title: A comprehensive investigation of mesophotic coral ecosystems in the Hawaiian Archipelago.
abstract: Although the existence of coral-reef habitats at depths to 165 m in tropical regions has been known for decades, the richness, diversity, and ecological importance of mesophotic coral ecosystems (MCEs) has only recently become widely acknowledged. During an interdisciplinary effort spanning more than two decades, we characterized the most expansive MCEs ever recorded, with vast macroalgal communities and areas of 100% coral cover between depths of 50-90 m extending for tens of km2in the Hawaiian Archipelago. We used a variety of sensors and techniques to establish geophysical characteristics. Biodiversity patterns were established from visual and video observations and collected specimens obtained from submersible, remotely operated vehicles and mixed-gas SCUBA and rebreather dives. Population dynamics based on age, growth and fecundity estimates of selected fish species were obtained from laser-videogrammetry, specimens, and otolith preparations. Trophic dynamics were determined using carbon and nitrogen stable isotopic analyses on more than 750 reef fishes. MCEs are associated with clear water and suitable substrate. In comparison to shallow reefs in the Hawaiian Archipelago, inhabitants of MCEs have lower total diversity, harbor new and unique species, and have higher rates of endemism in fishes. Fish species present in shallow and mesophotic depths have similar population and trophic (except benthic invertivores) structures and high genetic connectivity with lower fecundity at mesophotic depths. MCEs in Hawai'i are widespread but associated with specific geophysical characteristics. High genetic, ecological and trophic connectivity establish the potential for MCEs to serve as refugia for some species, but our results question the premise that MCEs are more resilient than shallow reefs. We found that endemism within MCEs increases with depth, and our results do not support suggestions of a global faunal break at 60 m. Our findings enhance the scientific foundations for conservation and management of MCEs, and provide a template for future interdisciplinary research on MCEs worldwide.
authors.affiliation: Natural Sciences, Bernice Pauahi Bishop Museum , Honolulu , HI , United States.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Pyle
authors.affiliation: Pacific Islands Fisheries Science Center, National Oceanographic and Atmospheric Administration, Honolulu, HI, United States; Hawai'i Pacific University, Honolulu, HI, United States.
authors.forename: Raymond
authors.initials: R
authors.lastname: Boland
authors.affiliation: Natural Sciences, Bernice Pauahi Bishop Museum , Honolulu , HI , United States.
authors.forename: Holly
authors.initials: H
authors.lastname: Bolick
authors.affiliation: Hawai'i Institute of Marine Biology, University of Hawai'i at Manoa , Honolulu , HI , United States.
authors.forename: Brian W
authors.initials: BW
authors.lastname: Bowen
authors.affiliation: Life and Environmental Sciences, University of California at Merced, Merced, CA, United States; Department of Oceanography, University of Hawai'i at Manoa, Honolulu, HI, United States.
authors.forename: Christina J
authors.initials: CJ
authors.lastname: Bradley
authors.affiliation: Environmental and Natural Resource Sciences, Washington State University , Pullman , WA , United States.
authors.forename: Corinne
authors.initials: C
authors.lastname: Kane
authors.affiliation: Papahānaumokuākea Marine National Monument, National Oceanic and Atmospheric Administration , Honolulu , HI , United States.
authors.forename: Randall K
authors.initials: RK
authors.lastname: Kosaki
authors.affiliation: Natural Sciences, Bernice Pauahi Bishop Museum , Honolulu , HI , United States.
authors.forename: Ross
authors.initials: R
authors.lastname: Langston
authors.affiliation: Natural Sciences, Bernice Pauahi Bishop Museum , Honolulu , HI , United States.
authors.forename: Ken
authors.initials: K
authors.lastname: Longenecker
authors.affiliation: Hawai'i Institute of Marine Biology, University of Hawai'i at Manoa, Honolulu, HI, United States; Pacific Islands Fish and Wildlife Office, U.S. Fish and Wildlife Service, Honolulu, HI, United States.
authors.forename: Anthony
authors.initials: A
authors.lastname: Montgomery
authors.affiliation: Pacific Islands Fisheries Science Center, National Oceanographic and Atmospheric Administration , Honolulu , HI , United States.
authors.forename: Frank A
authors.initials: FA
authors.lastname: Parrish
authors.affiliation: Department of Geology and Geophysics, University of Hawai'i at Manoa , Honolulu , HI , United States.
authors.forename: Brian N
authors.initials: BN
authors.lastname: Popp
authors.affiliation: Joint Institute for Marine and Atmospheric Research, University of Hawai'i at Manoa , Honolulu , HI , United States.
authors.forename: John
authors.initials: J
authors.lastname: Rooney
authors.affiliation: Department of Botany, University of Hawai'i at Manoa , Honolulu , HI , United States.
authors.forename: Celia M
authors.initials: CM
authors.lastname: Smith
authors.affiliation: Papahānaumokuākea Marine National Monument, National Oceanic and Atmospheric Administration , Honolulu , HI , United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wagner
authors.affiliation: Department of Botany, University of Hawai'i at Manoa , Honolulu , HI , United States.
authors.forename: Heather L
authors.initials: HL
authors.lastname: Spalding
keywords: Amino acid isotopic composition; Closed-circuit rebreathers; Endemism; Hawaiian Archipelago; Mesophotic coral ecosystems; Refugia