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 (tufA) 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 tufA 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.
Highlights
The marine green macroalgal genus Ulva, especially notorious for green tide formation, is comprised of approximately 100 species, of which 18 species have so far been recorded from Korea [1,2,3,4]
We find a total of 9 Ulva species and Blidingia spp. distributed across 23 sites in Jeju Island, based on a combined analysis of cpDNA tufA and nuDNA internal transcribed spacer (ITS)-based phylogenies
ITS marker in Generalized Mixed Yule Coalescent (GMYC) analyses suggested three clusters of Ulva species (Table 2) and could not recover further distinct groups, which was clearly found as a monophyly (e.g., U. torta) in both phylogenetic trees (Figs 3 and 4)
Summary
The marine green macroalgal genus Ulva, especially notorious for green tide formation, is comprised of approximately 100 species, of which 18 species have so far been recorded from Korea [1,2,3,4]. Molecular phylogenetic analysis of the genus Ulva in Jeju Island, Korea. 2016R1D1A1B03934959) to HJL and by a grant (NRF-2017R1C1B1010741) from the Basic Science Research Program, through the National Research Foundation of Korea (NRF), which is funded by the Ministry of Science, ICT and Future Planning to JHKang. The funder provided support in the form of salaries for author (JHKim), but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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