Article

Mapping the largest known cold-water coral reef habitat

Multi-partner effort reveals full extent of reefs offshore south-east US

By Derek Sowers, Larry Mayer, Giuseppe Masetti, Kasey Cantwell • July 7, 2025

More than a decade of mapping and exploration work by federal, academic and private-sector partners has uncovered what has been deemed the largest deep-sea coral reef habitat mapped to date. Spanning an area of over 10,000 square miles (26,064km², about three times the size of Yellowstone National Park in the US), this underwater seascape of cold-water coral (CWC) mounds is located about 100 miles offshore the south-east United States coast in a region called the Blake Plateau.

The reefs were mapped at depths ranging from 655 to 3,280 feet (200 to 1,000 metres), beyond the sunlit euphotic zone. Unlike tropical coral reefs that rely on sunlight and photosynthesis, corals at these depths filter particles out of the water for food. The largest nearly continuous expanse of reef mounds extends 310 miles (500km) from Florida to South Carolina and at some points reaches 68 miles (110km) wide. Data also revealed several additional subregions on the plateau that also contain cold-water coral mounds. Across the entire expanse of the Blake Plateau, mapping analysis revealed 83,908 individual peak features – providing the first estimate of the overall number of potential cold-water coral mounds mapped in the region to date. The full results of this study, Mapping and Geomorphic Characterization of the Vast Cold-Water Coral Mounds of the Blake Plateau, have been published in the journal Geomatics (Sowers et al., 2024).

Figure 1: Bathymetric terrain model synthesis grid of the Blake Plateau CWC mound study region. The white polygon represents the core area (2,400mi2 / 6,215km2) of very dense and nearly continuous CWC mound features in the largest CWC province on the plateau. The black dotted line polygon represents the maximum extent of continuous CWC features in the largest province (10,063mi2 / 26,064km2). The solid black polygon shows the existing boundaries of the Stetson-Miami Deep Water Coral Habitat Area of Particular Concern. At this scale, individual coral mound features are not discernible. (Figure adapted from Sowers et al., 2024)

The Blake Plateau: a globally important hotspot for cold-water corals

Large cold-water coral mounds were first documented offshore the south-eastern US in the 1960s (Stetson et al., 1962). Since then, extensive research has been conducted by regional experts to discover new mounds throughout the Blake Plateau and to document the ecological importance of these habitats (e.g. Reed et al., 2006; Ross and Nizinski, 2007). Fisheries managers have used this information to protect known coral areas from physical damage. The recently completed mapping effort in the region builds on this foundational work by revealing the full extent and characteristics of these important deep-sea coral mound features.

The most common reef-building coral in the region is Desmophyllum pertusum (previously referenced in the literature as Lophelia pertusa). Healthy living corals of Desmophyllum pertusum appear white in colour. The white in this case does not indicate coral bleaching (unlike shallow-water corals).

Figure 2: Dense thicket of the cold-water coral reef habitat found on the Blake Plateau in the Atlantic Ocean. (Image courtesy: NOAA Ocean Exploration, Windows to the Deep 2019)

Coordinated mapping to assess the full extent of Blake Plateau reefs

Multibeam sonar systems have proven effective in mapping complex mound and reef habitats remotely from surface ship hull-mounted sonars, with resolution directly related to the depth of the seafloor and the angular resolution of the multibeam system.

Approximately 50% of US marine waters have still not been mapped in detail with multibeam sonars. The US has a national strategy for mapping, exploring and characterizing US waters (NOMEC), and this project is a great example of the benefits of this work and the partnerships necessary to complete such a massive undertaking. Mapping work and analysis on the Blake Plateau was completed as part of a coordinated, multi-year ocean exploration campaign involving NOAA Ocean Exploration, NOAA Ocean Exploration Cooperative Institute partners Ocean Exploration Trust and the University of New Hampshire, the Bureau of Ocean Energy Management, Temple University and the U.S. Geological Survey, with contributions from Fugro, the NOAA Deep Sea Coral Research and Technology Program and the South Atlantic Fishery Management Council.

