SUMMARY During soil‐algological research in the mountainous area of Asian Russia near Lake Baikal, we isolated a new chlamydomonad strain, IRK–A 362. Morphological and ultrastructural features of this alga have been studied using light and transmission electron microscopy (TEM). Phylogenetic reconstructions were inferred based on the small subunit rDNA (18S rDNA), the internal transcribed spacers (ITS1‐ITS2), and the plastid‐encoded elongation factor Tu ( tuf A). Secondary structures of ITS1 and ITS2 were analyzed and compensatory base changes (CBCs) were investigated. Based on the obtained results, including molecular, morphological, and ultrastructural features, we describe the strain IRK–A 362 as the new species Edaphochlamys sudakovae sp. nov.
Brown algae, as multicellular organisms, possess plasmodesmata (PD) that connect adjacent cells and facilitate cell-to-cell interactions, similar to land plants. In brown algae, PD are tiny tubular cytoplasmic channels measuring 10-20 nm in diameter. The distribution of PD appears to depend on body structure: in uni- and multiseriate filaments, PD are scattered across cross walls, whereas in thalli undergoing cellular differentiation, PD are concentrated into localized regions known as pit fields (PF). However, it remains unclear how the developmental reorganization of PD contributes to the regulation of intercellular communication, as information on the size exclusion limit (SEL) in PF remains limited. In this study, we investigated early development from zygotes and protoplasts in sporophytes of Saccharina japonica, the brown alga with a highly differentiated thallus, to determine the timing of PD distribution and the properties of PF-mediated intercellular transport. We found that PF were already present at the two-celled stage in both the zygote- and protoplast-derived developmental pathways, in contrast to observations in Scytosiphon lomentaria, Mutimo cylindricus, Silvetia babingtonii, and Fucus distichus. Quantitative measurements revealed that PF width increased during development, whereas the spacing between individual PD remained relatively constant. Furthermore, analysis of intercellular transport using gold nanoparticles conjugated with 3 kDa and 10 kDa FITC-dextran, introduced into the epidermal cells of differentiated sporophytes by particle bombardment, demonstrated size-dependent movement through PF.
We identified 10 Caulerpa species collected from Okinoerabujima Island, Ryukyu Archipelago, Japan, using the tufA DNA barcode marker. Their tufA sequences showed 99.9-100% identity with tufA sequences available in GenBank. Among them, C. andamanensis and C. minuta, newly recorded species in Japan, were recognized by both morphological and molecular analyses. Caulerpa andamanensis is characterized by stolons and assimilator bases covered with short, acute processes and by minute spines produced at the branchlet tips, whereas C. minuta is characterized by simple, flattened, and roundish to oblong assimilators.
Twelve strains of thin filamentous cyanobacteria belonging to the genus Drouetiella were isolated from freshwater and subaerophytic environments in the Republic of Korea and examined using a polyphasic approach integrating morphological, ultrastructural, and molecular data. Of these, five strains (ACKU959-ACKU963) were clearly distinct from previously described Drouetiella species based on combined morphological and molecular evidence. Strain ACKU959 was characterized by wider cells than previously described Drouetiella species, frequent solitary or paired false branching, and rounded, swollen terminal cells. In the 16S rRNA phylogeny, strain ACKU959 was positioned within a clade comprising D. fasciculata, D. epilithica, and D. elegans; however, sequence similarity values (97.79-98.32%) to these taxa were below the 98.65% threshold generally accepted for species delimitation, supporting its recognition as a distinct species. Strains ACKU960-ACKU963 were morphologically indistinguishable, sharing olive-brownish cell coloration, wider cells than previously described Drouetiella species, and necridic cells appear in rows. These strains showed 100% 16S rRNA gene sequence similarity among themselves and formed a well-supported monophyletic clade in phylogenetic analyses. They were closely related to the Chinese strain Drouetiella sp. FACHB-3567, with a sequence similarity of 99.37%. Transmission electron microscopy corroborated observations from light microscopy, including the presence of a sheath and constrictions at the cross-walls, and revealed ultrastructural characteristics such as a parietal arrangement of thylakoids. The secondary structures of the 16S-23S ITS region (D1-D1 ', Box-B, and V3 helices), together with ITS percent dissimilarity (3.36-16.02%), further supported their distinction from previously described Drouetiella species. Accordingly, two novel species, Drouetiella lacustris sp. nov. and Drouetiella olivacea sp. nov., are described in accordance with the International Code of Nomenclature for algae, fungi, and plants.
