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Group of manatees in Homosassa Springs

Manatees inhabit rivers, bays, canals, estuaries and coastal areas moving freely between fresh, saline and brackish waters.  Florida estuaries and freshwater lakes, springs and rivers provide extensive beds of seagrass and abundant freshwater aquatic vegetation that provide the manatee’s primary food sources. Just as important is warm water habitat. Manatees cannot tolerate prolonged exposure to very cold water (below 68º F), and in the winter will migrate to areas of warm water for survival. To help sustain a healthy population of manatees in Florida, FWC, along with other partners and stakeholders, work together to manage the protection of Florida’s seagrass and warm water habitat resources. 

Aquatic Vegetation:

Syringodium thalassia

Manatees are herbivores and feed on a variety of submerged, emergent and floating plants.  These plants not only provide food to Florida’s manatees, but are also an important component of marine and freshwater ecosystems.

Freshwater Aquatic Vegetation
Hundreds of plant species inhabit Florida’s freshwater environments, providing an important food source for manatees.  Some common freshwater plants manatees are known to eat include Eelgrass and Coontail along with exotic species like Water hyacinth and Hydrilla.

Seagrasses are underwater flowering plants that live in Florida’s protected bays, lagoons, and other shallow coastal waters. Because seagrass requires sunlight, most seagrass is found in clear shallow waters. These grass-like plants form small patchy beds that develop into large continuous beds known as seagrass meadows. Manatees are known to consume all species of seagrass found in Florida, including Manatee grass, Turtle grass, Shoal grass, and others.

Importance of Aquatic Vegetation

  • Provide food and habitat for fish and wildlife
  • Increase water clarity
  • Stabilize sediments and shorelines
  • Affect nutrient cycles
  • Support local economies

Learn more about how seagrasses are a vital part of the marine ecosystem.

Threats to Aquatic Vegetation

Reduced water quality due to:

  • Dredging of waterways
  • Removal of shoreline vegetation and construction of seawalls
  • Excessive nutrient run-off from land (leading cause of phytoplankton blooms)
  • Shading from docks
  • Increased sediments from shoreline and off-shore construction
  • Propeller scars (“prop” scars)

Aquatic Vegetation Protection Efforts

biologists surveying seagrass beds

Seagrasses and freshwater aquatic vegetation grow throughout Florida’s waterbodies and are vital to the state’s economy due to the fishing and tourism industries that rely on the fish and wildlife that are dependent on this habitat for survival. Conservation and protection of aquatic vegetation involves many citizens, stakeholders and partners from government and industry. These conservation efforts include:

Related Review: Manatee Habitat and Human-related Threats to Seagrass in Florida: A Review

How you can help:

  • Practice smart boating by avoiding navigation through shallow grass beds.
  • Avoid contributing to the problem of changing water chemistry through run-off, be careful when applying fertilizers and pesticides.  Rain can wash excess chemicals into rivers or other water bodies which drain into the sea.
  • Use grating rather than planks when building or repairing a dock.  Grating allows sunlight to penetrate to grasses living below docks.
Herd of manatees
Kayakers in Three Sisters Springs
Group of manatees at CCEC's warm water aggregation area

Warm Water Refuges:

Manatees seek out warm water areas whenever the water temperature drops below about 68º F. Warm water refuges in Florida can come from natural sources, such as freshwater or Sulphur springs, or artificial warm water from power plant/energy center outfalls. The water temperature in these refuges must be consistent and reliable in order for manatees to seek out and reuse these sites on an annual basis.

Importance of Warm Water to Manatees

Manatees are regarded as tropical marine mammals, migrating to warmer waters during the colder months of the year. In the summer months, manatees are widely dispersed in Florida’s waterways and can even be found on rare occasions as far north as Massachusetts. When the water temperatures dip below about 68 o F (20 C), however, manatees seek out Florida’s warm water areas. Prolonged exposure to lower water temperatures causes manatees to lose body heat and inadequately digest their food, which can lead to a condition classified as "cold stress" and eventually can be fatal.

Historically, manatees relied solely on warm water springs and other natural areas for refuge in winter. With the advent of power plants and other industrial sources of warm water effluent, many manatees began using these discharge basins as winter refuges. It is estimated that currently about 60% of the manatee population is dependent upon industrial sources of warm water with many hundreds being found together at some sites during the cold season. Loss of warm water habitat is a serious long-term threat to manatees.

Link: Where are Florida's manatees

Threats to Warm Water Refuge Areas

Although climatic conditions affect spring flows greatly, human use of the aquifer water supplied to springs can reduce the warm water habitat available to manatees and other wildlife using the spring run. While human population growth within a spring basin is anticipated, and increasing demands on consumptive use of aquifer water may be reflected in proposed regional 20-year municipal water use plans, impacts like this are a concern because the withdrawal levels could reduce spring flows to levels that would not provide the volume of warm water necessary to support manatees during winter months.

Port Facilities and InletsThe development, maintenance and expansion of port facilities and inlets represent significant threats to the Florida manatee population due to alteration of habitat, habitat use patterns and direct physical threats from dredging, material transport, vessel access, blasting and other construction activities. It is of paramount importance to review all port and inlet projects with a responsible eye toward manatee and manatee habitat protection.

Many power plants may be retired in the coming years and the loss of these major warm water refuges could increase manatee cold-stress related deaths. It is crucial to have warm water alternatives, such as restored natural springs systems, before power plants go offline.

Warm Water Protection and Restoration Efforts

Mother and calf manatee in the St. Marks River

The FWC and U.S. Fish and Wildlife Service jointly developed the Manatee Warm-Water Habitat Action Plan which includes an overview of Florida’s natural and artificial warm-water sites and provides guidance for research and management of these habitats into the future.

  1. Establish minimum flows at Florida springs that protect the warm-water habitat
    requirements of manatees.
  2. Develop and implement plans to prevent significant future manatee mortality caused by potential changes in power plant operation.
  3. Enhance protection and restoration of seagrasses and freshwater vegetation in proximity to warm water habitats.
  4. Improve manatee access to natural spring systems.

Summary of Artificial Warm Water Refugia Issues - This is a synopsis of the FWC's endeavors regarding the topic of artificial warm water refuges.

The Effects of Proposed Restoration of the Ocklawaha River in the Vicinity of the Rodman Basin on Manatees and Manatee Habitat - This report summarizes the history of Rodman Reservoir, historical manatee use, mortality and habitat information for this reservoir and the previously free-flowing Ocklawaha River, and predicted effects on manatee habitat quality and regional manatee populations using this system after planned restoration efforts are completed.

Manatee Foraging Behavior near Warm Water Refuges

It has been speculated that during the winter manatees may be limited to foraging in close proximity to a thermal refuge due to their reliance on warm water. If this is typical manatee behavior it would be reasonable to assume that as the winter progresses food resources near the refuge would become depleted, resulting in manatees moving progressively further away from the refuge to other foraging sites.