INTRODUCTION
Phylogenetic surveys integrating genetic data with morphological observations provide a comprehensive approach to explore algal diversity and taxonomy (Sun et al. 2012, Muangmai et al. 2014b, Vieira et al. 2016a, 2019a). Through these combined analyses, many new algal species and cryptic diversity have been discovered (Muangmai et al. 2014a, 2017, 2022, 2025, Klomjit et al. 2022, Jurejan et al. 2024) as well as long-standing taxonomic uncertainties, previously unsolvable with morphology alone, have been clarified (Draisma et al. 2010, Pattarach et al. 2019, Dam et al. 2023, Vieira et al. 2023). Additionally, this approach enhances our understanding of seaweed evolution, biogeography, and potential applications (Zuccarello and Martin 2016, Gaubert et al. 2019, Bulan et al. 2022, Muangmai et al. 2023).
The genus Lobophora J. Agardh (Dictyotales) is an ecologically important marine brown alga, widely distributed in tropical and warm temperate water (Slattery and Lesser 2014, Camacho et al. 2019, Vieira 2020, Vieira et al. 2021b). This alga has flattened and fan-shaped thalli, exhibiting diverse forms ranging from crustose to erect, which are influenced by both species-specific traits and environmental conditions (Sun et al. 2012, Vieira et al. 2016b, Huisman 2019, Puk et al. 2020). Currently, 96 Lobophora species are taxonomically accepted and recognized worldwide (Jurejan et al. 2024, Guiry and Guiry 2025). Given the high morphological plasticity and cryptic diversity within the genus, several taxonomic studies have consistently reinforced that the most robust approach for accurately identifying Lobophora species involves first conducting DNA sequence analysis, followed by examination of morphological and ecological data (Camacho et al. 2019, Vieira et al. 2019a, 2021a, 2023, Klomjit et al. 2022).
The global diversity of Lobophora species is continuously being assessed and the number of newly discovered species has increased steadily in recent years (Vieira et al. 2017, 2021a, 2023, Jurejan et al. 2024). Currently, the highest Lobophora diversity has been recorded in the Central Indo-Pacific (CIP), with approximately 60 species, followed by the western Indian Ocean with 43 species (Vieira et al. 2017, 2021a). However, exploration of this algal diversity has focused on particular regions, such as western and southern Pacific and Australia, while other areas remain understudied. This limited survey coverage likely results in an underestimation of Lobophora species diversity. Accordingly, more comprehensive sampling across all regions is necessary to accurately document Lobophora species diversity.
In the Southeast Asian (SA) region, which is part of the CIP, Lobophora diversity has remained relatively less explored compared to other regions. Despite the limitations in sampling efforts and investigations, several novel Lobophora species have been documented in SA. For instance, three new species have been reported from Vietnam, including L. tsengii D. Tien & Z. Sun, L. vietnamensis D. T. Dam, M. L. Nguyen & C. W. Vieira, and L. quangtriensis D. T. Dam, M. L. Nguyen & C. W. Vieira (Sun et al. 2021, Dam et al. 2023). Additionally, five new species were described in Thailand, including L. andamanensis Jurejan, Draisma, C. W. Vieira & Muangmai, L. chumphonensis A. M. Klomjit & C. W. Vieira, L. phuketensis Jurejan, Draisma, C. W. Vieira & Muangmai, L. rachaensis Jurejan, Draisma, C. W. Vieira & Muangmai, and L. thailandensis A. M. Klomjit & C. W. Vieira (Klomjit et al. 2022, Jurejan et al. 2024). These recent discoveries suggest a possibly high diversity of Lobophora in these areas and highlight the need for intensive assessment of Lobophora diversity across the SA region.
The diversity of Lobophora in Thailand has been limitedly explored, with research mainly focused on specific areas, such as the east coast around the inner Gulf of Thailand (Klomjit et al. 2022) and the west coast near the Malacca Strait, including Phuket, Trang, and Satun provinces (Vieira et al. 2016a, 2017, Coppejans et al. 2017, Jurejan et al. 2024). This present study aims to conduct extensive sampling of Lobophora specimens along the east coast of Thailand and to reassess the species diversity through molecular analyses, followed by an examination of morphological and ecological data. Our findings delve into the diversity and distribution patterns of Lobophora in Thailand and contribute to addressing a significant gap in the understanding of Lobophora diversity and biogeography in Southeast Asia and globally.
