Deep Coral Habitat Characterization of the North End of Raita Bank, Papahānaumokuākea Marine National Monument in the Northwestern Hawaiian Islands

The purpose of this study is to characterize and explore the north end of Raita Bank in the Northwestern Hawaiian Islands, to assess where deep marine coral would most likely grow and flourish. The bank is located within the largest U.S marine protected area, the Papahānaumokuākea Marine National Monument (PMNM), 1120 km northwest of Honolulu, Hawaii. Multibeam sonar data were collected by the Schmidt Ocean Institute using the R/V Falkor’s Kongsberg EM302 and EM710 during an exploratory cruise within the PMNM in May-June 2014. Raita Bank hosts both shallow and deep coral; however, this study was focused on potential deep coral habitat at depths ranging 400 to 3000 m. The bank stretches approximately 44.0 km east-west and 35.8 km north-south and its shallowest point surveyed is 320 m. Overall gradients between 400 and 3000 m depths range from 0.10 to 0.26, including major terraces at 500 and 1000 m. The steeper gradients and terraced areas indicate favorable conditions for deep coral. A bathymetric map created with CARIS HIPS and SIPS 9.0 software was used to visualize seafloor geomorphology and characterize deep coral habitat by examining slope relief, distance to shelf edge, and other geomorphologic features. Additionally, backscatter was used to analyze the seafloor’s relative hardness to identify hard-bottom seafloor areas that would be more likely to support deep coral. Maps generated from this study will be invaluable for future explorations of deep coral habitat on the bank.