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Navicula

Navicula is a genus of pennate diatoms in the family Naviculaceae and order Naviculales, consisting of unicellular, eukaryotic microalgae with silica-based cell walls known as frustules.^[1] These organisms are distinguished by their elongated, boat-shaped valves that are symmetrical along both the apical and transapical axes, typically measuring 8–176 μm in length and 2–37 μm in width, with striae densities ranging from 5–24 per 10 μm.^[2] Primarily benthic and motile, Navicula species inhabit a wide range of aquatic environments, including freshwater streams, lakes, brackish waters, and marine sediments, where they glide using mucilage secretions expelled from their raphe slits.^[1]^[3] Established by Jean-Baptiste Bory de Saint-Vincent in 1822, the genus takes its name from the Latin navicula, meaning "little boat," reflecting the shape of its valves.^[1] The type species is Navicula tripunctata (O. F. Müller) Bory.^[1] Taxonomically, Navicula belongs to the class Bacillariophyceae within the phylum Ochrophyta and kingdom Chromista, though the genus has historically been a broad "catch-all" for symmetrical biraphid diatoms, leading to the reclassification of many taxa into genera such as Sellaphora and Luticola.^[4]^[3] Morphological features include lanceolate to elliptical valves with acute or rounded apices, loculate areolae in striae, and two large, rectangular chloroplasts per cell in live specimens.^[1] With over 10,000 described species, varieties, and forms—though many are synonyms or transferred—the genus remains one of the largest and most diverse in the diatoms.^[3] Ecologically, Navicula species play a crucial role as primary producers in aquatic food webs, contributing to oxygen production, carbon cycling, and nutrient fluxes through their photosynthesis.^[3] They are often used as bioindicators of water quality due to their sensitivity to pollution and environmental changes, with certain species dominating in oligotrophic to eutrophic conditions.^[2] Some Navicula taxa, such as N. directa, produce sulfated polysaccharides called naviculans, which exhibit antiviral properties against pathogens like HIV, HSV-1, HSV-2, and influenza A virus.^[5] While mostly free-living, a few species form mucilage tubes or attach to substrates, enhancing their prevalence in periphyton communities across North America and globally.^[1]^[3]

Taxonomy and Classification

Etymology and History

The genus name Navicula derives from the Latin word "navicula," meaning "small ship," a reference to the elongated, boat-like shape of the cells.^[6] The genus was formally established by Jean-Baptiste Bory de Saint-Vincent in 1822.^[7] Its type species is Navicula tripunctata (O. F. Müller) Bory, originally described as Frustulia tripunctata by O. F. Müller in 1786.^[8] Early classifications treated Navicula as a broad "wastebasket" taxon, encompassing over 10,000 species, varieties, and forms based primarily on superficial morphological similarities.^[3] Throughout the 20th century, electron microscopy revealed ultrastructural differences, such as variations in raphe structure, fibulae, and areola occlusions, leading to major taxonomic revisions that split off numerous genera from Navicula sensu lato, including Placoneis (Cox, 1987), Sellaphora (Mann, 1990), and Luticola (Round et al., 1990).^[9] These changes, detailed in seminal works like Round et al. (1990), reduced the circumscription of Navicula sensu stricto to species sharing specific internal features, such as a simple longitudinal canal and fibulate raphe.^[10] Recent molecular phylogenetics has further refined the taxonomy, highlighting polyphyly in the broader genus and prompting reclassifications based on genetic analyses such as SSU rRNA and rbcL genes.^[11] For instance, Navicula scopulorum Brébisson was transferred to Climaconeis Grunow in 1982 due to shared craticular bars and chloroplast arrangements, a move reaffirmed by recent molecular data confirming its placement outside Navicula sensu stricto.^[12] As of 2025, ongoing research continues to integrate molecular and morphological data, exemplified by discussions on the role of symmetry in classification and new genera like Gandhia established in 2023.^[13]^[9]

Phylogenetic Position

Navicula is classified within the domain Eukaryota, phylum Ochrophyta, class Bacillariophyceae, order Naviculales, family Naviculaceae, and genus Navicula.^[1] This placement positions it among the pennate diatoms, specifically in the symmetric biraphid category, characterized by bilateral symmetry and a raphe system that enables gliding motility.^[2] In classical systematics, the genus was outlined based on morphological features such as valve shape and striae patterns, as detailed in foundational works from the late 20th century. Molecular analyses using 18S rRNA and rbcL genes have since refined this understanding, supporting Navicula sensu stricto as a monophyletic clade within Naviculaceae, anchored by the type species Navicula tripunctata.^[14] However, the broader genus exhibits polyphyly, with numerous species phylogenetically nested in other genera, such as Haslea, necessitating taxonomic revisions.^[11] Post-2010 phylogenomic studies have further highlighted these divergences, employing concatenated gene alignments (e.g., 18S, rbcL, and psbC) to resolve relationships and confirm the transfer of species like those formerly in Haslea to Navicula or new genera like Envekadea.^[15] These analyses underscore the dynamic nature of naviculoid diatom classification, driven by integrating molecular data with ultrastructural morphology to delineate monophyletic lineages.^[16]

Morphology

Frustule Structure

The frustule of Navicula species is a rigid, silica-based cell wall composed of two overlapping valves—the larger epitheca and the smaller hypotheca—connected by a series of flexible girdle bands that allow for expansion during cell division. In lateral view, the overall structure appears boat-shaped, providing structural support while accommodating the cell's protoplast. The valves themselves are elliptical to lanceolate in outline, with lengths typically ranging from 5 to 200 µm, though most species fall between 10 and 100 µm. This siliceous composition imparts exceptional rigidity and intricate ornamentation that varies among species, enabling precise taxonomic identification.^[3]^[2]^[17]^[18] A defining feature of the valve surface is the longitudinal raphe, a narrow slit running along the central axis that facilitates gliding motility through mucilage secretion. Flanking the raphe is the axial area, a clear longitudinal zone, while the raphe terminates centrally at a thickened structure known as the central nodule. Parallel to the axial area, the valve face is adorned with fine striae—uniseriate rows of pores or areolae—that enable nutrient and gas exchange across the silica wall. These striae are often radial near the center and parallel or slightly convergent toward the apices, with densities varying from 5 to 24 in 10 µm depending on the species.^[3]^[19]^[3] Species within the genus exhibit morphological variations in frustule architecture, such as undulate valve margins or asymmetrical raphe endings, which contribute to biodiversity and ecological adaptation. For instance, the external proximal raphe ends may expand or curve, and the terminal ends can hook in opposite directions, while some taxa display a slightly lateral or undulating raphe path. The raphe briefly ties into motility by allowing directional movement along substrates. These features, combined with the silica's nanoscale porosity (e.g., pores of 100–200 nm), underscore the frustule's role in both protection and function.^[3]^[19]^[20]

