Florida Bay

Florida Bay: An Overview

Florida Bay Project Profile - 176

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Where is Florida Bay and why is it important?

Florida Bay is a shallow inner-shelf lagoon located at the southern end of the Florida peninsula adjacent to the freshwater Everglades. It is bordered to the east-southeast by the Florida Keys with its nearby coral reef community and to the west by the waters of the Gulf of Mexico. Most of the bay lies within the boundaries of Everglades National Park.

Florida Bay serves many valuable functions in the south Florida ecosystem. Its' nearly 1,000 square miles of interconnected basins, grassy mudbanks, and mangrove islands are nesting, nursery, and/or feeding grounds for a host of marine animals: the American crocodile, the West Indian manatee, the loggerhead sea turtle, and many gamefish. Parts of the bay are also the nursery grounds for the economically valuable pink shrimp and Caribbean spiny lobster.

What conditions characterize bay waters?

Different regions of the bay are influenced by different environmental conditions. The northern mangrove fringe and adjacent waters experience freshwater influxes from the surface waters flowing from the wetlands of the Everglades. This creates an estuarine environment with low salinity levels. Lacking the influence of freshwater inflow, the shallow interior region can experience salinity levels higher than normal seawater under dry, hot, conditions.

Bay waters are also affected by the carbonate sediments found on the bay bottom and banks. When these sediments are resuspended in the water column by storm-driven wave action, water clarity is reduced. In the late 1980's, the basins in the north central bay began to experience the loss of thousands of acres of seagrass, specifically turtle grass. This process not only released sediments originally trapped by the seagrasses, but the decaying grasses provided the nutrients necessary to fuel microalgal blooms which discolored surface waters and decreased water clarity. Sediments are resuspended more frequently during storm events and are a regular feature of the "mixed" bloom found in the western bay. Water quality biologists have documented the reduction in bloom intensity with the recovery of seagrass beds in recent years.

What led to the changes noted in the 1980's?

Geological studies indicate that variability in salinity levels, temperature, rainfall, and other factors is a feature of the natural system. However, the extreme environmental conditions prevailing in the 1980's were compounded by several activities which further reduced freshwater flows into the Everglades and Florida Bay. For years, surface waters on the mainland had been channeled away from the Everglades through an extensive canal drainage system. Additionally, numerous drinking wells dug into the porous limestone have lowered the underground water supply. Reduced freshwater input from the Everglades fostered marine, rather than estuarine conditions in the bay. Overcrowded turtle grass beds may have developed gradually over time because turtle grass thrives in marine, not estuarine, conditions.

The loss of turtle grass beds in the late 1980's is thought to have been triggered by a combination of physical and biological factors. South Florida was experiencing a regional drought which drove water temperatures to very high levels. This may have interfered with the metabolic balance of the grass shoots. High concentrations of toxic sulfides in the sediments probably reduced the amount of oxygen available to the plant's underground system. Crowding of the shoots may have made them more susceptible to extreme conditions and to a disease associated with dying plants. Although seagrass disease has spread to the western and southern bay in recent years, recolonization by certain algaes and grasses is taking place at some die-off sites.

What role does science play in the restoration process?

Research, guided by the Program Management Committee for Florida Bay and Adjacent Coastal Waters, provides managers with a better understanding of the ecological system. Federal, state, and local agencies are redesigning the drainage system and acquiring key wetlands to restore the flow of water to the Ever- glades. Computer models developed by scientists and engineers predict the effects of various restoration schemes on bay wildlife and water quality. Continued monitoring of the water quality, animal populations, and seagrass communities provides feedback about how well the plan is working and is essential to the restoration process.