Stabilization and Associated Benthic Recovery of Ship Grounding Sites after Boulder Deployment

Ship groundings are acute disturbances that alter benthic biological community composition and the physical characteristics of coral reefs. In 2006, two >170m commercial shipping vessels ran aground on the inner reef near Port Everglades offshore Fort Lauderdale, Florida. These groundings crushed and displaced corals, reduced rugosity, and created areas of loose rubble. In 2015, limestone boulders were deployed in the bow scars of both grounding sites to stabilize unconsolidated reef rubble and restore rugosity. This study examined the change in benthic biological community composition from 2016 to 2021 at permanent sites within stabilized (boulder) and un-stabilized (rubble) grounding areas and adjacent un-impacted reef areas. Belt and photo transects assessed species-specific demographics and taxa-specific benthic cover. Our results found stabilized sites had higher stony coral recruitment and inter-annual survival than un-stabilized sites. Other key taxa, including gorgonians and the Giant Barrel sponge (Xestospongia muta), had limited recruitment to stabilized and un-stabilized sites. Results from this study suggest boulder deployment promotes stony coral recovery, creating habitat more similar to un-impacted reef than unconsolidated rubble and demonstrates the value of long-term restoration monitoring to better understand reef succession after disturbance events.