A phylogenetic approach to octocoral community structure in the deep Gulf of Mexico Andrea M. Quattrini a,n , Peter J. Etnoyer b , Cheryl Doughty a , Lisa English a , Rosalia Falco a , Natasha Remon a , Matthew Rittinghouse c,1 , Erik E. Cordes a a Biology Department, Temple University,1900 N 12th Street, Philadelphia, PA 19122, USA b NOAA Center for Coastal Environmental Health and Biomolecular Research, Charleston, SC 29412, USA c JHT, Inc., 2710 Discovery Drive, Suite 100, Orlando, FL 32826, USA article info Available online 27 May 2013 Keywords: Phylogeny Species diversity Community composition Deep-sea Coral abstract Deep-sea communities are becoming increasingly vulnerable to anthropogenic disturbances, as fishing, hydrocarbon exploration and extraction, and mining activities extend into deeper water. Negative impacts from such activities were recently documented in the Gulf of Mexico (GoM), where the Deepwater Horizon oil spill caused substantial damage to a deep-water octocoral community. Although a faunal checklist and numerous museum records are currently available for the entire GoM, local-scale diversity and assemblage structure of octocoral communities remains unknown, particularly in deep water. On a series of recent cruises (2008–2011) using remotely operated vehicles, 435 octocorals were collected from 33 deep-water sites (250–2500 m) in the northern GoM. To elucidate species boundaries, the extended mitochondrial barcode (COI+igr1+msh) was successfully amplified and sequenced for 422 of these specimens, yielding a total of 64 haplotypes representing at least 52 species. Further, at least 29% of the species collected were either previously not known to occur in the GoM (12 species) or represent new species (at least three species). Overall, species richness at each site was fairly low (1–12 spp.). The greatest species richness occurred at the shallowest ( o325 m: GC140, n ¼8 spp.) and the deepest (2100– 2500 m: DC673, n ¼12 spp., DC583, n ¼10 spp.) sites, and minimum taxonomic and phylogenetic (Faith's Index) diversity was evident at 600–950 m. This pattern is the opposite of the typical pattern of deep-sea diversity in the GoM, which normally peaks at mid-slope depths. Sorensen's Index of taxonomic β- diversity indicated that six distinct (65–95% dissimilarity) species assemblages corresponded with five depth breaks at 325, 425, 600, 1100, and 2100 m. Further assemblage structure was observed within certain depth zones. Of note, within the 425–600 m depth range, species assemblages at the West Florida Slope differed from the other sites, corresponding to an established biogeographic barrier. The phylogenetic approach used in this study provided important insights into the species boundaries of many taxa while demonstrating that evolutionary history plays a critical role in community structure of deep-sea octocorals. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Deep-sea octocorals are becoming increasingly susceptible to damage as anthropogenic disturbances extend into deeper water. Negative impacts from such activities were recently documented in the Gulf of Mexico, where the Deepwater Horizon oil spill caused substantial damage to an octocoral community at 1300 m depth (White et al., 2012). Disturbances such as these could have widespread, adverse effects in the deep sea. Not only do 75% of all known octocoral species (  3000 extant spp.) occur at depths 450 m (Cairns, 2007), a majority of these are likely slow-growing and long-lived (Andrews et al., 2002; Roark et al., 2006). Moreover, octocorals increase habitat heterogeneity throughout the deep sea, thus supporting a diverse faunal assemblage that includes obligate (Mosher and Watling, 2009), endemic (Cordes et al., 2008), and commercially important (Krieger and Wing, 2002) species. Despite the profusion of octocorals in the deep sea, basic knowledge is severely limited throughout the sub-class. Funda- mental biological data (e.g., reproduction, longevity) of many species are missing and the phylogenetic relationships of octocor- als remain unclear (McFadden et al., 2010). Existing phylogenetic datasets have revealed extreme polyphyly at every level (order, sub-order, family, genus), numerous polytomies across the entire Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsr2 Deep-Sea Research II 0967-0645/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dsr2.2013.05.027 n Corresponding author. Tel.: +1 215 204 8871; fax: +1 215 204 6646. E-mail address: andrea.quattrini@temple.edu (A.M. Quattrini). 1 Current address: College of Charleston, 66 George Street, Charleston, SC 29424, USA. Deep-Sea Research II 99 (2014) 92–102