The red algal species Fredericqia deveauniensis (Phyllophoraceae, Gigartinales) was first reported from the Sea of Japan, as well as from the north-western Pacific. It is the second species of the genus confirmed in the north-western Pacific region. Specimens were collected from drift in two bays within Peter the Great Bay (Russian coast of the Sea of Japan) several times in 2025 and 2026. The specimens were identified based on molecular and morphological analyses. The rbcL sequence of the Russian specimens was almost identical to that of authentic specimens of F. deveauniensis from the Atlantic and British Columbia (north-eastern Pacific) and differed by only 0.08%. Further investigation involving additional field sampling along the coastlines of Korea, Japan, and China, and detailed molecular analyses of herbarium specimens are needed to understand, whether F. deveauniensis is widely distributed along the Asian coast or restricted to the Russian part of the Sea of Japan.
Coral bleaching, characterized by the loss of Symbiodiniaceae symbionts from corals, is promoted both by acute high-temperature events and by prolonged moderate thermal stress. However, the mechanisms responsible for decreases in Symbiodiniaceae cell densities within corals remain unclear. Symbiodiniaceae cells within corals proliferate through cell division; therefore, their population density is generally understood to be regulated by the host coral through symbiont cell expulsion. Coral bleaching may reflect a disruption of this balance, specifically between symbiont proliferation and host-mediated expulsion. In the coral Acropora selago, extreme temperatures (32 degrees C) induce extensive symbiont expulsion, whereas physiological damage is already evident at more moderate temperatures (30 degrees C). To detect early signals preceding symbiosis breakdown in this species, we conducted high-resolution monitoring of symbiont expulsion and cell division at 3-h intervals under thermal stress (30 degrees C), using 27 degrees C as control. At 30 degrees C, symbiont expulsion increased 1.7-2.3-fold, while dividing symbiont cells decreased by nearly 40% relative to 27 degrees C. To assess direct thermal effects on Symbiodiniaceae cells, eight culture strains from six genera (two free-living species and six host-derived species) were used to observe changes in growth and photosynthetic performance at 27 degrees C and 30 degrees C. Except for two strains of free-living species, photosynthetic performance showed no significant change, whereas four of the remaining host-derived species exhibited significantly reduced growth at 30 degrees C. Based on observations of Symbiodiniaceae both within A. selago and in culture strains, our results suggest that even slight increases in temperature can substantially suppress their proliferation. Although the increase in expulsion at 30 degrees C was less pronounced than the massive loss at 32 degrees C, acceleration of symbiont expulsion is already evident at this moderate temperature. Visible bleaching was not observed; nonetheless, these results indicate that even moderate thermal stress can trigger an imbalance between symbiont proliferation and host-mediated expulsion, processes essential for maintaining appropriate symbiont density within the coral.
We compared type material of Epithemia argentina described by Brun, as well as other collections with type material of two purported synonymous taxa, E. debyi and E. multicostata, described by Pantocsek, based on light and scanning electron microscopy. All three taxa were transferred to the genus Rhopalodia by M & uuml;ller. R. argentina has robust costate fibulae, a large tubular canal raphe, striae in single to double rows of areolae, and volate occlusions with a single point of attachment and positioned internally. R. argentina is distinguished from R. debyi and R. multicostata by costate fibula density and shape of the valves. The latter two species are considered heterotypic synonyms of each other. The distributions of these species over time and space are discussed.
