Long-term effects of a ship-grounding on coral reef fish assemblages at Rose Atoll, American Samoa

The nature and degree of impact of ship groundings on coral reefs and subsequent recovery is not well understood. Disturbed benthic and associated fish assemblages may take years-decades to return to pre-impact levels or may attain alternate stable states. Rose Atoll, a small, remote coral atoll in the central South Pacific, was impacted by a major ship grounding and associated contaminant spill in October 1993. Coral reef fish assemblages were quantitatively surveyed at the site of impact and compared to other nearby sites along the western outer reef slope in August 1995, February 2002, February 2004, and March 2006. In 1995, herbivorous surgeonfishes dominated the site, likely attracted to the early algal blooms. During 2002-2006, both numbers and biomass of pooled herbivorous fishes were significantly greater at the wreck site than at the other reef-slope survey sites. This greater abundance, where some corroding steel debris remained, was associated with significantly greater substratum cover by opportunistic algae (both turf and cyanobacteria). Thus, more than 13 yrs later, the grounding of this ship is still impacting algal growth and herbivorous reef-fish populations. While continued ecosystem monitoring at Rose Atoll is necessary for a full understanding of recovery rates by fish assemblages from such major anthropogenic disturbances, in the event of future groundings, containment of the contaminant spill and prompt removal of all metallic debris is recommended to preserve ecosystem integrity.