MATERIALS AND METHODS
Algal sampling
Lobophora specimens were collected from the eastern coasts of Thailand using both snorkeling and SCUBA diving methods at depths ranging from 1 to 15 m (Fig. 1, Supplementary Table S1). The specimens were obtained either by carefully scraping them from the substrate or by collecting them along with the substrate. A portion of the samples was preserved in silica gel for genetic analysis, while the rest was kept as herbarium voucher specimens for morphological study. The voucher specimens were deposited at the Thailand Natural History Museum (THNHM) in Pathum Thani, Thailand.
Genetic analyses
Extraction of DNA from silica gel-dried algal samples was performed using either the NucleoSpin Tissue Kit (Macherey-Nagel, Düren, Germany) following the manufacturer’s protocols or the CTAB method as described by Zuccarello et al. (2006b). Three different molecular markers, including one mitochondrial (cox3) and two chloroplast (psbA and rbcL) genes, were amplified using specific primer sets: for cox3, cox3-D1 (Sun et al. 2012)/cox3-P2 (Ni-Ni-Win et al. 2008); for psbA, psbA_F/psbA_R1 (Yoon et al. 2002); and for rbcL, rbcL68F (Draisma et al. 2001)/rbcL_R708 and rbcL_543F/rbcL_1391R (Bittner et al. 2008) (Supplementary Table S2). The polymerase chain reaction (PCR) reaction was carried out using the PCR master mix solution of the i-Taq iNtRON kit (iNtRON Biotechnology, Seongnam, Korea). The PCR products were commercially cleaned and sequenced by the U2Bio (Seoul, Korea).
All sequences were individually edited and assembled, then aligned and concatenated using the Geneious Prime 2023.2.1 software package (Biomatters Ltd., Auckland, New Zealand) employing the MAFFT (Katoh and Standley 2013) sequence alignment algorithm. For phylogenetic analyses, additional sequences of Lobophora were retrieved from GenBank (Supplementary Table S1) and included in our dataset. The alga species Padina boergesenii Allender & Kraft and Newhousia yhaga C. W. Vieira, De Clerck & Payri were selected as outgroups (Vieira et al. 2023, Jurejan et al. 2024). Genetic distances among sequences (635 bp of cox3, 945 bp of psbA, and 1,303 bp of rbcL) were calculated using the uncorrected p-distance method implemented in MEGA11 (Tamura et al. 2021), with pairwise deletion applied to handle gaps and missing data. Pairwise deletion was selected as the gap-handling method because our dataset includes sequences of varying lengths, particularly for cox3 where sequences ranged from partial fragments to full-length amplicons. This variation is common in molecular systematic studies that incorporate both newly generated sequences and previously published data from GenBank, as well as sequences from degraded herbarium specimens. Pairwise deletion calculates genetic distances based only on the positions present in both sequences being compared, allowing the inclusion of all available sequences while maintaining analytical accuracy. This approach prevents the excessive data loss that would result from complete deletion or trimming to the shortest common sequence length, which would eliminate phylogenetically informative sites. The use of pairwise deletion for datasets with heterogeneous sequence lengths is standard practice in molecular systematics (Tamura et al. 2021). Sequence alignments are available from the corresponding author upon request.
Phylogenetic analyses were conducted using both maximum likelihood (ML) and Bayesian inference (BI) methods on individual marker datasets as well as concatenated datasets (cox3 + psbA + rbcL). ML analyses were performed using IQ-TREE (Minh et al. 2020), with the best-fit model for each gene and codon position determined by ModelFinder (Kalyaanamoorthy et al. 2017) through the Bayesian information criterion, using 2,000 bootstrap replicates. BI was conducted using MrBayes v3.2 (Ronquist et al. 2012), with substitution models selected by Kakusan 4 (Tanabe 2011). Two independent runs, each with four chains, were performed simultaneously for three million generations, with sampling every 1,000 generations and a 25% burn-in. The remaining samples were used to construct the consensus tree and calculate Bayesian posterior probabilities. The optimal partition schemes and substitution models for both ML and BI methods across all datasets are detailed in Supplementary Table S3. The final ML and BI trees were edited and visualized using FigTree v.1.4.4 software (http://tree.bio.ed.ac.uk/software/figtree/).
