Diversity of Kallymeniaceae (Gigartinales, Rhodophyta) associated with Hawaiian mesophotic reefs

Small red algal morphologically variable blades have been extensively collected from Hawaiian reefs, but for many specimens their taxonomy remains poorly understood. In surveys of the Papahanaumokuakea Marine National Monument (PMNM) and Main Hawaiian Islands (MHI), we discovered two taxa of undescribed small (< 5 cm) red blades that matched the genera Psaromenia and Meredithia, based on morphology and molecular analyses. Neither genus has been previously recorded in the Hawaiian Islands, and neither group of specimens matched currently described species in these two genera. Accordingly, these specimens are described here as new species within the family Kallymeniaceae. Psaromenia laulamaula sp. nov., exclusively found at mesophotic depths (83-94 m) in PMNM, is easily distinguished from other members of the genus by its comparatively large, procarpic carpogonial branch system and solitary obovate pink-to-magenta blades. Conversely, Meredithia hawaiiensis sp. nov., occurring in both shallow (0-17 m) and mesophotic depths (55 m), has high morphological plasticity, with characters that overlap with other Meredithia species, and can only be distinguished based on DNA sequences. This study provides additional evidence of the extent of diversity in the Kallymeniaceae that is poorly characterized from mesophotic depths and provides further evidence that members of the macroalgal flora contain overlooked biodiversity.

Automated summary

Two new taxa of small red blades belonging to the genera Psaromenia and Meredithia were discovered, and described as new species within the family Kallymeniaceae. Psaromenia laulamaula sp. nov. is found exclusively at mesophotic depths, while Meredithia hawaiiensis sp. nov. occurs in both shallow and mesophotic depths with high morphological plasticity. This study provides additional evidence of poorly characterized diversity in the Kallymeniaceae from mesophotic depths and highlights overlooked biodiversity within the macroalgal flora.