Diatom Growth Research Articles

Material source, sedimentary environment, and mineralization process of Shengzhou diatomite deposit in Eastern Zhejiang Province, China

ABSTRACT The Shengzhou diatomite deposit, located in the Shengzhou-Xinchang basin, is recognized as one of the largest diatomite deposits in China. The scanning electron microscopy (SEM-EDS), mineral compositions and elemental geochemistry of the samples were analysed to identify the nutrient sources, depositional environments, and mineralization process. Through scanning electron microscopy, the predominant diatom species observed are Aulacoseira granulata (Ehrenberg) Simonsen and Cyclotella shengxianensis Huang and Cai. The results of X-ray diffraction (XRD) analysis results indicate that the mineral composition of diatomite mainly consists of opal-A, quartz, clay minerals, feldspar, carbonate minerals, and pyrite. The results of XRF and ICP-MS analysis show that the content of SiO2 ranges from 59.11% to 69.44%, and the trace nutrient elements such as Mo, U, V, Co, Ni, Cu, and Zn are enriched. The correlation of geochemical composition between diatomite and Cretaceous volcanic rocks in the study area indicates that the weathering of volcanic rocks provides nutrients for diatom growth. Multiple geochemical indicators (Sr/Ba, V/Cr, Ni/Co, U/Th, V/(V+Ni), C-value, CIA, and Sr/Cu) and palaeontological evidence indicate that the diatomite was formed in a freshwater, oxic, and hot-humid environment. As the diatomite is susceptible to denudation, the overlying basalt may protect the deposit.

Distribution characteristics and influencing factors of benthic diatoms on several typical beaches along the southern coast of China

Benthic diatoms are the primary beach vegetation on sandy coasts, acting as the main primary producers in such environments. Changes in their community structure and biomass can have substantial impact on both the entire micro-food web and the nearshore shallow marine ecosystem. This study focused on four typical beaches along the southern coast of China (Fuzhou Changle Beach, Xiamen Huizhan Beach, Xiamen Guanyinshan Beach, and Beihai Silver Beach). Analysis of benthic diatoms and environmental factors revealed that the distribution of benthic diatom communities on the studied beaches is influenced by elevation, salinity changes due to freshwater inputs, sediment composition, and hydrodynamic factors. The most important factor is elevation, which reflects the location of the beach in the tidal zone. On Beihai Silver Beach and the Xiamen beaches, the mid-tidal and low tidal zones are more conducive to growth and reproduction of benthic diatoms, and some diatom species show preference for different tidal zones. On dissipative beaches, benthic diatom abundance peaks in the mid-tidal zone, whereas on low tidal terrace beaches, diatom abundance is generally low in the high tidal zone and relatively high in the low tidal zone. Additionally, low tidal terrace beaches exhibit a “steep increase zone” of diatom abundance at the junction of the steep and gentle slopes, indicating that benthic diatom abundance responds more to this type of beach landform than to that of dissipative beaches.

Domoic Acid: A Review of Its Cytogenotoxicity Within the One Health Approach.

In this review, we toxicologically assessed the naturally occurring toxin domoic acid. We used the One Health approach because the impact of domoic acid is potentiated by climate change and water pollution on one side, and reflected in animal health, food security, human diet, and human health on the other. In a changing environment, algal blooms are more frequent. For domoic acid production, the growth of Pseudo-nitzschia diatoms is of particular interest. They produce this toxin, whose capability of accumulation and biomagnification through the food web impacts other organisms in the ecosystem. Domoic acid targets nervous system receptors inducing amnestic shellfish poisoning, among other less severe health-related problems. However, the impact of domoic acid on non-target cells is rather unknown, so we reviewed the currently available literature on cytogenetic effects on human and animal cells. The results of different studies indicate that domoic acid has the potential to induce early molecular events, such as oxidative imbalance and DNA damage, thus posing an additional threat which needs to be thoroughly addressed and monitored in the future.