Species delimitation was performed using ASAP (Assemble Species by Automatic Partitioning) (Puillandre et al. 2021) implemented in iTaxoTools v0.1 (Vences et al. 2021). The cox3 marker (635 bp) was selected due to its higher variability compared to psbA and rbcL (Sun et al. 2012, Vieira et al. 2016a) and the availability of a comprehensive dataset for this gene region. Genetic distances were calculated using the Kimura 2-parameter model, and the partition with the lowest ASAP score was selected as the optimal species delimitation hypothesis.
Morphological observation
The external and internal morphology of each Lobophora sample was examined. In the field, we observed the growth forms and color of the Lobophora thallus following Vieira (2020). For internal morphology, dried algal fragments from the herbarium were rehydrated in seawater before being cut with a razor blade. Transverse and longitudinal sections from the margin and middle of the specimens were placed on glass slides for microscopic analysis. Measurements of the dorsal and ventral cortical cells, as well as the medullary layer, including their length, width, and height, were taken according to Vieira et al. (2014).
Quantitative traits of Lobophora specimens were compared across thallus thickness, cell size, thallus height, and medulla dimensions. Means with 95% confidence intervals (CIs) were calculated using t-based estimates (Cumming and Finch 2005). Effect sizes were quantified with Hedges’ g, which corrects for small sample bias (Hedges and Olkin 1985, Lakens 2013). Non-overlapping 95% CIs were used as descriptive evidence of separation between groups. Differentiation was primarily assessed through effect sizes (Hedges’ g) and associated CIs, which provide information about the magnitude and uncertainty of differences. We did not conduct formal hypothesis testing or apply multiple comparison corrections; our approach is diagnostic rather than inferential.
RESULTS
Molecular phylogenetic analyses
Sequences from 106 Lobophora specimens were newly generated, comprising 72 sequences (151–635 bp) for the cox3 gene, 56 sequences for the psbA gene (490–945 bp), and 15 sequences for the rbcL gene (627–1,303 bp) (Supplementary Table S1). The concatenated alignment for phylogenetic analyses consisted of 2,917 bp, including 635 bp from cox3, 945 bp from psbA, and 1,303 bp from rbcL. Genetic divergence analysis revealed considerable variation across the three markers. The cox3 gene exhibited the highest divergence, ranging from 0.2 to 22%. The psbA gene showed moderate levels of variation with sequence divergences ranging from 0.1 to 10%, while the rbcL gene demonstrated divergence values between 0.9 and 11%.
Both ML and BI analyses yielded congruent topologies across the three individual markers (cox3, psbA, and rbcL) (Supplementary Figs S1–S3) and the concatenated dataset, with minimal topological incongruence observed only within certain clades of the L. obscura complex. The ML phylogenetic reconstruction based on the concatenated dataset (Fig. 2) clearly delineated our specimens into 14 distinct, well-supported monophyletic clades. Among these 14 clades, nine corresponded to previously described taxa: L. abscondita C. W. Vieira, Payri & De Clerck, L. asiatica Z. Sun, J. Tanaka & H. Kawai, L. chumphonensis, L. henae C. W. Vieira & F. A. Rasoamanendrika, L. lamourouxii Payri & C. W. Vieira, L. obscura12 C. W. Vieira, De Clerck & Payri, L. obscura13 C. W. Vieira, De Clerck & Payri, L. quangtriensis, and L. thailandensis, three of which, L. abscondita, L. henae, and L. quangtriensis were reported for the first time in Thailand (Supplementary Fig. S4). Additionally, one supported clade (consisting of three samples from Chonburi and Rayong provinces) formed a distinct position within the L. obscura complex (Vieira et al. 2019a) and is designated herein as L. obscura14 (Supplementary Fig. S4). The remaining four clades were genetically distinct from all previously described species, each exhibiting a unique combination of growth form, pigmentation, and thallus cell structure (Table 1). Consequently, these four clades are proposed as new species: L. lewmanomontiae sp. nov., L. ogawae sp. nov., L. thiemmedhii sp. nov., and L. velasquezii sp. nov.
ASAP species delimitation partitioned 99 cox3 sequences into 76 species groups through recursive clustering (Supplementary Fig. S5A). The barcode gap histogram (Supplementary Fig. S5B) shows intraspecific distances ranging from 0.00–0.07, interspecific distances ranging from 0.13–0.26, with a distinct barcode gap (0.08–0.12) where few to no pairwise comparisons occur, clearly separating within-species from between-species variation. The optimal threshold of 0.0076 falls within the intraspecific range, effectively distinguishing species boundaries. Alternative partitioning schemes are shown in Supplementary Fig. S5C, with the optimal partition selected based on the lowest ASPS score. The analysis consistently delimited all four newly described species, including L. lewmanomontiae, L. ogawae, L. thiemmedhii, and L. velasquezii, as distinct evolutionary lineages, further validating their taxonomic status (Supplementary Fig. S5).