Internal Cellular Features

The protoplast of Navicula cells is enclosed within the rigid silica frustule and features a typical eukaryotic organization adapted to the photosynthetic and motile lifestyle of these pennate diatoms. Live cells generally contain two large, plate-like chloroplasts positioned parallel to the girdle bands, one along each lateral side of the cell, facilitating efficient light capture in benthic environments.^[21]^[22] Each chloroplast typically includes a central pyrenoid, a proteinaceous structure that enhances carbon fixation by serving as a site for the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and starch storage, supporting energy reserves during periods of low light.^[23] A centrally located nucleus occupies the interior of the Navicula cell, housing the genetic material and regulating cellular processes such as division and response to environmental cues.^[24] Flanking the nucleus are anterior and posterior (polar) vacuoles, which play a key role in motility by storing and secreting mucilage through the raphe system, enabling the directional gliding characteristic of pennate diatoms.^[24]^[25] Active cytoplasmic streaming circulates organelles and nutrients throughout the cell, directly supporting this gliding mechanism by facilitating the flow of cytoplasm along the raphe canal and the extrusion of adhesive secretions from the polar vacuoles.^[25] Mitochondria are distributed in the cytoplasm, providing ATP for energy-intensive processes like photosynthesis and motility, while the Golgi apparatus produces vesicles that transport siliceous precursors during auxospore formation in the reproductive cycle.^[26]^[27] Transmission electron microscopy of Navicula species reveals ultrastructural details such as fibulae, which are transapical silica struts that internally bridge and support the raphe canal, maintaining structural integrity beneath the valve face.^[28]^[29]

Habitat and Distribution

Preferred Environments

Navicula species are predominantly benthic diatoms, inhabiting the sediment-water interface in a variety of aquatic systems where they attach to substrates such as sediments, rocks, and macrophytes to form biofilms.^[30] This lifestyle is characteristic across freshwater, brackish, and marine environments, with many species favoring low-flow conditions like springs and stream margins that allow for stable attachment and motility.^[30] These diatoms exhibit broad abiotic tolerances, thriving in waters ranging from oligotrophic to eutrophic conditions, with optimal pH levels between 6 and 9—spanning slightly acidic to alkaliphilic preferences—and temperatures from 5°C in cool mountain habitats to 30°C in warmer systems, though some tolerate extremes up to 60°C in thermal springs.^[30] While capable of surviving in low-light benthic zones, Navicula species preferentially position themselves in illuminated areas through active motility to optimize photosynthesis.^[31] Certain Navicula species serve as bioindicators of water quality; for instance, Navicula gregaria is commonly associated with polluted, nutrient-enriched streams, signaling eutrophication and organic pollution.^[30] Certain pennate diatoms, including some Navicula species, form resting spores that enable survival during adverse conditions, including desiccation, nutrient scarcity, or seasonal darkness, allowing populations to persist and recolonize when conditions improve.^[32]

Geographic Range

Navicula species exhibit a cosmopolitan distribution, occurring on all continents in a wide array of aquatic systems, including freshwater habitats such as rivers, lakes, and springs, as well as marine environments like coastal and estuarine zones.^[33]^[34] This global presence is documented across diverse regions, from North America and Europe to Asia, Africa, and oceanic islands like the Galápagos.^[35]^[36] Most Navicula species are absent from hypersaline environments, where high salinity exceeds their tolerance, but a few have been documented in such habitats, in addition to their persistence in brackish conditions.^[37]^[38] While present in subpolar and Antarctic freshwaters, extreme polar inland habitats show limited representation compared to temperate areas.^[39] Regional abundance of Navicula is particularly high in temperate zones, where environmental conditions favor diverse assemblages. For instance, over 200 species have been recorded in the freshwater systems of North America's Northern Great Plains and Rocky Mountains.^[40] In marine settings, species diversity is notably elevated in the Indo-Pacific region, with numerous taxa reported from coastal waters of Southeast Asia and the Pacific islands.^[41]^[42] This variation underscores the genus's adaptability to regional climate and hydrological gradients, contributing to its ecological success in mid-latitude ecosystems. Dispersal of Navicula species occurs primarily through water currents in connected aquatic systems, supplemented by overland transport via wind, birds, and aquatic insects.^[43]^[44] Human activities, such as shipping and water management, further facilitate their spread, enhancing invasive potential in disturbed or altered ecosystems where they can rapidly colonize new substrates.^[44] Endemism within Navicula is rare, with most species displaying broad distributions rather than strict geographic restriction.^[45] Nonetheless, a few taxa exhibit localized endemism, such as Navicula walkeri confined to Oregon and central California, and local morphological variants have been observed in isolated habitats like mountain springs.^[46]^[30] These patterns highlight the interplay between dispersal capabilities and habitat isolation in shaping the genus's biogeography.

