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ABOUT THE THOUSAND ISLANDS

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Article by Tim Kozusko
The first thought many people have when they see the Thousand Islands is that they are dredged. Though many of these islands have been modified by dredging, the Thousand Islands formation is natural. The Thousand Islands landform is probably the result of what is called a flood tide delta deposit. A flood tide delta forms when a storm surge cuts an inlet through a barrier island. The dune sand that has been washed into the lagoon is spread in a manner similar to the delta formed at the mouth of a river. A natural movement of sand called long-shore drift has since closed the inlet, but the islands remain. Two lines of evidence support this conclusion. First, visual evidence from aerial photographs points to a similarity in shape and general form between the Thousand Islands and known flood tide delta deposits. In Figure 1, aerial views of the Thousand Islands prior to significant modification and a recently deposited flood tide delta in North Carolina are compared. Similarities in general shape can be seen. Long-shore transport has since closed the inlet at Cocoa Beach, though a topographical low area still exists where the inlet probably once was.

Figure 1.
The Thousand Island (left) in 1956, before significant dredging, compared to a flood tide delta behind a barrier island in North Carolina. Cocoa Beach photo courtesy Brevard County Mosquito Control.
Figure 2.
Flood tide delta picture from Barrier Islands
S.P. Leatherman Ed., page 216.

Additionally, physical evidence from sediment cores indicates the presence of a sand layer consistent with a flood tide delta deposit. This is principally the existence of a layer of sand, free of the shells that are indicative of deposition in a normal lagoon-bottom environment. Shells are present in the upper approximately 10cm of sediment. Below this is a layer of varying thickness, comprised of sand, sometimes interspersed with pieces of woody vegetation. Below the sand layer, the cores generally exhibit the shell sand/silt layer similar to that found at the core surface. This uneven sand layer lacking shells suggests an interruption in the normal buildup of sediments by a rapid deposition of material being washed in by wave action. The date of this event is unknown. Since World War II, the Thousand Islands have been heavily impacted by development and mosquito control (Figure 2). Beginning around 1960, small ditches were dug through the islands to facilitate fish access to inner areas of the marsh for mosquito control. At about the same time, dredge and fill activities were begun in Cocoa Beach for housing development. This involved dredging of canals to provide fill material for houses. During the early 1970s deeper ditching by dragline was used as a stronger effort to control mosquitoes.

Figure 3.
Aerial view of Cocoa Beach during the 1980s.
Photo courtesy City of Cocoa Beach.

One effect of mosquito control dredging in the southern portion of the Thousand Islands is the creation of a maze of small canals that are useful for canoeing and kayaking. (Figure 3).

Figure 4.
Aerial view of a section of Thousand Islands showing canals.
Photo by T. Kozusko, July, 1999.

The vegetation communities of the Thousand Islands can be classified in three habitat types: natural marsh, dredge-spoil, and tropical hammock associated with shell middens. Of these three, the dredge-spoil community contains the highest plant diversity. This habitat also suffers the greatest degree of invasion by non-native plant species. Salt marsh in the Thousand Islands is somewhat different than in other areas of the Banana River Lagoon. Instead of the typical cord grass/needle rush plant community found on Merritt Island, Thousand Island salt marsh is dominated by succulent plants such as glasswort and saltwort. The islands are generally fringed by all three species of mangrove. Mangroves have three special adaptations for life in a flooded, salty environment. The can filter out salt, have special roots with which to acquire oxygen, and they don't produce seeds. The young plants germinate while on the parent tree. These adaptations allow them to thrive in salt marsh. However, freezing temperatures will kill them. The change in soils from wetland to upland resulting from spoil deposits allows upland plants to colonize areas previously tolerated only by species with adaptations to water-logged salty soils. The major non-native species found in this habitat are Brazilian pepper and Australian pine. However, the native species swamp privet and salt bush probably exhibit the greatest coverage. Shell middens are essentially garbage dumps left by the Ais people who lived in the area before the arrival of Europeans, and consist of discarded clam and oyster shells. The calcium in the shells changes the soil chemistry which allows tropical plants normally associated with the West Indies to colonize the islands where middens are found. Additionally, Central Brevard County lies in a transition zone between temperate climate to the north and subtropical to the south. These features allow species such as gumbo-limbo, stoppers, capers, and lead wood to grow among the mangroves.

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Figure 1. The Thousand Island (left) in 1956, before significant dredging, compared to a flood tide delta behind a barrier island in North Carolina. Cocoa Beach photo courtesy Brevard County Mosquito Control.	Figure 2. Flood tide delta picture from Barrier Islands S.P. Leatherman Ed., page 216.