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

Abstract

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 Papahānaumokuākea 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-tomagenta 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.

Unveiling mesophotic diversity in Hawai‘i: two new species in the genera <italic>Halopeltis</italic> and <italic>Leptofauchea</italic> (Rhodymeniales, Rhodophyta)

“…In addition, L. huawelau is sister to L. munseomica, known only from South Korea (Filloramo and Saunders 2015). Many marine algal species from Hawai'i have been demonstrated to be most closely related to taxa from the Northwestern Pacific or Australia (Abbott and Huisman 2003, McDermid and Abbott 2006, Cabrera et al 2022, which suggests an interesting biogeographic connection between the two regions, but more information on the mesophotic flora of the Pacific Islands is needed to know the true range and biogeographic processes that account for this distribution. In contrast to the broad distributional range of Leptofauchea in Hawai'i, Hawaiian Halopeltis specimens were collected from a much narrower range, which includes only Maui to Hawai'i Island in the MHI (the southeasternmost part of the archipelago).…”

“…However, there is still much to be done to categorize macroalgal diversity of mesophotic habitats. Multiple marine macroalgal species have been newly described from the Hawaiian mesophotic (e.g., Spalding et al 2016, Sherwood et al 2019, Cabrera et al 2022) and these species represent just a small fraction of the diversity that has yet to be categorized (Sherwood et al 2010). The two new red algal genera reported here from the Hawaiian mesophotic, Leptofauchea and Halopeltis, demonstrate the need for a better understanding of the biodiversity of deep reefs.…”

“…Mesophotic coral ecosystems (MCEs) host substantial biodiversity, much of it unique, and many species have been recently described from this habitat (e.g., Ballantine et al 2017, Schneider et al 2019, Cabrera et al 2022. The depth range for MCEs differs based on locality but is typically defined as 30 to >150 m in tropical and subtropical areas (Lesser et al 2009, Hinder-ses were conducted using MrBayes 3.2.7 (Ronquist et al 2012) on HPC under 1,000,000 generations using four chains of Metropolis-coupled Markov Chain Monte Carlo with sampling every 1,000 generations.…”

“…MCEs host a high level of organismal diversity (Rooney et al 2010, Harris et al 2013) and high levels of endemism (Kane et al 2014, Baker et al 2016, Pyle et al 2016, Kosaki et al 2017. This holds true for Hawaiian MCEs, where endemism levels are also high due to the isolation of the archipelago (Grigg 1988), and several new-to-science mesophotic algal species have recently been described (e.g., Spalding et al 2016, Cabrera et al 2022. Macroalgae are abundant in Hawaiian MCEs (Spalding et al 2019), and algal beds have been found as deep as 160 m (Spalding 2012).…”

“…Macroalgae are abundant in Hawaiian MCEs (Spalding et al 2019), and algal beds have been found as deep as 160 m (Spalding 2012). Influxes of cold water in the Hawaiian mesophotic provide suitable habitat for algae typically found in temperate zones (Abbott and Huisman 2003), resulting in certain species and genera being found only in the mesophotic and absent from the better-studied adjacent shallow waters (Cabrera et al 2022). In the Main Hawaiian Islands, mesophotic macroalgae may also be influenced by nearshore anthropogenically derived nitrogen via submarine groundwater discharge (Strait et al 2022).…”