Effects of Dredging on Seagrass Communities Adjacent to the Port of Miami 2005-2016

Two USGS projects sampled and surveyed in the same regions for spring and fall sampling seasons from 2005-2016. These projects studied the flora and fauna of southeast Florida. This paper will focus on the importance and impacts on seagrass communities in the North Biscayne Bay and the Port of Miami sample regions. USACE implemented the phase III Port of Miami dredging project to deepen channels and widen turning basins to allow larger container ships to enter the port. The dredging project occurred in close proximity to the sampling regions. Data will be compared from the earlier USGS project, which contains pre-dredging data, to the recent USGS project which contains during and post dredging data. Observations will be made to determine if dredging impacts adjacent seagrass communities. In each project sampling location, a 30-cell grid was utilized, creating 30 sample sites per location. A random sample was taken within each of the 30 grid cells. At each sample location, GPS coordinates were recorded along with environmental variables. Variables such as salinity, turbidity, temperature, sediment depth, and water depth were measured. One throw trap was utilized to measure fauna, and six quadrats were utilized to measure flora at each sample site. Within each quadrat, seagrass canopy height and abundance were measured. Seagrass was also identified down to the species. Seagrass canopy height, abundance-cover rating, turbidity, and sediment depth measurements were averaged per year for all sample years, location and season. The overall averages for sediment depth and turbidity showed a trend of being lower during the years before the dredging project and higher during the years during and after the dredging. The overall averages for canopy height and abundance-cover rating showed a trend of being higher in the years before the dredging and lower in the years during and after the dredging, but the trend was not always consistent. Comparisons between the two USGS projects display a negative relationship between dredging and seagrass communities, but not enough to fully support that dredging was the sole impactor on these seagrass communities. There are many environmental factors that may have affected turbidity and seagrass communities during the same time as the dredging project. For the future, fall 2016 data still needs to be collected. Once collected, perhaps more in depth statistical tests could be run on all the data to confirm trends