Ecology and Behavior

Motility Mechanisms

Navicula species, as raphid pennate diatoms, exhibit gliding motility powered by the secretion of extracellular polymeric substances (EPS), primarily mucilage, through the raphe slit in their silica frustule. This secretion creates adhesive trails that interact with the substrate, enabling propulsion without flagella or cilia. The process involves the extrusion of mucilage strands from the raphe, which anchor to the surface and are pulled by intracellular forces, generating forward movement.^[47]^[48] At the cellular level, motility is driven by an actomyosin system where myosin motors along actin filaments in the cytoplasm interact with the raphe-associated membrane, facilitating EPS secretion and force transmission. Gliding speeds typically range from 4 to 12 µm/s, with maximum reported velocities up to 20 µm/s under optimal conditions. Directional control is achieved through differential EPS secretion at the two ends of the raphe, allowing quasi-instantaneous reversals via opposing myosin activities that adjust thrust direction. The raphe structure briefly referenced here enables this asymmetric secretion, linking cytoplasmic mechanics to extracellular propulsion.^[49]^[50]^[51] Motility in Navicula is enhanced by environmental cues such as nutrient gradients and light intensity, promoting directed movement for resource acquisition. In phosphate-limited conditions, cells exhibit chemotaxis toward phosphorus sources, increasing speed and orienting along gradients to optimize uptake. Light triggers phototaxis, with moderate irradiance (around 100 µmol photons m⁻² s⁻¹) inducing upward migration for photosynthesis, while high light generates a transthylakoidal proton gradient that signals downward movement to evade photoinhibition; this can also aid in escaping predation by repositioning within sediments.^[52]^[53] This gliding mechanism is distinct from flagellar motility in centric diatoms or other algae, relying instead on substrate adhesion via EPS rather than fluid propulsion. The raphe system, a key innovation in pennate diatoms, evolved independently at least twice in diatom lineages, enabling this motility and contributing to their ecological success in benthic habitats.^[54]

Trophic Interactions

Navicula species, as photoautotrophic benthic diatoms, serve as primary producers in aquatic food webs, harnessing photosynthesis to convert light energy into organic matter. In intertidal mudflats and coastal sediments, they dominate microphytobenthic communities, contributing substantially to benthic primary productivity—often 20-50% of total primary production in shallow coastal ecosystems—through the formation of dense biofilms that support higher trophic levels.^[55]^[56] This productivity is enhanced by species-specific interactions within diverse diatom assemblages, where Navicula's biomass accumulation fuels carbon export to consumers and decomposers.^[57] As basal resources, Navicula cells are heavily grazed by a range of micro- and macrofaunal predators, integrating them into complex trophic networks. Protozoans, such as tintinnids and ciliates like Euplotes sp., actively consume Navicula and other diatoms, with grazing rates influenced by diatom silica content—low-silica cells are preferred due to easier digestion.^[58] Nematodes, including algal-feeding species from genera like Eudorylaimus, target benthic diatoms as a primary food source, exerting top-down control on biofilm density.^[59] Macroinvertebrates, such as gastropod snails, amphipods, and insect larvae (e.g., chironomids), scrape Navicula-dominated periphyton mats, consuming up to significant portions of daily production and thereby linking benthic primary production to secondary consumers.^[60] In response to grazing pressure, Navicula employs defenses including mechanical reinforcement of silica frustules, which reduces digestibility and ingestion efficiency by up to fourfold against copepod and protozoan predators, and chemical deterrents like oxylipins (reactive polyunsaturated aldehydes) that impair grazer reproduction without directly repelling feeding.^[61]^[62] Navicula engages in intense competition with co-occurring diatoms and microalgae for limiting resources, particularly dissolved silica essential for frustule formation and light for photic zone positioning. Silica limitation favors smaller, faster-growing Navicula species over larger rivals, altering community structure in silica-depleted environments like freshwater streams and marine sediments.^[55] Light competition drives vertical migration and biofilm stratification, with Navicula optimizing positioning to outshade competitors via mucilage production.^[63] Additionally, allelopathic interactions mediated by extracellular polymeric substances (EPS) allow Navicula to inhibit rival diatom settlement and growth; these EPS matrices release compounds that disrupt competitor metabolism, enhancing Navicula dominance in mixed biofilms without excessive energy expenditure.^[64] Symbiotic associations further embed Navicula in trophic dynamics, particularly through partnerships with heterotrophic bacteria that facilitate nutrient cycling in periphyton communities. In Navicula-bacteria consortia, diatoms supply organic carbon via EPS exudates, while bacteria recycle nitrogen through processes like ammonia oxidation and denitrification, achieving up to 85% nitrogen removal efficiency in symbiotic biofilms.^[65] These interactions, common in wastewater and natural periphyton mats, promote mutualistic nutrient exchange—bacteria mineralize diatom-derived organics into bioavailable forms, boosting Navicula growth and overall community resilience to nutrient pulses.^[57] Such symbioses underscore Navicula's role in stabilizing food webs by enhancing resource turnover in oligotrophic habitats.^[66]

Reproduction

Asexual Reproduction

Asexual reproduction in Navicula primarily occurs through binary fission, a mitotic process that allows for rapid vegetative propagation under favorable conditions. During division, the diploid nucleus undergoes mitosis to produce two daughter nuclei, while the chloroplasts—typically numbering one or two—duplicate and segregate equally to each half of the cell. The protoplasm then cleaves longitudinally, parallel to the valve surface, partitioning the cell contents into two uninucleate portions. Each daughter cell inherits one intact valve from the parent frustule (the epitheca becomes the epitheca of one daughter and the hypotheca of the other), and a new hypotheca forms within the space of the old girdle bands via silicification in dedicated silica deposition vesicles (SDVs). This process involves the uptake and polymerization of silicic acid into biosilica, with partial resorption of existing girdle band material providing recycled silica for the new valves, ensuring efficient resource use without auxospore formation in the vegetative phase.^[67]^[68] A key feature of this reproductive mode is progressive cell size reduction, governed by the MacDonald-Pfitzer hypothesis, where each successive fission yields daughter cells smaller than the parent due to the spatial constraints of forming new valves inside the rigid frustule. Over multiple generations, this leads to a diminution in average cell size within the population, eventually reaching a minimum threshold that impairs vitality and division capacity, prompting a shift toward sexual reproduction for size restoration. In Navicula species, such as N. phyllepta, this size decrement is evident across co-occurring populations, highlighting the hypothesis's applicability to pennate diatoms.^[69]^[70] Under optimal environmental conditions, including adequate light, nutrients, and silica availability, Navicula cells can complete binary fission every 24-48 hours, with reported division rates around 0.64 per day for certain marine strains, enabling exponential population growth. This rapid cycling facilitates the formation of dense blooms in nutrient-rich aquatic environments, where Navicula contributes significantly to primary productivity. Silica resorption and redeposition during valve morphogenesis are critical steps, as they minimize the energetic cost of frustule reconstruction and support sustained division rates.^[71]^[72]

