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Florida Bay is the bay located between the southern end of the Florida mainland (the Everglades) and the Florida Keys in the United States. It is a large, shallow estuary that while connected to the Gulf of Mexico, has limited exchange of water due to shallow mudbanks dividing the bay into many basins or lakes. The banks separate the bay into basins, each with its own unique physical characteristics.
While there is no sharp boundary between Florida Bay and the Gulf of Mexico, the westernmost edge of Florida Bay can be approximated by a line drawn from Long Key to Cape Sable on the mainland, which is very close to the boundary line of Everglades National Park. The northeastern edge of Florida Bay is at Jewfish Creek in Key Largo. Blackwater Sound, southwest of Jewfish Creek, is generally considered part of Florida Bay; Barnes Sound, on the other side of jewfish Creek, is not. Barnes Sound is generally considered part of the Biscayne Bay system. The bay consists of more than 50 shallow (one to three meters deep) basins or lakes separated by mud banks and mangrove islands. Such basins include: Little Blackwater Sound, Blackwater Sound, Tarpon Basin, Buttonwood Sound, Duck Key Basin, Eagle Key Basin, Madeira Bay, Calusa Key Basin, Crane Key Basin, Rankin Lake, Whipray Basin, Twin Key Basin, Rabbit Key Basin, and Johnson Key Basin.
Water flows between the basins in narrow channels and over the mud banks. 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 average tidal range along the western edge of the bay is 1 to 1.5 meters, but the tidal range diminishes quickly eastward in the bay due to the restricted flow of water between basins. Fresh water flow into the bay is restricted to Taylor Slough and Trout Creek in the northeast corner of the bay, and is only 10% of the freshwater supply to the bay (rainfall provides the rest of the fresh water). Due to the poor circulation of water within the bay, salinity increases rapidly away from the margins of the bay, except for the northeast part of the bay where it receives fresh water from rivers.
Examination of the paleontology of biota in Core sample from in Florida Bay have found that historically the salinity of water in Florida Bay has been primarily dependent on rainfall rather than flow from the Everglades.
Salinity partially controls the occurrence of biota in the bay. The particular species of foraminifera, , algae, and present in the waters of a locality in Florida Bay depend on the salinity. Analysis of 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. At a site called Bob Allen in the central part of the bay, sparse seagrass cover was present from the bottom of the core, and the species present indicated a salinity in 18 to 25 parts-per-thousand (ppt) range, from about 1810, until about 1840. 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. Those conditions continued until about 1910, when the pre-1840 conditions returned, with relatively dense vegetation on the bay floor. The bay floor remains covered with vegetation, but variations in the foraminifera and mollusc species present indicate rapid oscillations in salinity levels since 1940. Around 1970, changes in species and a reduction in the amount of vegetation for a few years indicated a sharp increase in salinity.
A second core from Russell Bank, also in the central part of the bay, goes back to about 1876. Until about 1884, salinity at the location was greater than 25 ppt. From 1884 to about 1900 salinity was below 25 ppt, and below 18 ppt at times. From about 1900 to about 1910 salinity rose above 25 ppt. From 1910 to 1940, salinity was between 18 and 25 ppt. Salinity rose to above 25 ppt around 1940, and stayed there until about 1960, when it fell to between 15 and 25 ppt until 1980. As at the Bob Allen site, there was a brief event around 1970 that severely disrupted the presence of various species at Russell Bank. Around 1980, salinity again rose above 25 ppt.
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. Without the freshwater, the water has become stagnant and salty with excess nitrogen from the fertilizer.Robert Mcclure And Don Melvin. (1993). "The Dead Zone Once A Teeming Marine Nursery, Florida Bay Today Is Dying". SunSentinel This hyper-salinity contributes to the massive seagrass die-offs and algal blooms, and kills submerged aquatic vegetation.
