Diatom Content Research Articles

Correlation analysis of diatom content in the organs and drowning mediums for the drowning death cases

ABSTRACT Diatoms detected in human organs have been considered as supportive evidence for the diagnosis of drowning. During drowning, the vast majority of diatoms are retained in lung tissues, and only few are transported to distant organs via the bloodstream. In this article, we quantitatively analysed diatom contents in the lung tissues, liver tissues, kidney tissues and the drowning mediums of 165 drowning death cases. The results showed that the diatom content in lung tissues was positively correlated with that in the water samples. However, there was no linear correlation between the diatom content in the liver tissues and that in the water samples. Our study also showed no linear correlation between the diatom content in the kidney tissues and in the water samples. The diatom contents in the liver tissues and kidney tissues were positively correlated, while no linear correlations of diatom contents were found between the liver tissues and lung tissues, and the kidney tissues and lung tissues. These correlations of diatom content in the organs and drowning mediums provide valuable information to interpret and analyse the quantitative results of diatom tests.

Climate change during the Little Ice Age from the Lake Hamana sediment record

Paleoenvironment and paleoclimate changes during the Little Ice Age (LIA) were investigated using sediments from Lake Hamana. This lagoon in central Japan is under a complicated climate system influenced by the East Asian summer monsoon (EASM), East Asian winter monsoon (EAWM), and strong typhoon events. Diatom assemblages and chemical components of a 1.3 m sediment core suggest historical events of rapid salination and cyclical ecosystem shifts accompanied by monsoon condition changes. Most research has indicated that Lake Hamana changed from a freshwater lake to a brackish lagoon because of the Meio earthquake in 1498 CE. However, based on results from the diatom assemblage and chemical components, this salination occurred because of changes in the Hamana paleoriver flow, and this change happened before the earthquake, around the mid-15th century. Furthermore, it is clear that Lake Hamana was an oligohaline lagoon before salination. The lithology of the lake sediments and the diatom assemblage changed during the LIA; sand, water, and total diatom contents decreased. However, the relative abundance of marine diatom taxa increased during the LIA. These changes were introduced by a weakening EASM coupled with low precipitation under low solar activity during the LIA. Several flood events represented by freshwater diatom taxa and magnetic susceptibility peaks co-occurred with strong El Niño events during the LIA. It is inferred that this strong El Niño during the LIA induced frequent typhoons causing floods in central Japan.

Enhanced Microalgal Lipid Production in Internally Illuminated Airlift Photobioreactor

AbstractInternal illumination systems are being considered for use as an alternative light supply technique in microalgal products. The main goal of the study was to analyze the roles of different light wavelengths in internally illuminated airlift photobioreactors (PBRs) providing the light energy in an efficient way for the biomass production, lipid yield, and fatty acid composition of Amphora capitellata. The maximum chlorophyll-a concentration per unit biomass (2.62 ± 0.16 mg L−1) was obtained under red light, which was only 14% higher than under blue light in internally illuminated airlift PBR, whereas low chlorophyll-a content was found under white light. Maximum specific growth rate of 0.317 day−1, which corresponded to a doubling time of 2.185 days, was obtained under red light for A. capitellata. It was found that lipid content increased with decreasing growth rate for A. capitellata. Palmitic acid (C16:0) and palmitoleic acid (C16:1) were the principal fatty acids accounting for between 31%‐33% and 31%‐32% of total fatty acids, respectively. It is important to underline that red and blue light spectrum ranges contribute to improved biomass growth, whereas white light has the potential to support lipid content of diatoms.

Evaluation of L/D ratio in a water-related case for the differentiation between drowning and postmortem immersion

It is a difficult task to determine the cause of death for decomposed bodies found in water. Diatom test has been shown to provide supportive evidence for the diagnosis of drowning. According to our previous studies, the ratio of diatom content in lung tissue to diatom content in drowning medium (L/D ratio) is a very useful indicator to distinguish between drowning and postmortem immersion. In this article, we presented a case of a highly decomposed body being recovered from water with no significant findings on its cause of death. We applied the microwave digestion-vacuum filtration-automated scanning electron microscopy method (MD-VF-Auto SEM) to detect diatoms in the organs and suspected drowning medium. In this case, positive results are found in diatom tests of lung tissue, liver tissue and kidney tissue, while the L/D ratio analysis suggested that the victim was more likely to suffer from postmortem immersion. Taking the result of L/R ratio and other findings into consideration, we can eliminate the possibility of drowning. With continuous study, the L/D ratio analysis would be a valuable tool in diagnosis of drowning.

