Quantifying Mesophotic Fish Assemblages of Hawai'i's Au'au Channel: Associations With Benthic Habitats and Depth

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 Lana'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.

Automated summary

This study conducted surveys of the mesophotic reef in the Au'au Channel between Maui and Lana'i islands using various methods. The results showed that depth, benthic substrates, and coverage have an impact on the distribution of fish assemblages in the mesophotic reef. Additionally, two distinct mesophotic assemblages were identified, one in the upper depths and the other in the lower depths.