Ultrastructure and Function of Setae of a Planktonic Diatom, Chaetoceros Coarctatus

Silica frustules of most planktonic diatoms have many shallow holes in which the length (L) is smaller than the width (W). The present study focuses on a silicic ultrastructure of the setae of a planktonic diatom having deep (L/W > 1) holes. Here, we characterized nanoholes on the silica walls of hollow setae of a colony of Chaetoceros coarctatus. Basically, tetragonal poroid arrangements with and without a costa pattern are observed on the inner and outer surfaces, respectively, for three kinds of curving hollow setae. Deep nanoholes ∼90 nm wide are elongated from 150 to 1500 nm (L/W ∼17) with an increase in the wall thickness of the polygonal tubes of the setae. The inside poroid array, with a period of 190 nm in the extension direction of setae, is lined by parallel plates of the costae. However, the poroid arrangement on the outer surface is disordered, with several holes obstructed with increasing wall thickness of the posterior terminal setae. According to the movement of a colony in a fluid microchannel, the thick curving terminal setae is suggested to involve attitude control and mechanical protection. Using an optical simulation, the patterned deep through-holes on the intercalary setae were inferred to contribute anti-reflection of blue light for the promotion of photosynthesis in seawater.

Diversity of Planktonik Diatom at Bengkalis Waters, Riau Province

This research was carried out in August to September 2019 at Bengkalis Waters, Riau Province. This study goals to describe the water quality statues and to determine the species composition, abundance and biological index of planktonic diatom in the Bengkalis waters. Survey method was applied in this research which are 5 stations established, with 3 sampling points in each station. The stations were determined purposively based on antrophogenic activities conducted in that area. Diatom samples were filtered from surface water as much as 100 liters by using plankton net number 25, and the samples were then observed using an Olympus CX 21 microscope (magnification 10 x 10 and 10 x 40) and were identified. The value of water quality at each station indicates that the water is in normal range and it may support the growth of diatoms. There were 20 spesies of planktonic diatoms recorded in the Bengkalis waters. There were 2 species, namely Coscinodiscus sp. and Navicula sp. that were found in each station. Meanwhile, the abundance of plankatonic diatoms ranged from 23,041.80 to 286,693.18 ind/l. The average of biological indices values are as follows: diversity index 1.39-2.32, dominance index 0.24 to 0,48 ind / l, and the uniformity index 0.55 to 0.87 ind / l. The biological indices values indicated that the Bengkalis Waters can be categorized as moderate polluted water and there is no dominant species.

A STUDY OF DIATOMS (BACILLARIOPHYTA) IN HOOR-AL-AZIM WETLAND, SOUTH-WEST IRAN, AND THEIR SEASONAL CHANGES

This study was aimed to identify the planktonic diatoms and their seasonal change in Hoor-AL-Azim wetlands, Iran. Diatoms are important algal groups in different aquatic ecosystem and considered as bioindicators for water quality and environmental health. Hoor-AL-Azim or Hoor-al-Hawizeh is one of the most extensive and ecologically important wetlands in the Middle East which is shared between Iran (south-west) and Iraq(south). A major part of the wetland area was exposed to drying completely or partially during last few decades due to two Country politics. The samples were taken on a monthly basis from four stations for year from January to end of December, for identification and seasonal changes of Diatoms (Bacillariophyta). In this study, totally 69 taxa belonging to 28 different genera were identified of which Nitzschia genus had the highest species diversity (13 species) and followed by Navicula genus (10 species) while the highest species diversity observed in autumn. The average density ranged from 4818 cells/ liter to 58625 cells /liter in spring and winter, respectively.