Sexual Reproduction

Sexual reproduction in Navicula diatoms occurs through auxosporulation, a process that restores cell size diminished by successive asexual divisions and introduces genetic variation via meiotic recombination. When vegetative cells reach a critical minimum size—typically after multiple binary fissions—meiosis is initiated within paired gametangia, producing two isogametes per cell. These gametes, each containing a single nucleus and chloroplast, are released into a shared mucilage envelope where they fuse to form a zygote.^[73]^[74] The zygote expands into an auxospore, initially lacking a siliceous wall and enclosed by a flexible organic perizonium composed of transverse bands that guide bipolar elongation. This auxospore grows to 2-3 times the size of the parent gametangia, with the protoplast contracting to form the initial epitheca and hypotheca within the perizonium; the primary transverse band is notably wider, followed by narrower split rings that accommodate expansion. Supernumerary nuclei from meiosis degenerate rapidly, ensuring diploidy in the zygote, while karyogamy may be delayed until late in auxospore development. The resulting initial cell, upon completing frustule formation, initiates a new cycle of size-stable vegetative reproduction.^[74]^[10]^[75] Auxosporulation is triggered by environmental cues such as nutrient stress, high cell density, elevated temperatures, or prolonged daylengths, though it remains rare in laboratory cultures and is more commonly observed during natural blooms in the field. This sexual phase contrasts with asexual cloning by promoting genetic diversity through recombination during meiosis, enhancing adaptability in variable habitats.^[76]^[74]

Diversity and Species

Number and Variability

The genus Navicula currently comprises approximately 1,200 accepted species, a significant reduction from the historical estimate of over 10,000 taxa assigned to it due to ongoing taxonomic splits and reclassifications.^[77] This high intraspecific variability is particularly evident in valve ornamentation, such as the arrangement and density of striae and areolae, which can differ substantially within populations of the same species. Variability in Navicula arises from both cryptic speciation and environmental plasticity. Scanning electron microscopy (SEM) and genetic analyses have revealed numerous cryptic species complexes, such as within the N. cryptocephala group, where morphologically similar forms are genetically distinct.^[78] Additionally, morphological plasticity allows adaptation to environmental gradients. Taxonomic challenges persist due to the polyphyletic nature of Navicula, which has led to the transfer of many species to other genera based on differences in raphe structure and striae patterns. For example, numerous taxa previously in Navicula sect. Punctatae have been reassigned to Luticola, while others with distinct canal-raphe systems and H-shaped chloroplasts have been moved to Fallacia.^[79]^[80]^[81] Recent taxonomic revisions, incorporating molecular data, continue to refine these boundaries.^[15] Diversity within Navicula is highest in freshwater lentic systems, such as lakes and ponds, where stable conditions support a wide array of microhabitats and reduce competitive pressures from flow-dependent taxa.^[82]

Notable Species

Navicula tripunctata serves as the type species for the genus Navicula, originally described as Vibrio tripunctatus and later transferred by Bory de Saint-Vincent in 1822.^[83] This cosmopolitan diatom is commonly found in freshwater environments, including ponds, rivers, and springs, where it thrives as a benthic, unattached, solitary cell.^[84] Valves are linear-lanceolate with wedge-shaped ends, measuring 32-60 µm in length and 6-10 µm in width, featuring a symmetric transversely rectangular or elliptical central area and striae of 9-12 in 10 µm.^[85] The species is named for three distinct puncta near the valve center, a characteristic evident in its original description, though modern observations emphasize the rectangular central area.^[86] Navicula gregaria is recognized as an indicator of polluted waters due to its tolerance for high nutrient levels, alkalinity, and conductance in eutrophic conditions.^[87] Predominantly occurring in marine and brackish habitats, such as estuaries and coastal streams, it often forms dense mats in benthic communities exposed to organic enrichment.^[88] Valve dimensions range from 16-35 µm in length and 4-7 µm in width, with lanceolate shape, protracted apices, and striae of 14-18 in 10 µm at the center.^[89] Its asymmetric elliptic central area and sharply bent external proximal raphe ends distinguish it morphologically in polluted assemblages.^[89] Navicula incerta has gained attention for its potential in aquaculture as a feed source, attributed to its high content of polyunsaturated fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which support larval nutrition.^[90] This marine benthic diatom inhabits coastal and brackish waters, as well as electrolyte-rich freshwaters and moist soils, often in year-round coastal assemblages.^[91] Cells are small, with linear-lanceolate to lanceolate valves typically in the micrometer range, and it exhibits robust growth under varied nutrient conditions suitable for cultivation.^[92] Its antioxidant properties and lipid profile make it valuable for enhancing fatty acid profiles in aquaculture systems.^[93] Navicula pavillardii is a coastal marine diatom frequently associated with benthic habitats in regions like the Black Sea and Mediterranean, including epizoic communities on sea turtle carapaces.^[94] Valves measure 22-28 µm in length and 5-6 µm in width, presenting a linear-lanceolate form with striae density of 13-14 in 10 µm.^[94] Notable for its active gliding motility, this species has been extensively studied using microchambers to analyze trajectory patterns and temperature effects on movement, highlighting its ecological role in dynamic coastal biofilms.^[95]