Lobophora lewmanomontiae A. M. Klomjit, J. Praiboon & N. Muangmai sp. nov. (Figs 3A & 4A–C)
Description
Thalli predominantly stipitate forming a fasciculate rosette, with a light brown to dark brown color, up to 7–8 cm (Fig. 3A). Algae possess a narrow or clear stipe at the base, with a cup-shaped holdfast, adhering firmly to various substrates (rock, dead coral, crustose coralline algae, or live coral) at depths of 3 to 12 m via basal rhizoids or holdfast rhizoids. Margins entire and smooth. Thallus thickness 72.5–137.5 μm, comprising 6–8 cell layers: a single-layered medulla flanked by a 3–4-layered dorsal cortex and a 2–3-layered ventral cortex (Fig. 4A–C). Reproductive structures not observed. This species differs from sympatric species by its erect, stipitate growth form, prominent cup-shaped holdfast, and uniform surface coloration lacking spots or radial pattern (Table 1). It forms a sister relationship with L. challengeriae from Oman (Fig. 2), with genetic divergence values of 1.6% in cox3, 0.5% in psbA, and 0.5% in rbcL genes (Supplementary Tables S4–S6). Intraspecific genetic variation ranges from 0–0.4% in cox3, with no variation detected in psbA and rbcL. The species occurs at Nangrong Beach and Yao Beach (Chonburi province) and Mannai Island (Rayong province), Thailand.
Holotype
THNHM-P-2021-0314, −8 m at Mannai Island, Rayong, Thailand (12°31′24″ N, 100°57′12″ E), Nov 20, 2021, leg. A. Klomjit.
Isotype
THNHM-P-2021-0315, −8 m at Mannai Island, Rayong, Thailand (12°31′24″ N, 100°57′12″ E), Nov 20, 2021, leg. A. Klomjit.
Paratypes
THNHM-P-2021-0316, THNHM-P-2021-0319 and THNHM-P-2021-0320, −8 m at Mannai Island, Rayong, Thailand (12°31′24″ N, 100°57′12″ E), Nov 20, 2021, leg. A. Klomjit; THNHM-P-2020-0296 and THNHM-P-2020-0297, −3 m at Nangrong Beach, Chonburi, Thailand (12°31′24″ N, 100°57′12″ E), Feb 15, 2023, leg. A. Klomjit; THNHM-P-2023-0157, −8 m at Yao Beach, Chonburi, Thailand (12°36′19″ N, 100°56′17″ E), Feb 15, 2023, leg. A. Klomjit. REL37 and REL38, Singapore (1°22′ N, 103°85′ E), Jan 30, 2020, leg. J. Fong.
Lobophora ogawae A. M. Klomjit, C. W. Vieira & N. Muangmai sp. nov. (Figs 3B & 4D–F)
Description
Thalli predominantly prostrate and thin, light to dark brown in coloration, up to 3–4 cm. Algae adhere firmly to substrates (rock or dead coral) at depths of 2 to 5 m via ventral rhizoids (Fig. 3B). Margins entire and smooth. Thallus thickness 65–117.5 μm, comprising 4–5 cell layers: a single-layered medulla flanked by a 2-layered dorsal cortex and a 1–2-layered ventral cortex (Fig. 4D–F). Reproductive structures not observed. This species differs from other sympatric species by its prostrate growth habit, uniform light to dark brown coloration (Table 1). It forms a sister relationship with L. providenceae from Pacific Islands (Fig. 2), with genetic divergence values of 6% in cox3 and 0.8% in psbA genes (Supplementary Tables S4 & S5). No intraspecific genetic variation detected in both genes. The species occurs at Mannai Island (Rayong province), and Kradat and Mak Islands (Trat province), Thailand.
Paratypes
THNHM-P-2022-0266 and THNHM-P-2022-0268, −2 m at Mak Island and Kradat Island, Trat, Thailand (11°49′57″ N, 102°30′9″ E and 11°50′14″ N, 102°31′9″ E), Dec 23, 2023, leg. A. Klomjit.
