Diatom Species Research Articles

A new freshwater species Achnanthes licunese sp. nov. (Achnanthaceae, Bacillariophyta) from pebbles of Licun River, Shandong Province, China

A new freshwater diatom species, Achnanthes licunese sp. nov., was found on pebble samples collected from Licun River in Shandong Province, China. The various taxonomic characteristics of Achnanthes licunese sp. nov. is observed under light and scanning electron microscope. The living cells of A. licunese sp. nov. possesses two chloroplasts. Its valves exhibit a linear to linear-lanceolate outline, slightly constricted in the middle part, with uniseriate striae. The central area of the raphid valves is expanded into a linear and thickened stauros, and the raphe is filiform. On the araphid valves, there is no central area, and the axial area (sternum) is located in the valve margin. The valve of the A. licunese sp. nov. possesses the marginal spines, but no marginal ridge and terminal orbiculi. By comparing the new species with similar Achnanthes species, A. licunese sp. nov. was confirmed to be sufficiently different regarding valve size, striae density, and the presence of marginal spines. The discovery of this species increases the diversity of freshwater diatoms.

Cocconeis crisscrossis sp. nov., a new monoraphid diatom (Bacillariophyta) from southern China

A novel monoraphid diatom species, Cocconeis crisscrossis You, Yu, Kociolek & Wang, sp. nov. is examined and described from the Qingyi River and Maolan Nature Reserve of southern China. The morphological description is based on light microscopy and scanning electron microscopy observations and the new species is compared with similar taxa in this genus. The characteristics unique to Cocconeis crisscrossissp. nov. include its central area extending irregularly to both sides, it having closed valvocopulae with heavily silicified fimbriate margins and poles of the valvocopulae have ‘sword-shaped’ siliceous extensions. These features differentiate this new species from others in the genus. This new species was found in alkaline waterbodies, including streams, waterfall and ponds. It was usually found as an epiphyte on the stones; however, it was present on other substrates such as mosses.

The effects of turbulence on the growth of three different diatom species

The effects of turbulence on phytoplankton growth have received considerable attentions. However, the complexity of turbulence poses a significant challenge to its systematic characterization in the laboratory, resulting in relatively limited data on the effects of turbulence on several algal species. Here, a laboratory turbulence simulation system was set up to systematically investigate the growth of three common diatom species (Thalassiosira pseudonana, Skeletonema costatum, and Phaeodactylum tricornutum) under stationary and turbulent conditions (at 60, 120, 180 rpm), and measurements were taken for the algal biomass, algal photosynthetic activity, and nutrients consumption. By comparing the growth of three algae species under different turbulence exposure intensities, this study found that different algae exhibit varying sensitivities to turbulence, and therefore have different shear thresholds. Meanwhile, cell morphology is the key factor influencing the different shear threshold values observed in the three diatom species. Additionally, turbulence could impact algal aggregation and light availability, and dramatically improve nutrient uptake by phytoplankton. Our study will provides theoretical support for future endeavors in using turbulence to cultivate phytoplankton or combat algal blooms.

Determination of ecological statuses of streams in the Ceyhan River Basin using composition and ecological characteristics of diatoms.

The present study aimed to evaluate the interactions between diatoms and ecological factors in various streams and to test the suitability of diatom indices to evaluate the ecological status of 44 streams in the Ceyhan River Basin during the spring and autumn periods of 2021 and the summer of 2022. Canonical correspondence analysis indicated the significant effects of electrical conductivity (EC), dissolved oxygen, biological oxygen demand (BOD5), total phosphorus (TP), and total nitrogen (TN) on the distribution of diatom species of streams in the Ceyhan River Basin. Of the streams, Aksu and Erkenez streams were associated with high EC, BOD5, and TP and characterized by pollution-tolerant species. Pollution-sensitive species showed close integration with Aksu Spring Brook, Gözpınar Creek, Göksun Creek, and Yeşilgöz Spring Brook, which related to a high dissolved oxygen gradient. Different eco-regional diatom indices displayed different scores, representing from bad to high ecological status in the Ceyhan River basin. Among the diatom indices, Trophic Index Turkey (TIT) proved to be the more suitable metric to assess the ecological status of streams. TIT indicated deterioration of water quality in Karasu (S06), Erkenez (S07) streams, and downstream areas of the Ceyhan River and the least distributed sampling stations in the basin. Results suggested that eco-regionally developed diatom indices, like TIT, are required to more accurately assess the ecological status of streams in the Mediterranean region. The study provides a fundamental assessment of the ecological status of streams in the Ceyhan River Basin using an appropriate diatom index before the Pazarcık-centered earthquake on February 6, 2023. Findings allow someone to assess the impact of the earthquake on diatom communities and ecological factors in the region in the future studies.

