Bathymetry derived terrain variables are indicative of seabed morphology and can be used as predictors of suitable benthic habitats. A digital elevation model (DEM) is a digital representation of the elevation of locations on the land surface, and in the case of this report can be used as a digital representation of underwater bathymetry. The DEM can be used to derive various benthic terrain variables of underwater systems (Pescus 2012). Some terrain variables include depth, slope, rugosity, aspect and terrain variability. Depth is a major environmental gradient which controls species distribution, as various under water organisms rely on photosynthesis to survive and grow. As depth increases, less sunlight penetrates the water, resulting in a limited source of energy for photosynthesizing organisms (Pescus 2012). Additionally bigger/older individuals often prefer deeper waters (Lauria et al. 2015).
Slope (expressed in degrees with values from 0° to 90°) describes the rate of change in elevation over distance. Low values of slope correspond to flat ocean bottom (or areas of sediment deposition) while higher values indicate potential rocky ledges. (Lauria et al. 2015) The slope of many marine systems has a strong influence on the distribution of benthic components, such as coral in coral reef systems. Slope can first be a derivative of a DEM and then calculated using spatial analyst tools in ArcGIS. The slope represents the rate of change of elevation for each DEM cell