Search Results (39)

Benthic marine diatoms are speciose but vastly underexplored eukaryotic microbes. Diatoms are identified by their intricately ornamented silica cell walls known as frustules, following removal of all organic matter with acid or strong oxidants. When living samples of diatom communities are examined, it is impossible to detect all the species present, as rare ones are easily obscured among the other materials present, and taxonomic identification of living diatoms can be uncertain or impossible, even with isolated cells. These features of diatom taxonomy have important consequences for biogeography, which we illustrate and discuss using new observations from two species. Despite being the mainstay for diatom descriptions, species described by light microscopy (LM) alone may conflate two species or (as in the case presented) lead to spurious new species; both need ultrastructural study to ascertain taxonomic and geographical boundaries. The species studied with scanning electron microscopy (SEM) over the last 45 years by Stephens & Gibson, Pennesi et al., and Lobban under the name of Mastogloia hustedtii is shown to be synonymous with M. grunovii. The former became known in the SEM era to bear both pseudoconopea (longitudinal flaps parallel to the sternum, invisible in LM) and silica plaques on the inner margins of the partecta (chambers on the valvocopulae), with the latter supposedly bearing neither, but there is a single, pantropical/Mediterranean species encompassed in the original description of M. grunovii. A new ultrastructural feature for the genus is reported from this species: marginal chambers formed by laminae over the mantle areolae and the first 2–3 areolae on the valve face. The second species studied, M. meisteri, had been reported a few times from one region based on very rare frustules, which do not meet the first criterion for biogeography: where did they live? Although we, too, did not observe living cells, the number of specimens present is evidence for a living population epiphytic on a Virgin Islands coral reef. The ultrastructure of this species is also shown for the first time. Because absence of evidence is overwhelming in microbial biogeography, the best we can say is that this species is potentially a regional endemic. Full article

This study presents the first comprehensive assessment of microalgal diversity in two Slovenian transitional waters (TWs): the shallow brackish lagoon of the Škocjanski Zatok Nature Reserve (SZNR) and the Rižana River estuary within the Port of Koper (PK) area. Between 2018 and 2021, water samples collected with a phytoplankton net were analyzed using light and scanning electron microscopy. In total, 240 species from 117 genera were identified in TW, dominated by diatoms and dinoflagellates, surpassing the diversity at a marine coastal station (91 species, 59 genera). Species richness was higher in PK (226) than in SZNR (154), mainly due to dinoflagellates and coccolithophores. Marine taxa predominated along the salinity gradient, with moderate contributions from brackish taxa and few freshwater forms, reflecting both natural and anthropogenic influences. Planktonic taxa dominated at all sites, while benthic forms were abundant in the lagoon, particularly in spring. Thirty-two taxa were recorded for the first time in Slovenian TW, mostly benthic or tychopelagic diatoms. The detection of Coolia monotis and five cyanobacterial genera with potentially harmful traits highlights the role of TW as an ecological interface. The taxonomic sufficiency analysis showed that the order level is sufficient to distinguish transitional from marine assemblages, beyond which ecological information is lost. Overall, this study highlights the importance of detailed taxonomic resolution for detecting microalgal diversity, including harmful and non-indigenous species to ensure robust ecological assessments under the WFD and MSFD directives. Full article

Diatoms are the most numerous of algae and scanning electron microscopy continues to reveal ever-increasing diversity. Two new species of Hyalosira from Florida add new characters distinguishing species in this recently redefined genus: H. ornata sp. nov. from Florida Bay has consistent and elaborate ornamentation on both valves and undulate valve margins; H. sertifera sp. nov., from the Atlantic coast of Key Largo, has a thick, consistent, garland-like ring of cristae on only one valve; the former species has deep septa on all copulae except the valvocopula, the latter shallow septa or none on the copulae. Hyalosira hesperia was also found in the Atlantic sample; this is the first record outside the Mediterranean. The number of species known from SEM is now twelve, including four with septa, a diversity potentially useful in exploring outstanding questions of septum function; a key to these species is appended. Full article

