Overall Health Index

The report card compares 26 indicators (benthic infauna, chlorophyll a, crocodilians, emergent aquatic vegetation, fish, goldspotted killifish, gulf pipefish, invasive reptiles, lake stage, marl prairie, nonnative fish, oysters, periphyton, prey abundance, prey availability, prey community, ridge & slough landscape, roseate spoonbill nesting, salinity, spotted seatrout, submerged aquatic vegetation, tree islands, wading bird nesting abundance, wading bird nesting interval, wading birds, water clarity) to scientifically derived thresholds or goals. These indicators are combined into an Overall Health Index, for each region which is presented as a percent score. The four regions are combined into the overall Everglades Health Score.

Benthic Infauna

Benthic Fauna measures the diversity of the benthic community (e.g. clams and others) living in or on the soft bottom areas of the St. Lucie Estuary. These organisms are a key food source for many species and integral to the food chain.

See the results for benthic infauna in the Northern Estuaries.

Chlorophyll a

Chlorophyll a is the green pigment in tiny marine algae (phytoplankton) that produces food. Measuring chlorophyll is based on the amount of phytoplankton (microalgae), which uses both nitrogen and phosphorus to grow. Too much algae in the water reduces water clarity, and decomposing algae leads to reduced dissolved oxygen. In a balanced ecosystem, phytoplankton provide food for fish, crabs, oysters, and worms. When too many nutrients are available, phytoplankton may grow out of control and form algal blooms that can harm fish, shellfish, mammals, birds, and even people.

See the results for Chlorophyll a in the Northern Estuaries, Lake Okeechobee, or Southern Coastal Systems.


Crocodilians are an important part of the Everglades ecosystem and are considered a keystone species in South Florida. Crocodiles and alligators belong to a group of reptiles called crocodilians, which are the largest of the living reptiles. Of only 23 different species in the world, 2 species are native to the United States, in particular, south Florida. This is the only place where both species coexist. The American alligator (Alligator mississippiensis) ranges throughout the southeastern United States, and Everglades alligators exist at the southern end of their range. American Crocodiles (Crocodylus acutus), inhabit coastal areas of south Florida where they are at the northern end of their range.

See the results for crocodilians in the Greater Everglades or Southern Coastal Systems.

Emergent Aquatic Vegetation

Emergent aquatic vegetation is an indicator of the littoral marsh condition in Lake Okeechobee. The Lake Okeechobee littoral marsh consists of approximately 100,000 acres bounded by the Herbert Hoover Dike and the 10 ft NGVD bathymetric contour. The distribution and composition of plant communities within this area is primarily a function of water depth, as well as the interaction between water depth and horizontal mixing of turbid, nutrient enriched water from the pelagic zone. Emergent aquatic vegetation provides important habitat for birds and other organisms.

See the results for emergent aquatic vegetation in Lake Okeechobee.


Fish are important indicators in Lake Okeechobee.

Black crappie are one of the most popular sport fisheries on Lake Okeechobee and provide important economic value to the region. They are sensitive to changes in vegetation and food; cultural eutrophication negatively impacts this community by shifting larval and juvenile macroinvertebrate prey-base from preferred taxa such as chironomids (non-biting midges) to one dominated by less preferred oligochaete (annelid worm) taxa.

Largemouth bass are the most popular sport fish on Lake Okeechobee, providing enormous economic benefits to the region. Four key factors have been found to influence the recruitment of bass into the adult population: availability of favorable spawning substrate; protection of nests from wind; availability of epiphytic invertebrates, forage fish, and other food resources; and protection from predators. These aspects are all directly related to the presence of a structurally complex vegetative community as fish habitat.

See the results for fish in Lake Okeechobee.

Fish and Fish Dynamics are an important indicator in the Southern Coastal Systems.

Three key fish species for the Southwest Coast sub-region are: Common Snook (Centropomis undecimalis), Florida Largemouth Bass (Micropterus salmoides floridae), and Sunfishes (genus Lepomis). The first two are economically-valuable recreational fisheries in the Everglades, while the third constitutes an important prey source for them. This long-term dataset shows that the abundance of these species is highly seasonal, with a quadrupling of the Snook and Bass abundance between the wet and dry seasons, and a 12-fold increase in the abundance of Sunfish prey in the dry season. These dry season increases in abundance are driven by a) the displacement of marsh inhabitants into the estuary upon marsh drying (the Bass and Sunfishes), and b) the upstream movement of estuarine residents (the Snook). Snook move upstream to take advantage of this seasonal prey pulse which occurs most years, and they partition with Bass. Catches of all 3 groups in our monitoring are negatively related to stage, such that more fish are caught at the lower stages of the dry season, showing this immigration and co-occurrence of predators and prey at the headwaters of the Shark river at the peak low flows of the dry season.