Sponge contribution to the silicon cycle of a diatom-rich shallow bay

In coastal systems, planktonic and benthic silicifiers compete for the pool of dissolved silicon, a nutrient required to make their skeletons. The contribution of planktonic diatoms to the cycling of silicon in coastal systems is often well characterized, while that of benthic silicifiers such as sponges has rarely been quantified. Herein, silicon fluxes and stocks are quantified for the sponge fauna in the benthic communities of the Bay of Brest (France). A total of 45 siliceous sponge species living in the Bay account for a silicon standing stock of 1215 tons, while that of diatoms is only 27 tons. The silicon reservoir accumulated as sponge skeletons in the superficial sediments of the Bay rises to 1775 tons, while that of diatom skeletons is only 248 tons. These comparatively large stocks of sponge silicon were estimated to cycle two orders of magnitude slower than the diatom stocks. Sponge silicon stocks need years to decades to be renewed, while diatom turnover lasts only days. Although the sponge monitoring over the last 6 years indicates no major changes of the sponge stocks, our results do not allow to conclude if the silicon sponge budget of the Bay is at steady state, and potential scenarios are discussed. The findings buttress the idea that sponges and diatoms play contrasting roles in the marine silicon cycle. The budgets of these silicon major users need to be integrated and their connections revealed, if we aim to reach a full understanding of the silicon cycling in coastal ecosystems.

Impact of climate change and industrialization on remote Lake Bolshoe Toko, Siberia

<p>To test if recent climate change and pollution affected remote lake ecosystems without direct human influence, we used paleolimnological methods on lake sediments from a large, prestine, and deep lake in Yakutia, Russia. We compared diatoms and sediment-geochemistry from before and after the onset of industrialization in the mid-nineteenth century, at water depths between 12.1 and 68.3 m in Lake Bolshoe Toko. We analyzed diatom species changes and geochemical changes including mercury concentrations. Chronologies were established using <sup>210</sup>Pb and <sup>137</sup>Cs revealing sedimentation rates between 0.018 and 0.033 cm y<sup>-1</sup> at shallow- and deep-water sites, respectively. Increase in light planktonic diatoms (<em>Cyclotella</em>) and decrease in heavily silicified euplanktonic <em>Aulacoseira</em> through time at deep-water sites can be related to warming air temperatures and shorter periods of lake-ice cover, causing pronounced thermal stratification. Diatom beta diversity changed only significantly in shallow-water communities which can be related to the development of new habitats with macrophyte growth. Mercury concentrations increased by a factor of 1.6 as a result of atmospheric fallout. Increases in the chrysophyte <em>Mallomonas</em> indicates a trend towards acidification. We conclude that also remote boreal lakes are susceptible to human-induced long-distance pollution and recent climate change.</p>

Effects of climate change and industrialization on Lake Bolshoe Toko, eastern Siberia

Industrialization in the Northern Hemisphere has led to warming and pollution of natural ecosystems. We used paleolimnological methods to explore whether recent climate change and/or pollution had affected a very remote lake ecosystem, i.e. one without nearby direct human influence. We compared sediment samples that date from before and after the onset of industrialization in the mid-nineteenth century, from four short cores taken at water depths between 12.1 and 68.3 m in Lake Bolshoe Toko, eastern Siberia. We analyzed diatom assemblage changes, including diversity estimates, in all four cores and geochemical changes (mercury, nitrogen, organic carbon) from one core taken at an intermediate water depth. Chronologies for two cores were established using 210Pb and 137Cs. Sedimentation rates were 0.018 and 0.033 cm year−1 at the shallow- and deep-water sites, respectively. We discovered an increase in light planktonic diatoms (Cyclotella) and a decrease in heavily silicified euplanktonic Aulacoseira through time at deep-water sites, related to more recent warmer air temperatures and shorter periods of lake-ice cover, which led to pronounced thermal stratification. Diatom beta diversity in shallow-water communities changed significantly because of the development of new habitats associated with macrophyte growth. Mercury concentrations increased by a factor of 1.6 since the mid-nineteenth century as a result of atmospheric fallout. Recent increases in the chrysophyte Mallomonas in all cores suggested an acidification trend. We conclude that even remote boreal lakes are susceptible to the effects of climate change and human-induced pollution.