Mastogloia is a large, morphologically diverse genus of primarily benthic marine species defined by the presence of partecta (chambers) on the valvocopula (girdle band next to the valve). Several genera have been found with valves that resemble Mastogloia but lack the ring of partecta; the most diverse group is in freshwaters, especially Aneumastus, but there are two marine genera, both monotypic. A third such species has been found in Cuba and is described here as Paramastogloia cubana gen. nov., sp. nov. Paramastogloia cubana, Mastoneis biformis, and Mastogloiopsis biseriata each resemble the valve structure of some species of Mastogloia but do not resemble one another. Paramastogloia is indistinguishable in light microscopy (LM) from naviculoid diatoms and had been identified as Navicula cf. sovereigniae. The resemblance of P. cubana to Mastogloia is in the areolae, particularly to those of M. umbra, M. dicephala, and M. mammosa, three species not likely to be in one monophyletic group. Mastoneis has been observed in LM from widespread warm-water localities and resembles some Mastogloia in having costae extending partway across the virgae (interstriae); new ultrastructural details are presented showing the girdle bands and absence of partecta, and a clearer genus diagnosis is proposed. The third genus, Mastogloiopsis, was established with ultrastructure and resembles species of Mastogloia sec. Marginulatae. The range of areolar characters that might be admissible to Paramastogloia is unknown, so the generic diagnosis has been left imprecise to allow for the possibility of other species. The relationships among these genera await genetic studies, which are still scarce in Mastogloiaceae. Full article

For the Cuban littorals in the Caribbean Sea, information on benthic diatoms is scarce, and hitherto non-existent for natural protected areas. Thus, to describe the structure of benthic diatom associations (BDAs) from a marine protected area in Cuba, sediment samples were collected in Playa Las Gaviotas (Refugio de Vida Silvestre Cayo Santa María) during dry (November) and rainy (July) seasons. Diatoms were separated, mounted in synthetic resin and identified under light microscopy. Species diversity of the BDA was estimated using Shannon (H′), Simpson (1 − λ) and Pielou evenness (J′) indices. We identified 354 taxa including 200 new records for Cuba; the nomenclature of 45 previously recorded taxa was updated. The currently recorded species richness of marine benthic diatoms for Cuba is 595. The most abundant taxa were Amphora cf. copulata, A. proteus, Diploneis smith var. pumila, Halamphora turgida, H. coffeiformis, Navicula zostereti, Nitzschia marginulata var. didyma and Psammodictyon panduriforme. The best-represented genus was Mastogloia with 70 taxa. Similarity values indicated homogeneous distribution of epipelic diatom taxa along the sandy bottom, suggesting a single diatom association. Mean values of H′ ranged from 4.91 bit/taxon in November to 4.95 bit/taxon in July. Structure analysis suggests a stable BDA with high species diversity characteristic of productive, pristine environments. Full article

Navicula incerta, a marine benthic diatom, holds promise for human nutrition and health as well as for aquaculture applications. However, the scarcity of organelle genome data within the Navicula clade has impeded a comprehensive understanding and utilization of this group. Our research presents a pioneering exploration into the complete mitochondrial and chloroplast genome sequences of N. incerta CACC 0356, shedding light on its phylogeny and evolutionary history. The mitochondrial genome (mtDNA) spans 61,320 bp with a GC content of 29.87%, comprising one circular DNA molecule that encodes for 34 protein-coding genes, 24 tRNAs, and 34 rRNAs. Whereas, the chloroplast genome (cpDNA) is larger at 129,090 bp, encompassing 127 protein-coding genes, 30 tRNAs, and 7 rRNAs. Notably, the cpDNA of N. incerta is approximately 2.1 times the size of its mtDNA. Our annotation identified four genes that are partially situated in the homologous regions between the mitogenome and chloroplast genome, totaling 372 bp, which represents 0.61% of the entire mitogenome. Comparative analyses revealed that N. incerta CACC 0356 is closely affiliated with Fistulifera saprophila and Fistulifera solaris, both members of the Naviculaceae order. This study significantly expands the mitochondrial and chloroplast genomic resources for algae and lays a foundation for the development of genetic diversity analyses in algae. Full article