Ecological and Human Significance

Role in Ecosystems

Navicula species, as prominent members of benthic microphytobenthos communities, play a crucial role in primary productivity within aquatic ecosystems, particularly in intertidal and shallow subtidal zones. These diatoms contribute significantly to carbon fixation and primary production in many benthic habitats through their photosynthetic activity.^[96] This process not only sequesters inorganic carbon but also generates oxygen, which diffuses into the overlying water and penetrates surface sediments, thereby oxygenating anoxic layers and supporting aerobic microbial processes.^[97] In nutrient cycling, Navicula diatoms facilitate the recycling of silica and other elements essential for ecosystem dynamics. Upon cell death or grazing, their siliceous frustules undergo dissolution, releasing dissolved silicic acid back into the environment and enabling reuse by other diatom populations.^[98] Additionally, photosynthetic oxygen production and organic exudates from benthic diatoms like Navicula influence nitrogen transformations, including associations with denitrification processes in sediments, where diatom-derived carbon can stimulate microbial nitrate reduction while oxygen may modulate its extent.^[99] Navicula contributes to biodiversity support by forming the foundational layer of aquatic food webs and enhancing habitat stability. As a primary food source, these diatoms sustain grazers such as protozoans, crustaceans, and mollusks, channeling energy to higher trophic levels, including commercially important fisheries. Their extracellular polymeric substances (EPS) production strengthens biofilms, binding sediment particles and reducing erosion in dynamic environments like intertidal flats.^[100] Furthermore, assemblages of Navicula species serve as bioindicators of environmental change, with shifts in community composition signaling eutrophication or acidification. For instance, increased abundance of certain Navicula taxa correlates with nutrient enrichment, as reflected in diatom-based indices such as the Trophic Diatom Index (TDI).^[101] Similarly, their sensitivity to pH alterations allows for assessment of acidification impacts in freshwater and coastal systems. Recent research also indicates that certain Navicula species are vulnerable to climate change effects, such as reduced precipitation in spring ecosystems, further emphasizing their utility as bioindicators.^[102]^[30]

Applications and Uses

Navicula species are integral to diatom-based indices employed in water quality assessments, particularly for tracking pollution in aquatic environments. The specific pollution sensitivity index (SPI), which assigns sensitivity scores to diatom taxa including various Navicula species based on their tolerance to organic pollution and nutrient enrichment, is widely used to evaluate ecological status in rivers and streams.^[103] Similarly, benthic diatom indices incorporating Navicula abundance have demonstrated efficacy in monitoring ecological conditions in subtropical streams, correlating diatom community shifts with nutrient levels and habitat degradation.^[104] In biotechnology, Navicula biomass serves as a promising feedstock for biofuel production due to its high lipid content, which can reach elevated levels under nutrient stress conditions such as silicon or nitrogen limitation. For instance, the oleaginous diatom Navicula phaeophila exhibits significantly increased lipid accumulation upon sequential nutrient removal, supporting its potential in third-generation biofuels.^[105] Additionally, Navicula incerta is utilized in aquaculture feeds owing to its production of omega-3 fatty acids, particularly eicosapentaenoic acid (EPA), which enhances the nutritional profile of shellfish and shrimp larvae.^[106] Pharmaceutical applications of Navicula leverage its bioactive compounds, including extracts with antioxidant properties derived from cellular components. Methanol extracts of Navicula incerta demonstrate strong free radical scavenging activity, positioning them as potential sources for natural antioxidants in drug formulations. Sulfated polysaccharides from N. incerta further exhibit antioxidant and anti-hemolytic effects, suggesting utility in oxidative stress-related therapies.^[93]^[107] In nanotechnology, the intricate silica nanostructures of Navicula frustules are harnessed for advanced applications such as drug delivery and biosensors. These porous biosilica shells, with pore sizes ranging from 50 nm to 1 µm, enable controlled release systems and enhanced sensitivity in molecular detection. For example, Navicula sp. frustules functionalized with fluorescent molecularly imprinted polymers have been developed for lysozyme sensing, achieving high selectivity and detection limits. However, large-scale utilization of diatom frustules, including those from Navicula, faces challenges such as low biomass productivity and high cultivation costs.^[108]^[109]