Reconstruction of phytoplankton productivity and community structure in the South Yellow Sea

The sedimentary environment and ecological system in the South Yellow Sea (SYS) changed dramatically due to sea level change caused by glacial-interglacial cycles. The authors report the use of marine biomarkers (brassicasterol, dinosterol and C₃₇ alkenones) and terrigenous biomarkers (C₂₈+C₃₀+C₃₂ <i>n</i>-alkanols) in core DLC70-3 from the SYS to reconstruct the variation in the phytoplankton productivity and community structure and possible mechanisms during the middle Pleistocene. The results show that the primary productivity and that of single algae presented a consistent trend for the whole core during the middle Pleistocene, which was high during interglacial periods and low during glacial periods, with the highest being in marine isotope stage (MIS) 5–9 and MIS 19–21. The main reason is that the Yellow Sea Warm Current (YSWC) carried much of high temperature, high salinity water into the SYS, causing upwelling and vertical mixing and stirring, which increased the nutrient supply in the photosynthetic layer. The phytoplankton community structure mainly showed an increase in the relative content of haptophytes in MIS 5–9 and MIS 19–21, while the relative content of diatoms and dinoflagellates decreased; there was no evidence for a haptophyte content in other stages. The results reveal a shift from a coccolitho-phorid-dominated community during MIS 5–9 and MIS 19–21 to a diatom-dominated community during the other stages, mainly as a result of surface salinity variation, attributed to the invasion of the YSWC during high sea level periods.

Reconstruction of Turgoyak lake (the Southern Urals) ecosystem changes in holocene

Object.Multi-proxy analysis of 265 cm long sediments core of Lake Turgoyak, one of the deepest lakes of the Southern Urals, is presented.Materials and methods.The lake ecosystem changes was reconstructed based on diatom, radiocarbon dating and geochemical analysis. Statistical treatment of the surface sediments composition and hydrochemistry data of 56 lakes from Southern and Middle Urals lakes database allowed to obtain geochemical indexes for reconstruction of water parameters: index of organic matter content (ОМ = LOI550ºС/(Al2O3 + TiO2 + Na2O + K2O)) and index of salinity (ММ = LOI950ºC/LOI550ºС). Results. Radiocarbon dating shows that sedimentation in Lake Turgoyak was began more than 12 cal kyr BP ago. Each of six lithological units of sediments core is characterized by its own geochemical features and associated with global (11.8, 11.2, 8.2 cal kyr BP) and regional (12, 10.3 cal kyr BP) climate events of the Northern Hemisphere. Four main stages of Lake ecosystem development were identified: 1) the beginning of lake sedimentation (&gt;12.1 cal kyr BP); 2) the stage of a subsaline shallow-water lake (12.1–11.2 cal kyr BP); 3) the stage of a freshwater lake with increased water-level (11.2–8.0 cal kyr BP); 4) the stage of water organic matter increase (&lt;8.0 cal kyr BP).Conclusions.High content of mesohalobic diatoms and salinity module values showed significant increase of lake water salinity as response to Early Holocene climate warming (11.8–11.2 cal kyr BP). Pantle-Buck’s Saprobity Index and OM values pointed to the lake water organic matter increase due to the next climate warming since 9–8 cal kyr BP. Thus, Lake Turgoyak water parameters were reapeatedly changed during the Holocene. However the response of lake ecosystem was different in different periods of its development.

Variation in growth, fucoxanthin, fatty acids profile and lipid content of marine diatoms Nitzschia sp. and Nanofrustulum shiloi in response to nitrogen and iron

Abstract The diatoms have numerous industrial and pharmaceutical applications, especially for carotenoids and lipid production. Here, the influence of different nitrogen (N) and iron concentrations on growth, fucoxanthin, lipid accumulation and fatty acids profile of two marine diatoms Nitzschia sp. and Nanofrustulum shiloi were investigated. Both diatoms displayed relatively high growth rate and biomass concentration under N-rich conditions. Iron-rich strategy for lipid production dramatically increased the lipid content (37.7 ± 0.77% in Nitzschia sp. and 37.44 ± 0.54% in N. shiloi). N-deficiency strategy had less impact on lipid accumulation in N. shiloi (28.06 ± 0.54%), while, it led to a significant increase of total lipid in Nitzschia sp. (37.7 ± 0.77%). N- and Iron-rich conditions led to a significant increase in fucoxanthin content of both diatoms as measured by HPLC-DAD and vice versa. The data suggested that marine diatoms Nitzschia sp. and N. shiloi could be potential candidates for fucoxanthin and lipids production.