Lobophora thiemmedhii A. M. Klomjit, C. W. Vieira & N. Muangmai sp. nov. (Figs 3C & 4G–I)
Description
Thalli predominantly prostrate to crustose and thin, exhibiting golden yellow to yellowish orange color with unevenly distributed small dark spots and gray radial lines, up to 5.5–6.5 cm (Fig. 3C). Specimens adhere firmly to hard substrates such as rock, dead coral, or artificial reef at depths ranging from 4 to 14 m via ventral rhizoids. Margins entire and smooth. Thallus thickness 60–127.5 μm, comprising 5–6 cell layers: a single-layered medulla flanked by a dorsal cortex of 2–3 cell layers and a ventral cortex of 2–3 cell layers (Fig. 4G–I). Reproductive structures not observed. This species differs from other Thai species by its distinctive golden yellow to yellowish orange coloration, characteristic surface pattern with dark spots and gray radial lines, and larger size (Table 1). It forms a sister relationship with L. boussoleae and L. sp. 55 (Fig. 2), from which it differs by at least 2.2% in cox3, 0.3% in psbA, and 0.3% in rbcL genes (Supplementary Tables S4–S6). No intraspecific genetic variation detected in all genes. The species is distributed around Tao Island in Surat Thani province, Thailand.
Holotype
THNHM-P-2022-0247, −4 m at Japanese Garden near Nang-Yuan Island, Surat Thani, Thailand, Aug 13, 2022, leg. A. Klomjit.
Isotype
THNHM-P-2022-0248, −4 m at Japanese Garden near Nang-Yuan Island, Surat Thani, Thailand (10°06′58″ N, 99°48′53″ E), Aug 13, 2022, leg. A. Klomjit.
Paratypes
THNHM-P-2022-0245 and THNHM-P- 2022-0246, −11 m at Hin Wong Bay, Surat Thani, Thailand (10°06′16″ N, 99°50′54″ E), Aug 13, 2022, leg. A. Klomjit; THNHM-P-2022-0233, THNHM-P-2022-0234, THNHM-P-2022-0235, THNHM-P-2022-0236 and THNHM-P-2022-0238, −14 m at Nang-Yuan Island, Surat Thani, Thailand (10°07′05″ N, 99°48′31″ E), Aug 12, 2022, leg. A. Klomjit; THNHM-P-2022-0243 and THNHM-P-2022-0244, −3 m at Mae-Haad Beach, Surat Thani, Thailand (10°05′10″ N, 99°49′28″ E), Aug 12, 2022, leg. A. Klomjit.
Lobophora velasquezii A. M. Klomjit, S. G. A. Draisma & N. Muangmai sp. nov. (Figs 3D & 4J–L)
Description
Thalli predominantly crust-like to prostrate, exhibiting brownish yellow to yellowish gold coloration with occasional small dark spots, up to 2–3 cm. Algae adhere firmly to hard substrates at depths of 2 to 6 m through ventral rhizoids (Fig. 3D). Margins entire and smooth. Thallus thickness 90–117.5 μm, comprising 6–7 cell layers: a single-layered medulla flanked by a 3-layered dorsal cortex and a 2–3-layered ventral cortex (Fig. 4J–L). Reproductive structures not observed. This species differs from other species by its relatively thick thallus with brownish-yellow coloration with scattered dark spots (Table 1). It forms a sister relationship with L. petila (Fig. 2), with genetic divergence values of 8% in cox3, 2.8% in psbA, and 3% in rbcL genes (Supplementary Tables S4–S6). Intraspecific genetic variation ranges from 0–1.4% in cox3, with no variation detected in psbA and rbcL. The species occurs at Nang-Yuan Island and Pha-Ngan Island in Surat Thani province, Thailand, growing on rocks and dead coral at depths of 2–6 m.
Holotype
THNHM-P-2022-0237, −6 m at Nang-Yuan Island, Surat Thani, Thailand (10°07′05″ N, 99°48′31″ E), Aug 12, 2022, leg. A. Klomjit.
Paratype
THNHM-P-2022-0272, −2 m at Waterfall near Moon Rock bar, Pha-Ngan Island, Surat Thani, Thailand (9°48′7″ N, 100°1′14″ E), Apr 14, 2022, leg. S.G.A. Draisma; THNHM-P-2021-0332, −5 m at Mae Haad Beach, Pha-Ngan Island, Surat Thani, Thailand (9°47′52″ N, 99°58′39″ E), Apr 13, 2021, leg. S.G.A. Draisma.