Lithophyllum Philippi (Corallinales, Corallinophycidae, Rhodophyta) is a diverse genus of non-geniculate coralline algae. Lithophyllum neo-okamurae and L. okamurae are commonly found in the intertidal and subtidal zones of Jeju Island, Korea, where they contribute to local benthic communities. Despite their ecological importance, their morpho-anatomical and genetic variation remain poorly understood in this region. We investigated these two species through morpho-anatomical and molecular analyses (psbA and rbcL) based on specimens collected from 13 sites around Jeju, Korea. Lithophyllum neo-okamurae exhibited both unattached, free-living (rhodolith) and attached forms, each showing distinct distributions associated with local hydrodynamic and substrate conditions. Molecular analyses revealed distinct haplotypes corresponding to the two forms, and morpho-anatomical analyses detected statistically significant differences in tetrasporangial conceptacle chamber dimensions (diameter and height) between them. In contrast, L. okamurae occurred exclusively as unattached rhodoliths and was mainly distributed in deeper subtidal rhodolith beds compared with L. neo-okamurae. Our findings demonstrate form-related morpho-anatomical and genetic differentiation in L. neo-okamurae and underscore the ecological role of L. neo-okamurae and L. okamurae as major rhodolith-forming species in Jeju, Korea.
Undaria pinnatifida (wakame) is a brown macroalga of high economic and ecological importance in Northeast Asia, where it is cultivated and harvested from wild populations. In addition to its native range, this species has become invasive in Europe, Oceania, and South America largely through aquaculture, ballast water, and hull fouling. In Japan, wild wakame is increasingly valued as a premium product, generating a demand for DNA-based traceability systems that can authenticate regional provenance. However, most genetic studies have focused on broad-scale phylogeographic patterns, and the commonly used mitochondrial markers cox3 and the intergenic region between tatC and tRNA-Leu, as well as microsatellites, provide limited resolution for distinguishing geographically proximate populations. To address this limitation, we analyzed four populations from northern Kyushu (Jinoshima, Shikanoshima, Amakusa, and Kunisaki) using a novel mitochondrial intergenic region between cox3 and atp6 (cox3-atp6). The novel marker exhibited higher nucleotide and haplotype diversity and enabled clear discrimination among closely situated populations, such as Jinoshima and Shikanoshima, which are separated by approximately 30 km. In contrast, most Kunisaki individuals were indistinguishable from the Amakusa haplotypes and a few were closely related to haplotypes from Shikanoshima, both located on the opposite coast of Kyushu. This pattern indicates that the Kunisaki assemblage has a composite origin dominated by affinities with Amakusa, with a minor contribution from Shikanoshima, and that recent human-mediated introduction from other regions into Kunisaki represents one possible explanation. In conclusion, the application of the cox3-atp6 region as a marker improved the resolution of U. pinnatifida population structure, facilitating the distinction between geographically proximate populations and the detection of human-mediated introductions, thereby supporting DNA-based traceability and regional branding.
We examined the seasonal growth and reproduction of the carrageenophyte Chondrus ocellatus in Hakampo, Korea (July 2014-April 2015), to understand its adaptation to environmental variability across the intertidal zone. Three hypotheses were tested: (1) growth is greater at the lower shore with reduced stress; (2) gametophytes dominate at the upper shore; and (3) the gametophytes: sporophytes (G:T) ratio varies with season and shore height. Biomass and frond weight were significantly higher at the lower shore than at the upper shore, with clear seasonal variation. Maximum biomass (1695.82 +/- 492.84 g wet wt. m-2, mean +/- SE) occurred in July, and maximum mean frond weight (797.27 +/- 67.97 mg) in October. In contrast, frond density did not differ significantly between seasons or shore heights. Gametophytes predominated at the upper shore, whereas tetrasporophytes were more abundant at the lower shore. Seasonal reproductive patterns were consistent, with tetrasporic and cystocarpic fronds peaking in October and reaching their lowest abundance in April. Tetrasporic fronds remained more abundant than cystocarpic fronds throughout the study period. The G:T ratio varied significantly with both season and shore height, ranging from 0.05 to 2.45. These findings indicate that intertidal environmental stress strongly affects the abundance and reproductive dynamics of Chondrus ocellatus, which shows a primary growth period from July to October and reproductive peaks in October and January.
