The effects of minimum map unit in coral reefs maps generated from high resolution side scan sonar mosaics

Changes in coral habitats from benthic maps at two minimum mapping units (4 and 400 m²) were examined across 600 ha at the Puerto Rico insular shelf. The maps were produced by visually interpreting high resolution side scan sonar seafloor mosaics. Comparisons were performed by using published spatial indices based on patch size and abundance. At the fine scale, small coral patches were dominant and had more complex shapes, while coarse scale maps lost information on small or rare habitats, but included new mixed habitat categories that helped conserve estimates of total habitat area. Variations in spatial indices occurred across spatial scales, but trends were not necessarily predictable. For instance, habitat diversity increased at the coarse scale maps, but habitat richness remained unchanged. Differences were related as much to the peculiarities of the abundance, shape and arrangement of habitats at the two sites as to changes in grain size.