Type locality
Nang-Yuan Island, Surat Thani province, Thailand, 10°07′05″ N, 99°48′31″ E, 6 m in depth.
Quantitative morphological analysis
Quantitative morphological analyses revealed clear morphological differentiation among the four novel Lobophora species (Supplementary Tables S7–S10). Lobophora lewmanomontiae was distinguished from L. challengeriae by five traits with non-overlapping 95% CIs, including thallus thickness (105.96 vs. 141.60 μm), dorsal cell height (34.30 vs. 51.60 μm), and ventral cell height (29.70 vs. 46.40 μm), with effect sizes ranging from 0.87 to 2.14 (Supplementary Table S7). Lobophora ogawae differed from L. providenceae in three key dimensions: dorsal cell height (24.83 vs. 31.30 μm), ventral cell count (1.33 vs. 1.20 cells), and medulla height (34.50 vs. 42.20 μm), with effect sizes of 0.29–1.71, plus distinct attachment substrate (rock vs. dead coral) (Supplementary Table S8). Lobophora thiemmedhii was separated from L. boussoleae by five traits showing non-overlapping CIs, particularly dorsal cell height (28.60 vs. 44.3 μm, effect size = 3.01) and thallus thickness (96.40 vs. 123.10 μm, effect size = 1.51) (Supplementary Table S9). Lobophora velasquezii showed the strongest morphological differentiation from L. petila, with all eight measured traits displaying non-overlapping CIs and exceptionally large effect sizes (1.15–5.32), including thallus thickness (106.30 vs. 57.00 μm) and dorsal cell count (3.00 vs. 1.80 cells) (Supplementary Table S10).
Distribution pattern
The distribution of each of the 14 Lobophora recorded from the Gulf of Thailand was mapped per province (Fig. 5). Among these taxa, Lobophora chumphonensis, L. obscura14, L. quangtriensis, and L. thailandensis demonstrate a broader distribution, occurring in both the northern and the western Gulf of Thailand (Fig. 5, Supplementary Table S1). In contrast, L. abscondita, L. asiatica, L. henae, L. obscura12, L. thiemmedhii sp. nov., and L. velasquezii sp. nov. have limited distribution, being found in only one province each. However, L. abscondita, L. asiatica, and L. henae are found outside the Gulf of Thailand, whereas the other species are at present only known from the Gulf of Thailand.
Surat Thani province, in the central gulf, had the highest species richness, with nine Lobophora species. Chonburi, Rayong, and Trat provinces, located in the northern part of the gulf, had moderate diversity with 4, 3, and 5 species, respectively (Fig. 5). The southern provinces of Nakhon Sri Thammarat and Pattani each possessed only one species: L. abscondita in Nakhon Sri Thammarat and L. lamourouxii in Pattani (Fig. 5).
DISCUSSION
This study presents the most comprehensive DNA-based assessment of Lobophora species from the east coast of Thailand to date, significantly enhancing our understanding of Lobophora species diversity and biogeography in Thailand and more broadly in the SA region. Among the lineages identified in this study, six were previously reported from Thailand (L. asiatica, L. chumphonensis, L. lamourouxii, L. obscura12, L. obscura13, and L. thailandensis), while one additional lineage of the L. obscura complex was detected (L. obscura14). Three lineages represent new records for the country (L. abscondita, L. henae, and L. quangtriensis), and four are newly described species (L. lewmanomontiae, L. ogawae, L. thiemmedhii, and L. velasquezii). Our findings increase the total number of Lobophora species in Thailand with molecular and morphological data to 21 species and elevate the count to 30 species in the SA region (Supplementary Table S11) (Vieira et al. 2016a, 2017, Coppejans et al. 2017, Kwan et al. 2021, Sun et al. 2021, Klomjit et al. 2022, Dam et al. 2023, Jurejan et al. 2024). Currently, the number of recorded Lobophora species in the Central Indo-Pacific region is 66 species, accounting for more than 65% of the 96 species worldwide.
