The orientation and distribution of sea fans on hardbottom habitats of the Mississippi/Alabama continental shelf

Abstract

Analysis of the densities and orientations of five common taxa of gorgonian and antipatharian sea fans was performed within five study areas on the Mississippi/Alabama continental shelf. Colonies exhibited a strong preference for areas containing hard substrate. Meso-scale (on the order of tens of meters) morphological differences in hard bottom substrate did not have an influence on colony densities. Mean exposure to suspended particle concentrations had a significant negative effect on the densities of gorgonian colonies belonging to the taxa Nicella spp, Bebryce cinerea/grandis, and Stenogorgiinae. Height above bottom had a significant positive effect on the distributions of the gorgonian Bebryce cinerea/grandis and the antipatharian Antipathes ?atlantica/gracilis. The gorgonian Thesea sp. had a significant negative relationship with height above bottom. After accounting for the above variables, colony distributions still exhibited non-homogenous distributions at both within-site and regional scales. A significant decrease in colony densities was found on two of the five study sites after the passage of a hurricane through the study area. Colonies exhibited a strongly preferred orientation at all of the five study sites. Mean colony orientations corresponded closely to the mean direction of time-averaged flow of current measured in the vicinity of the study sites.