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Natural Communities of Indian River Lagoon Aquatic Preserves Quick Topics

The Indian River Lagoon Aquatic Preserves straddle the boundary between a temperate zone and tropical/subtropical zone. This is roughly equivalent to the ten year freeze line, meaning that at least one extreme cold event is likely to happen each decade. As a result, the IRLAP represents an ecotone where flora and fauna of each province overlap. However, the conditions can be extreme in other ways.

The Indian River Lagoon is generally shallow with an average depth of four feet. Therefore, its capacity to store heat over time is relatively small. Water temperatures will rise sharply in summer, and decrease markedly during winter. However, temperatures at the bottom and surface tend to be very similar. Rainfall and temperature extremes of this shallow system directly modify salinity levels as well. During an extended drought in the spring and early summer of 2011, salinity levels in most of the lagoon exceeded that of the ocean.

General descriptions of these natural communities are available at Florida Natural Areas Inventory through links at the start of each community. The following describes the specific condition of the natural community at Indian River Lagoon Aquatic Preserves System. Click on the images for a larger image.

Algal Bed - Estuarine algal beds are floral-based natural communities. However, harmful algal blooms (HABs) of Aureoumbra lagunensis, Karenia brevis and Pryodium bahamense and cyanobacteria (blue-green algae) have been reported in the IRLAP System. Cultural eutrophication has resulted in increased frequency and intensity of harmful algal blooms. HABs such as the "Superbloom" of 2011 can result in the loss of seagrass communities, but seagrasses are rebounding.

Blackwater Stream  - There are two major tributaries within the aquatic preserves' boundaries of the IRLAP System which are characterized as blackwater stream. These include the St. Sebastian River and Turkey Creek, both located within Indian River-Malabar to Vero Beach Aquatic Preserve. Like many blackwater streams, the St. Sebastian River and Turkey Creek have been significantly altered for stormwater management. The construction of the Fellsmere Canal and the C-54 Canal eliminated the historic west prong of the St. Sebastian River and facilitated the discharge of large volumes of freshwater and nutrient-laden runoff from agricultural lands into the IRLAP System. The upper reaches of the north prong were canalized and most of the associated wetlands north of the preserve were developed for residential uses or converted to agricultural lands. Residential and agricultural development has occurred along most of the south prong. Turkey Creek has been impacted by the development of the Melbourne-Tillman Water Control District and associated C-1 Canal. As a result of these flood control efforts, Turkey Creek now serves as the primary conveyance of freshwater draining from the historic St. Johns River floodplain into the IRLAP System.

Turtlegrass in sandComposite Substrate - Typical combinations of plants, animals and substrates representing composite substrates include soft and stony corals with sponges on a hard bottom such as coquina outcrops (limited to the southern end of Jensen Beach to Jupiter Inlet Aquatic Preserve); psammophytic (grows in sand or sandy soil) algae and seagrasses scattered over a sand bottom; and patch reefs throughout a coralline algal bottom. Any of the remaining natural communities can grade into composite substrate communities. Management requirements are negligible, providing the composite community is adequately protected. Protection efforts will vary slightly based on components of the composite substrate community. Generally, degradation of physical and chemical water quality parameters should be prevented, as well as mechanical disturbance from anchoring, dredging, trawling and similar activities.

Freshwater Tidal Swamp -  A small portion of the IRLAP System is classified as freshwater tidal swamp. This habitat type occurs along floodplains just inland (upstream) from the mangrove tidal swamps in Turkey Creek and the St. Sebastian River, both within Indian River-Malabar to Vero Beach Aquatic Preserve. The swamps are flooded twice daily in response to tidal cycles and are often fed by oxbows and sloughs. They are extremely vulnerable to hydrologic modifications and have been impacted by past dredging operations.

Red mangrove rootsMangrove Swamp - The northern extent of mangrove forests is limited to the 10-year freeze line, located in Brevard County. Freeze events during the winters of 1985, 1990, 2010, and 2011 killed mangroves in Banana River Aquatic Preserve. Generally, the four Florida mangrove species are distributed by elevation or zones defined by varying water levels. The red mangrove (Rhizophora mangle) occupies the lowest zone, the black mangrove (Avicennia germinans) the intermediate zone, and white mangrove (Laguncularia racemosa) and buttonwood (Conocapus erectus) occupying the highest zones. However, in the IRLAP System, zonation is rare in part beacuse sections of the IRLAP System are microtidal. Buttonwoods are usually the species found at slightly higher elevations.

