Quantifying spatial heterogeneity in submarine canyons

Spatial variability in environmental conditions has been attributed as the main driver behind marine biodiversity in structurally complex environments. Despite this, spatial heterogeneity, reflecting terrain organisation of environmental conditions, is seldom quantified in the marine environment, especially at regional scale. In contrast, quantification of spatial patterns has been widely applied to characterise structural features of terrestrial landscapes and has been demonstrated to be of great use in landscape ecology and spatial planning. To address this discrepancy, we use landscape ecology indices (entropy-based contagion) and objective automated marine landscape mapping techniques to quantify marine landscape heterogeneity and evaluate the use of this metric as proxy for biodiversity in submarine canyons. Submarine canyons enhance marine landscape diversity at regional scales and provide unique habitats for diverse and abundant faunal assemblages. The deep and complex topography, strong currents and occurrence of specific oceanographic patterns affect the habitat heterogeneity potentially making canyons a hotspot for biological activity, with high faunal diversity. Here, multibeam bathymetry and sidescan sonar imagery were used to generate a marine landscape map for Whittard Canyon, NE Atlantic, using objective automated classification and object-based image analysis (OBIA). The resulting marine landscape map was characterised by seven landscape types, of which five were found to be ecologically relevant using species indicator analysis (IndVal). Spatial heterogeneity within the landscape map was then quantified with the entropy-based contagion index. Differences in the entropy-based contagion index were highly significant between canyon branches and the lower canyon. The two main canyon branches were not significantly different from each other. Differences in entropy-based contagion value across seabed areas can help to determine areas suitable for the establishment of Marine Protected Area