Widespread production of plant growth-promoting hormones among marine bacteria and their impacts on the growth of a marine diatom

BackgroundReciprocal exchanges of metabolites between phytoplankton and bacteria influence the fitness of these microorganisms which ultimately shapes the productivity of marine ecosystems. Recent evidence suggests that plant growth-promoting hormones may be key metabolites within mutualistic phytoplankton-bacteria partnerships, but very little is known about the diversity of plant growth-promoting hormones produced by marine bacteria and their specific effects on phytoplankton growth. Here, we aimed to investigate the capacity of marine bacteria to produce 7 plant growth-promoting hormones and the effects of these hormones on Actinocyclus sp. growth.ResultsWe examined the plant growth-promoting hormone synthesis capabilities of 14 bacterial strains that enhance the growth of the common diatom Actinocyclus. Plant growth-promoting hormone biosynthesis was ubiquitous among the bacteria tested. Indeed all 14 strains displayed the genomic potential to synthesise multiple hormones, and mass-spectrometry confirmed that each strain produced at least 6 out of the 7 tested plant growth-promoting hormones. Some of the plant growth-promoting hormones identified here, such as brassinolide and trans-zeatin, have never been reported in marine microorganisms. Importantly, all strains produced the hormone indole-3 acetic acid (IAA) in high concentrations and released it into their surroundings. Furthermore, indole-3 acetic acid extracellular concentrations were positively correlated with the ability of each strain to promote Actinocyclus growth. When inoculated with axenic Actinocyclus cultures, only indole-3 acetic acid and gibberellic acid enhanced the growth of the diatom, with cultures exposed to indole-3 acetic acid exhibiting a two-fold increase in cell numbers.ConclusionOur results reveal that marine bacteria produce a much broader range of plant growth-promoting hormones than previously suspected and that some of these compounds enhance the growth of a marine diatom. These findings suggest plant growth-promoting hormones play a large role in microbial communication and broaden our knowledge of their fuctions in the marine environment.4YJWCKdNErspcm2bUDNM6tVideo

Role of mesoscale eddies in the biogeochemistry of the Mozambique Channel

This study aims to characterize how eddies shape the biogeochemistry of the Mozambique Channel using a physical-biogeochemical model that realistically simulates its interannual dynamics. The 20-year-long numerical simulation provides a comprehensive dataset for robust statistical analysis of thousands of mesoscale features using an eddy detection method. We show that all eddy types significantly shape the biogeochemical landscape over the Mozambique Channel, with varying effects across different areas: (1) Sofala Bank and Delagoa Bay: Cyclonic eddies enhance diatom production. (2) Comoros Basin: Cyclonic eddies favor diatom growth via nutrient-rich waters from the NEMC. (3) Central Mozambique Channel: Anticyclonic eddies and rings promote nanophytoplankton through eddy-topography interactions. (4) Southern Mozambique Channel: A mix of eddies from the MC and South Madagascar influences diverse responses due to coastal upwelling. This diversity of processes results in distinct biological signatures of eddy types, leading to diverse ecosystem assemblages with a clear oligotrophic signature.

Cellular uptake of multi-walled carbon nanotubes is associated to genotoxic and teratogenic effects towards the freshwater diatom Nitzschia linearis