The spatio-temporal evolution of the genus Nitzschia Longissima at the level of the lagoon in Nador, Morocco

This work aims to study the spatio-temporal evolution of the genus Nitzschia longissima, one of the most important genera of marine plankton diatoms, from 3 sampling stations in the Nador lagoon and during 2 seasons (spring and summer 2018), Using Nitzschia longissima, as a study system, one of the most diverse and abundant genera among marine planktonic diatoms. This species counts, in addition to the form Nitzschia longissima forma parva Grunow, three varieties namely Nitzschia longissima var. closterium (W. Smith) Van Heurck, Nitzschia longissima var. longissima (Breb.) Ralfs and Nitzschia longissima var. reversa Grunow. Nitzschia Longissima genus density was high during the warm season (Summer 2018) with a value of 8000 cells/liter, and low during the cold seasons (Spring 2018), which may be caused by water temperature and zooplankton community structure; and underwater light intensity was an important factor influencing the spatial distribution of Nitzschia density.

Spatiotemporal Dissolved Silicate Variation, Sources, and Behavior in the Eutrophic Zhanjiang Bay, China

Dissolved silicate (DSi) is an important nutrient in coastal water, which is used by planktonic diatoms for cell division and growth. In this study, surface water samples were collected in the eutrophic Zhanjiang Bay (ZJB) in 2019, covering a seasonal variation of coastal water and land-based source water discharge. The spatiotemporal DSi distribution, land-based sources flux input and behaviors in ZJB were studied and discussed. The results show that the DSi concentration had significant differences in spatiotemporal scale. The average concentration of DSi in ZJB was 38.00 ± 9.48 μmol·L−1 in spring, 20.23 ± 11.27 μmol·L−1 in summer, 12.48 ± 1.42 μmol·L−1 in autumn and 11.96 ± 4.85 μmol·L−1 in winter. The spatiotemporal DSi distribution showed a decreasing gradient from the top to the mouth of ZJB, which was affected by land source inputs and hydrodynamics. The land-based sources’ input concentration of DSi in ZJB ranged from 0.021 to 0.46 mol·L−1, with an average of 0.14 mol·L−1, and the total annual flux of DSi was 1.06 × 109 mol, comprising up to 8.28%, 41.55% and 50.17% in dry, normal, and wet seasons, respectively. The Suixi River contributed the highest DSi flux proportion in all seasons. The DSi in land-based source water was mainly affected by water flow discharge, diatom uptake and impacts from anthropogenic activities. Compared with dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), the DSi was the limitation nutrient in ZJB. Additionally, the DSi concentration in the coastal water was negatively correlated with salinity. The seasonal DSi/DIN and DSi/DIP ratios in land-based sources discharge water was significantly higher than that in coastal water (p < 0.05). Land-based sources of DSi input played an important role in nutrients composition that sustained diatoms as the dominant species in ZJB.

Fish-killing diatom bloom in an urban recreational pond: An index case for a global warming scenario?

By the end of the exceptionally warm and stormy autumn of 2018, a fish kill occurred in a small hypertrophic pond located in a recreative green area in Buenos Aires (BA, Argentina). As there were no visible signs of an algal bloom, the causes for the die-off were investigated. On 1st June, the pond was sampled while fish, mostly Bryconamericus iheringii (Characidae) and Australoheros facetus (Cichlidae) were still dying. Despite low turbidity (18.9 NTU) and chlorophyll a concentration values (15.90 µg/L) as compared to similar BA waterbodies, a heavy bloom of planktonic araphid diatoms (161,600 ind/mL) was detected, mainly caused by Fragilaria saxoplanctonica (Fragilariaceae), Pseudostaurosira neoelliptica (Fragilariaceae) and Ulnaria cf. acus (Fragilariaceae). Previous records of high abundances of these or closely related planktonic diatoms around the world were associated with increased temperature and nutrient content, yet they did not cause other than nuisance blooms. Fish necropsy showed good body condition except for gill damage and mucus accumulation due to a large amount of frustules of these species, mainly P. neoelliptica, interspersed in the gill filaments. Although this is a common cause for die-offs in marine fish farms, it is unprecedented in freshwater systems, and particularly in urban waterbodies. Conversely to more common –and foreseeable- summer cyanobacterial blooms in these systems, this phenomenon was triggered by an autumnal weather anomaly. This fact is crucial, as non-summer heat waves and heavy storms are predicted to increase in frequency and intensity over the subtropical regions, yet their ecological consequences are less perceived, seldom studied, and far from understood. This could be the first documented case of many to occur in such heavily eutrophicated environments unless effective strategies for eutrophication control and management are taken.

