Figure 1: Underwater images of artificial reefs (A, B) and natural reefs (C, D) on the southeast US continental shelf. (A) Artificial reef created by a ship. (B) Artificial reef formed from a train boxcar. (C) High-relief rocky reef. (D) Low-relief rocky reef. Photos by John McCord/Coastal Studies Institute (A), Cory Ames/NCCOS (B), Dave Sybert (C, D). From Steward et al. 2022.

Increasing human uses of the ocean have led to the co-occurrence of both natural and artificial habitats, like reefs, across the seafloor. However, the distribution and extent of these two types of reef habitats (Figure 1) are not well understood, but are necessary pieces of information for ocean planning and resource management decisions.

A new study by NOAA’s National Centers for Coastal Ocean Science (NCCOS), NOAA Southeast Fisheries Science Center (SEFSC), Duke University, and state agencies calculates the amount of seafloor in the southeastern US (Figure 2) covered by artificial versus natural reefs. They found that artificial reefs cover several orders of magnitude less area on the seafloor than natural reefs.

Figure 2: Map of the study region from Cape Hatteras, NC to St. Lucie, FL. Artificial versus
natural reef extents were compared across the whole region and also by depth and by state.
Basemap credit: GEBCO / NOAA NCEI. Adapted from Steward et al. 2022.

The team partnered with state resource management agencies from North Carolina, South Carolina, Georgia, and Florida to first calculate the footprint of artificial reefs and determined that artificial reefs occupy <0.01 percent (1.2 mi², or about 560 American football fields) of the region. To our knowledge, this represents the first estimate of artificial reef extent in the region.

Seafloor mapping data and previously published models were then used to calculate natural reef extent, indicating that natural reefs constitute 2.6 percent (just over 1,000 mi², or about the size of Rhode Island) of the study region. This refines previous estimates of natural reef coverage in the area, which ranged from 3 - 30 percent, using the best available data.

By providing the first calculations of artificial versus natural reef extent in the region, this study helps fill information gaps regarding reef habitat coverage and provides support for fisheries and ecosystem-based management. It also exposes the need for expansive seafloor mapping and characterization efforts to help refine reef coverage estimates in the southeast US and in other regions of the country.

Citation: D.N. Steward, A.B. Paxton, N.M. Bacheler, C.M. Schobernd, K. Mille, J. Renchen, Z. Harrison, J. Byrum, R. Martore, C. Brinton, K.L. Riley, J.C. Taylor, and G.T. Kellison. 2022. Quantifying spatial extents of artificial versus natural reefs in the seascape. Frontiers in Marine Science 9: 980384. DOI: 10.3389/fmars.2022.980384.