Development of Guidelines for Dredged Material Disposal Based on Abiotic Determinants of Coral Reef Community Structure

To be protective of living marine resources the ocean disposal of dredged materials must be managed such that these activities do not significantly disrupt the natural environment upon which marine animal and plant communities depend. Two important controlling factors affecting the diversity, abundance and general health of hermatypic (stony) corals comprising reef communities in tropical and subtropical environments are sedimentation and the availability of sunlight for photosynthesis. Disposal activities result in residual sediment plumes which, when occurring near coral communities, can expose corals to increased suspended sediment levels and sedimentation rates and reduced light intensity. In order to avoid adverse impacts to corals, dredged material disposal guidelines should ensure that disposal activities do not add significantly to sedimentation and light attenuation caused by naturally occurring oceanographic and meteorological processes. The development of disposal guidelines requires an understanding of these processes and their influence on sedimentation and light availability. Studies of these processes are currently underway at the Miami, Florida Ocean Dredged material Disposal Site (ODMDS). Initial results of eight months of acoustical backscatter data collected from October 1998 to October 1999 suggest a marked seasonal difference in average natural background suspended sediment concentrations at reef locations inshore of the ODMDS. Fall seasonal averages were higher due in part to several hurricanes and tropical storms that caused high elevations of suspended sediments on reef communities for two to four day periods. Suspended sediment guidelines for dredged material disposal will depend on the importance of these major oceanographic and meteorological events as determining factors for coral reef structure and function.