Species composition, diversity, and distribution of the genus Ulva along the coast of Jeju Island, Korea based on molecular phylogenetic analysis

Abstract

Species diversity in the genus Ulva remains understudied worldwide. Using molecular analyses we investigated the species composition, diversity, distribution, and relative frequencies of the genus Ulva along the entire coast of Jeju Island, off the southern tip of Korea. Species identification was performed for 215 samples collected from 23 sites, based on comprehensive phylogenetic and model-based species delimitation analyses using the sequences of two molecular markers, chloroplast elongation factor Tu ( tuf A) and nuclear rDNA internal transcribed spacer (ITS). We identified 193 specimens as nine Ulva species, 14 specimens as Blidingia spp., and eight samples undetermined, based on the combined analysis of tuf A and ITS phylogenies. Two model-based approaches generally supported nine groups of Ulva species. Previously documented species complex, such as U . ohnoi−U . spinulosa and U . procera−U . linza showed discordant relationships between the two phylogenies. The occurrence of U . torta on Jeju Island was first observed, despite its existence on the mainland previously reported. Ulva australis [16 of 23 sites; 34.4% (relative frequency)], U . ohnoi (16; 21.9%), and U . procera (11; 14%) were found to be the predominant species. Our study highlights that molecular analysis is critical for species delimitation in the genus Ulva and provides fundamental information for an understanding of green-tide assemblages on the “biological hotspot” coastal ecosystem, Jeju Island in Korea. This study will also help to monitor and manage local green tides at the areas that are currently encountering rapid climate changes.

Taxonomy of <italic>Ulva</italic> causing blooms from Jeju Island, Korea with new species, <italic>U. pseudo-ohnoi</italic> sp. nov. (Ulvales, Chlorophyta)

“…Based on our tufA and rbcL DNA barcoding methods, the presence of with a close phylogenetic relationship to U. laetevirens based on rbcL and internal transcribed spacer (ITS) regions (Matsumoto and Shimada 2015). In addition, this organism was reported from the coast of Jeju Island, Korea (Kang et al 2019). U. pseudo-ohnoi sp.…”

“…Historically the identification of Ulva species in Korea has been conducted almost entirely based on morphology, and only a few studies have employed molecular analysis of this genus (Bae and Lee 2001, Kang et al 2014. Kang et al (2019) reported the proportional occurrences of Ulva species using molecular approaches. We determined that the most problematic Ulva bloom, which occurs in Shinyang, is composed of four distromatic and foliose species, U. australis, U. lactuca, U. laetevirens, and U. ohnoi (Table 1), that have attached and free-floating habits.…”

“…Although Kang et al (2019) conducted the molecular study of Ulva along the coast of Jeju Island, Korea based on the nuclear ITS and the plastid tufA regions, it was hard to resolve the species delimitation between U. ohnoi and the closely related species having marginal denticulation. By reassessing the species boundaries of them on tufA region including the sequences obtained in the http://e-algae.org Ulva blooms are becoming a regular and increasingly severe problem in estuarine systems and coastal areas worldwide.…”

“…Mao et al (2014) partially sequenced the plastid elongation factor gene (tufA) and placed specimens from Holly Pond, USA in a well-supported clade with published sequences of U. laetevirens (HQ610428) identified previously with no divergence. Kang et al (2019) described U. laetevirens inhabiting Jeju Island using tufA and ITS analyses. Based on our tufA and rbcL DNA barcoding methods, the presence of with a close phylogenetic relationship to U. laetevirens based on rbcL and internal transcribed spacer (ITS) regions (Matsumoto and Shimada 2015).…”

“…Although several studies have focused on the factors causing massive blooms around Jeju Island (Hwang et al 2005, Song et al 2016, Kwon et al 2017, little attention has been paid to the taxonomic identification of the Ulva species involved in these blooms. Recently, a study of Ulva from Jeju Island was performed to clarify its species composition (Kang et al 2019). They focused on the species diversity along the coast of Jeju without precisely determining the causative species of Ulva blooms.…”