The increase in industrial production of multi-walled carbon nanotubes (MWCNTs) raises concerns about their potential adverse effects associated to environmental releases, especially in aquatic environments where they are likely to accumulate. This study focuses on the environmental impact of MWCNTs, specifically on a benthic freshwater diatom (Nitzschia linearis), which plays a major role in the primary production of water bodies. The obtained results indicate that exposure to MWCNTs in the presence of natural organic matter (NOM) inhibits diatom's growth in a dose-dependent manner after 72 h of exposure. Interestingly, the photosystem II quantum yield (PSIIQY) in diatoms remains unaffected even after exposure to MWCNTs at 10 mg/L. After 48 h of exposure, MWCNTs are found to bind preferentially to extracellular polymeric substances (EPS) produced by diatoms, which could decrease their toxicity by limiting their interaction with this organism. However, measurement of genotoxicity and teratogenicity in diatoms exposed to MWCNTs revealed that the exposure to MWCNTs increased the occurrence of cells with micronuclei and abnormal frustules. Microscopy analyses including two-photon excitation microscopy (TPEM) revealed the internalization of MWCNTs. Investigations of the diatom's frustule structure using Scanning electron microscopy (SEM) indicated that the presence of pore structures constitutes a pathway allowing MWCNTs uptake. The presence in the diatom's cytoplasm of MWCNTs might possibly induce disturbances of the cellular components, leading to the observed genotoxic and teratogenic effects. In view of previous studies, this work underscores the need for further studies on the interaction between nanomaterials and different diatom species, given the species-specific nature of the interactions.

Utilization of rice husk ash as a potential catalyst for diatom growth and adsorbent for heavy metals in aquaculture systems

Many aquaculture environments suffer from significant silicon deficiencies and severe heavy metal contamination, posing substantial risks to both production and safety in aquaculture. This study aimed to assess the release of silicate from rice husk ash (RHA) and its impact on phytoplankton abundance and community composition, which are key factors affecting shellfish growth and survival. Additionally, the capacity of RHA to adsorb mercury (Hg2+) was examined using different modification methods. The results demonstrated that the concentration of dissolved silicate in seawater increased with higher RHA doses, reaching a maximum of 189.77 ± 45.61 μmol L−1 in the high RHA treatment (HR) with 1.0 g L−1 of RHA. Notably, the HR treatment group exhibited a significant increase in chlorophyll-a concentration for nano-phytoplankton (2–20 μm), with an up to eightfold rise in abundance compared to the control group. Moreover, the HR treatment resulted in a maximum diatom abundance of 4217 ± 741.98 cells L−1, benefiting diatom species such as Coscinodiscus sp., Nitzschia sp., and Cyclotella sp. These findings underscore the potential of RHA as a catalyst for diatom growth, which in turn supports the growth of shellfish. Furthermore, no concentrations of mercury (Hg), lead (Pb), cadmium (Cd), arsenic (As), copper (Cu), zinc (Zn), and chromium (Cr) were detected in any of the silicate enrichment treatments, confirming the safety of the RHA. The treatment of RHA with NaOH achieved an impressive removal efficiency of Hg2+, reaching up to 97.41 ± 0.33 %. This study highlights the promising application of agricultural waste RHA as a catalyst for diatom growth and an adsorbent for heavy metals in water systems relevant to aquaculture practices.

Soil remediation and nano-biosilica: a potential combination to improve the environmental quality of brackishwater aquaculture ponds affected by acid sulfate soils.

The successful management of ASS-affected brackishwater aquaculture ponds necessitates overcoming associated environmental limitations. This study investigated the potential application of nano-biosilica from rice husk ash (RHA) and soil remediation techniques to improve the environmental quality of ASS-affected brackishwater ponds. The study followed a completely randomized design (CRD) with four treatments and three replicates. The treatments comprised applying soil remediation, nano-biosilica fertilizer, and their combination. The study generally revealed that the combination of soil remediation technique and RHA-driven nano-biosilica improved the water quality of ASS-affected brackishwater ponds. Soil remediation improved water quality by reducing acidity levels. However, excessive lime application as an integral part of the remediation might release acidity and toxic metals into water, potentially increasing calcium-phosphorus fixation. Despite liming potential negative consequences, if mixed with nano-biosilica could increase diatom-phytoplankton growth by reducing dissolved Al and Fe levels while boosting P and Si availability. Liming could also help boost diatom photosynthesis and inhibit unwanted algae blooms by decreasing water turbidity and increasing sunlight penetration. This study emphasized that the effectiveness of nano-biosilica in promoting diatom growth depends on appropriate nitrogen (N) and phosphorus (P) concentrations and ratios, which should not be a limiting factor. However, the required N/P concentration and ratio are only met if the remediation method is effectively implemented. The combination of nano-biosilica and soil remediation treatment maintained SiO2 concentrations above the average natural seawater concentration; however, availability may be limited due to complexes containing Ca, Al, Mg, and Fe. Regularly applying cost-effective nano-biosilica fertilizer in combination with N and P fertilizers is recommended to enhance water remediation efficiency by boosting Si availability and decreasing the toxicity of dissolved toxic metal ions.

