Cryptic diversity in the genus Croisettea (Kallymeniaceae, Rhodophyta) from Hawaiian mesophotic reefs

Abstract

ABSTRACT Recent investigations into the species diversity of red blades in Hawai‘i have yielded several specimens of Kallymeniaceae from Hawaiian Mesophotic Coral Ecosystems. Our combined morphological and mitochondrial COI-5P and plastid rbcL phylogenetic analyses indicated widespread cryptic diversity among those specimens commonly identified as Kallymenia sensu lato based on morphology. These analyses resolved four unique genetic lineages of Hawaiian taxa in the genus Croisettea, which are all restricted to the lower mesophotic depths (c. 60–150 m). Croisettea currently includes three described species distributed in the North Atlantic, Indian and South Pacific Oceans, and the Mediterranean Sea. Croisettea is a new genus record for the Hawaiian Islands, expanding its biogeographic range to the North Pacific. The genus has now been enlarged to include seven species comprising previously described taxa as well as four new Hawaiian taxa (C. kalaukapuae sp. nov., C. haukoaweo sp. nov., C. ohelouliuli sp. nov. and C. pakualapa sp. nov.). The known distributions of the Hawaiian Croisettea species are restricted to areas around their type localities. Although this pattern hints at a remarkable degree of endemicity, both across depth gradients in a reef area and among islands, it is also linked to a limited sampling of the group, suggesting that additional species, and more accurate distributional ranges, remain to be detected not only in Hawai‘i but also worldwide.