Florida Bay Islands in the 1990s

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.

mapnumbered

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.

Sandy Key  in the western Bay close to the Gulf of Mexico in February 1992

1-Sandy Key in the western Bay close to the Gulf of Mexico in February 1992. West is to the left. Sandy Key is close to, or (depending on storms), narrowly connected to, the much smaller Carl Ross Key where there is  a campsite.

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.

 

Clive Key, situated in northwestern Florida Bay, is sufficiently elevated to support West Indian tree species subject to salt water flooding only after strong storms.

A closer view of Clive Key.   The dominant halophytic prairie soeues ubckuyde Borrichia spp., Batis maritima and Maytenus phyllanthoides.

A closer view of Clive Key. The dominant halophytic prairie species include Sesuvium portulacastrumBorrichia 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.

 

Cormorant Key in north-central is one of the higher islands somewhat similar in vegetation pattern to the nearby Clive Key

Cormorant Key  (#3) in north-central is one of the higher islands somewhat similar in vegetation pattern to the nearby Clive Key. Photographed in May 1993, in the height of the dry season. The yellowish feature is a prairie largely of Batis maritima.

 

NorthDumps is one of a pair of small islands where dieback of marginal red mangroves was perhaps first observed.

North Dump Key (#5) is one of a pair of small islands where dieback of marginal red mangroves was  observed in the early 1990s.

Jim Foot Key (#6) looking south. Long dead boles of black mangrove  perhaps dating back to the great 1935 were seen here.

Jim Foot Key (#6) looking south. Long dead boles of black mangrove perhaps dating back to the great 1935 hurricane were seen here.

 

Corinne Key, July 1993. Corinne is situated nearly  in the very center of Florida Bay and features a narrow raised peripheral berm occupied by red mangrove and large interior flats that may be inundated with fresh or brackish water or go dry in the winter dry season.

Corinne Key (#7), July 1993. Corinne is situated nearly in the very center of Florida Bay and features a narrow raised peripheral berm occupied by red mangrove and large interior flats which may be inundated with fresh or brackish water or go dry in the winter dry season.

Panhandle Key in the foreground, Spy Key behind. Taken Jully 1993.

Panhandle Key in the foreground, with Spy Key behind. Taken July 1993. Relatively little mangrove die-back even in the island interior. (#8)

Terrapin Point, a narrow extension of the mainland  points towards Big Key where  buttonwood hammocks still are present.

Terrapin Point, a narrow extension of the mainland points towards Big Key where
buttonwood hammocks still are present as are the more typical mixed mangrove forest and algal flats. (#9).

 

 

 

 

Club Key (#10) is similar to Russell Key (below). An increase in elevation of one or two inches is enough to support yhe salt-tolerant keys grass (Monanthochloe littoralis). Salicornia virginica and stunted black mangrove.

Club Key (#10) is similar to Russell Key (below). An increase in elevation of one or two inches is enough to support the salt-tolerant keys grass (Monanthochloe littoralis), Salicornia virginica and stunted black mangrove.

Mid-Black Betsy Keys, May 1993. Despite its plural name, this island feature consists of one large island at this time.

Mid-Black Betsy Keys (#11), May 1993. Despite its plural name, this island consists of one large island at this time but may not always have in the past.

 

A large, low island most of which us usually flooded and devoid of living trees in the interior.

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 bespeaks of an earlier time when mangrove forests  dominated 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.

 

Manatee Keys are just southeast of Russell Key near Key Largo. 1993

Manatee Keys (#13) are just southeast of Russell Key on the way to Key Largo.  Photographed in 1993. Mudbanks, which often are only barely submerged, are conspicuous.

 

The west end of Eagle Key a large island near the mainland and partially occupied by dwarf red mangrove thickets and tall black mangrove forests on peat.

The west end of Eagle Key (#14), a large island near the mainland. It is partially occupied by nearly impenetrable dwarf red mangrove thickets often less than a meter high and by a tall black mangrove forest on peat (not visible), yet  consists mostly of flooded mud flats and halophytic prairie..

 

North Nest Key in 1993. South Nest Key is in the rear. A stand of West Indian hardwoods and white mangrove is still holding out on a narrow small rise behind the narrow shelly beach.

North Nest Key  (#16) in 1993. South Nest Key is to the rear. A stand of West Indian hardwoods and white mangrove is still holding out on a  small rise behind a narrow shelly beach (to the (left). More typical mud flats and prairie characterize the interior.

 

 

 

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