Production Potential of the Chernavka Salt River (Elton Region)

Depending on the season, the primary production of planktonic communities determined by radiotracer analysis varied within a broad range, from 6 to 314 µg C/(L h). Primary production in cyanobacterial mats was 4.2‒10.9 × 103 µg C/(dm3 h), and Chl a content varied from 6‒13 to 132‒140 mg Chl a/m2. For the plankton, the highest values were revealed in summer (25‒46 mg Chl a/m3), with the maximum in August (223 mg Chl a/m3. High abundance of bacterioplankton (0.3‒7.4 × 106 cells/mL) and massive growth of diatoms (0.15 × 106 cells/mL) with predominance of the genus Chaetoceros were found. Sulfate reduction rates varied from 0.037 µmol S/(dm3 h) in the upper reach to 61.87 µmol S/(dm3 h) in the river mouth.

Seasonal changes in the protist communities of Hakodate Bay, southern Hokkaido, from 2020 to 2022

Hakodate Bay at the southern end of Hokkaido experiences physical and chemical environmental changes in the adjacent Tsugaru Strait. Harmful algal blooms have occurred since 2015. However, information on the response of protist community composition, photosynthetic activity to environmental variables or the mechanisms causing harmful blooms in the Hakodate Bay is lacking. We investigated the seasonal changes in the protist community using weekly sampling to reveal the relationship between the protist community and environmental variables in the Hakodate Bay. Based on cluster analysis, six groups were identified: Winter, Spring, Late Spring, Summer, Benthic, and Karenia. High Fv/Fm was seen in the Summer, Benthic and Spring groups supported by high nutrients, warm temperature and sufficient irradiance. From the Winter to Spring group, a species transition from low-temperature-adapting Thalassiosira spp. to Chaetoceros spp. was found. The Summer group comprised high salinity-tolerant species (the diatom Leptocylindrus danicus and dinoflagellate Prorocentrum spp.) because of high fluctuations in salinity due to precipitation. The other groups (Late Spring, Benthic, and Karenia) randomly filled the spaces between the three groups. The dinoflagellate Scrippsiella spp. was dominant in the Late Spring group because of accumulation by wind-driven currents. Because a strong relationship between benthic species and wind speed was exhibited, the Benthic group comprised benthic diatoms released into the water by mixing. The Karenia group was observed only from late August 2021 to early January 2022, when higher ammonium and lower light conditions (i.e., cloudy conditions) were detected. Owing to environmental conditions, diatom growth was restricted by low light intensity, whereas that of Karenia mikimotoi increased by taking advantage of the abundant nutrients. Seasonal changes in the protist community of the Hakodate Bay can generally be explained by temperature; however, in the short term (1–2 weeks), changes were also influenced by meteorological conditions (solar radiation, wind, and precipitation).

A Brief Review of Effects of Aluminum on Marine Diatoms.

Aluminum (Al) is the most abundant metal element in the Earth's crust, yet it is present in trace levels in seawater. Growing evidence suggests potential effects of Al on the biogeochemical cycles of carbon (C) and silicon (Si) in the marine environment. By accumulation, sinking, and deposition, diatoms play a center role in coupling these three elements' biocycles in the oceans. However, it is still a challenge to elucidate the behaviors of diatoms influenced by Al. Our review aims to present the current knowledge of Al biogeochemistry in marine environment and its impact on marine phytoplankton, with a focus on how Al influences diatoms. Previous researches indicate that Al can promote the growth of diatoms, and diatoms have the ability to incorporate Al into their frustules. Given this, we paid particular attention on the interaction between Al and diatom frustules, and the influences of Al on the physiology and ecology of diatoms. Furthermore, it is suggested that Al alters the accumulation of other nutrients such as nitrogen, phosphorus and iron in diatoms; the subsequent responses of diatoms are also discussed. The objective of this review is to address the potential roles of Al in diatoms and offer insights into the possible biogeochemistry implications.

