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Spoil Islands

Spoil islands are numerous along the Indian River Lagoon, and are composed of dredge spoil material resulting from the construction of navigation channels. The great majority of islands resulted from dredging associated with the Atlantic Intracoastal Waterway between 1951 and 1961, but many in Mosquito Lagoon are associated with dredging for the Canaveral and Saturn Barge Canals. The islands appear as mounds along the longitudinal axis of the lagoon, with varying degrees of vegetation cover and range in size from less than 1.2 acres to more than 7.5 acres.

Number of islands in different areas of the Lagoon

LocationNumber
Mosquito Lagoon 75
Brevard County 41
Indian River County 55
St. Lucie County 34
Martin County 7

Many spoil islands have developed into valuable and distinct habitats of the Indian River Lagoon. A survey by the Florida Department of Natural Resources (1990) listed 467 species of animals and plants occupying these islands. Species diversity and vegetation cover follows a latitudinal gradient increasing from north to south. Common native species include mangroves, cabbage palm, gumbo limbo, wax myrtle, live oak, strangler fig, and many herbaceous species. A common problem is the invasion of these substrates by exotic species such as Australian pines and Brazilian pepper. Seagrasses are often common along the shallows surrounding the islands.

Approximately 205 animal species were identified by the 1990 DNR survey. These included important invertebrates such as crabs, shrimp, and molluscs, as well as vertebrates such as fish, birds, and various mammals. Spoil islands house some of the most important bird rookeries in the Indian River Lagoon.

Ownership of the islands varies; the majority are owned by the State of Florida, whereas others are owned by Federal agencies, local governments, and private individuals. Management plans for the state-owned islands include "best use" designations for each island. These designations include:

  • Conservation
  • Passive Recreation
  • Education
  • Active Recreation
  • Combinations

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