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[22]
Navicula Bory de St. Vincent (1822) - Diatoms Ireland
Cells solitary, usually seen in valve view and often actively motile when live. Live cells with two plate-like chloroplasts lying along each side of girdle.Missing: type | Show results with:type
[23]
Navicula | Diatom Flora of Britain and Ireland
Dec 27, 2020 · Raphe straight, straight or hooked endings at the centre externally, simple straight endings at the centre internally, and hooked terminal ...
[24]
(PDF) Studies on the diatom genus Navicula Bory ... - ResearchGate
Aug 6, 2025 · Studies on the diatom genus Navicula Bory. Navicula scopulorum Bréb ... chloroplasts with a central pyrenoid [2, 4]. ... Sexual ...
[25]
Impact of Low-Temperature Storage on Growth ... - BioOne Complete
Impact of Low-Temperature Storage on Growth. Characteristics of Marine Diatom, Navicula sp. ... trally located nucleus with two vacuoles ... Effect of different ...
[26]
Thallus Structure of Navicula (With Diagram) - Biology Discussion
Due to presence of raphe Navicula shows gliding movement. This movement is caused “by streaming cytoplasm by circulation within the raphe, and by the extrusion ...
[27]
Diatom Molecular Research Comes of Age: Model Species for ...
B.E.. (. 1966. ). Studies on the biochemistry and fine structure of silica shell formation in diatoms. II. The structure of the cell wall of Navicula ...
[28]
Molecular regulation of the diatom cell cycle - Oxford Academic
Nov 25, 2013 · Cytoplasmic fine structure with emphasis on Golgi apparatus . Cytobiologie ... Valve morphogenesis in the pennate diatom Navicula cuspidata.Missing: streaming | Show results with:streaming
[29]
Origin and Evolution of the Canal Raphe System in Diatoms
We reconstructed the phylogeny of raphid pennate diatoms and included, for the first time, members of all three canal raphid diatom lineages, and used the ...
[30]
Glossary of Terms | Mendota Diatoms - Wix.com
In many kinds of diatoms the fibulae may look like thick bands that stretch from the raphe to the valve margin. ... This trait makes the diatom asymmetrical.
[31]
The Diatom Genus Navicula in Spring Ecosystems with the ... - MDPI
Sep 27, 2024 · In our recent taxonomic and ecological investigation on diatoms of El-Farafra Oasis springs and drilled wells, the most common Navicula species ...
[32]
Effect of Light Intensity and Light Quality on Diatom Behavioral and ...
In this study, we investigated the different photoregulation responses of diatom dominated natural biofilms to different light intensities and wavelengths.
[33]
Induction of resting-spores in the pennate diatom Navicula ...
Aug 10, 2025 · During resting-spore formation, however, both plastids remain arrested at their interphase location along the girdle sides. They inhibit contact ...
[34]
Environmental Requirements and Pollution Tolerance Of Freshwater ...
10. Geographical distribution and other pertinent information. Most of the diatoms included in this project are of cosmopolitan or worldly distribution. ...<|control11|><|separator|>
[35]
Insights into global diatom distribution and diversity in the world's ...
Feb 29, 2016 · We found only a few cosmopolitan ribotypes displaying an even distribution across stations and high abundance, many of which could not be ...
[36]
On the geographical distribution of Navicula nielsfogedii J.C. Taylor ...
Aug 9, 2025 · From a geographic point of view, Navicula is considered as a large and widespread genus across the globe. Reports of species include many ...
[37]
Diatoms (Bacillariophyta) of Isolated Islands: New Taxa in the Genus ...
The diatoms (Bacillariophyta) from a coastal lagoon from the Diablas wetlands (Isla Isabela, the Galápagos Islands) were studied in material from surface ...
[38]
Modern surface sediment diatom assemblages and conductivity ...
Two distinct mechanisms explain this ecological exclusion: (1) In meso-hypersaline to hypersaline lakes (EC > 50 mS/cm), high salinity directly excludes diatoms ...
[39]
[PDF] Diatoms as indicators of environmental change in Antarctic and ...
The species found on the polar plateau were 98% lacustrine taxa, including Luticola muti copsis (Van Heurck) Mann, Navicula shackletoni West and West,. Luticola ...
[40]
Seven new species in Navicula sensu stricto from the Northern ...
Aug 10, 2025 · Navicula, the most species-rich genus of the region, accounts for 209 of the 1368 taxa recorded from the region to date. Seven new species of ...
[41]
New diatom species Navicula davidovichii from Vietnam (Southeast ...
Jul 8, 2020 · New diatom species Navicula davidovichii from Vietnam (Southeast Asia) | Phytotaxa.
[42]
Marine tube-dwelling diatoms of the Pacific coast of North America. II ...
Aug 7, 2025 · The tube-dwelling cross-lineate Navicula species on the west coast are dominated by a taxon that belongs in or near the N. ramosissima – N.Missing: Indo- | Show results with:Indo-
[43]
[PDF] The diversity and distribution of diatoms: from cosmopolitanism to ...
Oct 12, 2007 · Diatom distribution ranges from global to narrow endemic, challenging the idea that their large populations prevent dispersal limitation.
[44]
Flow directionality, mountain barriers and functional traits determine ...
Apr 19, 2016 · Overland dispersal could be airborne dispersal by wind, or occur by virtue of organisms from aquatic insects, water birds to water-living ...
[45]
The diversity and distribution of diatoms: from cosmopolitanism to ...
Diatom distribution ranges from global to narrow endemic, challenging the idea that dispersal is not a constraint. Dispersal limitation is significant.
[46]
Valve morphology and systematic position of Navicula walkeri ...
Variation in valve size and ultrastructure is documented for Navicula walkeri, a freshwater diatom species endemic to Oregon and central California (USA).
[47]
The mechanism of diatom locomotion. I. An ultrastructural study of ...
Observations of raphe-associated cell structure of the diatom Navicula cuspidata suggest the involvement in cell locomotion of secretory vesicles, ...
[48]
Contribution of frustules and mucilage trails to the mobility of diatom ...
May 14, 2019 · Highly motile diatom species, such as Navicula sp., can adhere strongly to hydrophobic surfaces and drift in response to fluctuations in the ...Missing: invasive | Show results with:invasive
[49]
Ice gliding diatoms establish record-low temperature limits for motility in a eukaryotic cell | PNAS
### Summary of Gliding Motility Mechanisms in Ice Diatoms
[50]
Gliding motility of the diatom Craspedostauros australis coincides ...
Sep 23, 2024 · Raphid diatoms are one of the few eukaryotes capable of gliding motility, which is remarkably fast and allows for quasi-instantaneous directional reversals.
[51]
Maximum gliding speed of diatoms. - ResearchGate