Effects of the Water Diversion Project from the Three Gorges Reservoir to the Hanjiang River on diatom blooms in Middle and Lower reaches of the Hanjiang River

ABSTRACT The algal blooms in the Middle and Lower reaches of the Hanjiang River (MLHR) have become a great aquatic eco-environmental problem over recent years. The planned implementation of the Water Diversion Project from the Three Gorges Reservoir to the Hanjiang River (WDP-TH) would influence the growth and propagation of diatoms and the development of algal blooms. In this paper, a dynamic model of diatom growth is developed that considers factors such as light exposure, water temperature, total phosphorus, and flow velocity. The effects of the WDP-TH on algal density and blooms in the MLHR were predicted for a typical median year, a typical dry year, and an extremely dry year. The results showed that following the water recharge in a typical median year, the propagation of diatoms in the MLHR was significantly promoted because of an increase in total phosphorus concentration. However, following the water recharge in typical dry and extremely dry years, increased flow rate and improved hydrodynamic conditions significantly inhibited diatom growth and accelerated the transport process. The results of the hypothetical simulation showed that after the initiation of the WDP-TH, inhibition effects of improved hydrodynamic force on algae were more apparent than promotion effects of increased total phosphorus concentration in the MLHR.

Mixotrophic growth of a ubiquitous marine diatom.

Diatoms are major players in the global carbon cycle, and their metabolism is affected by ocean conditions. Understanding the impact of changing inorganic nutrients in the oceans on diatoms is crucial, given the changes in global carbon dioxide levels. Here, we present a genome-scale metabolic model (iMK1961) for Cylindrotheca closterium, an in silico resource to understand uncharacterized metabolic functions in this ubiquitous diatom. iMK1961 represents the largest diatom metabolic model to date, comprising 1961 open reading frames and 6718 reactions. With iMK1961, we identified the metabolic response signature to cope with drastic changes in growth conditions. Comparing model predictions with Tara Oceans transcriptomics data unraveled C. closterium's metabolism in situ. Unexpectedly, the diatom only grows photoautotrophically in 21% of the sunlit ocean samples, while the majority of the samples indicate a mixotrophic (71%) or, in some cases, even a heterotrophic (8%) lifestyle in the light. Our findings highlight C. closterium's metabolic flexibility and its potential role in global carbon cycling.

Physical Mechanisms Sustaining Silica Production Following the Demise of the Diatom Phase of the North Atlantic Spring Phytoplankton Bloom During EXPORTS

AbstractEach spring, the North Atlantic experiences one of the largest open‐ocean phytoplankton blooms in the global ocean. Diatoms often dominate the initial phase of the bloom with succession driven by exhaustion of silicic acid. The North Atlantic was sampled over 3.5 weeks in spring 2021 following the demise of the main diatom bloom, allowing mechanisms that sustain continued diatom contributions to be examined. Diatom biomass was initially relatively high with biogenic silica concentrations up to 2.25 μmol Si L−1. A low initial silicic acid concentration of 0.1–0.3 μM imposed severe Si limitation of silica production and likely limited the diatom growth rate. Four storms over the next 3.5 weeks entrained silicic acid into the mixed layer, relieving growth limitation, but uptake limitation persisted. Silica production was modest and dominated by the >5.0 μm size fraction although specific rates were highest in the 0.6–5.0 μm size fraction over most of the cruise. Silica dissolution averaged 68% of silica production. The resupply of silicic acid via storm entrainment and silica dissolution supported a cumulative post‐bloom silica production that was 32% of that estimated during the main bloom event. Diatoms contributed significantly to new and to primary production after the initial bloom, possibly dominating both. Diatom contribution to organic‐carbon export was also significant at 40%–70%. Thus, diatoms can significantly contribute to regional biogeochemistry following initial silicic acid depletion, but that contribution relies on physical processes that resupply the nutrient to surface waters.

