Modeling Seafloor Structural Complexity

Science Center Objects

This effort focused on understanding the patterns and scalability of roughness and topographic complexity of marine habitats, such as coral reefs.

Topographic complexity (TC) is an important habitat characteristic that encompasses the three-dimensional intricacy of structural components. In aquatic habitats, topographic complexity influences a number of ecological and environmental aspects, such as regulating species richness, providing refuge from predators and physical stresses (e.g., light level, temperature, desiccation, and wave action), and presenting secondary growth surfaces. Moreover, these influences occur over multiple spatial scales.

For coral reefs, TC influences a wide range of biological, chemical, and physical aspects, such as water flow and, consequently, nutrient uptake and mass transfer rates, species richness and biomass, and both refuge and larval-settlement space. Because of these impacts, quantifying and mapping the spatial variability in TC is important to understanding the functioning of a coral reef ecosystem.

Effort was focused on developing algorithms for quantifying TC, with emphasis on fractal geometry principles. Studies have been completed for portions of Biscayne National Park and the island of Navassa. 

Biscayne National Park

Within sight of Miami, Biscayne National Park lies at the northern extent of the Florida reef tract and occupies a carbonate platform seaward of Hawk Channel. The park encompasses approximately 700 km2, roughly 95% of which is underwater habitat, including numerous patch reefs and a discontinuous series of shelf-edge, bank-barrier reefs along the seaward boundary. Information about this study is available in the Journal of Coastal Research article "A Multiscale Analysis of Coral Reef Topographic Complexity Using Lidar-Derived Bathymetry."

Location and submerged topographic map of the study site

Location and submerged topographic map of the study site. This 5 km x 5 km area in the southern portion of Biscayne National Park, Florida, was chosen because of its mixture of reef types and the availability of a high-resolution digital-elevation model. (Public domain.)

Fractal dimensions of 500-m x 500-m tiles

Fractal dimensions of 500-m x 500-m tiles within the study site. For reference, the 7-m contour is plotted on top of the fractal map. (Public domain.)

Detailed view of four 500-m x 500-m tiles

Detailed view of four 500-m x 500-m tiles. The tiles are depicted both in plan and perspective views to convey a visual sense of roughness corresponding to their respective fractal dimensions. Tile A lies in the shallow patch-reef zone, Tile B covers a portion of a fused reef, Tile C falls within the deep patch-reef zone, and Tile D is situated on the crest of Pacific Reef. Note that Tile B has been rotated 180° from its true orientation to provide a better topographic view. The white streak in the lower left portion of this tile is a boat wake. (Public domain.)

Navassa Island

Navassa Island is located approximately 50 km west of the southwestern tip of Haiti, and is an uninhabited, pear-shaped island 4.64 km2 in area. In 1999, Navassa Island and a 12-mile radius of marine territory were designated as a National Wildlife Refuge under the jurisdiction of the U.S. Fish and Wildlife Service. Information about this study is available in the Geophysical Research Letters article "Topographic complexity and roughness of a tropical benthic seascape" and related USGS Data Series "Fractal Analysis of the Navassa Island Seascape."

Bathymetry map of Navassa Island

Maps of the study site. Navassa Island is an uninhabited island roughly 5 km2 in size that lies approximately 50 km west of the southwestern coast of Haiti. Bathymetry map created from data acquired by the National Oceanic and Atmospheric Administration, Center for Coastal Fisheries and Habitat Research. This 2006 survey was the first high-resolution, multibeam bathymetric survey around Navassa Island (See the full NOAA report for details). (Public domain.)

bathymetry plotted in 3D

Detailed views of two different seascape regions. For each region, bathymetry is plotted in 3-D and colored with the corresponding estimates of the surface fractal dimension. Region I lies off the eastern Navassa coast. Region II lies off the southern Navassa coast and partially encompasses the roughest portion of the seascape. Vertical exaggeration is 20X. (Public domain.)