Summary: We characterized the habitat formed by dredge material disposed in sites designated by the EPA offshore of Fernandina Beach, FL using SCUBA assessments, multibeam mapping, and hydroacoustic sampling of the fish community. The data was used to assess the value of the habitat informing future placement and disposal strategies for dredged material. Our assessment methods will also be used in future monitoring efforts at Ocean Dredge Material Disposal Sites in the Southeast.

Why We Care

The US EPA Ocean Dumping Program is charged with managing ocean dumping of dredge materials and monitoring the condition and status of offshore dump sites designated for the disposal of dredged material from the maintenance and expansion of ports along the US Atlantic Coast.  These dumped materials can sometimes provide benefits in the form of created habitats such as rocky reefs.

EPA Region 4 has identified a number of projects in the Southeastern U.S. where habitat has been created from dredged material disposal. Better understanding the value of the habitat through proper assessment and the critical factors in the design of the habitat will improve our understanding of how to design future placement and disposal strategies for dredged material to maximum the value of the habitat created. Two dredged material created habitat areas have been identified within the South Atlantic Bight (SAB). One was unintentionally created in the western portion of the Fernandina Beach Ocean Dredged Material Disposal Site (ODMDS) offshore northeastern Florida. The EPA has conducted some preliminary acoustic and diver rapid assessments of this habitat as part of its routine ODMDS monitoring, but was only able to map 30% of the site.

What We Did

The National Centers for Coastal Ocean Science (NCCOS) collaborated with EPA Region 4 Water Protection Division of Coastal and Marine Resources and Wetland Enforcement Section to assess Ocean Dredge Material Dump Sites (ODMDS) as essential fish habitat off the coast of Fernandina Beach, FL. The objectives of this project were to:

• establish common monitoring protocols for assessing benthic biological habitats and fish communities comparable to surveys previously conducted in the southeast region;
• evaluate fishery acoustic surveys and metrics of remotely sensed fish density as measures of the habitat value and beneficial use of rocky dredge material disposed at the Fernandina Beach ODMDS.

NCCOS and EPA scientists conducted multiple cruises aboard the NOAA Ship Nancy Foster in 2016 surveying the Fernandina ODMDS with multibeam sonar, in-water diver surveys, and EK60 fishery acoustic sonar. Dive teams conducted biological and topographical assessments of the benthic and fish communities on sites identified on the bathymetry maps, focusing on man-made rocky features and natural ledges.

What We Found

The updated bathymetry maps of the entire ODMDS clearly delineated dump sites and natural features while also revealing the proximity of these structures. Complexity data derived from bathymetry were used in concert with the topography and rugosity information collected at depth. Although dump sites and natural ledges seemed very different at depth, structure metrics were not significantly different.

Sponges, tunicates, octocorals, and hard corals dominated the benthic community of all sites, although, benthic cover of each organism differed by habitat type. Dump sites hosted greater numbers of tunicates, octocorals, and Oculina sp. which contributed to the greater frequency of taller biota at these locations. The sponge was the dominant invertebrate on Natural ledges lending to the lower average biotic height of those sites. The differences in depth and nature of abiotic structure along with the turbid water are the most probable forcing factors determining the composition of the benthic communities in each habitat type.

The use of fishery acoustic surveys overcame some of the limitations of low visibility experienced during dive surveys due to multiple storm systems. Fish densities surveyed at night were much higher in the eastern portion of the survey area in a region where rocky ledges and outcrops were mixed with sand compared to the area around the disposal material.   Acoustic densities assessed during the day around the dive stations were highly variable, with generally higher densities associated with the natural ledge features. Though sample sizes of high rugosity disposal material were low, it appears that high-relief, high-rugosity disposal materials influences the habitat use by fish.  This initial finding suggests taller disposal sites may provide higher value to fishes.

The relatively close proximity, similar benthic community composition, and like fish acoustic densities of the natural and artificial reef features raises interesting questions on connectivity across the habitat mosaic and benthic organism substrate preference between the two types of features.