East Asian Winter Monsoon and enhanced stratification in the western Pacific promoted giant marine diatom (Ethmodiscus rex) blooms during the last deglaciation

Late Pleistocene thick laminated mats of Ethmodiscus rex (E. rex) have been found on the seafloor of the western tropical Pacific. Exploring the causes of E. rex mats formation can improve our understanding of the role of diatom mats in the global carbon-silicon cycle. Nutrients, such as silicate, are a major factor contributing to the growth of diatoms. However, the origin of the nutrients necessary for E. rex to bloom remains unclear. Here we analysed the 14C ages and silicon isotope compositions (δ30Si) of E. rex mats from deep-sea sediment cores collected in the western Pacific to reveal the nutrient source of the diatom bloom. The results indicate that the age of the cores ranges from 11 ka to 19 ka. This is the first discovery of a last deglacial thick layer of E. rex mats in the western Pacific Hadal zone. Furthermore, the silicon isotope results show that, similar to previous studies in the western Pacific, all δ30Si of E. rex frustules are negative. This is in contrast to the North Atlantic upwelling region where all δ30Si are positive. According to the binary mixing model calculations, eolian dust were responsible for supplying 80%–90% of the silica during the last deglaciation, while upwelling waters accounted for only about 10%–20% of the silica. During Heinrich Stadial 1 (HS1) period, the strengthened East Asian Winter Monsoon (EAWM) transported a lot of eolian dust to the western Pacific, providing nutrients for diatom blooms. In addition, the enhanced stratification in the western Pacific since the late HS1 period was a significant factor that contributes to the blooms of E. rex when the supply of eolian dust material decreased.

Detrital Input Sustains Diatom Production off a Glaciated Arctic Coast

AbstractIn the Arctic and subarctic oceans, the relatively low supply of silicon (compared to other nutrients) can make it limiting for the growth of diatoms, a fundamental building block of the oceanic food web. Glaciers release large quantities of dissolved silicon and dissolvable solid amorphous silica phases into high‐latitude estuaries (fjords), but the role of these glacially‐derived silica phases in sustaining diatom growth in the coastal and open‐water sectors remains unknown. Here we show how stable and radiogenic silicon isotopes can be used together to address this question, using southwest Greenland as a case study. This study finds enhanced levels of detrital (i.e., mineral) amorphous silica, likely glacially‐sourced, sustaining a large portion of diatom growth observed off the coast, revealing how the phytoplankton community can function during high‐meltwater periods.

First Account of Epibiotic Diatom Taxa from the Carapaces of Green Swimming Crab Callinectes bellicosus (Stimpson 1859) (Decapoda, Portunidae)

Diatoms are among the most common epibionts and have been recorded on the surfaces of various living substrates, either plants or animals. However, studies on them are still scarce in view of the many substrata available. In this study, epibiotic diatoms living on Callinectes bellicosus were identified for the first time from a subtropical coastal lagoon in Northwest Mexico. We tested the null hypothesis that the diatom flora living on the carapaces of C. bellicosus would not be similar to that recorded for mangrove sediments, its typical habitat. The epibiotic diatoms were brushed off from the carapaces of two specimens, acid-cleaned, mounted in synthetic resin, and identified based on frustule morphology. This way, 106 taxa from 46 genera were recorded, including 25 singletons, and 6 new records for the Mexican northwest region. The best-represented genera were Nitzschia (10 taxa), Mastogloia (9), Diploneis (8), Navicula (7), Amphora (5), Cocconeis (5), Tryblionella (4), and Gyrosigma (4). Species composition included 93% of local taxa, thus refuting the proposed hypothesis and supporting the alternate one. Although the estimated species richness was lower than that in sediments, it deems the green crab carapace a favorable substrate for the growth of benthic diatoms.