Prioritization of prospective third-generation biofuel diatom strains

Energy has been playing a pivotal role in the progress and prosperity of a nation. Growing demands with dwindling stock of fossil fuels with the associated greenhouse gas (GHG) footprint and the consequent changes in the climate during the post-industrialization era have necessitated the exploration for sustainable energy alternatives. Biofuels are gaining importance as viable alternatives to fossil fuels during the last decade. Microalgae, especially diatoms, have shown prospects to be viable third-generation biofuel feedstocks, due to its higher lipid productivity, shorter cycling time and ubiquitous presence. This investigation focuses on identifying robust diatom strains that can sustain the vagaries of nature and yield higher lipid. This would avert the imminent risks of contamination associated with pure cultures and higher costs. The current research involved inventorying diatom consortia across diverse lentic and lotic habitats of the Aghanashini estuary with varied levels of nutrients primarily influenced by distribution of flora and fauna to understand the role of environmental parameters and nutrient levels in species composition, community structure. This effort is an essential prelude to phyco-prospecting potential candidates for third-generation biofuel production. The results obtained from the present study provide insights into an optimal habitat conditions, more specifically ideal nutrient concentrations for enhanced growth of different clusters of diatoms, a determining factor for higher biomass and lipid productivity. Multivariate statistical analyses revealed an occurrence of 27 tolerant diatoms species belonging to genera’s Amphora, Cyclotella, Navicula, Nitzschia and Pleurosigma. Linkages of the dominant and productive clusters of diatoms with habitat nutrient concentrations were investigated through agglomerative hierarchical clustering. Probable empirical relationship among varying environmental conditions and corresponding lipid content of diatoms were explored through regression analyses. Investigations of species tolerant to higher nutrient loads and assessment of lipid aided in prioritizing the strains with benefits of phyco-remediation as well as prospects of biofuel.

High-resolution and high-precision correlation of dark and light layers in the Quaternary hemipelagic sediments of the Japan Sea recovered during IODP Expedition 346

The Quaternary hemipelagic sediments of the Japan Sea are characterized by centimeter- to decimeter-scale alternation of dark and light clay to silty clay, which are bio-siliceous and/or bio-calcareous to a various degree. Each of the dark and light layers are considered as deposited synchronously throughout the deeper (> 500 m) part of the sea. However, attempts for correlation and age estimation of individual layers are limited to the upper few tens of meters. In addition, the exact timing of the depositional onset of these dark and light layers and its synchronicity throughout the deeper part of the sea have not been explored previously, although the onset timing was roughly estimated as ~ 1.5 Ma based on the result of Ocean Drilling Program legs 127/128. Consequently, it is not certain exactly when their deposition started, whether deposition of dark and light layers was synchronous and whether they are correlatable also in the earlier part of their depositional history.The Quaternary hemipelagic sediments of the Japan Sea were drilled at seven sites during Integrated Ocean Drilling Program Expedition 346 in 2013. Alternation of dark and light layers was recovered at six sites whose water depths are > ~ 900 m, and continuous composite columns were constructed at each site. Here, we report our effort to correlate individual dark layers and estimate their ages based on a newly constructed age model at Site U1424 using the best available paleomagnetic datum and marker tephras. The age model is further tuned to LR04 δ18O curve using gamma ray attenuation density (GRA) since it reflects diatom contents that are higher during interglacial high-stands. The constructed age model for Site U1424 is projected to other sites using correlation of dark layers to form a high-resolution and high-precision paleo-observatory network that allows to reconstruct changes in material fluxes with high spatio-temporal resolutions.

Causes of spatial distribution of subfossil diatom and chironomid assemblages in surface sediments of a remote deep island lake

Until recently, the distribution of diatom and chironomid assemblages and their attributes (species richness/diversity) in relation to water depth and sedimentary environments have been identified but not quantified. The influence of environmental variables on assemblage distribution and taxa richness in a deep, monomictic lake in Sao Miguel Island is assessed. Attention is given to community variation along a water-depth gradient. Sediment core samples were analysed for diatom content, chironomids, and grain-size clastic particles along three transects from the shoreline to the central deep basin of the lake at a resolution of 1 m water depth. Linear and unimodal regressions were used to test taxon richness, taxon diversity and taxon evenness versus water depth of each transect. A hump-shaped relationship between species richness and water depth was noted, with a peak occurring at mid-depth, meaning that samples located at that depth better represented the total subfossil assemblage living in lake Azul. Moreover, data indicate that both assemblages in Lake Azul, and taphonomic effects, were influenced by processes of clastic transport depending on the lake morphology. Results from this study allow us to access the spatial distribution of biological assemblages in clastic-dominated lakes with a high topographic gradient, and provide us with principal criteria that will allow us to determine coring locations that capture the true species diversity for studies in lakes.

