Florida Bay
The eastern and southern edge of the bay is defined by the Florida Keys, with only a few natural passages between islands connecting to the Atlantic Ocean.
[8] The bay consists of more than 50 shallow (one to three meters deep) basins or lakes separated by mud banks and mangrove islands.
The bay is open to the Gulf of Mexico to the west, but connection to the Atlantic Ocean to the east is restricted to narrow channels between the Florida Keys.
The particular species of foraminifera, molluscs, algae, and seagrasses present in the waters of a locality in Florida Bay depend on the salinity.
Analysis of core samples extracted from mud banks have provided a record of past salinity levels in a few parts of the bay, going back about two centuries in one case.
Around 1840, the foraminifera and mollusc species present changed, and vegetation almost completely disappeared from the bottom, indicating a rise in salinity to above 25 ppt.
The bay floor remains covered with vegetation, but variations in the foraminifera and mollusc species present indicate rapid oscillations in salinity levels since 1940.
[17] The 2015 drought period of low precipitation combined with high temperatures and calm winds that produced rapid evaporation caused salinity to increase in the semi-enclosed basins in north-central Florida Bay.
[22] The Miami Limestone of Florida Bay formed during the Sangamon interglacial between the most recent glacial period, the Wisconsin, and the preceding Illinoian, centered on about 125,000 years ago.
[24] During the last 6,000 to 7,000 years a wet climate allowed sawgrass-dominated wetlands resembling the Evereglades to develop on the land that is now under Florida Bay.
Between 3,000 and 5,000 years ago, the continued rise of the sea level flooded the gently sloping southernmost part of the Everglades to form Florida Bay.
As the bay flooded, a layer of grey to black calcium carbonate mud, rich in hydrogen sulfide, formed on the bottom.
[27] As the rising sea level flooded the area that is now Florida Bay between 3,000 and 5,000 years ago, peat deposits from tree islands, shore levees, and irregularities in the bedrock surface served as nuclei for mud banks.
[28] The growth and development of mud banks is controlled by biological processes, including the baffling of water movement and binding of sediment by seagrasses.
The lowest facies of Upper Cross Bank, 15 to 25 centimetres (5.9 to 9.8 in) thick, is a basal packstone, which is also found widely on the bottom of basins in the bay.
[30] The bay's many basins that are broken up by banks serve as plentiful fishing grounds for snook (Centropomus undecimalis), redfish (Sciaenops ocellatus), spotted seatrout (Cynoscion nebulosus), tarpon (Megaflops atlanticus), bonefish (Albula vulpes), and permit (Trichinous falcatus), among others.
Most notably, Roseate spoonbills (Platalea ajaja), Reddish egrets (Egretta rufescens), and Great White Herons (Ardea herodias occidentalis) have unique subpopulations that are largely restricted to Florida Bay.
[36] The first major die-off occurred from 1987 to 1991 as thousands of hectares of turtlegrass beds (Thalassia testudinum) were devastated by high levels of toxic dissolved sulfide.
[19] Then, following the 2015 drought, extreme temperatures and heightened salinity reduced the amount of oxygen that could remain dissolved in the water, causing periods of anoxia during nighttime and thereby damaging the health of the turtlegrass in the bay.
[38] Cyanobacterial harmful algae blooms (also known as blue-green algae) have flourished in the bay due to a variety of environmental stressors: Agricultural fertilizer run-off increases nutrients in the delicately balanced environment and the excess increases the bacteria's rate of growth; The newly hyper-saline environment provides an ideal breeding ground for cyanobacteria;[39] Rafts of dead seagrass floating on the surface of the water as well as decaying on the bay bottom leads to anoxia and in turn, algal blooms.
[42] The cyanobacteria has also been linked to liver cancer, chronic fatigue illness, skin rashes, abdominal cramps, nausea, diarrhea and vomiting.
[44] By the mid 1930s, the three main species of wading birds in the bay (Roseate spoonbills, Reddish egrets, Great herons) were driven to near extinction by human harvesting for food and feathers.
[46] These environmental conditions are far from ideal for the seatrout and add additional difficulties for the survival of juveniles as well as important prey such as larval shrimp and small fish.