The estuarine area of Luanhe River is an important fisheries ground in China’s Bohai Sea. In 2016, Tangshan Marine Ranching Co., Ltd. constructed a 2 km² artificial oyster–macroalgae reef area by placing artificial reefs on the seabed adjacent to the Luanhe River Estuary. This action resulted in sustainable annual economic outputs through the fishing and sea cucumber put-and-take fishery. Although Luanhe River runoff and reef construction are important to the local phytoplankton community and fisheries’ production, little is known about how these factors affect phytoplankton community structure in the local coastal ecosystem. In this study, we conducted field surveys to investigate the spatiotemporal variations in species composition, abundance, dominant species, diversity indexes, niche width and overlap, and interspecific connection of the phytoplankton community in the ecosystem of oyster–macroalgal reefs. From July 2016 to August 2017, we collected data before and after reef construction in areas inside and outside of the benthic reefs in both the flood and dry seasons of Luanhe River runoff. We found a total of 79 species, with the majority represented by diatoms and dinoflagellates. The dominant species were Paralia sulcata and Coscinodiscus sp. The total species number and abundance increased from May to September. The species number in the reef area was greater than that outside the reef. Species abundance from August to September was greater in the reef area than in the control area, which was opposite the situation from May to June. We found more phytoplankton abundance in the flood season compared with that in the dry season. Our results suggest that reef construction can benefit the local phytoplankton community and that further studies of the relationship among oysters, macroalgae, and phytoplankton in the system are warranted. Moreover, we provide baseline data about variations in the phytoplankton community in a sea ranch area. Full article

Yap diatoms—from freshwater streams through estuaries and mangroves to the marine coral reefs—had been sampled in 1988 and 2014 and a few species from the 1988 collections described in a 2009 report. The present paper documents 168 new records, including seven new species, mostly from coral reef habitats, but including some interesting new species from mangroves, and incorporates records published in taxonomic papers. In addition, 44 Mastogloia records were published separately, bringing the taxon total to 245. In the present paper, 32 records are new for Micronesia, while many others are species described from neighboring Guam in the past 15 years. The total represents probably less than one-quarter of the species present on the reef because many specimens of Navicula, Nitzschia, Amphora, etc., have so far been identified only to genus. Floristic studies of benthic diatoms are limited partly by the shortage of taxonomic studies, and we present the taxa for which we can make reasonable arguments for identification, supporting light microscopy with scanning electron micrographs whenever possible. New taxa include Ehrenbergiopsis gen. nov. for Ehrenbergiulva hauckii; Biddulphiella cuniculopsis sp. nov.; Campylodiscus tatreauae sp. nov.; Cymatoneis belauensis from Palau and Cymatoneis yapensis from Yap; Diploneis denticulata sp. nov.; Entomoneis yudinii sp. nov.; and Nitzschia pseudohybridopsis sp. nov. Interesting new records include: Achnanthes cf. brevipes; Actinocyclus decussatus; Caloneis ophiocephala; Licmophora cf. hastata; Lyrella cf. rudiformis; and an unidentified cymatosiroid. One sediment sample included the remains of a planktonic community with Chaetoceros peruvianus, Skeletonema grevillei, Thalassiothrix gibberula and two species of Lioloma, rarely seen in the oligotrophic waters of Micronesia. Full article

During a floristic inspection of sediment samples from Playa Las Gaviotas, 69 specific and infra-specific taxa of Mastogloia were identified in the diatom taxocenosis, including 42 unrecorded taxa for the Cuban coasts. These are added to the 59 Mastogloia taxa previously listed. In this way, currently, the 101 Mastogloia comprised in the benthic diatom associations of the Cuban coast constitute the highest number of taxa ever recorded in similar floristic studies, which also indicates their tropical affinity. Furthermore, observations are made on misidentified taxa such as Mastogloia (Orthoneis) aspera, M. asperuloides, M. (Orthoneis) clevei, M. floridensis, M. latecostata, M. laterorostrata, M. ovata, M. sigillata, M. pseudolatecostata, and others. Full article

The area of the city of Shenzhen at the Pearl River Delta in Guangdong Province, China, comprises rocks that preserve, with few interruptions, around 1.8 billion years of geological history. However, to date, only few scientific studies within a palaeontological context have been conducted on the sediment rocks in Shenzhen. Herein, the fossil record and heritage potential of Shenzhen is reviewed. The few existing previous investigations revealed a rich terrestrial and marine fossil record and show the great potential of this area for future palaeontological research, particularly on the upper Palaeozoic and Mesozoic strata: Carboniferous successions show plant remains and a diverse benthic marine fauna; fossils from Upper Triassic–Middle Jurassic sediment rocks provide important data for terrestrial and marine palaeoecosystems of this time; and the discovery of dinosaur nests in the Upper Cretaceous strata complements the previously known distribution of dinosaurs in South China. Additionally, micropalaeontological and palynological data from the upper Palaeozoic as well as Cenozoic successions in Shenzhen reveal diverse assemblages of foraminifera, ostracods, diatoms, and sporomorphs. Moreover, fossil finds in equivalent rocks in adjacent areas indicate great potential for the units in the Shenzhen area, in which, so far, no fossils have been found. Full article

