Chemical defense of hydrothermal vent and hydrocarbon seep organisms: a preliminary assessment using shallow-water consumers

Organisms at deep-sea hydrothermal vent or cold-seep communities represent oases of prey in an otherwise prey-poor desert. Why deep-sea consumers that remove other dense food patches do not rapidly remove the high biomass of prey from these communities is unclear. One potential explanation is that hydrogen sulfide, or other metabolites, in these chemoautotrophic prey could be serving as chemical defenses against generalist consumers; however, neither the palatability of these prey nor their potential defenses have been assessed. We fed tissues from 10 species of deep-sea polychaetes and 2 species of bivalves to shallow-water fishes Fundulus heteroclitus and Leiostomus xanthurus or crabs Callinectes similis and Pachygrapsus crassipes to assess their palatability to generalist consumers. Tissues from 4 polychaetes (Archinome rosacea, Lamellibrachia luymesi, Riftia pachyptila, and Seepiophila jonesi) and 1 bivalve (Calyptogena magnifica) were rejected by some consumers. Blood, which can be sulfide-rich, from R. pachyptila did not deter feeding. Sharp setae deterred feeding on the polychaete A. rosacea, while the other unpalatable species produced chemical extracts that deterred feeding. All of the chemically deterrent species contained chemoautotrophic endosymbiotic bacteria, suggesting that these microbial symbionts may produce metabolites that defend their host species. In several instances, consumers encountering novel, deep-sea prey consumed more on the first day of feeding than on later dates, or initially rejected the foods, but then consumed them after repeated encounters. Investigations with predators from the deep-sea are required to more fully understand the ecological role of prey defenses for deep-sea species.