This article formally describes Craticula vanensis sp. nov., a new species of diatom from Lake Van, the largest soda lake in the world, and the fifth new species identified in the lake following an 81-years gap in investigations. A genomic approach based on short reads allowed the complete cluster of nuclear rRNA genes to be retrieved alongside the complete plastome, both later used in several single or multigene phylogenies, which surprisingly tended to associate C. vanensis to species of the genus Dorofeyukea. The complex structure of the mitogenome could only be resolved by long-read sequencing. It is characterized by its large size (116,698 bp), the presence of several introns in the cox1 gene, the use of an alternative genetic code with the putative reassignment of the UGA codon to arginine and the unexpected presence of six copies of the rRNA genes and nine copies of truncated nad2 sequences. A survey of published metabarcoding datasets suggested the presence of C. vanensis in a soda lake from Central Europe (Kakasszéki, Hungary), which was later confirmed by microscopy and suggests an extended distribution of this taxon.

Eelgrass (Zostera spp.) forms productive and biodiverse marine meadows throughout the world. There eelgrass provide living substrata for epiphytes, including diatoms, which contribute substantially to primary productivity. Despite their important role, there are many gaps in our understanding of the diversity and ecology of epiphytic diatoms. Here, we combined morphological identification by scanning electron microscopy and light microscopy with Illumina sequencing of the 18S rRNA and rbcL marker genes to survey the diatom community on eelgrass (Zostera marina) from Galiano Island, British Columbia across a gradient of tissue age. We detected 76 genera of diatoms, 47 with both molecular and morphological methods. Using a spatially explicit morphological census, we observed a significant increase in density and a moderate increase in diversity across tissue age. We found that changes in community composition are driven by nestedness rather than turnover. The diatom community diversity and composition detected by molecular data did not differ by tissue age. We suggest that this is because molecular data surveyed a larger area (5 cm2 vs. 200 mu m2), so rare taxa are more likely to be present. Overall, we found that integrating morphological and molecular datasets enhances detection of diversity and provides context for interpreting ecological patterns.

Evolution is often uneven in its pace and outcomes, with long periods of stasis interrupted by abrupt increases in morphological and ecological disparity. With thousands of gene histories, phylogenomics can uncover the genomic signatures of these broad macroevolutionary trends. Diatoms are a species-rich lineage of microeukaryotes that contribute greatly to the global cycling of carbon, oxygen, and silica, which they use to build elaborately structured cell walls. We combined fossil information with newly sequenced transcriptomes from 181 diverse diatom species to reconstruct the pattern, timing, and genomic context of major evolutionary transitions. Diatoms originated 270 Mya, and after >100 My of relative stasis in morphology and ecology, a radiation near the Jurassic–Cretaceous boundary led to the diversity of habitats and cell wall architectures characteristic of modern diatoms. This transition was marked by a genome duplication and high levels of gene tree discordance. However, short generation times increase the probability of coalescence between speciation events, minimizing the impacts of incomplete lineage sorting and implicating sequence saturation and gene tree error as the main sources of discordance. Nevertheless, a rigorous tree-based approach to ortholog selection resulted in strongly supported relationships, including some that were uncertain previously. Three pulses of accelerated speciation were detected, two of which were associated with the evolution of novel traits and ecological transitions. The first 100 My of diatom evolution was a slow-burning fuse that led to a burst of innovations in ecology, morphology, and life history that are hallmarks of contemporary diatom assemblages.

