Animals and Plants of the Indian River Lagoon

The term “biodiversity” is shorthand for “biological diversity” and refers to the amount of variety we find in living organisms. Scientists typically measure biodiversity in three ways:

• Habitat diversity
• Genetic diversity
• Species diversity

Each biodiversity type links to the others’ health. Together, they comprise the wealth of ecosystems.

Florida has three species of mangroves: red (Rhizophora mangle), black (Avicennia germinans) and white (Laguncularia racemosa). Mangroves dominate the IRL shoreline in natural areas. They act as a habitat for numerous animals, such as by providing roosting and nesting areas for the lagoon’s birds.

Their leaves act as a food source for fiddler crabs, mullet and other animals. Roots are also important habitats for stationary creatures like oysters, mussels, sponges, tube worms and sea squirts that settle onto the roots. Well-developed mangrove areas provide protection from damaging hurricanes, help stabilize shorelines to prevent erosion and help trap sediments and pollutants running off from the land.

Seven species of seagrasses exist in the IRL, representing three primary families: Cymodoceaceae, Hydrocharitaceae and Ruppiaceae.

Seagrasses are sensitive to water quality conditions and tend to reflect these conditions in their growth habits. That’s why they’re excellent measures of overall lagoon health. When water is clean and clear, seagrasses grow well; if conditions deteriorate, they grow poorly and sometimes disappear.

They also provide critical habitat and nursery areas for estuarine animals. Most fishes in the lagoon spend at least part of their lives in seagrass habitats, where they can remain hidden from larger predators while finding ample food. Seagrasses enhance water quality by trapping sediments and removing nutrients from the water.

The lagoon’s wading birds represent two primary families: Ardeidae (herons and egrets) and Threskiornithidae (ibises and spoonbills), among others. Wading birds are important sentinel species because, as top predators, their health reflects the health of their prey species. In turn, those species’ health reflects overall habitat and water quality in the environment.

When wading birds are present in an estuary, it typically means water quality is good and supports ample food resources. Stormwater runoff, sediments and other pollution sources that cause muck deposits and other issues can reduce the abundance of invertebrates and fish that wading birds prey upon. When food becomes less available, these birds relocate to more suitable areas.

Ospreys (Pandion haliaetus), also called fish hawks, are distinctive residents that often build large nests atop dead trees or utility poles adjacent to the lagoon. Their diets consist almost exclusively of fish, which they hunt by plunging feet-first into water to grasp prey with their talons.

These birds form bonds with mates by performing aerial flight displays and by courting mates with food. Pairs may use the same nest site year after year, adding material to it each season to eventually produce a huge nest. Both partners incubate eggs, but once hatched, the female osprey remains in the nest to protect the young as the male brings food.

Scrub jays (Aphelocoma coerulescens) are endemic to Florida, meaning they’re a unique Florida species and found nowhere else. These birds are extremely habitat-specific and live only in sandy scrub habitats in the back-dunes of barrier islands and along the mainland coast. Dry, sandy soils and low-growing shrubs with few, if any, tall trees characterize scrub.

Florida scrub jays live in family groups and breed cooperatively, meaning some birds breed while others act as helpers to defend territory, raise young and stockpile food. They’re a threatened species, primarily due to the disappearance of suitable scrub habitats that are also prime areas for coastal development. Fewer than 5% of birds in a territory migrate further than 5 miles from where they were born.

Ten species of rays live in the IRL, including three species of stingrays: manta (Mobula birostris), spotted eagle (Aetobatus narinari) and cownose (Rhinoptera bonasus). Relatives of sharks, rays have evolved a flattened body. Rays can detect the electric field around other organisms and use this ability, along with excellent senses of touch and smell, to detect prey.

They eat invertebrates such as worms, crustaceans, bivalves and brittle stars. Many feed by settling on the bottom and lying motionless. If they detect prey, they excavate a shallow pit with their pectoral fins. This serves to both expose prey items buried in the sandy bottom and help contain prey once exposed.

The IRL is a vitally important nursery region for bull sharks (Carcharhinus leucas). Female bull sharks enter the IRL in the spring when they’re ready to give birth after carrying offspring for approximately 10–11 months. They bear between one and 13 pups, which are typically born in seagrass beds and near mangrove habitats.

They feed primarily on stingrays, fish and turtles. Most bull sharks in the lagoon measure less than 3 feet in length. Young sharks often remain in the IRL until they reach 6 feet in length, then migrate to offshore adult habitats. Mature bull sharks can reach 9-11 feet in length and weigh 500 pounds or more.

Manatees (Trichechus manatus latirostris), the IRL’s gentle giants, may reach an average of 8–10 feet in length and weigh 1,000 pounds. Most of a manatee’s diet consists of seagrasses and other aquatic plants, which they graze from the lagoon bottom. That’s why they’re also called “sea cows.”

