Commensalism and Reproductive Biology of the Brittle Star Ophiocreas oedipus Associated with the Octoral Metallogorgia melanotrichos on the New England Corner Rise Seamounts

• Main Author: Mosher, Celeste V.
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2008
• Subjects: Coral reef ecology; North Atlantic Ocean; Seamounts; Oceanography; Terrestrial and Aquatic Ecology; North Atlantic
• Online Access: https://digitalcommons.library.umaine.edu/etd/1516; https://digitalcommons.library.umaine.edu/context/etd/article/2537/viewcontent/MosherCV2008.pdf

While temperate-water coral ecosystems of seamounts have been gaining more attention in the last decade, the organisms that live within and rely upon these corals for survival are studied to a lesser degree. Throughout the New England and Corner Rise seamounts of the western North Atlantic, several ophiuroid species are conspicuously epizoic on octocorals. One objective of this study was to investigate the association between Ophiocreas oedipus and its host octocoral Metallogorgia melanotrichos on these seamounts. Coral colonies with their brittlestar epibionts were collected from 11 seamounts in 2003, 2004, and 2005 at depths between 1300 and 2200 m via submersible. O. oedipus is obligately associated with M. melanotrichos, leading a solitary existence on all octocorals observed. O. oedipus gains feeding and protective benefits while M. melanotrichos appears to neither benefit nor be disadvantaged by this commensalism. M. melanotrichos exhibits a distinct developmental pattern that can be categorized into three growth stages. The positive correlation between size of O. oedipus and growth stage of its host is highly significant suggesting the brittlestar may grow up with M. melanotrichos. A further objective of this study was to investigate the reproductive biology of O. oedipus. Paraffin histology reveals that O. oedipus is gonochoristic and likely a broadcast spawner with a lecithotrophic larval stage. The gonadal tubules of O. oedipus occur in pairs of up to four within the proximal arm segments of each arm. The tubules exhibit synchronous gametogenesis within each pair but asynchronous development between pairs within the same individual. Findings suggest O. oedipus may use continuous reproduction throughout the year to maintain its population while limited by its dependence on M. melanotrichos as a host.