Spatial dynamics of the quantity and diversity of natural and artificial hard bottom habitats in the eastern Gulf of Mexico

The eastern Gulf of Mexico continental shelf (approximately 144,000 km(2)), while dominated by unconsolidated sediments, contains diverse hard bottom habitats critical to economically important reef fishes. Although high resolution mapping exists for several well-known hard bottom features (e.g. Florida Middle Grounds, The Sticky Grounds), the majority of the shelf remains unmapped. Through mapping efforts conducted in support of fisheries independent resource surveys, hard bottom habitats were identified and classified from 4208 randomly distributed, small-scale (2 km(2)) side-scan sonar surveys conducted between 2010 and 2018. Thirty-three natural and artificial hard bottom habitat types were identified, with Flat Hard Bottom comprising both the greatest area coverage (131.7 km(2)) and number of individual features classified (n = 42,829). Classification and regression tree analyses were conducted to identify spatial patterns of hard bottom habitat composition based on both area coverage and number of individual hard bottom features. These maps identified distinct spatial variability in the availability of several habitat types, such as increased number of Pothole habitats in deep shelf waters off the Florida Peninsula and increased coverage by artificial reef habitats within the Florida Panhandle. Extrapolating results from this representative, broad scale approach to habitat mapping indicated that approximately 3854 km2 (2.6%) of the shelf is comprised of natural hard bottom habitat. The value of comprehensive habitat data is highlighted within recent efforts toward generating absolute abundances of reef fish species as well as continuing efforts toward ecosystem-based approaches to fisheries management.