areas, the effects on the local fauna may differ from species to species. 

 Changes in existing physical and chemical features of the borrow areas will 

 influence the short- and long-term effects on the fauna. Therefore, the 

 overall impacts of borrowing operations may differ greatly between areas. 



1. Physical Effects . 



Dredging of borrow pits increases the suspended sediments and turbidity of 

 the offshore water in the vicinity of the dredging operation. Courtenay, et al. 

 (1974) and Maragos, et al. (1977) described sediments suspended during offshore 

 dredging as generally localized and rapidly dissipating when dredging ceased. 

 Maragos, et al. (1977) noted that after dredging ceased the turbidity plume 

 remained visible for several hours, but usually dissipated by the following 

 morning. Factors that influence sediment spread and turbidities are water 

 currents and water depth. 



Another possible adverse effect associated with offshore dredging is the 

 change in the bottom topography by creating deep borrow areas. Fine sediments 

 may settle into the borrow pits, causing further changes in the composition of 

 the bottom. Many species of marine animals which are found closely associated 

 with specific sediment types may be excluded by sediment changes. Thorson 

 (1964) observed that bentViic fauna are sensitive to sediment composition and 

 will not settle until suitable substrate is contacted. Undesirable substrate 

 changes sometimes can be prevented by shallow dredging to minimize topographic 

 and sediment changes and keeping the substrate in the photic zone (Thompson, 

 1973; Pisapia, 1974) or by selecting borrow sites in unstable areas that are 

 under the influence of strong currents (Thompson, 1973; Saloman, Naughton, 

 and Taylor, 1982). In unstable areas, benthic populations are generally low 

 and are more adaptable to change. The borrow areas are also more likely to 

 fill and return to near predredging conditions if there is adequate transport 

 of sediments under the influence of strong currents, as observed at Panama City 

 Beach, Florida (Saloman, Naughton, and Taylor, 1982; Culter and Mahadevan, 1982). 



2 . Effects on Benthic Communities . 



The most serious impact of offshore dredging is the loss of major commercial 

 species of benthic shellfish or the damage to coral reefs. These damages can 

 be minimized by the proper selection of borrow areas and by precisely locating 

 dredging equipment to avoid sensitive resources. Repopulation of the dredged 

 area by benthic animals will depend on the magnitude of the disturbance, the 

 new surface sediment, and the water quality of the borrow site. The borrow 

 area will be recolonized by migration of organisms from adjacent areas; however, 

 the population may not be of the same magnitude or species diversity as it was 

 formally. The stability and bottom sediments at the site after dredging are 

 major factors in determining species recolonization. 



Several studies have assessed the faunal change in the vicinity of offshore 

 borrow sites. Applied Biology, Inc. (1979) performed a qualitative and quanti- 

 tative analysis of core samples from the vicinity of a borrow area in Duval 

 County, Florida. The density of individuals and number of taxa were studied 

 for 14 months. Mo clear differences in community parameters between control 

 and affected transects were found. Statistical comparisons showed an occa- 

 sional reduction in organisms from the vicinity of the borrow area. The authors 

 suggested these differences were related to natural variability in the substrate. 



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