See the results for fish in the Southern Coastal Systems.

Goldspotted Killifish

Goldspotted killifish are one of the important species that makes up the epifauna community in Biscayne Bay.

See the results for goldspotted killifish in the Southern Coastal Systems.

Gulf Pipefish

Gulf pipefish are one of the important species that makes up the epifauna community in Biscayne Bay.

See the results for gulf pipefish in the Southern Coastal Systems.

Invasive Reptiles

Burmese pythons, northern African pythons, Argentine black and white tegus, Nile monitors, and spectacled caiman are invasive reptiles in the Greater Everglades. They negatively impact the system by taking over areas from native species, and by consuming other organisms like fish and birds.

See the results for invasive reptiles in the Greater Everglades.

Lake Stage

Lake stage or the stage envelope is the level or depth of the water in Lake Okeechobee. Lake stage is an important indicator because it effects almost every aspect of the environment in Lake Okeechobee. While the upper reaches of the marsh tend to be completely dried for months during droughts, lower water levels in the nearshore zone, coupled with decreased mixing with turbid pelagic water, promotes vegetation and periphyton recovery; revitalizing the submerged aquatic vegetation, emergent plant, and epipelon communities at the deeper ends of the marsh. This leads to increased nutrient uptake, increased water clarity, and reductions in algal blooms, all of which constitute good habitat conditions for associated faunal communities. Conversely, exceedances above the stage envelope lead to declines in vegetation and periphyton abundance in the nearshore region and enable nutrient laden water to move farther into the interior marshes.

See the results for lake stage in Lake Okeechobee.

Marl Prairie

In the Everglades, both Shark River Slough and Taylor Slough are flanked by short hydroperiod (3–8 months) marl prairies, habitat of the endangered Cape Sable seaside sparrow. In the marl prairie landscape, a normal dry season is essential for its characteristic vegetation and habitat quality.

See the results for marl prairie in the Greater Everglades.

Nonnative Fish

Nonnative fish are species that are invasive. They take over habitat that native species need and can outcompete them. This can cause native species to decline and cause negative changes in the ecosystem dynamics.

See the results for nonnative fish in the Greater Everglades.


The eastern oyster (Crassostrea virginica) is a natural component of estuaries in south Florida and can provide water quality benefits including reduction of nutrients and particulate matter, and the control of phytoplankton. They also provide habitat and food for many estuarine species, and are an important commercial, recreational, and economic resource for coastal communities. Oyster reefs also protect shorelines by the attenuation of wave action and other perturbations from recreational boating.

See the results for oysters in the Northern Estuaries.


Periphyton is an important indicator in the Greater Everglades. Periphyton is a key metric of the oligotrophic nutrient status. When marshes receive phosphorus at concentrations exceeding background levels, the microbes (algae, bacteria, fungi) comprising the periphyton mats of the Everglades remove the added phosphorus from the water. A series of ecological changes ensues, beginning with a change in species comprising the periphyton. Mat-forming blue-green algae and diatoms that are only found in the Everglades and other similar Caribbean wetlands (endemic species) are replaced by “weedy” species that occur in phosphorus-enriched environments all over the world. When the endemic species are replaced, the mats disintegrate, resulting in a loss of calcareous periphyton mat biomass that provides habitat and food for aquatic animals. Ultimately, a cascade of changes occurs that result in a transition to a cattail-dominated marsh. Because all of these ecosystem transitions resulting in a degraded state can occur without a change in water phosphorus concentration, periphyton serves as an important early-warning indicator of water quality degradation.

See the results for periphyton in the Greater Everglades.

Prey Abundance

The abundance of small fish and crustaceans is a key metric of Everglades food webs because they feed iconic apex predators including wading birds and alligators. Diminished production and availability of fish and crustaceans during the critical nesting season has been linked to diminished nesting success of these key predators. Abundance of prey species is closely tied to hydrological variation and periphyton quantity and quality, which are sensitive to management actions affecting timing and quantity of water delivery and water quality. Small fish and crustaceans have short generation times, a year or less, and their abundance responds to hydrological management at an annual time scale, recovering from marsh drying events over three to seven years.

See the results for prey abundance in the Greater Everglades.

Prey Availability

The dry season prey concentrations project monitors the spatial patterns of aquatic fauna densities across the Everglades landscape. Of particular interest, are the inter-annual variation and correlations with local site characteristics, hydrologic patterns, wet season fauna production, and ultimately, predatory wading bird nesting numbers. This monitoring is based on the framework of the trophic hypothesis, which states that wading bird population size is limited by the availability of aquatic fauna that are, in turn, affected by hydrologic patterns and conditions.

See the results for prey availability in the Greater Everglades.

