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C_1 f Wiwi River County Manatee Protection nod ligating Safety Comprehensive Management Plan by even miner decreases in water clarity, which is now recognized as the predominant threat to seagrass communities. Therefore, the depth at which seagrasses are found is limited by water clarity. In 1989, an estimated 3,260 acres (1,320 hectares) of SAV existed throughout the portion of the IRL located in Indian River County. Factors affecting water column light transmission include turbidity, color, and shading of overwater structures. Causes of turbidity include nutrient enrichment, boat wakes, wind energy, coastal construction, stormwater runoff, and dredging. In Indian River County, extensive and lush beds of seagrasses are found south of the City Limits of Vero Beach, from Oslo Road and the Moorings to the south county line. The sparsest area of seagrass occurs within the City limits of Vero Beach. Figure 2 identifies the location and relative abundance of SAV within the IRI, (SJRWMD, 1969). A study of seagrass distribution, conducted in 1986 by Seagrass Ecosystem Anaiysts, determined that seagrass distribution patterns were primarily affected by water clarity and depth; with seagrass diversity correlated to distance from an inlet, and the highest diversity and densest coverage occurring near an inlet. SAV communities identified within the IRL include seven (7) species of seagrasses. In relative order of abundance, these scagrasses include: Cuban shoal grass (Halodule wrighl l), manatee grass (Syringodium ftl forme), turtle grass (Thalassia testudinum), widgeon grass,. (Ruppia marithna) paddle grass (Halopkila decipiens), star grass (Halophila englemanni) and Johnson's grass (Hal©phila johnsonfl). These seagrasses are illustrated in Figure 3. Studies suggest that the observed association of manatees and seagrass beds could be related to zonation of seagrass species by nutritive quality and/or density, or a preference by manatees to remain in deeper waters adjacent to their forage source (presumably to allow for avenues of escape). Additionally, studies have found that manatees prefer specific areas which have healthy seagrass beds adjacent to relatively deep water with little boat traffic. Generally, boat facilities have two potential direct impacts on scagrass habitat. During construction, the IRL's substrate is disturbed by installation of the pilings and water clarity declines due to siltation. Once completed, boat facilities and single-family docks create shade that has the potential to adversely affect existing seagrass beds or prevent the establishment of new seagrass beds. Older docks and roofed boat structures along the IRL that were constructed close to the mean high water line (MI-IWL) have resulted in degraded seagrass beds. Under Chapter 18-20, F.A.C., new boat facilities and single-family docks permitted in aquatic preserves are required to be elevated a minimum of five (5) feet above the MIIWL, where the dock crosses over a scagrass bed, and are required to be a maximum of four (4) feet in width to reduce shading potential. Also, walkway planking is required to be no more than eight (8) inches wide and spaced no less than one-half (112) inch apart to increase light penetration. Boat facilities also have significant indirect adverse effects. Dredging (both mechanically and via boat propellers) immediately adjacent to docks and the associated travel corridors to and from the docks may significantly affect seagrass beds if appropriate turbidity controls are not used. Additionally, the shading caused from moored boats and boats on boatlifts can substantially increase the associated seagrass damage. Community Development Department Page 11