It’s a misconception that manatees harm seagrasses by tearing up their roots. They seldom tear out the underground stems or roots from these plants. The Florida Fish and Wildlife Conservation Commission estimates that as of 2022, an estimated statewide abundance for manatees was 8,350–11,730. Of these, approximately 3,960–5,420 resided on the west coast and 3,940–6,980 on the east coast.

However, manatees remain vulnerable to a number of threats, including loss of habitat and feeding areas, cold stress, fishing gear entanglement and watercraft collision. An unusual mortality event was declared for manatees in 2021 when more than 1,100 manatees were lost to starvation in the IRL. The state closed this event in 2025.

Bottlenose dolphins (Tursiops truncatus) are a well-known and charismatic species and a common lagoon inhabitant. They may be full-time residents of the IRL or may visit it from time to time from offshore. They range from 6 to 12 feet in length and may weigh 300–1,400 pounds.

Dolphins can live more than 50 years, with females tending to outlive males. They operate singly or in groups that hunt cooperatively to feed on invertebrates and fish. Females carry their calves for 12 months and have an average of one calf every 3 years.

Five species of sea turtle live in Florida: green (Chelonia mydas), loggerhead (Caretta caretta), leatherback (Dermochelys coriacea), hawksbill (Eretmochelys imbricata) and Kemp’s ridley (Lepidochelys kempii). Most of the loggerhead population in the Atlantic nests on Florida’s beaches each year, forming the largest nesting concentration of loggerheads in the world.

The sea turtle diet varies widely. For example, green turtles are completely vegetarian as adults; hawksbill turtles feed primarily on sponges and other soft-bodied reef organisms. Loggerhead and Kemp’s ridley turtles have jaws that are adapted for crushing crabs, mollusks, shrimp and jellyfish prey. Leatherbacks have delicate jaws adapted for soft-bodied organisms like jellyfish.

The IRL is one of the premier inshore saltwater fishing areas in the U.S. and offers world-class game-fishing experiences to anglers of all abilities. Big gamefish like common snook (Centropomus undecimalis), tarpon (Megalops atlanticus), redfish (Sciaenops ocellatus) and seatrout (Salmonidae) are perhaps the most prized.

However, the lagoon’s diverse fish population offers a wide variety of desirable species. These include ladyfish, snapper, black drum, croakers and sheepshead, as well as many seasonal migratory species like flounder, bluefish, jacks and pompano.

About 160 species of bivalves inhabit the lagoon. These include clams, oysters, mussels, arks, cockles, coquina and other shellfish types. Bivalves are important to the lagoon because they remove small particles, algae and other materials from the water while feeding, helping improve water clarity.

Oysters (Crassostrea) have proven particularly important in this role. A single adult oyster in the IRL can filter approximately 20 gallons of water each day. Tens of thousands of oysters may inhabit an oyster reef, providing tremendous water quality benefits daily. In recent years, a number of organizations have developed robust, highly successful volunteer efforts focused on restoring filter feeders to the lagoon.

Terrapins (Emydidae) are unique because they prefer to live in the brackish salt marshes and mangroves of estuaries rather than in freshwater. They survive salty conditions by secreting excess salt from tear glands and by drinking rainwater.

In the late 1800s, humans hunted terrapins for turtle soup, and populations declined almost to the point of extinction. However, harvest limits helped terrapins recover. Today, terrapins face threats like habitat loss, drowning in crab traps and other fishing gear, and predation from racoons and other animals.

Eight species of fiddler crab (Ocypodidae) live in the IRL. Fiddler crabs are common along the lagoon’s shoreline and often feed in large groups. We can easily identify these tiny crustaceans by males’ unequal claws, with one greatly enlarged claw and one small claw.

Rather than helping the male fiddler crab feed, the large claw actually makes feeding more difficult because fiddlers are detritus feeders. This means they eat decaying mangrove leaves and aquatic plants, algae and bacteria. The male uses the large claw to attract females and to communicate with other males.

Females incubate their eggs for about 2 weeks inside a burrow in the sand. When the eggs are ready to hatch, the female returns to the surface to release them into the water.

Two species of pelicans exist in the IRL: brown pelicans (Pelecanus occidentalis), present year-round, and white pelicans (Pelecanus erythrorhynchos), visiting during the winter. They’re common throughout the lagoon region and often live in large groups when nesting on its spoil islands or resting in marina areas.

Brown pelicans feed almost exclusively on marine fish and crustaceans that they capture by diving head-first into water from heights of 20–45 feet. A brown pelican’s large bill pouch can hold about 3 gallons of water. The bird uses it like a dip net during prey capture and as a feeding trough for young pelicans learning how to capture food.