Nestedness of benthic diatom metacommunity in relation to species niche width and environmental variables in a large near-natural catchment

Insight into the non-random distribution patterns of species in different regions is a foundational aim of research in community ecology and biogeography. The nestedness pattern, which investigates changes in species composition and abundance, has been widely used in numerous studies. However, studies on the nestedness of benthic diatoms are extremely rare, and consequently little has been mentioned of their assemblage mechanisms. To fill this gap, based on 168 benthic diatom species from 147 sampling sites in the Thousand Island Lake (TIL) catchment, we calculated their nestedness and niche width with the aim of i) analyzing the nestedness of benthic diatoms communities with different attachment abilities in TIL; ii) calculating niche width differences between nested and idiosyncratic species with different attachment abilities; iii) investigating the differences in alpha and beta diversity between nested and idiosyncratic sites; iv) examining whether environmental variables influencing the nestedness of benthic diatom communities are dependent on attachment ability. The results demonstrated a significant nestedness pattern in the benthic diatom metacommunity, and the sampling sites of low attachment species not only exhibited a nestedness pattern, but also with a lower nestedness value compared to the sampling sites of all species. Nested and idiosyncratic species differed in niche width, whereas differences between nested and idiosyncratic species of low attachment species were smaller. Additionally, significant differences in alpha and beta diversity were observed between nested and idiosyncratic sites. Furthermore, it was revealed that the nestedness of benthic diatom metacommunity in our study area were mostly influenced by local environmental variables. Our study contributes to the understanding of the significant nestedness observed in benthic diatom metacommunity in TIL, highlighting its relevance to biodiversity conservation efforts.

Channels of Evolution: Unveiling Evolutionary Patterns in Diatom Ca2+ Signalling.

Diatoms are important primary producers in marine and freshwater environments, but little is known about the signalling mechanisms they use to detect changes in their environment. All eukaryotic organisms use Ca2+ signalling to perceive and respond to environmental stimuli, employing a range of Ca2+-permeable ion channels to facilitate the movement of Ca2+ across cellular membranes. We investigated the distribution of different families of Ca2+ channels in diatom genomes, with comparison to other members of the stramenopile lineage. The four-domain voltage-gated Ca2+ channels (Cav) are present in some centric diatoms but almost completely absent in pennate diatoms, whereas single-domain voltage-gated EukCatA channels were found in all diatoms. Glutamate receptors (GLRs) and pentameric ligand-gated ion channels (pLGICs) also appear to have been lost in several pennate species. Transient receptor potential (TRP) channels are present in all diatoms, but have not undergone the significant expansion seen in brown algae. All diatom species analysed lacked the mitochondrial uniporter (MCU), a highly conserved channel type found in many eukaryotes, including several stramenopile lineages. These results highlight the unique Ca2+-signalling toolkit of diatoms and indicate that evolutionary gains or losses of different Ca2+ channels may contribute to differences in cellular-signalling mechanisms between species.

Late Holocene decoupling of lake and vegetation ecosystem in response to centennial-millennial climatic changes in arid Central Asia: A case study from Aibi Lake of western Junggar Basin

Central Asian lakes are crucial for sustaining fragile oasis ecosystems in arid regions. Understanding the response of ecosystems in these lake basins to climate change is essential for predicting future variations in these ecosystems. Aibi Lake is a notable terminal lake in arid Central Asia. In this study, a 95 cm lacustrine sediment core was drilled from Aibi Lake to investigate the response of lacustrine and terrestrial ecosystems in the lake basin to climate change over the past 3200 years. Accelerator mass spectrometry (AMS) 14C dating and multi-proxy analyses of diatoms, pollen, grain size, total organic content (TOC), total nitrogen (TN), and total hydrogen (TH) are applied to the sediment core. The grain size and geochemical results show that the lake experienced elevated levels and improved productivity and nutrition during the periods of 708–181 BCE, 0–740 CE, and 1428–1900 CE. The periods align with the Roman Warm Period, Dark Age Cold Period, and Little Ice Age, respectively. For the past 3200 years, benthic diatoms have consistently been the dominant species in the lake. During the climatic transition periods of the Dark Age Cold Period, Medieval Warm Period, and Little Ice Age, there were significant changes in the abundance and survival of certain species of diatoms. Specifically, the halophilic species (Nitzschia dissipata and Nitzschia hungarica), basophilic species (Synedra acus), and the nutrition level-relevant species (Navicula menisculus) experienced notable shifts. These changes ultimately resulted in a noticeable alteration in the structure and function of the diatom community. Over the past 3200 years, the lake ecosystem has undergone three noticeable regime shifts. In contrast, the vegetation in the lake catchment has remained relatively stable, primarily consisting of desert steppe. These results suggest that aquatic ecosystems in arid central Asia are more susceptible and exhibit more rapid responses to climate change compared to terrestrial vegetation.