Mollusk Reef - The IRLAP System has large expanses of mollusk reef along its shorelines and surrounding islands. The American oyster (Crassostrea virginica) is a recreationally and commercially important species that occupies hardbottom (consolidated substrates) in brackish and saltwater environments. Mollusks are filter feeders which clean the water, but can be overwhelmed by polluted waters and harmful algal blooms. Nearby pollution sources such as runoff, stormwater inputs, and sewage are usually the biggest threat.

Salt Marsh - Salt marshes are most abundant and extensive in Florida north of the normal freeze line, being largely displaced and interspersed among mangrove swamps south of that line. Consequently, the prevelance of salt marsh diminishes in a southerly direction throughout the IRLAP System. Furthermore, the disruption of hydric regimes caused by mosquito impoundments has resulted in large areas of salt marsh transitioning into monospecific mangrove swamps. The dominant species of salt marhses in the northern IRL are black needlerush (Juncus roemerianus) and smooth cordgrass (Spartina alterniflora) which usually form dense, uniform stands depending on the tide and elevation.

Manatee grass with epiphytesSeagrass Bed - Through the late 1990s, seagrass coverage in the IRLAP System had generally declined since 1943, the earliest year for mapped seagrass coverage.[1] A 1999 survey of seagrass coverage showed the highest acreage loss since 1943, up to 60 percent, was immediately north of Indian River-Malabar to Vero Beach Aquatic Preserve. Beginning in 2001, however, seagrass coverage began increasing steadily in areas which had been previously experiencing losses. The increases were attributed to depth-limit expansion of seagrasses, which appeared to be in response to modest increases in light availability.[2] In some cases, drastic seagrass loss and subsequent recovery can be part of a natural cycle. Scientists documented an event where more than 247 acres of seagrass in northern IRL completely disappeared from 1996 to 1997 and then recovered by 2000. However, in the 2011 Superbloom, seagrass declines far exceeded any past documented events in regards to geographic scale, bloom intensity and duration, and rate and magnitude of seagrass loss. By the end of 2011, overall seagrass bed coverage reduced by 60 percent. However, seagrass coverage has again rebounded, regaining approximately half of the lost acreage.

Spoil island SL14Spoil Islands - One of the most important biological components of the Indian River Lagoon is not a natural community at all. Spoil islands were created from dredge material, and consist of sand, shell, muck, and limestone rubble, but have evolved into ecological communities which significantly contribute to the biodiversity of the Indian River Lagoon. Much of the vegetation on spoil islands is exotic - primarily Brazilian pepper (Schinus terebinthifolius) and Australian pine (Casuarina spp.) - but numerous species of native fish, invertebrates, reptiles, birds and mammals inhabit the spoil islands. Notably, spoil islands support the majority of bird rookeries in the Indian River Lagoon. The shallow edges of spoil islands have been colonized by mangrove forest, salt marsh and seagrass beds, providing a base for restoration work. There are more than 120 spoil islands within the IRLAP System, most of which are owned by the state and managed by the IRLAP office.

Unconsolidated Substrate - Unconsolidated substrates are important in that they form the foundation for the development of other marine and estuarine natural communities when environmental conditions become appropriate. Disturbances directly affecting unconsolidated substrates within the IRLAP System include unmanaged anchorages and sunken/abandoned vessels, In addition, runoff from roads, stormwater discharges, and leachate from septic tanks can contaminate sediments which may kill infaunal organisms.

  1. Steward J.S., Brockmeyer, R., Gostel, P., Sime, P., & Van Arman, J. (2003). Indian River Lagoon Surface Water Improvement (SWIM) Plan, 2002 Update. St. Johns River Water Management District, Palatka, FL and South Florida Water Management District, West Palm Beach, FL.
  2. Robbins, B., Howard, B., Bachmann, L., & Penny, H. (2011). Summary Report for the Southern Indian River Lagoon System. In Seagrass Integrated Mapping and Monitoring Program for the State of Florida, Mapping and Monitoring Report No. 1. Yarbro, Laura A. and Paul R. Carlson Jr. (Eds). St. Petersburg, FL: Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute.

Indian River Lagoon Aquatic Preserves

If you want to help preserve the Indian River Lagoon, consider joining Friends of the Spoil Islands at http://friendsofspoilislands.org.

Last updated: November 10, 2016

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