Prey Community

Prey community is an indicator in the Southern Coastal Systems in the Florida Bay sub-region. The prey community structure is simply the percentage of the fish prey base that are classified as freshwater species. This is based on the finding that prey are more abundant and have higher biomass when a significant component of all prey base fishes are freshwater species. Simply stated; prey productivity is greater at lower salinity and the presence of freshwater species is representative of that increased production.

See the results for prey community in the Southern Coastal Systems.

Ridge & Slough Landscape

Ridge and slough (R&S) landscape includes distinct linear sawgrass-dominated ridges that are oriented in the direction of predominant water flow and separated by a network of similarly oriented sloughs with sparse emergent, submerged, and floating-leaved plant species. In the pre-drainage Everglades, the R&S landscape had ridges ≥ 30 cm higher in elevation than the sloughs. A healthy R&S system is characterized by distinctness in vegetation composition, bimodality in elevation, and directionality in landform orientation. A deviation from this vegetation distinctness and elevation bimodality and loss of directionality represents degraded landscape. The degradation process might include the simultaneous decline in both topographic variation and vegetation distinctness, or degradation in one may be the leading indicator of future degradation in the other.

See the results for ridge and slough landscape in the Greater Everglades.

Roseate Spoonbill Nesting

Roseate spoonbills (Platelea ajaja) have been demonstrated to be an umbrella indicator species for Everglades restoration efforts that affect Florida Bay and metrics have been defined to assess the response of spoonbills to restoration efforts.

See the results for roseate spoonbill nesting in the Southern Coastal Systems.


Salinity levels are important in estuarine systems. To maintain a healthy, naturally diverse, well-balanced estuarine ecosystem, the salinity regime must be suitable for the species residing there. Altered salinity regimes adversely affected the ecosystems by; exposing local estuarine inhabitants to high freshwater inflows during the wet season, which leads to acute declines in species abundance, and allowing too little freshwater inflow during the dry season or drought periods, which leads to gradual increases in predation, disease, and mortality rates.

See the results for salinity in the Northern Estuaries or Southern Coastal Systems.

Spotted Seatrout

Spotted seatrout is an important sportfish in Florida Bay.

See the results for spotted seatrout in the Southern Coastal Systems.

Submerged Aquatic Vegetation

Aquatic grasses provide critical habitat to key species and can improve water clarity. Seagrasses are submerged plants found in shallow waters and are a critical part of the water that provide a number of benefits like buffering coastal communities from storms, removing pollution from the water, and providing shelter for animals.

See the results for submerged aquatic vegetation in the Northern Estuaries, Lake Okeechobee, or Southern Coastal Systems.

Tree Islands

Tree islands are an integral component of the Everglades, but they have undergone extensive damage from extreme flooding, drought, fire, tropical storms, and invasive species. These islands are also sensitive to ongoing small to large-scale restoration activities of the Comprehensive Everglades Restoration Plan. Changes in hydrologic regimes due to restoration projects, including construction of Tamiami Bridges and other Central Everglades Project Planning project components, are likely to alter the impact of drivers and stressors on tree islands. While such alterations in the impact of these stressors at the broader scale influence the spatial distribution pattern of tree islands within the landscape, the hydrologic alterations also affect the plant community structure and function on individual tree islands.

See the results for tree islands in the Greater Everglades.

Wading Bird Nesting Abundance

Wading birds are an important indicator of foraging and nesting habitat quality, which itself is affected by nutrients and hydrology, similar to other indicators. Long-term hydrological patterns and nutrient impairment affect the distribution and composition of vegetation used for foraging and nesting, while short-term hydrology affects prey densities and predator access to colonies. Important wading birds in Lake Okeechobee are Great Egret, Snowy Egret, and White Ibis.

See the results for wading bird nesting abundance in Lake Okeechobee.

Wading Bird Nesting Interval

Wading birds are an important indicator of foraging and nesting habitat quality, which itself is affected by nutrients and hydrology, similar to other indicators. Long-term hydrological patterns and nutrient impairment affect the distribution and composition of vegetation used for foraging and nesting, while short-term hydrology affects prey densities and predator access to colonies. Important wading birds in Lake Okeechobee are Great Egret, Snowy Egret, and White Ibis.

See the results for wading bird nesting interval in Lake Okeechobee.

Wading Birds

Wading birds are a key component of the Greater Everglades ecosystems. Some of the key species are Wood Stork, Great Egret, and White Ibis.

See the results for wading birds in the Greater Everglades.

Water Clarity

Water clarity is a measure of how much light penetrates though the water column. Water clarity is dependent upon the amount of particles (e.g. suspended sediment and plankton) and colored organic matter present. Clear water is especially critical for seagrasses since, like all plants, they need to be able to absorb the sun’s rays to grow. Excess sediment in the water reduces water clarity by blocking sunlight to seagrasses. Fish and other organisms in the water need aquatic grass habitat to thrive.

See the results for water clarity in Lake Okeechobee.