Microzooplankton grazers induce chain length plasticity in colonial diatoms

AbstractMany diatoms form long chains and the distribution of chain lengths within a species depends on several environmental factors, among them grazing risk. Larger grazers, such as copepods, efficiently handle and ingest even very long chains but are less efficient with individual cells, whereas most smaller grazers are unable to feed on chains exceeding a few cells in length. Copepod cues make several species shorten their chain length, and theory predicts that cues from small grazers should induce increased, but this remains to be tested, despite the importance of diatoms in marine food webs. Here, we expose three species of chain‐forming diatoms, Skeletonema marinoi, Chaetoceros affinis, and Thalassiosira rotula to cues from various actively feeding micrograzers and record their response. The effect of grazer presence on chain length varies depending on both the type of grazer and the diatom species. For example, S. marinoi increased its chain length when exposed to grazing cues from the heterotrophic dinoflagellate Gyrodinium dominans and the ciliate Euplotes sp. but not to a copepod nauplii (Temora longicornis). C. affinis also responded to cues from grazing G. dominans by increasing chain length, and the response increased with exposure time. Finally, T. rotula did not respond to grazing cues from G. dominans, but rather inhibited the dinoflagellates' ability to feed, presumably through the release of chemical compounds. Our results suggest that some chainforming diatoms can sense and appropriately respond to fast‐growing micrograzers, thus contributing to the success of diatoms in marine environments.

Widespread Production of Polyunsaturated Aldehydes by Benthic Diatoms of the North Pacific Ocean's Salish Sea.

Diatoms are key primary producers across marine, freshwater, and terrestrial ecosystems. They are responsible for photosynthesis and secondary production that, in part, support complex food webs. Diatoms can produce phytochemicals that have transtrophic ecological effects which increase their competitive fitness. Polyunsaturated aldehydes (PUAs) are one class of diatom-derived phytochemicals that are known to have allelopathic and anti-herbivory properties. The anti-herbivory capability of PUAs results from their negative effect on grazer fecundity. Since their discovery, research has focused on their production by pelagic marine diatoms, and their effects on copepod egg production, hatching success, and juvenile survival and development. Few investigations have explored PUA production by the prolific suite of benthic marine diatoms, despite their importance to coastal trophic systems. In this study, we tested eight species of benthic diatoms for the production of the bioactive PUAs 2,4-heptadienal, 2,4-octadienal, and 2,4-decadienal. Benthic diatom species were isolated from the Salish Sea, an inland sea within the North Pacific ecosystem. All species were found to be producers of at least two PUAs in detectable concentrations, with five species producing all three PUAs in quantifiable concentrations. Our results indicate that production of PUAs from Salish Sea benthic diatoms may be widespread, and thus these compounds may contribute to benthic coastal food web dynamics through heretofore unrecognized pathways. Future studies should expand the geographic scope of investigations into benthic diatom PUA production and explore the effects of benthic diatoms on benthic consumer fecundity.