Marine diatoms are essential members of both phytoplankton and phytobenthic communities, able to colonize submerged artificial and natural surfaces, contributing to benthic microbial biomass. Diatoms have developed different adaptative mechanisms to cope with various environmental stresses, including high concentrations of heavy metals. The aim of this study was to investigate the arsenic resistance of diatoms, isolated from microbial mats collected from an arsenic-rich brackish pond (Lake Mergolo della Tonnara, Italy), by evaluating (i) their ability to form biofilms in the presence of arsenite (As^III) or arsenate (As^V), and (ii) the variations in the photosynthetic pigments’ contents (i.e., chlorophyll a and c) in their biofilms. The mats were dominated by members of the genus Amphora, and isolates were affiliated with species of A. capitellata, A. coffeaeformis, and A. montana. The strains grew better in the presence of As^V than As^III, which is generally less toxic. After seven days of incubation, each strain exhibited a different ability to form biofilms on glass surfaces in the presence of arsenic (25 ppm), with A. montana strain 27 being the most effective (86%) in the presence of As^III, and A. coffeaeformis strain 26 (74%) with As^V. Photosynthetic pigment levels (chlorophyll a and c) differed in each biofilm, being poorly reduced by As^III in strain 27, and by As^V in strain 26, indicating a species-specific response to arsenic stress. Our results indicated that Amphora species thriving in this environment can form biofilms as an As-resistance mechanism, maintain their levels of photosynthetic pigments, and support the functioning of the pond ecosystem, with A. montana being favored in the presence of As^III, whereas A. coffeaeformis 26 in the presence of As^V. As producers of biofilms, these strains could be useful to develop new strategies to remediate arsenic pollution. Full article

This article is about the diversity of diatoms in the benthos of the upper sublittoral near Kazantip Cape, located on the shore of the Sea of Azov in the northeastern part of Crimea. The study was conducted in 2022 and 2023 at a depth of 0.1 to 1 m at temperatures from 3.7 °C to 29 °C and salinity from 13.6 to 15.6 psu on the following 11 species of macroalgae: Phaeophyta of Ericaria crinita, Gongolaria barbata, and Cladosiphon mediterraneus; Chlorophyta—Bryopsis hypnoides, Cladophora liniformis, Ulva intestinalis, and Ulva linza; and Rhodophyta—Callithamnion corymbosum, Ceramium arborescens, Polysiphonia denudata, and Pyropia leucosticta. A total of 97 taxa of Bacillariophyta belonging to 3 classes, 21 orders, 30 families, and 45 genera were found. The highest number of diatom species was found on U. linza (61 species), P. denudata (45), E. crinita (40), the lowest number was recorded on thalli P. leucosticta (9). On macroalgae were found of 80% benthic diatoms, 50% marine species, 36% brackish-marine, 9% freshwater, 5% brackish, and 36% cosmopolites. The maximum abundance of the diatom community was 243.4 × 10³ cells/cm² (P. denudata in September at 23.9 °C and 15.0 psu) with dominance by the diatom of Licmophora abbreviata, and the minimum was 3.8 × 10³ cells/cm² (P. leucosticta in January at 3.7 °C and 15.0 psu). The presence in the epiphyton of diatoms—indicators of moderate organic water pollution (32 species), which developed in masse in late summer—indicate a constant inflow of organic matter into the coastal waters of the Kazantip Cape. The bioindicator and statistical studies indicate the effectiveness of the conservation regime, especially at stations within the IUCN reserve, despite relatively high saprobity rates at stations exposed to recreational pressure and poorly treated domestic wastewater. Full article