Samples from Teahupo'o fringing reef, Tai'arap & umacr; peninsula, Tahiti-iti (Society Archipelago, South Pacific), have a high species richness of benthic marine Achnanthales. Cocconeis adamantina sp. nov., a small-celled and abundant taxon, pertaining to the Loculatae section, has an SV similar to that of Cocconeis sp. 1 previously observed in Madagascar, but with RV uniseriate striae up to the margin and a constant morphology. A less abundant and larger member of the Loculatae, first observed in the South Pacific, is provisionally named herein as C. olympica. It is characterized by having an elliptic to discoid valve shape and areolae in the median sector of the SV with only one apical bar (as in C. scutellum f. decussata), whereas at the valve periphery, it shows secondary bars. The RV of the former taxon is different from that in C. scutellum f. decussata. A wide phenotypic plasticity may be associated with the Loculatae or a local endemism (small-scaled endemism), hypotheses that will only be disentangled via genetics. Campyloneis grevillei is common in Teahupo'o, while apparently absent in previous South Pacific collections. Campyloneis is a genus with morphological characters difficult to fix. Cocconeis testudo Giffen 1963, is here transferred to Campyloneis as C. testudo comb. nov. Among several rare and insufficiently documented taxa, a small Cocconeis may pertain to group 2B, previously defined as part of a complex comprising C. peltoides. The Achnanthales assemblage from Teahupo'o is particularly diverse, with several taxa ranked as morphs (or formae), pointing to the possible influence of local geology on the establishment and diversification of benthic diatoms, allowing for the differentiation of highly silicic environments (volcanic high islands with a more or less restricted coral reef), versus old and more calcic environments (such as atoll lagoons with low connection to the open ocean).

Two marine diatom genera bearing raphe on the valve mantle are described based on light and scanning electron microscopy. These diatoms possess dorsiventral frustules and attach to sand grains or filamentous seaweed with their ventral girdle faces. Periraphis banzuensis gen. et sp. nov. exhibits external hook-like distal raphe endings on the valve face, similar to some Eunotia species; however, the valves lack a rimoportula, and the number and placement of the chloroplasts and the manner of areolar occlusion differ. Andrzeja gen. nov. including Andrzeja arcuata sp. nov. and Andrzeja fenestrata sp. nov. has arcuate outer raphe fissures on the mantle, distinguishing it from Periraphis by its external distal raphe endings on the mantle, a unique characteristic among raphid diatoms. The morphological and functional adaptations of these genera to unstable environments are discussed.

Indonesia is listed as a region with high marine biodiversity, especially when considering the three large tropical ecosystems: seagrass beds, mangroves and coral reefs. It is likely that the biodiversity of diatoms in this area is also high. Samples for this research were taken from the remote area of Bawean Island and Tomini Gulf in Central Sulawesi. In this research, we explored marine benthic diatoms from coral reef areas and presented two new genera: Paracatenula and Wallaceago, and seven new species: Paracatenula porostriatasp. nov., Wallaceago porostriatussp. nov., Catenula boyanensissp. nov., C. komodensissp. nov., C. decusasp. nov., C. densestriatasp. nov., and Catenulopsis baweanasp. nov. The new genus Paracatenula is characterized by its perforated cingulum, and the genus Wallaceago is distinguished by its proximal and apical raphe ends bent to the ventral side and the presence of a stauros in the mantle.

In this study, we describe Halamphora vantushpaensissp. nov., a newly identified diatom species found in the highly alkaline Lake Van in Eastern Turkey (Türkiye). This new species is characterized morphologically by light and scanning electron microscopy, performed on both wild and cultivated samples. Two monoclonal cultures were submitted to a genome-skimming approach, giving access to the complete sequence of their nuclear rRNA cluster of genes, mitochondrial and plastid genomes. Both strains were highly similar from the genomic point of view, with few mutations noted, although in organellar genomes some of them concerned protein coding genes and were non-silent. Also, the group II intron in the mitochondrial cox1 gene was found to display a relatively high number of polymorphisms. The plastome also distinguishes itself from other Halamphora spp. by the extension of its inverted repeat at the expense of the two single copy regions of the genome. Maximum likelihood molecular phylogeny inferred from a concatenated three genes dataset (18S, psbC and rbcL) positions this species within the K clade, which is known to contain hypersaline to freshwater species.

