New species in the cryptic genus Gloiocladia J.Agardh (Faucheaceae, Rhodophyta) from Hawaiian Mesophotic Coral Ecosystems

Crypsis – high morphological similarities of adult thalli of distinct species of algae – is a common challenge in algal taxonomy, where multiple taxa are characterized as the same species due to identical morphologies. Algal genera with cryptic species and similar morphologies may contain underestimates of both diversity and endemism. Extensive studies of Mesophotic Coral Ecosystems (MCEs; from c. 30 to >150 m depths) have revealed high levels of endemism in the Hawaiian Archipelago using DNA sequence-based analyses augmented by morphological analyses. Here, we characterize specimens collected from both the Papahānaumokuākea Marine National Monument and the Main Hawaiian Islands corresponding to the genus Gloiocladia J.Agardh; previous reports from Hawai‘i included only a single subtidal species (G. iyoensis (Okamura) R.E.Norris). Phylogenetic analyses using both plastidial (ribulose-1.5-biphosphate carboxylase/oxygenase) and mitochondrial (cytochrome oxidase subunit 1) markers revealed three clades of Hawaiian specimens with strong sequence divergence. However, the gross morphology of these specimens was nearly identical, except for small differences in the number of layers and sizes of cortical and medullary cells, which can easily be overlooked. This study extended the depth record of G. iyoensis to 63 m (aside from a previous report of a dredge sample from 66 m) and revealed one new species exclusive to MCEs (described here as G. laukuamoo K.R.Allsopp, F.P.Cabrera & A.R.Sherwood, sp. nov.), as well as one new intertidal species (formal description awaiting analysis of further collections) present in the Hawaiian Archipelago, including the Papahānaumokuākea Marine National Monument (PMNM) and the Main Hawaiian Islands.