Environmental filtering and neutral processes shape octocoral community assembly in the deep sea

• Published in: Oecologia 2017-01, Vol.183 (1), p.221-236
• Main Authors: Quattrini, Andrea M., Gómez, Carlos E., Cordes, Erik E.
• Format: Article
• Language: English
• Subjects: Animals; Anthozoa; Biodiversity; Biological Evolution; Biomedical and Life Sciences; COMMUNITY ECOLOGY – ORIGINAL RESEARCH; Community structure; Deep sea; Ecology; Environment; Environmental factors; Environmental gradient; Gulf of Mexico; Hydrology/Water Resources; Life Sciences; Phylogeny; Plant Sciences; Species diversity; Stochastic processes; Water depth
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-016-3765-4

The ecological and evolutionary processes that interact to shape community structure are poorly studied in the largest environment on earth, the deep sea. Phylogenetic data and morphological traits of octocorals were coupled with environmental factors to test hypotheses of community assembly in the deep (250–2500 m) Gulf of Mexico. We found lineage turnover at a depth of 800–1200 m, with isidids and chrysogorgiids at deeper depths and a diversity of species from across the phylogeny occupying shallower depths. Traits, including axis type, polyp shape, and polyp retraction, differed among species occupying the shallowest (250–800 m) and deepest (1200–2500 m) depths. Results also indicated that octocoral species sort along an environmental gradient of depth. Closely related octocoral species sorted into different depth strata on the upper to middle slope, likely due to barriers imposed by water masses followed by adaptive divergence. Within any given depth zone down to 2000 m, the phylogenetic relatedness of co-existing octocorals was random, indicating that stochastic processes, such as recruitment, also shape community structure. At depths >2000 m, octocorals were more closely related than expected by chance due to the diversification of chrysogorgiids and isidids, which retain conserved traits that impart survival at deeper and/or colder depths. Polyp density, size, and inter-polyp distance were significantly correlated with depth, particularly in plexaurids and isidids, highlighting trait lability across depth and supporting that environmental gradients influence octocoral morphology. Our community phylogenetics approach indicates that both environmental filtering and neutral processes shape community assembly in the deep sea.