sable, seagrasses are virtually eliminated 

 by drainage from the Everglades with its 

 increased turbidity and reduced salinity. 

 Seagrasses are then found only in rela- 

 tively small beds within bays and estuar- 

 ies until north of Tarpon Springs, where 

 an extensive (3,000 km- or l,15Cmi-) bed 

 exists on the extremely broad shelf of the 

 northern gulf. Several bays on the gulf 

 coast, including Tampa Bay and Boca Ciega 

 Bay, formerly possessed extensive seagrass 

 resources, but dredge and fill operations 

 and other human perturbations have greatly 

 reduced the extent of these beds. 



This profile is primarily directed at 

 the seagrass ecosystem of southern Flor- 

 ida. It is necessary, however, to draw on 

 the pertinent work that has been done in 

 other seagrass systems. 



Florida possesses one of the largest 

 seagrass resources on earth. Of the 

 10,000 km- (3,860 mi- ) of seagrasses in 

 the Gulf of Mexico, over 8,500 km^ (3,280 

 mi) are in Florida waters, primarily in 

 two major areas (Bittaker and Iverson, in 

 press). The southern seagrass bed, which 

 is bounded by Cape Sable, north Biscayne 

 Bay, and the Dry Tortugas, and includes 

 the warm, shallow waters of Florida Bay 

 and the Florida coral reef tract, extends 

 over 5,500 km- (2,120 mi- ). Although cov- 

 erage is broken in numerous places, over 

 80% of the sea bottom contains seagrass in 



1.5 SEAGRASSES OF SOUTH FLORIDA 



Plants needed five properties to suc- 

 cessfully colonize the sea, according to 

 Arber (1920) and den Hartog (1970): 



(1) 



(2; 



(3; 



The ability 

 med i urn . 



to 1 ive in a sal ine 



The ability to 

 fully subinerged. 



function while 



A well- 

 tern. 



developed anchoring sys- 