Wetland technology for the treatment of HCH-contaminated water – Case study at Hajek site

Hexachlorocyclohexanes (HCH) isomers and their transformation products, such as chlorobenzenes (ClB), generate severe and persistent environmental problems at many sites worldwide. The Wetland technology employing oxidation-reduction, biosorption, biodegradation and phytoremediation methods can sufficiently treat HCH-contaminated water. The treatment process is inherently natural and requires no supplementary chemicals or energy. The prototype with a capacity of 3 L/s was installed at Hajek quarry spoil heap (CZ), to optimize the technology on a full scale. The system is fed by drainage water with an average concentration of HCH 129 μg/L, ClB 640 μg/L and chlorophenols (ClPh) of 16 μg/L. The system was tested in two years of operation, regularly monitored for HCH, ClB and ClPh, and maintained to improve its efficiency. The assessment was not only for environmental effects but also for socio and economic indicators. During the operation, the removal efficiency of HCH ranged from 53.5 % to 96.9 % (83.9 % on average) depending on the flow rate. Removal efficiency was not uniform for individual HCH isomers but exhibited the trend: α = γ = δ > β = ε. The improved water quality was reflected in a biodiversity increase expressed by a number of phytobenthos (diatoms) species, a common biomarker of aquatic environment quality. The Wetland outranked the conventional WWTP in 10 out of the 15 general categories, and it is the most relevant scenario from the socio, environmental, and economic aspects.

Gyrosigma dongtingense sp. nov. (Bacillariophyta) from Dongting Lake, China

Dongting Lake is China’s second largest freshwater lake; some new diatom species have been described from this lake recently. The current study describes a new diatom species from this lake, Gyrosigma dongtingense sp. nov. Gyrosigma dongtingense sp. nov. belongs to the section Strigiles sensu H. Peragallo and it is characterized by: 1) its large cell size (valves are 161–218 μm long and 24–29 μm wide), 2) having two curvatures for each half of its raphe sternum, 3) the transverse stria density (12–14 in 10 μm) lower than the longitudinal stria density (16–18 in 10 μm), 4) both the external proximal raphe fissures deflecting towards the convex side of each corresponding half-valve, 5) T-shaped internal proximal raphe fissures, and 6) a prominent axial costa presents along the primary side of the raphe sternum. The isomorphism and dimorphism of the external proximal raphe fissures are reviewed, and similar taxa are discussed.

Development of a new kappa-carrageenan hydrogel system to study benthic diatom vertical movements.

Benthic diatom vertical movement has been investigated mainly through indirect measurements based on chlorophyll a fluorescence and spectral reflectance signals. The presence of sediment hinders direct imaging and grazers activity renders the work under controlled conditions very difficult. This study provides a tool to study diatoms movement in a 3D hydrogel matrix. Synthetic and natural hydrogels were tested to find the best 3D transparent scaffold where diatoms could grow and freely move in all directions. Polyamidoamines (PAAm) hydrogels were no-cytocompatible and hyaluronic acid (HA) only allowed diatoms to survive for 2-days. Natural hydrogels made of gelatin/Na-alginate, Na-alginate and kappa-carrageenan (KC) were cytocompatible, with KC showing the best properties for diatom growth and movement on a long term (up to 2 months). Comparing Nitzschia spathulata, Gyrosigma limosum and Navicula phyllepta growth in liquid media vs in KC gels, we found that diatoms reached a significantly higher final biomass in the hydrogel condition. Hydrogels were also useful to isolate large size diatom species e.g., Nitzschia elongata, that did not survive in suspension. Finally, we showed three ways to study diatom species-specific movement in KC hydrogels: 1) controlled species mix; 2) natural diatom assemblages with grazers; and 3) natural diatom assemblages without grazers. With our system, single diatoms could be imaged, identified, and counted. In addition, different stimuli, e.g., light intensity and light composition can be applied and their effects on movement and physiology studied without being masked by sediment or impaired by meiofauna.

Detection of Autumnal Concentration of Coscinodiscus granii in the Southern Baltic—A Method for In Situ Measurement of Marine Particles

Efficient means for measuring the abundance and species composition of phytoplankton in situ continue to pose a big challenge to scientists. Hitherto, analyses and interpretations have been based mainly on small numbers of data acquired from microscopic examinations of water samples. Hence, information on devices facilitating such measurements is highly desirable. This paper examines the opportunities offered by the LISST-100X instrument for measuring in situ the concentrations and spatially variable biovolumes of a species dominant in the southern Baltic during the autumnal bloom. Microscopic analysis of phytoplankton in water sampled from different locations in the southern Baltic confirmed earlier results, indicating that this bloom was due to the overriding prevalence of one microplankton diatom species—Coscinodiscus granii. Combining the microscopic measurements of C. granii cell sizes with the size distribution ranges employed by the LISST-100X yielded equivalent spherical diameters (EDSs) ranging from 47.4 to 188.0 µm, with maxima in the 78.4–92.6 and 92.6–109 ranges. Comparative analysis of the particle size distribution (PSD) spectra was used to separate the abundance of C. granii from the total suspended particulate matter (SPM). Spatial in situ measurements in 2012 and 2014 of C. granii concentrations in surface waters showed that both its abundance and its percentage contribution to the total SPM were highly variable. Over a distance of several km, these concentrations varied from values close to zero to 0.2 µL L−1 in 2012 and from 0.3 to 0.9 µL L−1 in 2014, whereas the percentage in the total SPM was found to vary locally from a few to c. 50%. The proposed method and results demonstrate the success of the LISST-100X instrument in detecting size and volume concentrations of phytoplankton in size classes ranging from 1.25 to 250 μm. However, the correct interpretation of LISST data requires that the dominant phytoplankton species concentration in the suspensions be large enough for the signal (peak) to be readily visible against the background PSD of other SPM.