Maximum gliding speed reported for diatoms was ∼20 μm s −1 ( Yamaoka et al., 2016) (Table 1), but this was attained in the very specific situation of gliding.
[52]
Selective chemoattraction of the benthic diatom Seminavis robusta ...
In this diatom, motility and chemoreception are also essential for the finding of mating partners for sexual reproduction within pheromone gradients (Gillard et ...
[53]
Light induced transthylakoidal proton gradient is a key signal driving ...
Jul 1, 2025 · Pennate diatoms are photosynthetic microorganisms capable of directed motility in response to light. In sedimentary habitats, many epipelic ...
[54]
Origin and evolution of the canal raphe system in diatoms - PubMed
Mar 25, 2011 · The canal raphe appears to have evolved twice, once in the common ancestor of Bacillariales and once in the common ancestor of Rhopalodiales and ...
[55]
Ecosystem services provided by freshwater and marine diatoms
Sep 1, 2022 · ... Navicula mutica var. ... Predicting the potential distribution of the invasive freshwater diatom Lindavia intermedia in New Zealand lakes.
[56]
Do diatoms dominate benthic production in shallow systems ... - ASLO
Sep 29, 2020 · We found that the contribution of diatoms to benthic production in a seagrass habitat was substantial (71–83%). Diatom contribution in the water ...
[57]
Diatom-Bacteria Interactions Modulate the Composition and ...
Benthic diatoms are dominant primary producers in intertidal mudflats and constitute a major source of organic carbon to consumers and decomposers residing ...
[58]
Effect of the Silica Content of Diatoms on Protozoan Grazing - Frontiers
Stocks of these two predators were concentrated using reverse filtration to remove the prey from the medium. They were then resuspended in 0.2 μm filtered ...
[59]
Algal Grazers - an overview | ScienceDirect Topics
Although the food source of the omnivore-predator has not been confirmed, other species of Eudorylaimus are fungal or algal grazers or predators on other ...
[60]
Aquatic Insects and Benthic Diatoms: A History of Biotic ... - MDPI
Oct 21, 2020 · Compared to shredders or predators, lotic grazers are exposed to higher hydraulic stress, as their food sources colonize the top of boulders ...Missing: nematodes | Show results with:nematodes
[61]
Diatom defence: Grazer induction and cost of shell‐thickening
Jul 15, 2020 · Thus, a six-fold increase in silica content in a variety of diatoms decreased the predation mortality due to a copepod grazer by four-fold and ...
[62]
Diatom/copepod interactions in plankton: the indirect chemical ...
It was assumed that diatoms represent a generally good food source for the grazers but recent work indicates that some species use chemical defenses.
[63]
Microphytobenthic dynamics in a Wadden Sea intertidal flat – Part I
The extracellular polymeric substances (EPS) produced by migratory diatoms in section III were unable to consolidate during the short emersion period (about ...<|separator|>
[64]
Allelopathic interactions in benthic biofilms: Effects of abiotic ...
Aug 10, 2025 · We examined the interaction between abiotic variables (light, nutrients, and salt stress) and allelopathy by analyzing the effects of culture ...
[65]
Silicate intervention in Navicula-bacteria symbiosis system: nitrogen ...
Oct 15, 2025 · It is crucial to recognize that diatoms are active participants in the nitrogen cycle. They can absorb NO3−-N via nitrate reductase (NR) ...
[66]
Interactions between Diatoms and Bacteria - PMC - NIH
Diatoms and bacteria have cooccurred in common habitats for hundreds of millions of years, thus fostering specific associations and interactions.
[67]
Notes on Diatoms
Diatoms reproduce asexually by cell division to produce two daugther cells by mitosis; each daughter cell receives one valve and it is reproduced by furrowing.Missing: Navicula binary fission process
[68]
Understanding Diatom Cell Wall Silicification—Moving Forward
Silica structures in diatoms are formed within a membrane-bound compartment called the silica deposition vesicle (SDV) (Drum and Pankratz, 1964; Reimann et al., ...
[69]
Genome size differentiates co-occurring populations of the ...
Jan 2, 2010 · Diatoms, however, are unique in that cell-wall structure causes size reduction during asexual reproduction ... Navicula phyllepta ( ...
[70]
[PDF] Morphometric allometry of representatives of three naviculoid ...
(1869) and Pfitzer (1869) each independently described this peculiarity, and it is now known as the MacDonald–Pfitzer hypothesis (Koci-olek & Stoermer 2010).
[71]
The Cell Division Rates of Ten Species of Attaching Diatoms in ...
4-5 day-1 of exchange rate of seawater, the cell division rates were as follows: Cymbella sp., 0.57 day-1; Stauroneis sp., 0.49; Gyrosigma sp., 0.80; Navicula ...
[72]
Plankton Analysis - epa nepis
a Reproduction Reproduction in diatoms is by binary fission. This potential for geometric increase in population size contributes to "blooms" under ...
[73]
Sexual reproduction and systematics of Navicula protracta
Aug 9, 2025 · Sexual reproduction in N. protracta is isogamous, although one gametangium often dehisces, releasing its gametes, before the other gametangium has completed ...Missing: autogamy | Show results with:autogamy
[74]
Auxospore formation, reproductive plasticity and cell structure in ...
Mar 9, 2022 · In most pennate diatoms where automixis has been reported, it is obvious that automixis takes place because the gametangia are unpaired (Geitler ...
[75]
[PDF] AUXOSPORE FORMATION AND THE MORPHOLOGY OF ... - CORE
After sexual reproduction, the zygote. (auxospore) expands and an initial cell is formed with- in it. The evolutionary significance of auxospore struc- ture ...
[76]
(PDF) Diatom Reproductive Biology: Living in a Crystal Cage
Here I review what is known about sexual reproduction in pennate and centric diatoms from both a morphologic/behavioural and an ecologic standpoint.
[77]
[PDF] Diversity of Navicula (Diatom) from Sulwade Barrage of ... - JETIR.org
... Navicula tripunctata as type species. It is boat shaped diatom, very large genus comprising over 1200 species (Guiry, 2015). True Navicula species have ...
[78]
[PDF] A new freshwater diatom genus Trialacinia gen. nov. (Naviculaceae
He suggested that species belong to Navicula if they have frustules symmetrical about three axes, raphe with a more or less developed silicified sternum (“ ...
[79]
A new species, Navicula lothargeitleri sp. nov ... - ResearchGate
Aug 6, 2025 · Recently published phylogenetic analyses of 52 strains of Navicula cryptocephala -like diatoms confirmed the existence of genetically ...
[80]
Effects of salinity on growth and on valve morphology of five ...
Jan 27, 2011 · We found a significant effect of salinity on stria density in N. frustulum and in N. pusilla, and on width in all five species studied ...
[81]
Algae World: Sellaphora: Taxonomy
