A new species of Gibsmithia (Dumontiaceae, Rhodophyta) from mesophotic depths of the Papahānaumokuākea Marine National Monument, Hawai‘i, USA Phycologia

Molecular phylogenetic analyses of Hawaiian members of the red algal family Dumontiaceae were used to clarify the species diversity of Dudresnaya and Gibsmithia from Hawaiʻi. Although no new species of Dudresnaya were detected in the analyses, D. babbittiana is newly recorded by Lalo, Manawai, and Oʻahu; however, this record remains tentative until the type material is sequenced. A new species of Gibsmithia, G. punonomaewa A.R. Sherwood, is described here and reported from the mesophotic depths (79–104 m) of the Papahānaumokuākea Marine National Monument, Hawaiʻi. This new species differs from all others in the genus based on the following combination of characters: moderate thallus size (up to 11 cm), smooth and terete gelatinous lobes, presence of a stipe (which is often branched), globose carposporangia, and a non-isodiametric shaped cell subtending the tetrasporangia. This new taxon increases the number of Gibsmithia species recorded from Hawaiʻi to three. Phylogenetically, G. punonomaewa is most closely related to G. dotyi (type locality, Lord Howe Island, Australia) and G. larkumii (type locality, One Tree Island, Queensland, Australia), which are both reportedly widespread in distribution. The relatively dark habitat of the mesophotic in Papahānaumokuākea Marine National Monument contrasts with the surface waters of tropical and subtropical habitats where most Gibsmithia species are found, further highlighting the uniqueness of the species. We thank the officers and crew of the NOAA ship Hi‘ialakai for access to the Hawaiian MCEs. We gratefully acknowledge the NOAA Papahānaumokuākea Native Hawaiian Cultural Working Group for their invaluable development of the specific epithet for the new Hawaiian species of Gibsmithia. Field work and specimen collections were authorized under the Papahānaumokuākea Marine National Monument research permits This work was supported by the US National Science Foundation (DEB-1754117), the US National Fish & Wildlife Foundation (NFWF 0810.20.068602) and the National Oceanic and Atmospheric Administration (NOAA) Papahānaumokuākea Marine National Monument. Permit no. PMNM-2014-15 Permit no. MNM 2015-029 Permit no. PMNM-2018-029