Biogenic Phosphonate Utilization by Globally Distributed Diatom Thalassiosira pseudonana.

Phosphonates are a class of organic phosphorus (P) compounds that contribute ~25% of dissolved organic P. Recent studies reveal the important role of phosphonates mediated by prokaryotes in the marine P redox cycle. However, its bioavailability by eukaryotic phytoplankton is under debate. 2-Aminoethylphosphonic acid (2-AEP) and 2-amino-3-phosphonopropionic acid (2-AP3) are two biogenic phosphonates in the marine environment. Here, Thalassiosira pseudonana, a common diatom species in the ocean, is able to recover growth from P starvation when provided with 2-AEP and 2-AP3. Moreover, 2-AEP cultures exhibited a more similar growth rate at 12 °C than at 25 °C when compared with inorganic P cultures. The cellular stoichiometry of 2-AEP groups was further determined, the values of which are in-between the P-depleted and DIP-replete cultures. This study provides evidence that biogenic phosphonates could be adopted as alternative P sources to support diatom growth and may provide physiological adaptation.

Description of Naviculavanseea sp. nov. (Naviculales, Naviculaceae), a new species of diatom from the highly alkaline Lake Van (Republic of Türkiye) with complete characterisation of its organellar genomes and multigene phylogeny.

The current article describes Naviculavanseeasp. 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 Naviculacincta and Naviculamicrodigitoradiata.

New taxa of the Rhaphoneidaceae Forti (Bacillariophyta) from the middle Eocene

Rhaphoneis amphiceros (Ehrenberg) Ehrenberg is one of the commonest extant rhaphoneid diatoms and has been reported from multiple fossil deposits, but our work suggests this taxon may not be as common in the fossil assemblages as indicated by the literature. Indeed, the original description of the species, made by Ehrenberg, is not as detailed as modern descriptions, which can lead to confusion when identifying taxa. Recent studies show that diatom species previously reported to occur over time intervals of tens of millions of years may actually represent groups of taxa lumped together due to inaccurate identifications. In this article, we present two new species that, without careful SEM examination, can be confused with R. amphiceros. These new species, interpreted to represent two new genera in the Rhaphoneidaceae, were found in middle Eocene sediments from Ocean Drilling Program (ODP) Hole 1050A (30°06’N, 76°14.1’W), drilled on Blake Nose, western North Atlantic. Rhomboneis shtapovii Figus & Witkowski and Rosaforma paillesiae Figus & Witkowski show unique morphological characteristics that lead us to create new genera. Rhomboneis shtapovii has two rimoportulae per valve and an unusual type of velum occluding the areolae. Rosaforma paillesiae has a peculiar asymmetric apical pore field occupying half the valve pole, the other half contains a rimoportula with two apical pores.

Temperature-dependent toxicity of fluoxetine alters the thermal plasticity of marine diatoms

Anthropogenic activities have led to the emergence of pharmaceutical pollution in marine ecosystems, posing a significant threat to biodiversity in conjunction with global climate change. While the ecotoxicity of human drugs on aquatic organisms is increasingly recognized, their interactions with environmental factors, such as temperature, remain understudied. This research investigates the physiological effects of the selective serotonin reuptake inhibitor (SSRI), fluoxetine, on two diatom species, Phaeodactylum tricornutum and Thalassiosira weissflogii. Results demonstrate that fluoxetine significantly reduces growth rate and biomass production, concurrently affecting pigment contents and the thermal performance curve (TPC) of the diatoms. Fluoxetine reduces the synthesis of chlorophyll a (Chl a) and carotenoid (Car), indicating inhibition of photosynthesis and photoprotection. Furthermore, fluoxetine decreases the maximum growth rate (μmax) while increasing the optimum temperature (Topt) in both species, suggesting an altered thermal plasticity. This shift is attributed to the observed decrease in the inhibition rate of fluoxetine with rising temperatures. These findings emphasize the physiological impacts and ecological implications of fluoxetine on phytoplankton and underscore the significance of considering interactions between multiple environmental drivers when accessing the ecotoxicity of potential pollutants. The present study provides insights into crucial considerations for evaluating the impacts of pharmaceutical pollution on marine primary producers.