The current article describes Navicula vanseeasp. nov., a new species of diatom from Lake Van, a highly alkaline lake in Eastern Anatolia (Türkiye). The description is based on light and scanning electron microscopy performed on two monoclonal cultures. The complete nuclear rRNA clusters and plastid genomes have been sequenced for these two strains and the complete mitogenome for one of them. The plastome of both strains shows the probable loss of a functional ycf35 gene. They also exhibit two IB4 group I introns in their rrl, each encoding for a putative LAGLIDADG homing endonuclease, with the first L1917 IB4 intron reported amongst diatoms. The Maximum Likelihood phylogeny inferred from a concatenated alignment of 18S, rbcL and psbC distinguishes N. vanseea sp. nov. from the morphologically similar species Navicula cincta and Navicula microdigitoradiata.

Diploneis gravelleana Hagelstein was described in 1939 from Puerto Rico but may later have been confused with Diploneis interrupta var. afra Giffen, described in 1960 from South Africa. Both are small (ca 20 mu m in length), strongly constricted species indistinguishable in light microscopy. When we found a similar species in Micronesia, we needed to determine if it matched either of these species. We obtained mud samples from the US Virgin Islands containing D. gravelleana and unmounted type material of Giffen's original material for SEM imaging. All three populations differed ultrastructurally and hence the Micronesian species is described as Diploneis carolinensis sp. nov. Lobban et Witkowski. Diploneis carolinensis was found in mangrove samples from Yap and Palau. These simulacra suggest that D. afra may not be as widely distributed as supposed.

During a survey of the Indonesian diatoms, five Luticola D.G.Mann taxa that could not be identified, based on the available literature were discovered. Based on light microscopy, scanning electron microscope observations and comparisons with similar taxa, all of them are described as new species. All taxa were found on mosses growing on tree trunks and concrete on the islands of Banda Besar and Seram and from spring on Java Island. Luticola insularis sp. nov. is most similar to L. aequatorialis and L. simplex, but it can easily be distinguished from both taxa, based on the lower striae density, the narrower valves and the well-developed silica ridges on the valve face/mantle junction. Luticola bandanensis sp. nov. resembles L. frequentissima, but they can be easily distinguished, based on their valve widths and the direction of the grooves located on the distal and proximal raphe endings. Luticola elliptica sp. nov. is most similar to L. sparsipunctata, L. tenuis and L. bryophila. Amongst all the species compared, L. elliptica sp. nov. is the only one with a highly asymmetrical central area, with the isolated pore located on the wider side. Luticola malukuana sp. nov. shares similarities with L. dismutica and L. areolata, but it has a notably higher stria density. From L. areolata, it can also be separated by the morphology of striae and the lack of ghost areolae in the central area. Luticola poliporea sp. nov. is unique in the whole genus due to the presence of multiple isolated pores.

Abstract. Luthfi OM, Risjani Y, Subramani N, Rybak M, Park J, B?k M, Witkowski A. 2024. Diversity of epilithic diatoms from coral reef ecosystem of Bawean Island, Indonesia. Biodiversitas 25: 4642-4663. This study investigates the diversity and community structure of epilithic diatoms in the coral reef ecosystems of Bawean Island, Indonesia. A total of 137 taxa from 49 genera were identified from coral rubble habitats across four distinct locations. The Shannon-Wiener Diversity Index (H') and Dominance Index (C) were used to assess species diversity and dominance, revealing that Station 4 exhibited the highest diversity (H' = 3.88) and lowest dominance (C = 0.03), while Station 2 had the lowest diversity (H' = 2.55) and highest dominance (C = 0.09). Evenness values (E = 0.9) were consistent across all sites, indicating a uniform distribution of species. The findings suggest that coral rubble provides unique microhabitats conducive to diatom diversity, challenging the conventional understanding that habitat diversity correlates positively with species diversity. The study also compares Bawean Island's diatom diversity with other regions, noting its intermediate diversity level, which may be influenced by its geographical position between Kalimantan and Java. The presence of dominant species like Diploneis crabro, Petroneis marina, Halamphora coffeiformis, and Trachyneis aspera underscores the ecological significance of these diatoms in coral reef ecosystems. This research fills a significant gap in our understanding of the marine biodiversity and ecological dynamics of Bawean Island, highlighting the importance of diatoms in maintaining the health and stability of coral reef ecosystems and its potential implications for future research and conservation efforts.

