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Comprehensive Plan Conservation Element The ecology of drift algae and its value to the productivity of the IRL have only recently come under review. These recent studies were limited to drift algae communities associated with SAV. Studies concerning drift algae communities not associated with SAV have yet to be published, but the drift algae habitat is believed to significantly contribute to the primary productivity, standing crop, and overall complexity of the IRL system. • Submerged Aquatic Vegetation Submerged aquatic vegetation (SAV) consists of submergent flowering plants (seagrasses) and algae that live underwater, produce oxygen and recycle nutrients. Seagrasses require sunlight to grow; therefore, the depth at which seagrasses are found is limited by water clarity. Within Indian River County, it is estimated that approximately 2,930 acres, or approximately 18 percent of the total ±16,300 acre IRL, are covered by SAV. Seagrasses in the Indian River Lagoon are important natural resources that perform many significant functions: 1) they help maintain water clarity by trapping fine sediments and particles with their leaves; 2) they stabilize the lagoon bottom with their roots; 3) they provide habitat for the fish, crustaceans and shellfish that thrive within the lagoon; 4) they provide a habitat for organisms that grow on them and serve as food sources for many marine animals; and, most importantly, 5) they are nursery areas for many species of marine life, over 80 of which are vital to the local fish and shellfish industries. Within the IRL, moderate SAV coverage extends south of Sebastian Inlet to Johns Island. Due to reduced water quality, SAV communities are sparse north of the 17th Street Bridge and within the City limits of Vero Beach. In Indian River County, the most extensive and lush beds of seagrasses are found just north of the Indian River -St. Lucie County line. Figures 8.20 (A -G) identify the location and relative abundance of seagrasses within the IRL. There are seven (7) species of seagrasses within the M. In relative order of abundance, these grasses are manatee grass (Syringodium Filiforme), shoal grass, (Halodule wrightii), Johnson's grass (Halophila johnsonii), turtle grass (Thalassia testudinum), paddle grass (Halophila decipiens), star grass, (Halophila englemanni) and widgeon grass, (Ruppia maritima). These seagrasses are depicted in Figure 8.21. Syringodium is the most abundant seagrass, and is generally densest and most dominant in the mid - depth range of one foot to three feet. Halodule is the second most abundant seagrass, and generally dominates the shallowest zone - just below the intertidal region to a depth of approximately one foot. Ruppia occurs in scattered beds in the shallow regions of the IRL with Halodule. Halophila decipiens is also a relatively abundant SAV species. Thalassia is the most robust species, is supposedly the dominant species in a successional sense, is usually located in the mid -depth range, and is occasionally found at depths down to six (6) feet. The northern limit of Thalassia is the Sebastian Inlet. The species, however, is most often located near the Indian River County -St. Lucie County line. Halophila johnsonni is the rarest species of SAV. Community Development Department Indian River County 62