Journal of Phycology最新文献

Coralline algae form highly calcified thalli, creating key substrate that promotes biodiversity in nearshore marine environments. Although calcification and decalcification are critical for coralline growth and ecological function, their underlying mechanisms are not fully understood. We capitalized on the unique morphology of articulated coralline algae, assembling tissue-specific transcriptomes for calcified (intergenicular), uncalcified (genicular), and actively decalcifying (young genicular) tissues in the coralline alga Calliarthron tuberculosum and compared gene expression to identify putative calcification and decalcification genes. We captured the greatest differences in gene expression between calcified and uncalcified tissue, with 17.7% (5238 genes) of the genes in the transcriptome differentially expressed, the majority of which (10.9%) were upregulated in calcified tissue. There were also significant differences between decalcifying and uncalcified tissue, with 14.3% (4420 genes) of the genes in the transcriptome differentially expressed. We used functional gene annotation to identify 18 putative calcification genes and 10 putative decalcification genes. Results showed calcium-binding proteins, a vacuolar calcium transporter, and a calcium ATPase may be important for transporting calcium ions during calcification, whereas a proton ATPase may be important for maintaining pH homeostasis in calcified tissue. Additional genes for hydrogen ion transport were highly expressed in uncalcified tissues, including a sodium/hydrogen exchanger and hydrogen pump, which may be important for accumulating hydrogen ions to maintain uncalcified tissues. Differential expression of carbonic anhydrases and aquaporins indicated potential mechanisms for dissolved inorganic carbon transport in calcified and uncalcified tissues. This study has created valuable molecular resources for coralline algae and lent new insights on mechanistic details surrounding calcification and decalcification.

Japanese Dictyoteae have been documented since 1838, with a historical checklist of 21 names recorded prior to 1990. Persistent misidentifications—particularly of species originally described from Europe and the Americas—have complicated the taxonomy of the group in Japan. We reevaluated historical records and revised the national checklist for Canistrocarpus, Dictyota, Dilophus, and Rugulopteryx using integrated morpho-genetic analyses. Broad sampling from Hokkaido to Okinawa, including Japanese type localities, together with sequence data from type localities of species described elsewhere but reported in Japan, corrected persistent taxonomic ambiguities. The long-standing misapplication of the Asian D. dichotoma as D. spathulata was resolved. The revised checklist recognizes 19 species: 17 Dictyota, Canistrocarpus cervicornis, and Rugulopteryx okamurae. Species richness peaks in Kyushu with 15 species, whereas only D. spathulata extends to Hokkaido. Eight taxa appear native to the Northwest Pacific, including D. coriacea, D. haenyeosa, D. spathulata, D. spinulosa, D. sumbisoria, D. taewakia, Dictyota churaumia sp. nov., and R. okamurae. Twelve taxa exhibit broad, transoceanic distributions. We describe Dictyota churaumia sp. nov. and formally report nine species from Japan for the first time: Dictyota acutiloba, D. ceylanica, D. haenyeosa, D. humifusa, D. liturata, D. pfaffii, D. sandvicensis, D. sumbisoria, and D. taewakia. By integrating molecular data with morphological analyses, we resolved major taxonomic misidentifications and implemented the necessary taxonomic treatments (synonymies and typifications) to provide an updated taxonomic framework for the Dictyoteae flora of Japan. The presence of unique morphologies in historical herbarium specimens, coupled with unexplored regions of Japan, indicates a potential for additional, unidentified species.

In a molecular-assisted alpha taxonomic study of the genus Spyridia in Bermuda, several new species were discovered in a complex previously recognized as the two species S. aculeata and S. filamentosa in the islands. Known in Bermuda since 1857, S. aculeata is genetically confirmed for all isolates bearing uncinate spines on their determinate branches, thus including all specimens that had in the past been identified as S. complanata and S. hypnoides. The most abundant species in the flora is S. consimilis sp. nov. found subtidally around the islands and historically thought to be S. filamentosa, a species with which it is morphologically cryptic. The other three new genetically distinct species are also non-uncinate: S. bernatowiczii, S. rhizoidea, and S. struanii. Spyridia bernatowiczii would have likely been also identified as S. filamentosa in the past and is genetically and morphologically distinct from S. consimilis. The remaining two species are smaller, forming cushions or tufts in intertidal and shallow subtidal habitats.

Systematics studies within the freshwater red algal order Batrachospermales have used only one to a few genes to infer evolutionary relationships. The phylogenetic trees presented in these studies recovered monophyletic genera with strong support, but the relationships among genera were often not well supported. Chloroplast genome sequencing may provide the necessary data to obtain a fully resolved, strongly supported phylogeny. In order to test the efficacy of this approach, we focused on a subclade of seven genera and sequenced chloroplast genomes from 10 species. Utilizing new and previously published data, a phylogeny was constructed from 132 chloroplast-encoded genes. The relationships among all seven genera had strong statistical support. The phylogeny and gross morphology of genera showed concordance. Lemanea and Paralemanea with tube-like pseudoparenchymatous gametophytes formed a clade, and five genera—Batrachospermum, Lympha, Sirodotia, Tuomeya, and Volatus—with beaded gametophytes formed a second clade. Within the clade of five genera, Batrachospermum with pedicellate carposporophytes was sister to the other three genera with axial carposporophytes and Sirodotia with prostrate carposporophytes along the axis. The results highlight the potential for chloroplast genome data to clarify evolutionary relationships in the Batrachospermales, offering a promising approach for future studies aimed at understanding the broader evolutionary history of this group.