The genetic information of the authentic strain of Chlamydomonas kakosmos var. ovoidea has not been reported. In this study, the 18S-ITS rDNA of the authentic strain SAG 26.87 was sequenced, and its taxonomic position was determined. The 18S-ITS rDNA sequence of the strain SAG 26.87 was identical to the strain SAG 68.81, the authentic strain of Heterochlamydomonas callunae. Phylogenetic analysis based on 18S rDNA revealed that this strain belongs to Heterochlamydomonas. Light microscopy showed that this strain satisfies the diagnostic characteristics of Heterochlamydomonas, including two flagella arranged in parallel and of different lengths. In addition, the strain SAG 26.87 was morphologically indistinguishable from C. kakosmos var. kakosmos and H. callunae. Based on these results, Heterochlamydomonas kakosmos comb. nov. is proposed, and H. callunae is considered its synonym.
In the planozygotes of chlorophytes, parental flagella and eyespot(s) are generally arranged in a coordinated manner in the cell following the fertilization of biflagellate gametes. This phenomenon can be attributed to the process of gamete-gamete fusion occurring at a specific location on the cell surface, which is designated as the mating structure/cell fusion site. Notably, this structure/site occupies distinct positions in the gametes of opposite mating types or sexes. To ascertain whether analogous cell fusion processes and planozygote formation are observed in species lacking eyespots, the fertilization of the markedly anisogamous marine green macroalga Codium fragile was observed using fluorescence microscopy, field emission-scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Both the female and male gametes were biflagellate and, presumably, lacked the mating structure. Following the mixing of female and male gametes, the male gametes immediately gathered around the female gamete and adhered to its surface within 10 s. Subsequently, one male gamete entered the female gamete at the vicinity of the flagellar base, where the female nucleus was located. In the mating gametes, gamete-gamete adhesion and fusion occurred between the lateral side of the male gamete, which was parallel to the flagellar beat plane, and the cell anterior of the female gamete, which was close to the flagellar base. This suggests that cell fusion occurred at the limited region of the gamete cell surface. Consequently, female and male flagella became a pair and showed a Y-shaped arrangement in the planozygote when viewed from the cell anterior.
Four species of marine macroalgae are described from Rangit & amacr;hua, the northern islands of the New Zealand archipelago. The flora of this region has been considered to have its strongest affinities with other warm-water regions of the Pacific and Indian Oceans, with very low levels of endemism. Many of the taxa from the region have been known from three or fewer collections, and previously many were only identified to genus as key morphological, and anatomical features required for species-level identifications were not available, and there were few species for which sequence data were available. Three of the new species, belonging to the genera Codium, Delisea, and Pyropia, were previously reported from Rangit & amacr;hua under other names. Sequence data have revealed them to differ from species from mainland New Zealand and the wider Pacific, and they are currently considered to be endemic to the region. The discovery of a new species of the New Zealand endemic genus Psilophycus, also confirmed by sequence data, is of particular interest given the genus has been regarded as monotypic and endemic to the northern North Island of New Zealand. This research provides new insights into the relationships of the flora, with additional newly discovered taxa revealed through sequencing data awaiting description.
