<^ 





Figure 26. Housing development in south Florida . Portions of this development were 

 built over a dredged and filled seagrass bed. This has historically been the most 

 common form of nan-induced disturbance to submerged seagrass meadows. 



Van Eepoel and Grigg (1970) found 

 that a decrease in the distribution and 

 abundance of seagrasses in Lindbergh Bay, 

 St. Thomas, U.S. Virgin Islands, was re- 

 lated to turbidity caused by dredging. In 

 1953 lush growths of turtle grass had been 

 recorded at depths up to 10 m (33 ft), but 

 by 1971 this species was restricted to 

 sparse patches usually occurring in water 

 2.5 m (8 ft) deep or less. A similar pat- 

 was observed by Grigg 

 Brewers Bay, St. Thomas. 

 Harbor, St. Croix, U.S. 

 removal of material 



tern of decline 

 et al. (1971) in 

 In Christiansted 

 Virgin Islands, 



dredging of a ship channel 

 landfill projects increased 

 volume by 14% from 1962 to 

 tion in areas adjacent to 

 caused extensive suffocation; 

 deeper water resulted, sediment 



conditions 

 growth. 



for 



combined with 



the harbor's 



1971. Silta- 



the channel 



and v;here 



and light 



became unsuitable for seaarass 



Reduced light penetration was obser- 

 ved in grassflats adjacent to the dredging 

 site of an intracoastal waterway in Red- 

 fish Bay, Texas (Odum 1963). Odum sug- 

 gested that subsequent decreases in pro- 

 ductivity of turtle grass reflected the 

 stress caused by suspended silts. Growth 

 increased the following year and Odum 

 attributed this to nutrients released from 

 the dredge material. While dredging 

 altered the 38-m (125-ft) long channel and 

 a 400 m (1300 ft) zone of spoil island and 

 adjacent beds, no permanent damage occur- 

 red to the seagrasses beyond this region. 



Studies of Boca Ciega Bay, Florida, 

 reveal the long-term impact of dredging 

 activities. Between 1950 and 1968 an 

 estimated 1,400 ha (3,453 acres) of the 

 bay were filled during projects involving 

 the construction of causeways and the 

 creation of new waterfront homesites. 



85 