The non-geniculate coralline genus Boreolithothamnion currently includes eight species with a Northern Hemisphere distribution. To date, only a few studies have focused on the systematics of Boreolithothamnion species. Here, we performed morphological and phylogenetic analyses, based on rbcL, psbA, and SSU rRNA gene datasets, on Boreolithothamnion from Korea as well as DNA-sequenced type material representing nine names. The analyses supported the proposal of three new species of Boreolithothamnion from Korea: B. acuminatum sp. nov., B. homoglobosum sp. nov., and B. jejuensis sp. nov. Boreolithothamnion acuminatum is distinguished by its encrusting to warty growth form, acuminate to cylindrical protuberances, and raised to low-domed tetra/bisporangial conceptacles having bordered pore canals with three to four roof cells. Boreolithothamnion homoglobosum is characterized by a fruticose or unattached rhodolith and simple to bifurcated protuberances. Boreolithothamnion jejuensis is distinguished by an encrusting to undulate or knobby growth form with unbranched protuberances. Phylogenetic analysis of the holotype of Lithothamnion japonicum (TRH C16-3267) based on the psbA gene strongly supported its transfer to the genus Boreolithothamnion, B. japonicum comb. nov. Eight other type specimens of Lithothamnion were also observed to cluster within the Boreolithothamnion clade and were resolved with previously accepted species. This study expands the biogeographical range of Boreolithothamnion in the Northwest Pacific.

As climate change is having increasingly visible impacts on coastal regions, it is urgent to better understand its effects on the state of ecosystems and the services they provide. To assess the direction and magnitude of change in the high-use waters of the Sept-Îles region in the Gulf of St-Lawrence, we sampled 35 sites along the coast and explored the relationship between surface diatom assemblages and 21 environmental variables. Temperature (14.62%), Secchi depth (12.97%), dissolved silica (6.91%), and magnesium (6.23%) were determined to be significant and independent variables explaining variation in diatom distribution, together explaining 28.6% of the assemblage variance. Temperature and Secchi depth met the λ₁/λ₂ > 0.5 criterion, but only temperature was selected to develop a transfer function, as these two variables were strongly correlated. A diatom-based temperature transfer function was then developed using weighted-averaging partial least squares (WAPLS; 3; r² = 0.59, RMSEP = 0.45°C), based on a training set of 32 sites and 55 benthic taxa. However, the model exhibited sensitivity to spatial autocorrelation and may have been influenced by secondary and unmeasured variables. Despite these limitations, the model provides valuable insight into the spatial variability of diatom assemblages and offers potential for paleoenvironmental reconstructions. For optimal inferences, the model should be applied within the studied area. This study contributes to understanding how coastal diatom assemblages respond to environmental gradients and highlights the importance of diatom-based monitoring to assess ongoing ecological changes in aquatic environments.

Naked dinoflagellates are a regular component of the Antarctic phytoplankton but remain poorly studied. In December 2016, the first massive bloom (9.5 × 10⁶ cells · L⁻¹) of small (~15 μm) naked dinoflagellates was recorded in the western Antarctic Peninsula. To identify these organisms, we performed Illumina next-generation sequencing analysis on field samples to obtain genetic information (SSU rDNA 18SV9 and 16SV4-V5). In addition, we performed polymerase chain reaction (PCR) amplification and Sanger sequencing using dinoflagellate-specific primers (LSU rDNA D1-D3 and ITS/5.8S), as well as traditional light and scanning electron microscopy observations. Phylogenetic analyses revealed that these organisms belonged to the Gymnodinium sensu stricto group and may represent an undescribed species. These analyses also indicated that the observed organisms were closely related to the species Gymnodinium dorsalisulcum, G. impudicum, Barrufeta bravensis, and B. resplendens, as well as to the genera Lepidodinium and Wangodinium. This work has provided the LSU rDNA gene sequence from an Antarctic species belonging to the Gymnodinium sensu stricto group along with a description of the observed morphology of these Antarctic blooming dinoflagellates. We compared the 18S V9 amplicon sequence variant (ASV) that dominated the bloom with global databases and observed that it is widely distributed in the Antarctic Peninsula as well as in the global ocean. This study highlights the need for further efforts to identify and describe the diversity of naked dinoflagellates in Antarctic waters.

The development of the auxospore is reported in the surirelloid diatom Campylodiscus cf. neofastuosus. As in most pennate diatoms, growth of the auxospore is accompanied and constrained by the formation of a transverse perizonium composed of finely structured bands, which are added one after another as the auxospore expands. However, unlike in most pennate diatoms, in which the transverse perizonium develops bidirectionally from a hoop-like or shortly cylindrical primary band formed around the equator of the zygote, in C. cf. neofastuosus, development is unidirectional, outward from a heart-shaped cap at one end of the auxospore. Limited evidence from other surirelloid diatoms suggests that unidirectional perizonium development may be typical of the group. This developmental pattern correlates with the profound symmetry shifts that have occurred during the evolution of the circumferential raphe system of Surirellaceae and may have a common origin with these, despite the difference in life-cycle stage. The longitudinal perizonium of Campylodiscus also exhibits differences from the arrangement typical of most raphid diatoms, since it comprises three concentrically organized bands, including a unique, heavily silicified secondary band, which runs around the whole circumference of the wide primary band. In this and some other Surirellaceae, the longitudinal perizonium seems to play an important role in the morphogenesis of the initial cells by controlling the shape of the protoplast during a contraction before the formation of the initial epivalve. Small extra perizonial elements, unlike any reported previously in raphid diatoms, were detected beneath the suture formed by the ends of the transverse perizonial bands.