Abstract
Mesophotic reefs (30–150 m) occur in the tropics and subtropics at depths beyond most scientific diving, thereby making conventional surveys challenging. Towed cameras, submersibles, and mixed-gas divers were used to survey the mesophotic reef fish assemblages and benthic substrates of the Au‘au Channel, between the Hawaiian Islands of Maui and Lāna‘i. Non-parametric multivariate analysis: Non-metric Multidimensional Scaling (NMDS), Hierarchical Cluster Analysis (HCA), Multi-Response Permutation Procedure (MRPP), and Indicator Species Analysis (ISA) were used to determine the association of mesophotic reef fish species with benthic substrates and depth. Between 53 and 115-m depths, 82 species and 10 genera of fish were observed together with 10 types of benthic substrate. Eight species of fish (Apolemichthys arcuatus, Centropyge potteri, Chaetodon kleinii, Chromis leucura, Chromis verater, Forcipiger sp., Naso hexacanthus, and Parupeneus multifasciatus) were positively associated with increasing depth, Leptoseris sp. coral cover, and hard-bottom cover, and one species (Oxycheilinus bimaculatus) of fish was positively associated with increasing Halimeda sp. algae cover. Fish assemblages associated with rubble were not significantly different from those associated with sand, Montipora coral beds and Leptoseris coral beds, but were distinct from fish assemblages associated with hard bottom. The patterns in the data suggested two depth assemblages, one “upper mesophotic” between 53 and 95 m and the other deeper, possibly part of a “lower mesophotic” assemblage between 96 and 115 m at the edge of the rariphotic and bottomfish complex.
Highlights
Mesophotic Coral Ecosystems (MCEs) are the most understudied coral reef ecosystems in the world
This study investigates the MCE reef fish assemblages of the Au‘au Channel between Lana‘i and Maui in the main Hawaiian Islands using archived MCE survey data collected between 2007 and 2011 by the National Oceanic and Atmospheric Administration (NOAA) National Marine Fisheries Service (NMFS) These surveys utilized three distinct platforms: Towed Optical Assessment Device (TOAD), submersibles Pisces IV and V (SUB), and mixed-gas scuba diving (SCUBA)
2 substrate types, and 8 fish species were significantly correlated with Axis 1 (Table 2)
Summary
Mesophotic Coral Ecosystems (MCEs) are the most understudied coral reef ecosystems in the world. Many studies have investigated various aspects of MCE benthic habitats in the main Hawaiian Islands including coral beds, algal meadows, coral physiology, fish life histories, and fish trophic ecology (Boland and Parrish, 2005; Kahng and Kelley, 2007; Rooney et al, 2010; Blythe-Skyrme et al, 2013; Costa et al, 2015; Pochon et al, 2015; Bradley et al, 2016; Pyle et al, 2016; Spalding et al, 2016; Asher et al, 2017; Weijerman et al, 2019), with the number and spatial extent of surveys increasing in recent years (2009–2018) (Spalding et al, 2019). Seven studies conducted in the NWHI have been published to date, focusing on benthic substrate cover, fish assemblages on banks, a comparison of shallow reef vs. mesophotic fish, foraging habitat of the Hawaiian Monk Seal and/or levels of fish endemism (Parrish et al, 2000; Parrish and Boland, 2004; Rooney et al, 2010; Kane et al, 2014; Fukunaga et al, 2016, 2017; Kosaki et al, 2016)
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