Climate change and nutrient enrichment are increasing the frequency of algal blooms, with sometimes significant impacts on coastal ecosystems. Haslea ostrearia blooms have been documented in oyster ponds and are not harmful, yet their effects in open environments remain underexplored. Marennine, a blue pigment produced by H. ostrearia, can display a range of biological properties in laboratory conditions, including antibacterial and allelopathic properties. Other blue Haslea species, forming blooms, synthesize bioactive marennine-like pigments. This study aims to understand if and how these blooms could affect the underlying community of microorganisms living in the biofilms. Morphological and molecular techniques were used to assess community dynamics during bloom events. Our findings indicate that blue Haslea blooms do not significantly alter the diatom or bacterial populations. However, they are paired with enhanced alpha diversity in the microbial communities. These observations suggest a complex interaction between bloom events and microbial dynamics. Additionally, this study expands our understanding of the bioactive properties of marennine-like pigments and their ecological roles, suggesting new avenues for biotechnological applications. This work underscores the importance of further research into the environmental and biological implications of blue Haslea blooms.

Diploneis gravelleana Hagelstein was described in 1939 from Puerto Rico but may later have been confused with Diploneis interrupta var. caffra Giffen, described in 1960 from South Africa. Both are small (ca 20 μm in length), strongly constricted species indistinguishable in light microscopy. When we found a similar species in Micronesia, we needed to determine if it matched either of these species. We obtained mud samples from the US Virgin Islands containing D. gravelleana and unmounted type material of Giffen's original material for SEM imaging. All three populations differed ultrastructurally and hence the Micronesian species is described as Diploneis carolinensis sp. nov. Lobban et Witkowski. Diploneis carolinensis was found in mangrove samples from Yap and Palau. These simulacra suggest that D. caffra may not be as widely distributed as supposed.

Until recently, the data on the diversity of the entire microbial community from the Baltic Sea were relatively rare and very scarce. However, modern molecular methods have provided new insights into this field with interesting results. They can be summarized as follows. (i) Although low salinity causes a reduction in the biodiversity of multicellular species relative to the populations of the North-East Atlantic, no such reduction occurs in bacterial diversity. (ii) Among cyanobacteria, the picocyanobacterial group dominates when considering gene abundance, while filamentous cyanobacteria dominate in means of biomass. (iii) The diversity of diatoms and dinoflagellates is significantly larger than described a few decades ago; however, molecular studies on these groups are still scarce. (iv) Knowledge gaps in other protistan communities are evident. (v) Salinity is the main limiting parameter of pelagic fungal community composition, while the benthic fungal diversity is shaped by water depth, salinity, and sediment C and N availability. (vi) Bacteriophages are the predominant group of viruses, while among viruses infecting eukaryotic hosts, Phycodnaviridae are the most abundant; the Baltic Sea virome is contaminated with viruses originating from urban and/or industrial habitats. These features make the Baltic Sea microbiome specific and unique among other marine environments.

Diploneis gravelleana Hagelstein was described in 1939 from Puerto Rico but may later have been confused with Diploneis interrupta var. caffra Giffen, described in 1960 from South Africa. Both are small (ca 20 µm in length), strongly constricted species indistinguishable in light microscopy. When we found a similar species in Micronesia, we needed to determine if it matched either of these species. We obtained mud samples from the US Virgin Islands containing D. gravelleana and unmounted type material of Giffen’s original material for SEM imaging. All three populations differed ultrastructurally and hence the Micronesian species is described as Diploneis carolinensis sp. nov. Lobban & Witkowski. Diploneis carolinensis was found in mangrove samples from Yap and Palau. These simulacra suggest that D. caffra may not be as widely distributed as supposed.