Genetically, our findings demonstrated that cox3 was the most variable marker for species delineation in Lobophora, exhibiting consistently higher divergence values compared to the chloroplast markers psbA and rbcL, and revealing clear phylogenetic patterns among species (Fig. 2). This pattern has been documented across several Lobophora studies (Vieira et al. 2014, 2021a, Camacho et al. 2019, Klomjit et al. 2022, Jurejan et al. 2024). In our analysis, the interspecific divergence of cox3 among the four new Thai Lobophora species and their closely related species was consistent with the genetic distance threshold that varied considerably, ranging from a minimum of more than 1.2% (e.g., in Lobophora rickeri Kraft and Lobophora undulata C. W. Vieira, Payri & De Clerck) (Vieira et al. 2014, 2016a) to a maximum of more than 7% (e.g., in L. asiatica Z. Sun, Ji. Tanaka & H. Kawai and L. pachyventera Z. Sun, P.-E. Lim, Ji. Tanaka & H. Kawai) (Sun et al. 2012). These results align with previous molecular studies and confirm the utility of cox3 as an effective barcode marker for Lobophora (Sun et al. 2012, Vieira et al. 2014, Camacho et al. 2019). Based on these results, we recommend DNA sequence analysis using preferably cox3, rather than psbA or rbcL, for reliable Lobophora identification.
While previous studies have demonstrated that diagnostic morphological characters for distinguishing among Lobophora species are quite limited (Vieira et al. 2014, Camacho et al. 2019, Klomjit et al. 2022), our comprehensive morphological observations revealed several useful external features that aid in distinguishing the four new Thai species from their sister taxa (Table 1, Fig. 2). Lobophora lewmanomontiae is characterized by its distinctive stipitate growth habit with a fasciculate rosette pattern and cup-shaped holdfast, contrasting with the flabellate, ruffled thallus of L. challengeriae (Vieira et al. 2019a, Kwan et al. 2021). Lobophora ogawae exhibits a firmly attached prostrate growth form with variable light to dark brown coloration, differentiating it from both the flabellate, consistently dark brown, weakly attached L. providenceae (Vieira et al. 2019a) and the thinner (approx. 40–50 μm), mat-forming L. henae with its distinctive lighter margins (Vieira et al. 2021a). Furthermore, L. thiemmedhii displays a distinctive golden yellow to yellowish orange coloration with characteristic gray radial lines and substantially larger size (up to 5.5–6.5 cm), in contrast to the smaller (up to 2–2.5 cm), reniform, dark brown L. boussoleae (Vieira et al. 2019a, Dam et al. 2023). Lobophora velasquezii is characterized by its brownish yellow to yellowish gold coloration with occasional small dark spots, substantially thicker thallus, and greater number of cell layers (6–7 cell layers), differing markedly from the thinner (40–70 μm), fan-shaped L. petila with light to dark brown coloration and only 3–5 cell layers (Vieira et al. 2014). These distinctive morphological features, including differences in color, size, shape, and surface patterns, when integrated with molecular and ecological data, provide robust evidence for accurate species delimitation in the genus. For future research, we recommend comprehensive sampling across broader geographical regions to fully assess the species diversity of Lobophora, applying integrative taxonomic approaches that combine molecular analyses with detailed morphological, ecological and geographic observations (Vieira et al. 2014, 2021a, Camacho et al. 2019, Dam et al. 2023, Jurejan et al. 2024).
Among the 21 Lobophora species found in Thai waters, L. chumphonensis, the L. obscura complex, L. quangtriensis and L. thailandensis are relatively common in the Gulf of Thailand, occurring in numerous locations (see Fig. 5, Supplementary Table S1). Additionally, several Lobophora species exhibit distinct distribution patterns and geographic ranges. For instance, L. lamourouxii and L. asiatica are widely distributed across both the Pacific and Indian Oceans (Vieira et al. 2020, 2021a), whereas L. thailandensis and L. quangtriensis are limited to the South China Sea, specifically in Peninsular Malaysia, Vietnam, and eastern Thailand (Sun et al. 2012, Klomjit et al. 2022, Dam et al. 2023). The present study also extends the known geographic range of L. henae, previously reported only for Madagascar (Vieira et al. 2021a), into the Pacific basin. The geographic range of L. abscondita, previously only known from the South Pacific Ocean (Vieira et al. 2014, 2019a, 2023), was extended into the Northwestern Pacific Ocean. Furthermore, current data suggest that eight Lobophora species (i.e., L. chumphonensis, L. lewmanomontiae, L. ogawae, L. quangtriensis, L. thailandensis, L. thiemmedhii, L. velasquezii, and L. vietnamensis) may be confined to the South China Sea (Klomjit et al. 2022, Dam et al. 2023, present study). However, it is crucial to notice that these biogeographic range assessments are based on current sampling efforts and may not represent the full distribution of the respective species, as numerous studies on algal diversity have demonstrated that increased sampling effort consistently reveals greater variation and broader distribution patterns (Zuccarello et al. 2006a, Muangmai et al. 2022, 2023). This sampling limitation is particularly relevant for cryptic taxa like Lobophora, where morphologically similar species may be overlooked without molecular analysis, emphasizing the need for further research to establish a more comprehensive understanding of Lobophora species distribution and endemism patterns in the region.