This study examines the response of the Mediterranean native macroalgae Caulerpa prolifera and of its allochthonous invasive congeneric C. taxifolia to temperature and explores the structure of their associated epiphytic bacterial community, aiming to understand the role of bacteria on algal thermal stress tolerance and adaptability. Two experiments were performed in controlled conditions. In the first, the algae were exposed to three different temperatures (20, 24, and 28 degrees C), and the main morpho-functional traits, the abundance, and the composition of their bacterial communities were assessed. In the second, algae exposed to their intermediate and most stressful temperature were treated with antibiotics. Once again, the main morpho-functional traits were determined for the different treatments. The results revealed opposite responses of C. prolifera (CP) and C. taxifolia (CT) to temperature. At 28 and 20 degrees C, respectively, for C. prolifera and C. taxifolia, higher mortality rates (CP: 33% and CT: 18%) and a reduction of all the traits were observed. The health condition of both species worsened when antibiotics were used, especially in stressful conditions, where the highest mortality rates occurred (CP: 75% and CT: 81%). Moreover, the epiphytic bacterial communities of both species significantly changed in response to temperature without antibiotics, showing greater bacterial abundance at 28 and 20 degrees C (CP28: 25 x 106 cells/cm; CT20: 30 x 106 cells/cm). Under suboptimal temperatures, algae were associated with the genera Suttonella and Bacillus, known for their role in enhancing algal tolerance. Overall, these findings prove the role of the epiphytic microbiota in supporting the temperature adaptability of these two seaweeds, suggesting its contribution to the invasiveness of C. taxifolia in the Mediterranean.
A dinophyte strain, WY98, was established by incubating an ellipsoid cyst from recent sediments collected in a freshwater reservoir in Fuzhou, China. Cell morphology and life cycle were examined using light and scanning electron microscopy. Motile cells of strain WY98 have an archetypical plate pattern similar to that of Peridinialean/Gonyaulacalean, exhibiting a plate pattern of 4 ', 4a, 7 '', Z, 4s, 6 ''', and 2 ''''. This strain is characteristic in having a horseshoe-shaped eyespot, a smooth thecal surface, and two antapical plates of unequal size. This strain is described as Sphaerodinium shuikouense sp. nov. Sphaerodinium shuikouense showed a diurnal migration and turned motile in a light period and immotile in a dark period. Asexual reproduction begins during the immotile stage, but the division is completed during the motile stage. Molecular phylogenetics using concatenated ribosomal RNA gene sequence data identified Sphaerodiniaceae as a member of the Suessiales and Sphaerodinium shuikouense as a relative of S. cracoviense and one Cystodinium species. The relatively high number of thecal plates suggests that Sphaerodinium occupies an intermediate phylogenetic position between suessioid and peridinioid dinophytes.
Kelp forests are threatened by rising ocean temperatures. However, the effects of warming on early life stage interactions among co-occurring kelp species, particularly competitive dynamics and reproductive timing, remain poorly understood. This study investigates the effects of temperature on embryonic sporophyte competitive interactions and reproductive timing of three co-occurring kelp species: Macrocystis pyrifera, Pterygophora californica, and Nereocystis luetkeana through laboratory-based sporophyte density and gametogenesis experiments. Results indicate that temperature significantly affects kelp sporophyte competitive dynamics. P. californica sporophytes outcompeted M. pyrifera sporophytes at lower temperatures (8 and 12 degrees C), while M. pyrifera sporophytes outcompeted both P. californica and N. luetkeana sporophytes at 16 degrees C. N. luetkeana exhibited consistently lower sporophyte density compared to the other species. Reproductive timing also varied with temperature, with earlier egg production observed at higher temperatures for all three kelp species. These findings suggest that climate-induced warming could alter the competitive landscape of kelp forests, potentially favoring M. pyrifera over other species. Understanding these complex interactions is crucial for predicting the ecological consequences of ocean warming and developing effective conservation strategies for kelp ecosystems.
We describe Epithemia fragarioides sp. nov., a diatom species from Japan. Our description is based on morphological analyses using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), supplemented by molecular phylogeny. Under LM, E. fragarioides has valves with a nearly straight ventral margin, a convex dorsal margin, narrow capitate apices, and distinctly separated areolae. SEM observations reveal that the areolae are slightly depressed below the valve face and exhibit occlusions with small projections. This fine structure is the most distinctive characteristic of this species compared to similar taxa, such as Rhopalodia michelorum and Rhopalodia tholulata . The ecological optimum of this species appears to be associated with neutral to slightly acidic wetlands with moderate electrical conductivity. Additionally, we relate our findings to the systematic understanding of the genus Epithemia / Rhopalodia .
