Sedimentation caused by dredging can have detrimental effects on benthic habitats by limiting photosynthetic light, interfering with coral reproduction, and harboring deadly coral pathogens. While informative, most dive-based monitoring methods are limited in scope by only surveying stony corals. This study took a more holistic approach by developing a rapid dive-based survey protocol to assess dredging-induced sediment stress in stony corals, octocorals, and sponges in Southeast Florida.
For this comparative study, four reef habitat types/major coral reef features (Nearshore Ridge Complex [NRC], Inner Reef [IR], Middle Reef [MR], and Outer Reef [OR]) were chosen near Port Everglades and Port Miami in South Florida. Both of these ports are commercially important with a history of dredging and future expansion plans. Using stratified survey locations within the four reef habitats starting at approximately 100m north and south of the two dredged port channels, 54 surveys were conducted at Port Everglades while 42 surveys were conducted in Port Miami. Surveys took place between 2017 and 2023 in Port Everglades and in 2019 and 2022 in Port Miami. Divers conducted 30-m sediment depth transects measured at 1-m intervals, two 10-m belt transects to record visual signs of stress in corals, octocorals, and sponges (categorized as healthy, sediment-stressed, reduced condition, or dead), video documentation for quality control, and collection of surficial sediment samples for laboratory grain size analysis.
The results showed lower levels of benthic sediment accumulation and lower sediment-related biotic stress in Port Everglades, while Port Miami showed the opposite findings across the entire survey area, and higher proportions of fine-grained sediment. This was consistent with expectations for Port Miami (recently expanded in 2013 – 2015) versus Port Everglades, which has not been expanded since the 1980s. Notably, octocorals and sponges showed sediment stress similar to that of stony corals, highlighting the long-lasting detrimental effects of dredging on these biotic taxa.
Sedimentation patterns and biotic stress indicators also differed across reef habitats likely due to ocean current patterns, nearshore activities (i.e., beach restoration and terrestrial run-off), ocean outfalls, and weather/storm events. Though not considered a “rapid assessment tool”, analyzing grain size can offer valuable insights on the likely source of sedimentation (natural vs. anthropogenic) on coral reef habitats.
Overall, these findings suggest that rapid indicators of stress should include stony corals and other benthic taxa, such as octocorals and sponges, to improve the understanding of sediment disturbances, species-specific vulnerabilities, and the development of sediment thresholds for better adaptive management of dredging operations.
Management Implications
- Include other benthic taxa when conducting rapid assessments to help inform the development of sedimentation thresholds to use in adaptive management.
- Consider using rapid monitoring methods during active dredging operations to observe finer-scale patterns of sedimentation on benthic taxa.
- These methods can also be used for other major sediment disturbance events (e.g., terrestrial run-off or storm events).
- Refine the rapid-assessment methodology to align with project goals and conduct long-term monitoring to provide actionable data for adaptive management.
Author: Xaymara S.M., D. H. Chacin, K. Mack, K. Gregg, M. Parsons, M. Ladd, W. Lehmann, J. Wolfe, J. Karazsia
Year: 2026
Marine Pollution Bulletin. 222: 118629. doi: 10.1016/j.marpolbul.2025.118629