Samples from coastal tropical waters of Central Sulawesi, Bangka Island and Bawean Island in Indonesia and from the Great Barrier Reef at Fitzroy Island in Queensland, Australia were analysed for species composition of diatom assemblages with a focus on Olifantiella. Whereas samples from Fitzroy Island littoral in Australia retrieved only one species of Olifantiella, in Poso Bay, Indonesia, we observed at least six species. All established taxa were documented with light (LM) and scanning electron microscope (SEM) and principal component analysis (PCA) analysis was used to compare the species, based on the basic valve parameters of length, width, length to width ratio and striae density. A new species of the genus Olifantiella, O. gondwanensis is described from Australia. In addition, we showed the distinct nature of O. pilosella var. rhizophorae permitting to species status. Particular attention is placed on girdle bands in this genus.

SUMMARY The canal‐bearing diatom genus Nagumoea , described based on only morphological evidence, was tentatively assigned to the order Bacillariales, although its phylogenetic position remained unclear. Because three isolates of Nagumoea (SK002, SK024 and SK053) were successfully established from Japanese coasts, we performed their morphological observations and molecular phylogenetic analyses to discuss the phylogeny and taxonomic position of this genus. Strains SK002 and SK024 were identified as Nagumoea africana , whereas SK053 conformed with Nagumoea serrata . There was high interspecific divergence between N. africana and N. serrata in the rbc L sequences (8.03–8.17%), indicating their distinctness. Furthermore, intraspecific variations were detected within N. africana (2.35%) in the rbc L, implying its cryptic diversity. The maximum likelihood and Bayesian phylogenetic trees inferred from the plastid rbc L, psb C and nuclear 18S rDNA genes recovered Nagumoea as monophyletic with strong statistical support and embedded within an unresolved, poorly supported lineage containing Achnanthes , Craspedostauros , Staurotropis and Undatella in the canal‐bearing order Bacillariales (= the family Bacillariaceae). Although the constrained tree based on the monophyly of Nagumoea and the other canal‐bearing clade (Surirellales and Rhopalodiales) was statistically rejected by the topology tests, the phylogenetic position of Nagumoea with other Bacillarialean members remains equivocal. The possession of two plastids positioned fore and aft, observed in the present study, and lack of keel, typical of the Bacillariales, indicate the possibility of Nagumoea being part of the ingroup of the Bacillariales or its closely related outgroup.

At unprecedented resolution we investigate the nature of Dansgaard-Oeschger events in the Fram Strait, the gateway between the Nordic Seas and the Arctic Ocean. The new reconstructions of biomarkers and sea ice variability, stable isotopes and IRD will be seen in context of sea ice conditions, ocean hydrography and climate of the Nordic Seas as seen in multi-model output from three transient glacial GCM simulations (NorESM, CESM, MPI-ESM) and high-resolution reconstructions from an eastern Nordic Seas transect (from the Faeroe-Shetland Channel, via the Norwegian Sea to the Fram Strait). The combined results show that ocean-atmosphere-sea ice processes and dynamics during the transition from H4 to GI8 are strongly coupled. Both model results and reconstructions suggest subsurface ocean warming and polynya events in the southern- and northernmost Nordic Seas during the cold stadial. For a short time during the stadial to interstadial transition, a corridor of open water and hence sea ice-free conditions existed from the southern Nordic Seas all the way to the Fram Strait. The breakup of the sea ice cover is likely caused by the overshoot of AMOC during the transition and the associated enhanced ocean heat transport into the Nordic Seas. After the transition, winter sea ice grows back in the Fram Strait during the interstadial state, but the Southern Nordic Seas remain ice-free.