Florida Bay, immediately south of the southern end of Florida, is bordered to the south and east by the Florida Keys. Westward, Florida Bay extends imperceptibly to the gentle slope of the adjacent Gulf of Mexico, while northward, the bay adjoins the mangrove forests and coastal prairies of the mainland. Florida Bay is a shallow estuarine lagoon divided into basins by a series of calcareous mud banks. The banks support almost half of the bay’s seagrass standing crop and provide most of the foraging habitat for the bay’s wading birds. The banks developed in shallow marine or brackish waters and often lie near, or even just above, the water surface. Five natural passes extend through the mud banks permitting partial exchange of bay waters with the reef tract and Atlantic Ocean. The banks occupy nearly 75% of the western bay, but only 13% of the eastern bay where they become narrow and anastomosing and are cut by numerous channels. The 170 islands within the bay primarily occupy slightly higher sites on the banks. The bay occupies 1500 sq. km (580 sq. mi.) of which the islands comprise about 1.7%.
Most of the islands are partially flooded by storm surges and extreme high tides. Many of the islands, especially the larger ones, contain large interior flats occupied by algal mats and by halophytes like Batis maritima, Salicornia spp., red (Rhizophora mangle) and black (Avicennia germinans) mangrove, and the mat-forming key grass, Monanthochloe littoralis). Southwestern winds force water into the bay with extreme depths reaching as high as 3.5 m above normal during strong storms. In contrast, northeastern winds, which prevail in winter, push water out of the bay during storms, lowering the water level down to near the sediment surface or below. During the dry season (Nov. to May) and in droughts, the flats function somewhat like evaporation basins, driving substrate salinity in island interiors to 70 or more parts per thousand with resultant partial or complete dieback of mangroves and some of the herbaceous halophytes.
Below is a map of Florida Bay produced by the U.S. National Park Service which administers most of the bay (within the green line) as part of Everglades National Park. Islands and banks are depicted and named. Those that are numbered correspond with the photographs below.
The photographs were taken in the 1990s either from helicopter overflights or from the islands themselves. Copies of photographs were scanned and are not modified from originals. However some decline in quality has resulted from the copying and scanning process and the elapsed time. The photographs depict islands in a generally west to east direction.
Unlike most keys in Florida Bay, Clive Key (#2), situated in the northwestern bay east-northeast from Sandy Key, is, like Sandy Key, sufficiently elevated to support well-developed mangrove and buttonwood (Conocarpus erecta) forests and, in slightly lower areas where flood water or rainwater accumulates, halophytic prairie. Parts of the island are subject to salt water flooding after strong storms. Photograph taken in 1995.
A closer view of Clive Key. The dominant halophytic prairie species include Sesuvium portulacastrum, Borrichia spp., Batis maritima, Maytenus phyllanthoides and the tall prickly grass Cenchrus myosuroides. Many other species occur. Red mangrove forests occur along island perimeters on elevated sediment deposits. Buttonwood (Conocarpus erectus) and black mangrove are the principal species of the interior forests. However thickets on higher ground are comprised of West Indian hardwoods like Pithecellobium keyense, Bumelia celastrina and Randia aculeata. Coconut palm (3 clumps of which are visible in the left foreground) and agave also occur on the island.
Jim Foot Key (#6) looking south. Long dead boles of black mangrove perhaps dating back to the great 1935 hurricane were seen here.
Russell Key (#12) is a large, low island most of which is usually flooded and devoid of living trees in the interior.
The largest upright bole found on Russell Key is photographed here. It bespeaks of an earlier time when mangrove forests dominated the interior. Photographed in Feb. 1995. These trees were most likely killed by a major hurricane such as Donna in 1960 or the great storm of 1935.