39. Gorgonian Corals

Mesophotic gorgonian corals comprise a polyphyletic group of octocorals mostly with a proteinaceous branching axial skeleton. Dense assemblages of gorgonian corals usually dominate the seascape in mesophotic coral ecosystems (MCEs). In this chapter, we review the mesophotic gorgonian coral biodiversity, followed by a synthesis of the ecological implications of inhabiting this environment, as well as the threats that these communities face. MCEs include ~87 gorgonian corals genera distributed worldwide, where the Indo-Pacific (65) is almost twice as diverse as the Caribbean and Gulf of Mexico (37) and Brazil (23), whereas the Tropical Eastern Pacific has only eight genera. We discuss several predictions on the nature of mesophotic gorgonian corals in areas such as microbial endosymbiosis to understand the health, ecology, and evolution of these assemblages. A notable colonization of shallow-water species into MCEs in the Caribbean suggests that colonizing deeper environments promotes ecological divergence. MCEs are not immune to the influence of natural events such as tropical storms and/or anthropogenic encroachment from coastal development, pollution, global climate change, ocean acidification, and overfishing; yet, gorgonian corals in general appear resilient to many of these threats.