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Title: Transplanting of the seagrasses Zostera marina and Halodule wrightii for sediment stabilization and habitat development on the East Coast of the United States
Authors: Fonseca, Mark S.
Kenworthy, W. Judson.
Thayer, Gordon W.
Heller, D. Y.
Cheap, K. M.
Keywords: Seagrasses
Sediment control
Soil stabilization
Publisher: Environmental Laboratory (U.S.)
U.S. Army Engineer Waterways Experiment Station.
Series/Report no.: Technical Report;EL-85-9
Abstract: There is little information on procedures for evaluating potential eelgrass (Z. marina) and shoalgrass (H. wrightii) planting sites. One major reason for the sparcity of information is that some critical environmental factors controlling eelgrass and shoalgrass growth are poorly documented for transplanting conditions. Study sites were selected which represent a wide range of environmental conditions under which eelgrass and shoalgrass locally occur. The environmental factors considered were temperature, salinity, light and depth, sediment characteristics, and hydraulic regime. Local temperature and salinity ranges were stenotypic across the sites, but light and depth and hydraulic regimes (which control sediment characteristics) displayed wide variations and had intrinsic control over the distribution of these two seagrasses. Annual temperature and salinity for all sites ranged from 9° to 29° C and 24 to 36 parts per thousand, respectively. Light and depth interactions produced light energy variations from 1.2 to 36 percent of incident photosynthetically active radiation. The hydraulic regimes of the study were described by currents ranging between sites from 2.5 to 92.0 cm/sec and sediment height changes up to 0.6 cm/day (50-day average). At sites which meet evaluation criteria, the mean vegetative growth rate of transplanted seagrass can be predicted. Actual on-site vegetative growth rates can vary from this mean by 25-50 percent because of local environmental conditions. Vegetative recovery of appropriate sites can be accelerated dramatically by use of eelgrass and shoalgrass transplanting techniques, often by time measured in years. Site design guidelines for sediment stabilization concentrate on placing nonchemically polluted material at an appropriate depth while maintaining the physical integrity of the site. Semienclosed embayments protected from prevailing winds are suggested as preferred planting sites. Unconsolidated sediments may be protected by artificial wave-dampening devices until seagrass transplants coalesce, as well as by conjunctive planting with other plant species across adjacent intertidal habitat. Transplant stocks for either species should consist of mature, vegetative shoots with rhizomes collected from high-current areas. Shoalgrass stock should have a high percentage of terminal meristems. Bundles of shoots are attached to anchors and planted. Equations are given for determining amount of transplant stock and spacing required to cover sites in a specified number of days. About 614 man-hours are required per acre of bottom planted, although this value may be considerably lower for some environments. Planting may be done by wading or SCUBA-assisted workers depending on water depth. The major value of seagrasses in sedimentary dynamics is stabilization, rather than accretion of sediments. In most natural seagrass meadows, sedimentary accretion appears to be balanced by erosion.
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