Abstract
Coral reefs are invaluable to the ecology and economy of Southeast Florida, yet they face numerous threats to their existence including climate change, bleaching, disease, and intense hurricanes. Turbidity and sediment deposition generated by dredging negatively impact corals by reducing their ability to feed both autotrophically and heterotrophically, reducing reproductive viability, and by smothering them. All these impacts deplete corals’ energy reserves to fight off other stressors, increase susceptibility to disease, and can result in partial to complete mortality of the colony. Port of Miami Expansion, a dredging project completed in 2015 to ensure safe passage for post-Panamax ships, resulted in unexpected and potentially catastrophic impacts to nearby reefs. Data from turbidity monitoring reports required during the project were mined and analyzed to evaluate if existing turbidity monitoring standards protect corals, and if new management practices can be developed to better protect corals in future dredging projects. While correlations of turbidity to sediment deposition during this project were insignificant, significant differences were found between turbidity produced by different dredges and ancillary equipment, before and after a quasi-baseline period, and before and after discontinuation of green valve use. Impact and background site measurements were interpolated within GIS and subtracted using map algebra to illustrate spatial patterns of background turbidity, turbidity after dredging, and turbidity levels above background. Turbidity monitoring for future projects could be improved by reducing the standard from 29 NTU above background, incorporating environmental windows (i.e. dredging in winter to avoid bleaching and spawning times), monitoring at night, incorporating data from MODIS satellites and LiDAR into monitoring, and using sensors to monitor suspended sediment in the water column and sediment deposition rates in real time. Monitoring should also include abiotic (i.e. light transmission, extinction coefficient) and biotic (berms, halos, and sediment accumulation on corals and sponges) factors that affect resource health. The turbidity story of Port of Miami can be used to build the foundation for the next chapter in effective dredging and coral reef management.