Assessing the relationship between geomorphology and deep-sea coral and sponge communities on the West Florida Slope
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Proux, Zach
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The distribution of deep-sea corals, and other sessile megafauna, depends primarily on depth, presence of hard substrate, and vertical relief of the seafloor, but less is known about how those assemblages vary among different geomorphologic features. The primary goal of this study was to compare abundance, composition, and diversity of deep-sea megafaunal assemblages as they relate to flats, mounds, and ridges; these features are common on the West Florida Slope between 400 and 700 m. This study focused on four proposed Habitat Areas of Particular Concern (pHAPC) recommended for regulation by the Gulf of Mexico Fishery Management Council (GMFMC) with depths ranging between approximately 300 and 750 m. High-resolution multibeam echo sounder data from surveys by NOAA Ship <i>Nancy Foster</i> in 2008 and R/V <i>Falkor</i> in 2012 provided reference surfaces. Additionally, megafauna larger than 10 cm were identified and enumerated in 148 ROV dive transects from six different expeditions in order to generate densities and correlate these to biotype. A non-metric multidimensional scaling ordination (nMDS) was produced, based on an underlying Bray-Curtis similarity matrix. Analysis of similarity (ANOSIM) indicates coral and sponge communities were significantly different among flats, mounds, and ridges (R = 0.514, P = 0.001) but not between distant localities, here defined as pHAPCs, separated by 111 km of latitude (R = 0.146, P = 0.001). Follow-up Principal Components Analysis (PCA) and similarity percentage analysis (SIMPER) analysis identified <i>Lophelia pertusa</i>, <i>Plumarella</i> sp., <i>Muriceides</i> sp., Isididae, and Demospongiae as key taxa driving the observed differences. Future expeditions onto the West Florida Slope can use geomorphology to predict coral presence and relative density, but not the composition of the species assemblage. Managers can use this study to focus their efforts in areas with geomorphology that is correlated with presence of protected species.