The brown algal order Asterocladales, which contains the single genus Asterocladon and is the sister order of the Ectocarpales, has stellate chloroplasts. We investigated newly established isolates of Asterocladon from southern/subtropical Japan to reveal their taxonomic positions based on morphological and molecular analyses using rbc L and psa A genes. An isolate of Asteronema breviarticulatum , which was so far classified in the Scytothamnales, was revealed to belong to Asterocladon , and thus Asterocladon breviarticulatum comb. nov. is proposed. Two other isolates of Asterocladon are described here as new species, Asterocladon iriomotense sp. nov. and Asterocladon discoideum sp. nov. Asterocladon iriomotense was characterized by small filamentous thalli having oligostichous parts, phaeophycean hairs, and globular masses on which plurilocular sporangia are formed. Asterocladon discoideum was characterized by small discoid thalli with phaeophycean hairs and globular or semiglobular masses, cells of which were differentiated into plurilocular sporangia.
Pyropia haitanensis is a vital economically cultivated seaweed in China. However, the frequent occurrence of extreme high-temperature events has posed a severe threat to its industrial sustainability. To develop new heat-resistant strains of Pyropia, this study conducted a crossing experiment using genetically distinct parental strains. The female parent was the mutant strain (SH-3) of P. haitanensis. The male parent (HR-6) was an interspecific hybrid between P. haitanensis and Pyropia radi. From the F1 blades derived from heterozygous conchocelis, a heat-resistant strain named Ph-c-2 was successfully isolated. When conchospores of the three strains were subjected to high-temperature culture at 30 degrees C for 14 days, the survival rate of Ph-c-2 conchospore germlings reached 46.1%, which was 1.2-fold and 3.1-fold that of SH-3 and HR-6, respectively. After being cultured for 30 days at a suitable temperature (25 degrees C), the mean length of Ph-c-2 blades was 22.0 cm, comparable to HR-6 but 3.1-fold longer than SH-3. At 60 days of culture, Ph-c-2 blades exhibited a mean length of 184.3 cm, which was 1.4-fold and 2.8-fold longer than SH-3 and HR-6, respectively. The contents of pigments and pigment proteins in 45-day-old blades of Ph-c-2 were significantly higher than those in both parental strains. When blades cultured at 25 degrees C for 30 days were further cultured at 30 degrees C for 30 days, HR-6 blades showed massive cell death, chromatophore morphology shifting from star-shaped to diffused, and growth stopped. In contrast, SH-3 and Ph-c-2 blades exhibited extremely few dead cells and maintained relatively rapid growth rates. In summary, compared with the two parental strains, the hybrid recombinant strain (Ph-c-2) showed greater advantages in terms of growth rate, pigment protein content, and heat resistance of conchospores and young blades, etc. It is expected to be cultivated into a new variety for production applications.
Two new Chlorella-like microalgal strains, Mei-3 and Mei-4, were isolated from rock surfaces in the intertidal zone of Japan, a habitat with high irradiation, high salinity, and periodic dryness. The two strains grew well in a freshwater medium and showed high tolerance to photooxidative stress conditions. A phylogenetic analysis based on SSU rDNA-ITS sequences revealed that the strains Mei-3 and Mei-4 belong to the family Chlorellaceae, and Mei-4 represents an independent lineage within the family. Secondary structural analysis of ITS2 revealed compensatory base changes between Mei-3 and its most closely related species in the genus Chlorella. Based on light and transmission electron microscopy, the mature cells of the two strains are spherical or oval shaped with smooth cell walls, and each cell contains a single pyrenoid penetrated by thylakoid membranes, a typical morphological feature of the family Chlorellaceae. However, Mei-4 showed morphological changes in response to stress, with an accumulation of oil droplets along the extremely thickened cell wall. On the basis of molecular and morphological analyses, we propose Chlorella intertidalis sp. nov. for Mei-3 and Apricichlorella intertidalis gen. et sp. nov. for Mei-4.
