Sea bottom types of a coral reef marine protected area revealed by side scan survey

Besides being one of the most biodiverse ecosystems in the world, coral reefs are also very interesting from a geological point of view. The "StructureScan", present in modern commercially available chartplotters, such as Simrad's NSS7, provides echosounding with SideScan and DownScan options, and is an imaging echosounder operating at 455 kHz and 800 kHz frequencies in two side beams and one downscan beam. When combined with seafloor samples, it is able to provide an understanding of the differences in material and texture of the seabed. The different textural responses from sediments and objects on the seafloor make it possible to differentiate and precisely locate them. These objects can be natural, such as reefs and isolated stones, or manmade, such as shipwrecks. This work consisted on mapping the sedimentary structures and different bottom types of the reefs from the Parque Municipal Marinho da Coroa Alta/BA, by using the aforementioned side scan mounted permanently on Iamany, a 7 m-long, fiberglass-hull, twin-engine boat. Simultaneously, bathymetric data was acquired in order to generate a complete bathymetric map of the area and generate a digital elevation model of the seabed. Later, the results from the reef scanning will be compared with satellite images of the seabed and granulometric /compositional analysis from the sediments, in order to check how accurate this remote method of mapping is for coral reef areas. Several different bottom types are easily recognised, including coral and algal reefs, flat areas of hard bottom sediments, sand waves and sand sheets covering both reef tops and flat areas, and, eventually, man-made objects, such as a possible shipwreck.