The U.S. Army Corps of Engineers, Jacksonville District announces the release and posting of the Miami Harbor Deepening Project one-year post-construction assessment for hard-bottom middle and outer reef benthic communities. The report includes data relevant to an assessment of temporary and permanent project effects at channel-side sites as per the Florida Department of Environmental Protection (FDEP) permit conditions for construction.
The overarching goal of the monitoring plan is to assess status and trends of physical (e.g. sedimentation) and biological responses to construction activities.
To assess project effects, scientists examine the before (pre-construction baseline) and after (post-construction) condition of the area, as well as compare a control (reference site) with the impact site (restoration site). Before and after sampling helps to determine how the construction project changed the site through time from its existing or baseline condition. Control and Impact sampling allows scientists to discern the effects of construction actions from natural variability, random events, and underlying trends in the larger area.
Scientists compared the Miami Harbor project’s one-year post construction surveys with baseline surveys at 19 permanent monitoring stations located at channel-side locations and control sites. The FDEP identified the permanent monitoring stations.
The report focuses on impacts to channel-side hard-bottom communities, including corals, octocorals, sponges and other benthic invertebrates. Scientists studied thousands of photos and videos, and hundreds of hours of dive-time observations from more than 7,000 dives.
The Corps is awaiting data relevant to potential effects of project sedimentation on hard-bottom communities outside the channel. Results are anticipated in late summer.
The report highlights:
Project effects were documented as an increased percentage of sediment cover at channel-side sites as compared with control sites.
Six of 224 channel-side tagged corals (2.7%) were buried as a direct result of sediment accumulation during dredging and is considered a permanent impact of the project. This is a representative statistic and does not include all channel-side corals. Divers had previously removed identified staghorn coral from the near channel area.
Partial mortality associated with sediment affected, on average, about 65% of corals across the nine channel-side sites. Partial mortality related to sediment also affected about 19% of the corals at the ten control sites. Roughly 46% of corals at the channel-side sites experienced partial mortality that can be attributed to the dredging project. On average, corals affected by partial mortality at both the channel-side and control site lost 13% or less of their live tissue.
Significant coral mortality associated with regional white-plaque coral disease and coral bleaching was documented at channel-side and control sites over the course of the project (monitoring began in 2014).
In addition, the report highlights mitigation details, including more than 2 acres of surplus artificial reef (nearly 12 acres created in total); moving and out-planting 3,099 fragment colonies of listed species and 924 colonies of non-listed species; and enabling the removal of 643 additional colonies and 50 large sponges.
This is one of two assessment surveys for the project site. The other survey is designed to assess impacts that may have occurred farther afield than the channel side locations. The Corps is also conducting a sediment tracer study that is key to potentially drawing conclusions to the status and trends of the physical environment. Officials anticipate those study results in the fall.
Once all data collection and assessments are complete, the Corps will continue to work in partnership with FDEP and National Marine Fisheries Services to analyze the data and determine the permanent, as opposed to transient, effects of the deepening project, the success of the mitigation efforts, and the need, if any, for additional mitigation.
The report is posted on the District website at www.saj.usace.army.mil, click Ports at right, click Miami Harbor Deepening at right.