The study area is nearly the size of Florida, and stretches approximately from Miami, Florida, to Charleston, South Carolina. Data from 31 separate multibeam sonar mapping surveys completed between 2003 and 2021 were synthesized into a seamless bathymetric terrain model with 35m grid resolution to accommodate all the data sources. The largest areas were covered by 17 expeditions led by NOAA Ocean Exploration on NOAA Ship Okeanos Explorer, five mapping surveys completed by NOAA Ship Nancy Foster, two expeditions led by the DEEP SEARCH project on NOAA Ship Ronald H. Brown and R/V Atlantis, and one mapping survey that Fugro vessel Brasilis completed for NOAA Ocean Exploration. The majority of multibeam sonar mapping completed on the Blake Plateau was conducted as part of the Atlantic Seafloor Partnership for Integrated Research and Exploration (ASPIRE) and the DEEP SEARCH: DEEP Sea Exploration to Advance Research on Coral/Canyon/Cold seep Habitats campaigns.

Figure 3: Example of what CWC mounds can look like in multibeam sonar bathymetry data. This oblique 3D perspective figure shows the bathymetry of the Richardson Mounds subregion of the Blake Plateau. Image created in QPS Fledermaus software with 4× vertical exaggeration. (Figure from Sowers et al., 2024)

Classifying the geomorphology of the seafloor

Beyond synthesizing all the mapping data on the Blake Plateau and identifying the largest continuous areas of CWC mound distribution, this study applied a repeatable and objective approach to characterizing the geomorphology at the scale of individual mound features as well as the region as a whole. An objective geomorphic landform classification of the region was derived from the bathymetry using the bathymetry- and reflectivity-based estimator for seafloor segmentation (BRESS) method (Masetti et al., 2018). The following landform types were selected to meet the study goals while enabling the classification of a continuous geomorphic map of the region: flat, slope, valley, ridge and peak.

23 submersible dives on the mound features, and found that coral rubble was the dominant substrate component within the peak, ridge and slope landforms explored, thereby validating the interpretation of these bathymetric features as cold-water coral mounds. Once peak features were classified from the bathymetry, ArcGIS Pro software was used to quickly quantify the overall number of peaks and calculate the areal coverage of each landform type. Cumulative areas were calculated for each of the five geomorphic landform classes: peaks (159mi² / 411km²), valleys (1,389mi² / 3,598km²), ridges (1,406mi² / 3,642km²), slopes (8,912mi² / 23,082km²) and flats (39,709mi² / 102,848km²).

The vertical relief of CWC mounds was deemed to be an important defining characteristic to quantify across the entire study area and within each subregion. Therefore, five metrics were calculated pertaining specifically to mound relief within each of these areas: minimum, maximum, mean, median and standard deviation. The complex geomorphology of eight subregions was characterized qualitatively with geomorphic ‘fingerprints’ and quantitatively by measurements of mound density and vertical relief. The median mound relief for the entire study region was 52 feet (16m), with individual mound features ranging 10–741ft (3–226m) above the adjacent seafloor. These results demonstrated that CWC mound spatial distribution, density, vertical relief and morphology varied greatly among subregions of the Blake Plateau.

Figure 4: A 3D view example of how input bathymetry data is classified into five different landform types using BRESS. The bathymetry and vertical relief of a typical mound feature is shown on the left, and the automatically classified landform features from BRESS (draped onto the bathymetry) are shown on the right. (Figure from Sowers et al., 2024)

The importance of the Blake Plateau cold-water corals

Cold-water coral reefs play an important role in recycling nutrients in the deep sea to support the surrounding ecosystem, sequestering carbon and providing a complex structure and hard substrate that provides a habitat for many associated corals, sponges, invertebrates and fishes (including commercially important species). They are therefore essential in supporting biodiversity, ocean health and recreational and commercial fisheries in the south-east US and beyond.

Cold-water coral habitats are slow-growing, long-lived and fragile, making them particularly vulnerable to physical damage from human activities that disturb the seafloor. Threats include trawling, hydrocarbon and mineral exploration and production, and cable and pipeline placements. The ecological importance and vulnerability of these deep-sea reefs has resulted in increased national and international efforts to map, characterize and protect them.

Even before the new mapping data was acquired, in response to improved information from many researchers in the region on the nature and distribution of CWC resources on the Blake Plateau, the South Atlantic Fishery Management Council (SAFMC) designated the Stetson/Miami Terrace Deep Water Coral Habitat Area of Particular Concern (HAPC) in 2010 to protect the seafloor in this area. The designation prohibits the use of bottom-contact fishing gear (bottom longline, bottom and mid-water trawl, dredge, pot and trap), anchoring by fishing vessels and possession of deep-water coral. Most coral mounds documented in this research are located within the protected area, but new mapping data revealed that 9.3% of mound features (7,782 individual mounds) are located outside the existing protection area boundary. All the information collected and presented in this study is public information and available to support informed management decisions.