A lightweight convolutional neural network (CNN) model for diatom classification: DiatomNet.

Diatoms are a type of algae with many species. Accurate and quick classification of diatom species is important in many fields, such as water quality analysis and weather change forecasting. Traditional methods for diatom classification, specifically morphological taxonomy and molecular detection, are time-consuming and may not provide satisfactory performance. However, in recent years, deep learning has demonstrated impressive performance in this task, just like other image classification problems. On the other hand, networks with more layers do not guarantee increased accuracy. While increasing depth can be useful in capturing complex features and patterns, it also introduces challenges such as vanishing gradients, overfitting, and optimization challenges. Therefore, in our work, we propose DiatomNet, a lightweight convolutional neural network (CNN) model that can classify diatom species accurately while requiring low computing resources. A recently introduced dataset consisting of 3,027 diatom images and 68 diatom species is used to train and evaluate the model. The model is compared with well-known and successful CNN models (i.e., AlexNet, GoogleNet, Inceptionv3, ResNet18, VGG16, and Xception) and their customized versions obtained with transfer learning. The comparison is based on several success metrics: accuracy, precision, recall, F-measure, number of learnable parameters, training, and prediction time. Eventually, the experimental results reveal that DiatomNet outperforms the other models regarding all metrics with just a few exceptions. Therefore, it is a lightweight but strong candidate for diatom classification tasks.

Cross-domain diversity effects: linking diatom species richness, intraspecific richness, and biomass production to host-associated bacterial diversity

Abstract Interactions between bacteria and microalgae are important for the functioning of aquatic ecosystems, yet interactions based on the biodiversity of these two taxonomic domains have been scarcely studied. Specifically, it is unclear whether a positive biodiversity-productivity relationship in phytoplankton is largely facilitated by niche partitioning among the phytoplankton organisms themselves, or whether associated bacterial communities play an additional role in modifying these diversity effects. Moreover, effects of intraspecific diversity in phytoplankton communities on bacterial community diversity have not been tested. To address these points, we factorially manipulated both species and intraspecific richness of three diatoms to test effects of diatom species/strain diversity on biomass production and bacterial diversity in algae-bacteria communities. The results show that diatom intraspecific diversity has significant positive effects on culture biomass and the diversity of the associated free-living bacterial community (0.2-3 μm size fraction), which are comparable in magnitude to species diversity effects. However, there were little to no effects of diatom diversity on host-associated bacterial diversity (>3 μm size fraction), or of bacterial diversity on biomass production. These results suggest a decoupling of bacterial diversity from the diatom diversity-productivity relationship and provide early insights regarding the relations between diversity across domains in aquatic ecosystems.

Two new diatom species of the genus Gomphonemopsis (Bacillariophyceae) from the coast of China and two new combinations for the genus.

Two new diatom species belonging to the genus Gomphonemopsis are described, Gomphonemopsisnanasp. nov. and Gomphonemopsisgaoisp. nov. These two species were compared in detail with congeners. Gomphonemopsisnana is distinguished by its high stria density and small size. This species was found so far to be epiphytic only on the eelgrass collected from Qingdao Bay (Yellow Sea). Gomphonemopsisgaoi is characterized by its isopolar valves, simple proximal raphe endings and acutely rounded apices. This taxon was separated from the exoskeleton of marine copepods sampled from the Futian Mangrove Nature Reserve (South China Sea). In addition, two new combinations, Gomphonemopsisoahuensis (Hustedt) Lang Li, Yuhang Li & Changping Chen, comb. nov. and Gomphonemopsisplatypus (Østrup) Lang Li, Yuhang Li & Junxiang Lai, comb. nov. are proposed. This study increases the records and knowledge of Gomphonemopsis along the coast of China.