Environmental controls on the interannual variability in chlorophyll and phytoplankton community structure within the seasonal sub surface chlorophyll maximum in the western English channel

The subsurface chlorophyll maximum (SCM) is increasingly recognised as an important but understudied locus of primary production particularly in shelf seas. Here we report the results of a 4 year, repeat station, summer sampling programme (2013–2016) of a seasonally recurrent SCM in the Western English Channel. Interannual variability in phytoplankton community structure and chlorophyll distribution and intensity was strongly related to water column stability at the depth interval of the SCM and also to water temperature. The phytoplankton community was statistically distinct in each year. High stability, as evidenced by large Richardson numbers and a well-developed strong thermocline appeared to favour the growth of larger dinoflagellates (autotrophs or mixotrophs) and diatoms. Such conditions led to development of the most intense SCMs and these were sometimes dominated by a single or a few key species most prominently in 2015 with near monospecific concentrations of the dinoflagellate Tripos fusus with average peak SCM chlorophyll concentrations of 7.3 ± 4.4 μg l−1. By contrast, in years with low water column stability and intermittent turbulence at the thermocline (2014, 2016) there was greater chlorophyll dispersal and less intense SCM. In these low stability conditions, red fluorescent nano-phytoplankton, such as naked dinoflagellates, chlorophytes and prymnesiophytes, made a greater contribution to the community, possibly as a result of the advantages that motility and enhanced light utilisation efficiency confer within an SCM exposed to turbulence. It is also likely that turbulence disrupted the stability required by the larger dinoflagellates and diatoms. Several of the key SCM taxa were absent from surface waters including the dinoflagellates Tripos fusus, Tripos lineatus, and most of the Rhizosolenia/Proboscia diatoms, consistent with adaptations more suited to survival at depth in stratified waters. These traits include luxury nutrient uptake and storage and survival in low light (both groups) and mixotrophy (dinoflagellates). On the other hand, in 2013, diatoms including Pseudo-nitzschia spp. were abundant in both surface, SCM and bottom waters. The relatively cooler waters (11.6–12.1 °C on average in 2013 and 2016) were characterised by smaller diatoms (Chaetoceros spp. and Pseudo-nitzschia spp.) whereas the warmer waters (13.1 °C on average in 2014) contained larger diatoms (large Rhizosolenia spp., Lauderia annulata and Leptocylindrus danicus). There did not appear to be continuity of key species between years, other than for the dinoflagellate Tripos lineatus, which was significant in both 2013 and 2014 and present in 2015. In any given year, there was no correspondence between the key spring bloom phytoplankton species as monitored in the nearby Western Channel Observatory L4 station and the key SCM taxa.

Effect of increased CO2 on calcium homeostasis and signaling in a marine diatom

AbstractOcean acidification influences photosynthesis, respiration, and metabolism in marine diatoms, leading to changes in diatom growth performance and shifts in phytoplankton communities. Previous studies have demonstrated that increases in seawater CO2 concentrations affect the uptake of trace metals such as iron, zinc, copper, and cobalt by marine diatoms. However, the influence of increased CO2 on calcium, which plays a vital role as a secondary messenger in various signaling pathways within organisms, has received limited attention so far. This study examined the effect of increased CO2 on Ca homeostasis and signaling in the marine diatom Phaeodactylum tricornutum. While seawater acidification had little effect on the diatom's growth, it significantly changed cell properties (surface topography, adhesion, and surface potential). Elevated CO2 concentrations reduced calcium accumulation P. tricornutum and lowered the rise of cytosolic Ca2+ transients stimulated by toxic aldehyde, phosphorus supplement, and hypo‐osmotic stress. Our results suggest that a continuous rise in atmospheric CO2 may alter diatoms' response to environmental cues.

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.