Many previous studies have demonstrated a pattern of variation in algal species composition and genetic diversity between the two coasts of Thailand, as observed in other seaweeds, including the green alga Halimeda J. V. Lamouroux (Pongparadon et al. 2015), the brown alga Padina Adanson (Wichachucherd and Prathep 2013), and the red alga Bostrychia Montagne (Saengkaew et al. 2016). These patterns are likely facilitated by differences in sea-surface currents and environmental conditions between the coasts of Thailand. Our results show that the Gulf of Thailand and Andaman Sea coasts harbor completely different Lobophora species. Interestingly, we found substantial Lobophora diversity in the Gulf of Thailand, which has traditionally been considered less diverse for marine algae compared to the Andaman Sea. Seven Lobophora species have been recorded from the Thai Andaman west coast, i.e., L. andamanensis, L. phuketensis, L. rachaensis, L. ruae C. W. Vieira, A. D. R. N’Yeurt & M. Zubia, L. sp. 24, L. sp. 49, and L. sp. 56 (Vieira et al. 2016a, 2017, 2023, Coppejans et al. 2017, Jurejan et al. 2024). None of them were found on the Thai gulf east coast. The discovery of four new species in the Gulf challenges our understanding of seaweed diversity distribution along the Thai-Malay peninsula and suggests that more species might be discovered with increased sampling effort on the Andaman side. This apparent disjunction in species distribution could be partly due to sampling bias, as Lobophora collections from the west coast were primarily from Phuket Island (Jurejan et al. 2024). More thorough sampling of the typically more diverse Andaman coast might reveal even greater Lobophora diversity, which could help explain broader distribution patterns between the Indian and Pacific Oceans. Further studies are needed to clearly elucidate the diversity of Lobophora on the west and to provide a comprehensive view of this algal diversity in Thailand, which could potentially explain the biogeography of Lobophora between the Indian Ocean and the Pacific Ocean.
Lobophora species exhibit diverse ecological preferences across substrates including bedrock, coral rubble, and live corals (Diaz-Pulido and McCook 2004, Vieira et al. 2014, 2016b, 2019b, Klomjit et al. 2022, Dam et al. 2023). Our present study along the Gulf of Thailand documented species-specific interactions with corals: L. chumphonensis (Supplementary Fig. S4C) and L. quangtriensis (Supplementary Fig. S4F) grew on crustose coralline algae before encroaching onto live corals, with L. chumphonensis shown overgrowing Porites lutea (Supplementary Fig. S6A). Lobophora lamourouxii overgrew Acropora sp. after storm disturbance (Supplementary Fig. S6B), and L. lewmanomontiae directly colonized various live coral species (Supplementary Fig. S6C–G). These interactions mirror previous findings where L. chumphonensis preferentially colonizes Porites sp., L. obscura13 favors Favites sp. (Klomjit et al. 2022), and L. hederacea can overgrow Seriatopora caliendrum Ehrenberg, 1834 (Vieira et al. 2015). Despite these potentially competitive interactions, Lobophora typically poses minimal threat to coral ecosystems when herbivory and coral defenses remain intact (Vieira et al. 2016a, 2020). Additionally, multiple Lobophora species frequently coexist. For example, L. lewmanomontiae and L. chumphonensis co-occur at Nangrong Beach and Chorakhe Island. Similar coexistence has been observed in Vietnam (Dam et al. 2023) and Thailand (Klomjit et al. 2022, Jurejan et al. 2024). This suggests these species partition ecological niches through differences in substrate preference, light requirements, or depth tolerance. Further research should investigate the specific ecological mechanisms facilitating these coexistence patterns and clarify whether direct ecological relationships exist between Lobophora species and corals.
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