Figure 5: Oblique perspective 3D views of a section of the core area of dense mounds in the largest expanse of corals. Bathymetry of mound features in metres (upper panel). Geomorphic landform classification draped onto the bathymetry (lower panel). Note the delineation of the white peak features from the rest of the CWC mounds (inset) to enable the enumeration of mounds. Figure created using QPS Fledermaus software with 7x vertical exaggeration. (Figure from Sowers et al., 2024)

Conclusion: implications for characterizing cold-water corals and other marine habitats

The global distribution of CWC species remains poorly understood, given that most of the global deep ocean is yet to be mapped or explored. The region of the Blake Plateau with the most dense and abundant coral mounds is directly underneath the massive marine food conveyor belt of the Gulf Stream current. This suggests that there may be other parts of the world with large cold-water coral mound ecosystems waiting to be discovered, associated with large and consistent ocean currents. The methods used in this study provide a pragmatic standardized approach for identifying, characterizing and quantifying CWC mound-forming habitats and could be applied to other CWC provinces to enable more direct comparisons among geographically diverse settings.

As more of the seafloor is mapped to modern standards through initiatives such as Seabed 2030 and NOMEC, newly generated datasets will be ripe for comprehensive geomorphic analysis. This study demonstrates the value of applying an objective automated terrain segmentation and classification approach to geomorphic characterization of a highly complex CWC mound province. Manual delineation of these features in a consistent repeatable way with a comparable level of detail would not have been possible. As inevitably larger regions of the oceans become mapped and explored, and the technological capability to map extensive seafloor features in high resolution with autonomous underwater vehicles expands, the importance of semi-automated classification approaches will only increase. Sole reliance on manual delineation and expert judgment is not a practical approach as datasets increase in size and complexity. Whereas traditional methods of geomorphological characterization can make it difficult to reproduce results across large ocean regions, this study highlights the benefits of applying an automated terrain analysis approach using repeatable methods and standardized terminology.

Acknowledgments
This research was made possible by years of dedicated investments in expedition planning and staff resources from NOAA Ocean Exploration. The data collected for this study represents countless hours of field data collection at sea by the dedicated officers, crew members and scientists of the vessels from which data was obtained.

References

Masetti, G., Mayer, L. A., & Ward, L. G. (2018). A Bathymetry- and Reflectivity-Based Approach for Seafloor Segmentation. Geosciences, 8(1), 14. https://doi.org/10.3390/geosciences8010014

Reed, J. K., Weaver, D. C., & Pomponi, S. A. (2006). Habitat and fauna of deep-water Lophelia pertusa coral reefs off the southeastern U.S.: Blake plateau, Straits of Florida, and Gulf of Mexico. Bull. Mar. Sci., 78, 343–375.

Ross, S. W., & Nizinski, M. S. (2007). State of deep coral ecosystems in the U.S. Southeast Region: Cape Hatteras to Southeastern Florida. In The State of Deep Coral Ecosystems of the United States; Lumsden, S. E., Hourigan, T. F., Bruckner, A. W., & Dorr, G., Eds.; NOAA Technical Memorandum CRCP 3; National Oceanic and Atmospheric Administration: Silver Spring, MD, USA; 239–269.

Sowers, D. C., Mayer, L. A., Masetti, G., Cordes, E., Gasbarro, R., Lobecker, E., Cantwell, K., Candio, S., Hoy, S., Malik, M. A., White, M., & Dornback, M. (2024). Mapping and Geomorphic Characterization of the Vast Cold-Water Coral Mounds of the Blake Plateau, Geomatics, 4(1), 17–47.

Stetson, Thomas R., Squires, Donald F., & Pratt, Richard Murray. (1962). Coral banks occurring in deep water on the Blake Plateau. American Museum of Natural History. https://www.biodiversitylibrary.org/bibliography/207174

Multimedia links:

Video about exploration of the Blake Plateau

NOAA Press Release

Figure 6: Geomorphic landform overview map with analysed CWC subregions labelled A–H, each with unique morphologies that were apparent after classification. Note how the landform map provides a strong immediate visual contrast between flat areas and complex terrain. Black circles show the location of submersible dives with video footage of the seafloor used to ground-truth substrates. (Figure from Sowers et al., 2024)

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