Planktonic diatom assemblage seasonal diversity used to assess environmental health in a coastal wetland of southern Chile

ABSTRACTAlthough planktonic diatoms are one of the most abundant taxonomic groups in coastal wetlands, their assemblages have not been used to determine the environmental health of these ecosystems. Studies of ecosystem environmental health have been based on other taxonomic groups; we propose that diatom genera diversity represents a viable alternative for this purpose. Thus, our aim was to determine the alpha and beta diversities of the planktonic diatom assemblage present in Caulín Bay, Chiloé Island (41° 49’S; 73° 38’O), southern Chile, during the austral winter and spring of the years 2012 and 2014. Inasmuch Caulín Bay is an important site for aquatic bird observation and conservation, hunting is prohibited on a national scale and, internationally, the site has been declared an Important Bird and Biodiversity Area (IBA). Our results indicate different diversities between sampling stations, but not between the years studied. In total, we recorded 53 diatom genera, of which the most abundant were Coscinodiscus (21.99%) and Cocconeis (16.23%). The study area presented high genera diversity (i.e., H’(log2) >3.74) and beta diversity indicated that Caulín presents a low level of heterogeneity and is a low genera replacement environment. Consequently, we infer that Caulín Bay is productive and environmentally stable ecosystem. This leads us to conclude that diatom diversity determination is a viable alternative to establish aquatic ecosystem environmental health and we recommend that future conservation strategies be established for Caulín Bay.RESUMENSi bien las diatomeas planctónicas son uno de los grupos taxonómicos más abundantes de los humedales costeros, sus ensambles no se han utilizado para determinar el estado ambiental de estos ecosistemas. Aunque se han realizado estudios de la salud ambiental de un ecosistema utilizando otros grupos taxonómicos, nosotros proponemos que la diversidad de géneros de diatomeas representa una alternativa viable. Por lo tanto, el objetivo de este estudio fue determinar las diversidades alfa y beta del ensamble de diatomeas planctónicas presentes en la Bahía de Caulín, Isla de Chiloé (41 ° 49’S; 73 ° 38’O), sur de Chile, durante las temporadas de invierno y primavera austral de los años 2012 y 2014. Bahía Caulín es un sitio importante para la observación y conservación de aves acuáticas por lo que a nivel nacional se ha prohibido la caza y a nivel internacional fue decretada un Área Importante para la Conservación de Aves, AICA. Los resultados de este estudio indicaron diferencias en las diversidades entre las estaciones de muestreo, pero no entre los años estudiados. En total, se identificaron 53 géneros de diatomeas; los más abundantes fueron Coscinodiscus (21,99%) y Cocconeis (16,23%). El área de estudio presentó una alta diversidad de géneros (i.e., H’(log2) >3.74) y la diversidad beta indicó que Caulín presentó bajo nivel de heterogeneidad y es un entorno con bajo reemplazo de géneros. Así, inferimos que Bahía Caulín es un ecosistema productivo y ambientalmente estable, por lo cual concluimos que la determinación de las diversidades de diatomeas es una alternativa para establecer la salud ambiental de los ecosistemas acuáticos y recomendamos establecer futuras estrategias de conservación para Bahía Caulín.PALABRAS CLAVE: diatomeas, diversidades ecológicas, plancton, humedales costeros, desembocadura