The Miami Limestone of Florida Bay formed during the Sangamonian between the most recent glacial period, the Wisconsin, and the preceding Illinoian, centered on about 125,000 years ago. The sea level stood higher then than at present, covering much of what is now southern Florida. A coral reef grew on the eastern edge of the Florida platform, while the shallow, protected waters west of the reef formed or hosted large fields of .
There are tree islands throughout the Everglades, clusters of trees growing on slight elevations. Tree islands accumulate plant litter which becomes peat, which in turn facilitates the creation of caliche, a dense limestone crust on the limestone bedrock. As the bay flooded, a layer of grey to black calcium carbonate mud, rich in hydrogen sulfide, formed on the bottom. The mud layer is thicker on islands covered by , and in banks connecting the islands. Peat and caliche remnants from the Everglades tree islands remain under the islands and banks.
Mud banks in the central part of the bay tend to run in a northwest to southeast direction, corresponding to the direction of approach of across the bay. The mud bank called Upper Cross Bank is long and wide. Upper Cross Bank is eroding on the windward (east) side at a rate of vertically and laterally over five years, while the leeward (west) side is growing at a rate of vertically and laterally 0ver the same five years.
Mud mounds are made up of facies, thin layers of different types of rock. The lowest facies of Upper Cross Bank, thick, is a basal packstone, which is also found widely on the bottom of basins in the bay. The packstone resembles stone that commonly forms on limestone at the bottom of lakes. The presence of remnants of the algae Halimeda in the packstone may indicate that it formed when the bay was more open. Mud mounds appear to be migrating over the basal packstone in the basins. The basal packstone in the basins has also been reworked by hurricanes.
The bay is home to many species of wading birds. Most notably, Roseate spoonbills ( Platalea ajaja), ( Egretta rufescens), and Great White Herons (A rdea herodias occidentalis) have unique subpopulations that are largely restricted to Florida Bay. Other bird species include , seagulls, , , , , and .
Bay land animals include , , , and .
Blue-green algae causes numerous severe health consequences for the marine ecosystem as well surrounding human populations. Blooms result in reduced dissolved oxygen concentrations, alterations in aquatic food webs, algal scum lining the shores, the production of compounds that cause distasteful drinking water and fish flesh, and the production of toxins severe enough to poison aquatic as well as terrestrial organisms. Blooms have been reported throughout the continental United States, and resulting cyanotoxins have been associated with human and animal illness and death in at least 43 states.Hudnell, H.K., ed., 2008, Cyanobacterial harmful algal blooms– State of the science and research needs: Advances in Experi- mental Medicine and Biology, v. 619, 950 p. Most cyanobacteria produce the neurotoxin beta-N-methylamino-l-alanine (BMAA) that has been implicated as a significant environmental risk in the development of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). The cyanobacteria has also been linked to liver cancer, chronic fatigue illness, skin rashes, abdominal cramps, nausea, diarrhea and vomiting.
The 2002 algal bloom in the central portion of the Florida Bay was associated with high concentrations of dissolved organic nitrogen and organic phosphorus, whereas the eastern bay regions bloom was associated with high concentration of inorganic nutrients.
The cyanobacteria create an oxygen-free environment teaming with toxic gases, creating an unsuitable living environment for many marine and terrestrial animal species.David Biello, (2008). " Oceanic Dead Zones Continue to Spread". Scientific American As a result, seasons during which algal blooms flourish cause a temporary loss in wildlife.
Spotted seatrout populations in the coasted Everglades are declining. As the second most commonly caught species of fish in the Florida Bay, spotted seatrout comprise a large portion of the fishing industry and are integral to the ecosystem as well as surrounding economy. Water temperature of less than and salinity levels below 37.5 parts per thousand (ppt) are ideal for seatrout spawning; however, water management stations in the Everglades and Florida Bay reported salinity levels of 64.4 ppt in July 2015 and recorded water temperatures of up to . 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.
/ref> Boating in Florida Bay off the Intracoastal Waterway is considered challenging, because of shallow depths, mud, and seagrass.U.S. National Park Service.
"Florida Bay, Everglades National Park."
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