... Navicula was not only large and heterogeneous, but probably also polyphyletic. However, although SEM provided many new insights and suggested how some ...
[82]
Description of five new Luticola D.G.Mann (Bacillariophyta ...
Jan 5, 2024 · The genus Luticola was distinguished from Navicula to accommodate species included in the Naviculaesect.Punctatae with Luticolamutica ...
[83]
(PDF) The Types of 22 Navicula (Bacillariophyta) Species Described ...
Aug 6, 2025 · On the basis of this examination, six Navicula species were transferred to other genera. ... shows that this species belongs to the genus Fallacia ...
[84]
https://sherubtsebotmal.wordpress.com/wp-content/uploads/2017/10/navicula.pdf
[85]
Navicula tripunctata (O.F.Müller) Bory - AlgaeBase
Type Species This is the type species (holotype) of the genus Navicula. Status of Name This name is of an entity that is currently accepted taxonomically ...Missing: three puncta
[86]
[PDF] navicula.pdf
HABITAT. It is freshwater alga which is commonly found in ponds and rivers usually free floating with other algae. It is found in the marshy and stagnant wa ...
[87]
Navicula tripunctata | Species - Diatoms of North America
Size Range, µm3. 1001-10000 · Motility. Moderately motile · Attachment. Unattached · Habitat. Benthic · Colony. Solitary · Occurrence. Rare · BCG. BCG 4 · Waterbody.Missing: type features
[88]
[PDF] Observations on the Tube-Dwelling Diatom Navicula Tripunctata var ...
Navicula tripunctata (0. F. Mull) var tripunctata is described by Patrick and Reimer (1966) to possess a rectangular central area. N.
[89]
Navicula gregaria | Species - Diatoms of North America
Navicula gregaria · Category. Symmetric Biraphid · Length Range. 16-35 µm · Width Range. 4.1-7.0 µm · Striae in 10 µm. 14-18 in the center valve.Missing: pollution mats
[90]
[PDF] Structure and productivity of marine benthic diatom communities in a ...
ceiving less exposure to desiccation supported dense mats of combined living ... Navicula gregaria Donk,. Navicula grevillei (Ag. ) Heil,. Navicula lyre ...
[91]
Guide to Navicula gregaria | Species - Diatoms of North America
Valves are lanceolate with protracted apices, 4.1-7.0 µm wide. The central area is asymmetric and elliptic. The external proximal raphe ends are sharply ...
[92]
Optimization of growing conditions for pigments production from ...
The diatom Navicula incerta ... Blackwell Sci 1, 207–252. Mustafa T. Variation in growth, fucoxanthin, fatty acids profile and lipid content of marine diatoms ...
[93]
Navicula incerta Grunow - AlgaeBase
Along the coast in brackish waters. In inland salt springs, in freshwaters with a high electrolyte content and in moist soils.Missing: size | Show results with:size
[94]
Complete Sequence and Characterization of Mitochondrial and ...
Abstract. Navicula incerta, a marine benthic diatom, holds promise for human nutrition and health as well as for aquaculture applications.Missing: internal | Show results with:internal
[95]
(PDF) Growth characteristics and antioxidant properties of the ...
Aug 7, 2025 · Diatoms of the genus Navicula are the most abundant benthic diatoms occurring year-round on the coast of Jeju Island, Korea. We isolated an ...
[96]
[PDF] Some New Records for Marine Diatom Flora of Turkey from Akliman ...
Dimensions: Valve length 22.54 -28.36 µm and breadth 5.08-5.59 µm, 13-14 striae in 10 µm. Distribution: Black Sea (Witkowski et al., 2010). Navicula pavillardii ...
[97]
Single cell analysis using a glass microchamber for studying ...
We propose a new technique for quantitative trajectory analysis of gliding phenomenon of Navicula pavillardii (NP) and Seminavis robusta (SR) diatom cells ...
[98]
WHOLE‐LAKE FERTILIZATION EFFECTS ON DISTRIBUTION OF ...
Apr 1, 2001 · However, only 10–40% of primary production was benthic at the highest fertilization rates.
[99]
Oxygenation of intertidal estuarine sediments by benthic microalgal ...
Empirical evaluation of the terms of the model showed that epipelic diatom photosynthesis as a source of oxygen at low tide may exceed atmospheric diffusion by ...
[100]
The role of aggregation for the dissolution of diatom frustules
The rate of silica dissolution from diatom frustules determines the fraction of silica recycled within the euphotic zone where it is available for new ...
[101]
Effect of settled diatom‐aggregates on benthic nitrogen cycling - PMC
In sediment incubations, the settlement of diatom‐aggregates markedly enhanced benthic O2 and NO 3 − consumption and stimulated NO 2 − and NH 4 + production.
[102]
The interaction between benthic diatom films and sediment transport
We conclude that sediment stabilization by biofilms must be studied on a spatial scale of centimetres, and a temporal scale of days to weeks. The most ...
[103]
Benthic diatoms as indicators of eutrophication in tropical streams
Sep 30, 2006 · Diatoms are frequently used as indicators of eutrophication in temperate systems, but little is known about their application to impacted African tropical ...Missing: acidification | Show results with:acidification
[104]
[PDF] A WFD compatible approach to assess acidification using diatoms in ...
The method described here will sit alongside the diatom metric that currently assesses the extent of eutrophication. The developed model was validated using ...
[105]
What do diatom indices indicate? Modeling the specific pollution ...
Apr 5, 2024 · The specific pollution sensitivity index (SPI) is one of the most frequently used indices, which assigns scores to diatom taxa based on their sensitivity to ...
[106]
Benthic Diatom Based Indices for Water Quality Assessment in Two ...
This study compared the performance of 14 widely-applied diatom indices in assessing ecological conditions in subtropical streams in South East Queensland (SEQ ...
[107]
Improved Lipid Production in Oleaginous Brackish Diatom Navicula ...
Nov 5, 2019 · A significant increase in lipid content was observed on the complete removal of the nutrients silicon and urea one at a time, while the biomass ...
[108]
Autotrophic vs. Heterotrophic Cultivation of the Marine Diatom ...
Many marine microalgae species naturally produce EPA and DHA as components of glycerolipids [9,10], thus resulting in a sustainable source of these fatty acids ...
[109]
Sulfated polysaccharide-rich extract from Navicula incerta
A sulfated polysaccharide from Navicula incerta (SPNi) was extracted, and its physicochemical characteristics, antioxidant activity, and anti-hemolytic ...
[110]
Recent Advances on Diatom-Based Biosensors - MDPI
Nov 28, 2019 · Lim et al. used fluorescence molecularly imprinted polymer based on Navicula sp. frustules for lysozyme sensing. The authors demonstrated a ...
[111]
Nature engineered diatom biosilica as drug delivery systems
Jul 10, 2018 · Each frustule or biogenic silica shells [40] of diatom species shows definite nanostructures [41] and enriched with important features like ...