Effects of Dredging-Induced Sedimentation and Turbidity on Two Species of Stony Corals of Southeast Florida

Sedimentation parameters, turbidity, extension (linear) growth, bleaching and polyp expansion were examined prior to, during, and after the dredge and fill activities associated with the first renourishment of Hollywood and Hallandale beaches, 1991. During the project, approximately 1.1 million cubic yards of beach compatible material was taken from two offshore borrow areas and placed on 5.3 miles of beach. Treatment stations were at offshore (adjacent to the borrow area) and nearshore (adjacent to fill area) locations. Control stations were placed at least 3km north, offshore of John U. Lloyd Beach State Recreation Area. Two coral species abundant in this area, Solenastrea bournoni and Dichocoenia stokesii, were monitored monthly on each reef for signs of bleaching and polyp expansion, indicators of stress and surface clearing ability respectively. After dredging was completed, the corals were collected for growth analysis (linear extension) by the Alizarin stain method. At treatment stations, associated with dredging, a significant decrease in extension growth rate in S. bournoni but not D. stokesii occurred. A decrease in fossa length of D. stokesii suggested that dredging effects caused a change in columella shape. Bleaching occurred in many of the colonies but may have been caused by an unknown factor. Polyp expansion, a means of sediment rejection, did not correlate with the proximity to dredging. The corals may be relying on other means of sediment removal. This study suggests that the effects of dredging on stony corals are species specific