Research Technical Report

Does Predation Play an Important Role in the Population Dynamics of Deep-sea Corals?

Barry, J., C. Boch, K. Buck, E. Burton, A. DeVogelaere, A. Kahn, C. King, L. Kuhnz, S. Litvin, C. Lovera, T. Guilderson, and P. Whaling (July 2019)

Oral presentation at 7th International Symposium of Deep-sea Corals, Cartagena, Columbia

ABSTRACT

Deep-sea corals are known for their slow growth and great longevity, apparently plodding slowly through life in dark, cold waters for centuries or more. In contrast, at least some coral predators (e.g., sea stars) appear to romp along at a much quicker tempo, preying on corals at rates that seemingly outpace the capacity of corals to recover. Does predation on juvenile and adult coral colonies affect the demographic rates of coral populations? We have attempted to evaluate the incidence and importance of predation on several deep-sea coral taxa at depths of 800-1300 m at Sur Ridge, off the central California coast. Surveys were performed along benthic video transects to measure the incidence of potential predators and other epibionts on coral taxa. Several coral colonies were marked and revisited over 2-3 years to assess changes in polyp cover in relation to predator occurrence. We performed manipulative experiments to assess the behavioral response of predatory sea stars (Hippasteria spp.) exposed to portions of coral colonies from several taxa (Paragorgia arborea, Keratoisis sp., Isidella tentaculum). While the incidence of predators and other epibionts was low on all three coral taxa, I. tentaculum had the lowest epibionts density, presumably related to the shield of nematocyst-laden tentacles at the base of colonies. Short field experiments indicated that the basal branches of I. tentaculum were repellent to the sea stars, which quickly leapt (at a sea star pace) from basal tentacles, but began feeding on I. tentaculum branches covered with feeding polyps. Sea stars placed on Keratoisis sp. and P. arborea branches were not repelled. Repeated observations of isidid colonies under active predation by Hippasteria spp. or large nudibranchs (Tritonia tetraquetra) or both indicated that these predators can denude entire coral colonies within months. How can corals survive this apparent paradox of rapid predation damage amidst the slow tempo of coral colony life?