Seagrasses appear to maintain an active sulfur cycle (Wood, Odum, 

 and Zieman, 1969) . An accumulation of detritus leading to anaerobiosis 

 below the sediment surface and an abundance of sulfur bacteria lead to 

 this cycle. The thin, dxidized sediment surface layer promotes sulfate 

 accumulation, but sulfides are produced in the lower layers. Fenchel 

 (1973) found the decomposition of material in the underlying anaerobic 

 sediments slow but favoring the release of mineral nitrogen, phosphorous, 

 and readily assimilable organic ponstituents. 



Seagrass detritus is extremely important in nutrient cycling within 

 and across ecosystem boundaries. Detritus from decaying leaves is de- 

 posited in sediments in seagrass meadows, but may be flushed out of the 

 system. Fenchel (1977) reported that microbial decomposition of sea- 

 grass detritus is of prime importance in nutrient release and cycling. 

 Many nutrients are released as plant exudates during plant growth. 

 Bacteria form a film around detritus particles, enriching the particles 

 with nitrogen and phosphous which, in turn, provides enriched nutrients 

 for animal ingestion. 



6. Currents and Waves . 



Churchill, Cok, and Riner (1978) reported that tidal currents as low 

 as 0.82 knot (1.5 kilometers per hour) completely washed out trans- 

 plants of eelgrass sprigs within 3 months in dredged materials in Great 

 South Bay, New York. Plugs of eelgrass were washed away within 2 weeks 

 in currents of 1.3 knots (2.4 kilometers per hour) in Great South Bay. 

 In Puget Sound, Washington, some of the most vigorous eelgrass 

 flourished where tidal currents approached 3.5 knots. 



Shoalgrass plugs were presumably washed away by 2 weeks of heavy 

 surf with waves 4 to 6 feet (1.2 to 1.8 meters) high at Port St. Joe, 

 Florida (Phillips, Vincent, and Huffman, 1978). This occurred after 

 a year of excellent growth of the plants on dredged materials. Thorhaug 

 (1976) reported that heavy wave action and periodic boat wakes adversely 

 affect the establishment and growth of turtle grass seedlings. 



Eleuterius (1974) found that planting sites with bottom slopes 

 of more than 12° and heavy wave and current action did not favor the 

 establishment of turtle grass, shoalgrass, and manatee grass. He 

 added that submerged transplanting operations were hindered by wind 

 velocities above 8 knots (15 kU-lometers per hour) and that low tides 

 favored submerged transplanting. In the Mississippi Sound, anchors 

 were required for seagrass sprigs. Waves and currents washed all un- 

 anchored sprigs from control and dredged material sites. All transplants 

 in dredged materials failed because of instability of the bottom. 

 Erosion in the area was severe because of very strong tidal currents. 

 In one 6-month period, 24 inches (61 centimeters) of sand was deposited 

 over the transplants. Eleuterius (1974) reported that sediment deposi- 

 tion rates greater than 1 inch (2.5 centimeters) per month exceeded the 

 growth rates of turtle grass and manatee grass, and a deposition rate 

 greater than 2 inches (5 centimeters) per month exceeded the growth rate 

 of shoalgrass. He theorized that initial transplants could not adjust 

 to rapid increases in substrate elevation. He found that few transplants 

 were killed by moderate erosion rates of 2 inches per month or less. 



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