Identification of small-scale coral reef habitats from high resolution Side Scan Sonar imagery

A detailed characterization of habitat is important to understand how organisms react and use their immediate environment and to study many ecological processes occurring at these scales. However, detailed habitat knowledge needs to be extended over broad areas to determine the spatial distribution of benthic habitats and their connectivity. This large scale habitat assessment is crucial to determine the effects of disturbance, heterogeneity and dispersal between habitat patches on marine populations. Unfortunately, detailed habitat identification over large areas is unknown for the majority of reef areas. In this work, a total of 60 km(2) off La Parguera, Puerto Rico were surveyed using a Side Scan Sonar (SSS). The acquired imagery has high spatial resolution (0.15 m) and allowed the identification of 21 different habitat types. The most structured habitats (6) were dominated by corals and gorgonians, which covered 28% of the area. Vegetated habitats (8) represented 13% of the area, while unconsolidated habitats (7) occupied 59% of the area Abundant coral patches on a sandy matrix, small coral patches surrounded by a seagrass halo, dominance of coral limestone patches, aligned parallel to the prevalent waves, deep sand channels, and extensive gorgonian plains are all examples of previously uncharted habitats. Mangrove habitat could not be mapped with SSS. Habitats recognized were related to biologically relevant measures -structure, rugosity, benthic community composition and abundance- that are known to be the factors affecting fish community structure. Therefore, SSS is a particular valuable technique for quantitative assessments of habitat distributions important for fish management e.g., habitat abundance and connectivity for essential fish habitat or MPA design.