Blue Haslea species are marine benthic pennate diatoms able to synthesize a blue-green water-soluble pigment, like marennine produced by H. ostrearia Simonsen. New species of Haslea synthetizing blue pigments were recently described (H. karadagensis, H. nusantara, H. provincialis and H. silbo). Their marennine-like pigments have allelopathic, antioxidative, antiviral and antibacterial properties, which have been demonstrated in laboratory conditions. Marennine is also responsible for the greening of oysters, for example, in the Marennes Oléron area (France), a phenomenon that has economical and patrimonial values. While blue Haslea spp. blooms have been episodically observed in natural environments (e.g., France, Croatia, USA), their dynamics have only been investigated in oyster ponds. This work is the first description of blue Haslea spp. benthic blooms that develop in open environments on the periphyton, covering turf and some macroalgae-like Padina. Different sites were monitored in the Mediterranean Sea (Corsica, France and Croatia) and two different blue Haslea species involved in these blooms were identified: H. ostrearia and H. provincialis. A non-blue Haslea species was also occasionally encountered. The benthic blooms of blue Haslea followed the phytoplankton spring bloom and occurred in shallow calm waters, possibly indicating a prominent role of light to initiate the blooms. In the absence of very strong winds and water currents that can possibly disaggregate the blue biofilm, the end of blooms coincided with the warming of the upper water masses, which might be profitable for other microorganisms and ultimately lead to a shift in the biofilm community. Full article

As the production of cultured bivalve mollusks is increasing worldwide, there is a growing need to study the biodiversity and ecology of microalgae in the mariculture zones. This study presents multiannual data (obtained in 2015–2016 and 2018–2020) on the species composition, abundance, biomass, and community structure of microphytobenthos from three mussel farm ecotopes (mussel shells, the epiphyton of twenty macroalgal species, and sediments under collectors). In total, 150 microalgal taxa were found, including 135 diatom species with a predominance of benthic (76%), marine (65%), and cosmopolite (30%) ones. In all habitats, 10 potentially harmful species and 44 indicators of organic pollution were noted. The maximum values on the mussel shells (abundance N = 119 × 10³ cells/cm² and biomass B = 0.0489 mg/cm²) were recorded in winter with the dominance of Tabularia fasciculata; in summer, the epiphyton was on the brown alga Nereia filiformis (N = 1001 × 10³ cells/cm² and B = 2.06 mg/cm²) with the dominance of toxic Pseudo-nitzschia seriata, on the red alga Phyllophora crispa (N = 1118 × 10³ cells/cm² and B = 3.24 mg/cm²) with the dominance of T. fasciculata, and in sediments (N = 104 × 10³ cells/cm³ and B = 0.046 mg/cm³) with the dominance of T. fasciculata and Bacillaria paxillifer. Statistically significant effects of the ecotope and sampling season on the diatom composition were noted. The strongest effect of temperature is observed for the mussel shell diatoms, for which the trend of abundance and biomass increase in winter and their decrease in summer is most noticeable. But in sediments, the effect of the season is reflected only in the permanent changes of the microalgae species composition. For the epiphyton, it was shown that it is temperature, rather than substrate macrophyte species, that affects its numerical structure. Full article

The monounsaturated fatty acid 7(E)-9-keto-hexadec-7-enoic acid (1) and three structurally related analogues with different oxidation states and degrees of unsaturation (2–4) were discovered from a marine benthic cyanobacterial mat collected from Delta Shoal, Florida Keys. Their structures were elucidated using NMR spectroscopy and mass spectrometry. The structure of 1 contained an α,β-unsaturated carbonyl system, a key motif required for the activation of the Keap1/Nrf2−ARE pathway that is involved in the activation of antioxidant and phase II detoxification enzymes. Compounds 1–4 were screened in ARE-luciferase reporter gene assay using stably transfected HEK293 cells, and only 1 significantly induced Nrf2 activity at 32 and 10 µM, whereas 2–4 were inactive. As there is crosstalk between inflammation and oxidative stress, subsequent biological studies were focused on 1 to investigate its anti-inflammatory potential. Compound 1 induced Nqo1, a well-known target gene of Nrf2, and suppressed iNos transcript levels, which translated into reduced levels of nitric oxide in LPS-activated mouse macrophage RAW264.7 cells, a more relevant model for inflammation. RNA sequencing was performed to capture the effects of 1 on a global level and identified additional canonical pathways and upstream regulators involved in inflammation and immune response, particularly those related to multiple sclerosis. A targeted survey of marine cyanobacterial samples from other geographic locations, including Guam, suggested the widespread occurrence of 1. Furthermore, the previous isolation of 1 from marine diatoms and green algae implied a potentially important ecological role across marine algal eukaryotes and prokaryotes. The previous isolation from sea lettuce raises the possibility of dietary intervention to attenuate inflammation and related disease progression. Full article