Late holocene environmental changes in the Southwestern Chukchi Sea inferred from diatom analysis

The environmental changes in the southern part of the Chukchi Sea over the last 2300 years (two warmings during the ~262 BC–630 AD and ~630–1300 periods AD and 1 cooling ~1300–1840 AD) were inferred from changes in the content of diatoms in sediments (per gram), the ratio of dominant species, and the ecological structure of diatom assemblages. The sediment age was determined based on the recent 210Pb sedimentation rates at the sampling point (0.43 mm/yr) and radiocarbon dating of mollusk shells. The environmental changes in the southern Chukchi Sea that were inferred from the diatom analysis correlate with global climate changes, viz., the warming events of the early (Roman) and the middle (Medieval) Subatlantic and the cooling of the late (Little Ice Age) Subatlantic.

Effect of the Silica Content of Diatoms on Protozoan Grazing

This study examined the effect that silica content in diatom cells has on the behavior of protists. The diatoms Thalassiosira weissflogii and T. pseudonana were cultured in high or low light conditions to achieve low and high silica contents, respectively. These cells were then fed to a heterotrophic dinoflagellate Noctiluca scintillans and a ciliate Euplotes sp. in single and mixed diet experiments. Our results showed that in general, N. scintillans and Euplotes sp. both preferentially ingested the diatoms with a low silica content rather than those with a high silica content. However, Euplotes sp. seemed to be less influenced by the silica content than was N. scintillans. In the latter case, the clearance and ingestion rate of the low silica diatoms were significantly higher, both in the short (6-h) and long (1-d) duration grazing experiments. Our results also showed that N. scintillans required more time to digest the high silica-containing cells. As the high silica diatoms are harder to digest, this might explain why N. scintillans exhibits a strong preference for the low silica prey. Thus, the presence of high silica diatoms might limit the ability of the dinoflagellate to feed. Our findings suggest that the silica content of diatoms affects their palatability and digestibility and, consequently, the grazing activity and selectivity of protozoan grazers.

Changes in the Basic Index Properties of Clays in Relation to the Content of Diatoms

In the framework of the research project of the Technology Agency of the Czech Republic TA 02011350 “Investigation of properties of diatomaceous clays and methods for improving their structure", clay properties have been investigated depending on the content of diatoms. To investigate the effects of diatom microfossil content on the index properties of clay soils, measuring tests were performed on cohesive soils with different diatom microfossils content.

The enigmatic consolidation of diatomaceous sediment

Marine diatomaceous sediments are common along the polar belts and equator, but very little is known about their effect on sediment geotechnical properties and slope stability. Consolidation state analysis is frequently applied to derive past maximum overburden stress, to quantify over- or underconsolidation, or to infer excess pore water pressure, all relevant to assess risk of slope failure. Diatoms significantly alter geotechnical and other fundamental engineering properties usually observed in organic or inorganic sediment. The consolidation state of diatomaceous sediments is ambiguously discussed because geological evidence and laboratory data do not always correspond. A literature review revealed a near systematic overconsolidation of shallow diatomaceous sediments (<100mbsf) and normal or underconsolidation in deeper sediment sequences. One-dimensional compression tests are carried out on material sampled during the R/V POLARSTERN cruise ANT XXIX/4 to a landslide-prone area of the South Sandwich Trench, and on generic clayey-silt - diatomaceous earth sample mixtures. Results indicate that diatoms alter geotechnical properties to an extent that in situ stress conditions may not well be inferred from common consolidation state analysis. Undrained vane shear strength underestimates the in situ undrained shear strength and leads to underestimated normalized undrained shear strength ratios. Enhanced secondary compression with overburden and diatom content leads to a natural curvature of consolidation lines, the latter occasionally falsely interpreted as preconsolidation stress. The observations are furthermore dependent on the predominant diatom order. Moreover, inverse trends of porosity are not necessarily related to excess pore water pressure, but solely to a gradual increase of diatoms with depth.

