MEPS 626:135-143 (2019)  -  DOI: https://doi.org/10.3354/meps13060

ABSTRACT: Ascidians can settle and grow on corals and have become one of the main threats to hard corals in some areas of world, covering and smothering live coral tissues. We studied the biology of infestation of a solitary tunicate, Phallusia nigra Savigny, 1816, on hard corals in Chabahar Bay, a subtropical bay in the northern Gulf of Oman. Infested corals were bleached and eroded at epibiont attachment surfaces. The magnitude of infestation by the tunicate differed between Pocillopora and Acropora coral colonies, with more tunicates inhabiting Pocillopora colonies. This preference of P. nigra for Pocillopora may be attributed to differences in morphology (e.g. narrower branch spaces in Pocillopora) of the coral genera. Outbreaks of ascidians on coral reefs are usually associated with anthropogenic activities. P. nigra may have more localized damaging effects on hosts, in contrast to colonial ascidians that can kill entire coral colonies. These effects may be exaggerated by non-contact effects (e.g. decreased pH).

KEY WORDS: Phallusia nigra · Hard coral · Bleaching · Skeletal damage · pH