Journal of Phycology最新文献

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.

The well-known Bryopsidalean genus Codium has a worldwide distribution and contains almost 150 species, with cryptic diversity confusing the actual number. In the Hawaiian Islands, 15 species have been previously recorded, with several of these described in the past several decades, largely from specimens collected from mesophotic coral ecosystems. We assessed the diversity of Codium in Hawai‘i from both shallow and mesophotic habitats by employing DNA barcoding and phylogenetic analyses of partial rbcL and tufA gen plastid markers and morphological characterization. DNA sequence analyses supported 18 species of Hawaiian Codium (eight of which are considered endemic), which is a 20% increase in recognized species richness for this genus in Hawai‘i. Ten previously reported species were confirmed or provisionally confirmed, six new species have been described (C. pikoii sp. nov., C. upohoae sp. nov., C. hakakaupilii sp. nov., C. kanepohihiae sp. nov., C. torulosum sp. nov., and C. iolekaae sp. nov.), and two new records have been reported (C. “geppiorium4” and C. taylorii). Twenty-eight percent of Hawaiian Codium clades were mesophotic only, and 22% were shallow only, while 50% of clades were known from both shallow and mesophotic depths. Recent emphasis on the systematics of Hawaiian mesophotic algae has sufficiently increased specimen numbers from this habitat to allow a more complete assessment of the genus in this location, making it one of the most thoroughly collected and studied marine algal genera from Hawai‘i and an excellent model for future examination of both horizontal (i.e., spatial) and vertical (i.e., depth) distributional trends.

Marine heatwaves (MHWs) have increased in frequency by 34% since 1990 and are projected to rise further with global ocean change, posing significant risks to marine ecosystems. Kelps (order Laminariales) provide essential habitats and play key ecological roles, but they are increasingly threatened by MHWs. Tasmania, SE Australia, is a global warming hotspot, but the impacts of recurrent MHWs on the physiological performance of the ecologically dominant kelp Ecklonia radiata remain poorly understood. To address this, we investigated how the frequency of MHWs influenced the physiological and biochemical performance of E. radiata, both during and after MHWs, to evaluate immediate responses and recovery potential. In laboratory experiments, juvenile sporophytes were exposed to three experimental treatments: no-MHW, a single 6-day MHW, and double 6-day MHWs followed by 7-day recovery periods. Ecklonia radiata sporophytes were resilient to the single 6-day MHW, but double MHWs negatively impacted recovery, with reduced growth rates and increased tissue erosion. Although photosynthetic rates remained unaffected, changes in pigment ratios and increased antioxidant activity indicated a mitigation of physiological stress. We propose that energy may be diverted from growth toward repair processes and the maintenance of essential functions. These findings suggest there was cumulative stress caused by repeated MHWs, leading to progressive physiological decline. More frequent MHW events may hinder E. radiata's recovery capacity, with potential ecosystem implications, considering its key ecological role.