Influence of diatom microfossils on sediment shear strength and slope stability

AbstractDiatom microfossils have been detected in many natural marine sediment deposits around the globe and are held responsible for the disobedience to well‐established geotechnical relationships between index‐properties and shear strength. We revisit the static shear strength and present the first cyclic undrained shear strength experiments on diatom microfossil—clayey‐silt mixtures to study the role of diatoms on submarine slope stability. It is attested that the angle of internal friction (Φ) increases with diatom content, however, we provide evidence for a significant overestimation of Φ in previous studies. Based on direct shear tests at varying normal stresses ≤ 600 kPa we find Φ = 32° in contrast to 43° in pure diatom. Similarly, to static shear strength, cyclic shear strength increases with diatom content, however, in contrast to static shear strength the most drastic increase does not occur from 0% to 25% diatoms but from 75% to 100%. Interestingly, diatomaceous sediments tend to fail by liquefaction although well‐established relations between index properties and liquefaction susceptibility predict the opposite. Liquefaction failure is observed solely in samples containing ≥ 50% diatoms whereas samples with lower diatom content fail by cyclic softening. We conclude diatom microfossils in marine sediments significantly contribute to an increased slope stability under static and cyclic loading conditions since diatoms lead to higher resistance independently of the loading mode. The strength increase is interpreted as a result of particle interlocking and surface roughness, which is very efficient given the highly variable habitus of diatom species.

Interactive effects of nitrogen and light on growth rates and RUBISCO content of small and large centric diatoms

Among marine phytoplankton groups, diatoms span the widest range of cell size, with resulting effects upon their nitrogen uptake, photosynthesis and growth responses to light. We grew two strains of marine centric diatoms differing by ~4 orders of magnitude in cell biovolume in high (enriched artificial seawater with ~500 µmol L−1 µmol L−1 NO3−) and lower-nitrogen (enriched artificial seawater with <10 µmol L−1 NO3−) media, across a range of growth light levels. Nitrogen and total protein per cell decreased with increasing growth light in both species when grown under the lower-nitrogen media. Cells growing under lower-nitrogen media increased their cellular allocation to RUBISCO and their rate of electron transport away from PSII, for the smaller diatom under low growth light and for the larger diatom across the range of growth lights. The smaller coastal diatom Thalassiosira pseudonana is able to exploit high nitrogen in growth media by up-regulating growth rate, but the same high-nitrogen growth media inhibits growth of the larger diatom species.

Mediterranean rivers: Consequences of water scarcity on benthic algal chlorophyll a content

Mediterranean rivers are subjected to strong seasonality with drought during the hot season and extreme flows in autumn-winter. In particular, drought episodes and water scarcity alter the river morphology, with repercussions on primary production and the trophic chain. In this paper, we aimed at analysing the different responses in terms of chlorophyll a content of the three main photosynthetic groups composing stream periphyton, namely diatoms, cyanobacteria and green algae. This work was conducted in the Ligurian Alps (NW-Italy) on five oligotrophic streams (Argentina, Impero, Merula, Quiliano and Vallecrosia), similar in terms of physico-chemical parameters. We measured chlorophyll a content of diatoms, cyanobacteria and green algae by means of an in situ fluorimetric probe (BenthoTorch®). Data were collected from April to October 2014 in: i) impacted sites, where the water scarcity was exacerbated by human pressure; ii) control sites. We applied Generalized Linear Mixed Models to investigate the response of total chlorophyll a and its relative proportions among the three algal groups in relation to the following environmental predictors: water depth, flow velocity, canopy shading, microhabitat isolation, sampling season, dissolved oxygen, temperature, pH, nutrients, and macrophyte coverage.Results showed an opposite response of diatoms and green algae. Diatoms were favoured in the control sites and under moderate flow conditions, while the probability of green algae presence was higher in the impacted sites and during the drought season. Cyanobacteria showed a response similar to green algae, preferring warm, isolated pools typical of the drought period. Diatoms proved to be the most sensitive to drought. More specifically, we found out that percentages of diatoms below 51% with respect to total benthic chlorophyll a indicate high hydrological disturbance. This study provides the first evidence that the proportion of chlorophyll a produced by diatoms can be a suitable indicator for monitoring programs aiming at determining the effects of water scarcity on river ecosystems.

Effect of Diatom Silica Content on Copepod Grazing, Growth and Reproduction

Diatoms are often a major food source for zooplankton and contribute significantly to vertical POC flux through sinking of dead cells, aggregates and zooplankton fecal pellets. The silica content of diatoms varies among different species and within a species growing under different environmental conditions and physiological status. However, to-date there has been no investigation of the effect of diatom silica content on zooplankton grazing, growth and reproduction. We conducted a series of experiments using the diatom Thalassiosira weissflogii with different silica content achieved by growth under high and low light and these cells were fed to a copepod, Parvocalanus crassirostris. Our results show that this copepod strongly preferred cells with low silica content over high silica-containing cells, with the ingestion rate on low silica diatoms being 2-3 times higher than that on high silica diatoms. Fecal pellet production rate was significantly higher for copepods feeding on highly silicified cells. Furthermore, copepod growth rate (measured as an increase in wet weight), egg production rate and hatching success were all severely compromised under a high silica diatom diet. Females of P. crassirostris feeding on a low silica diatom diet produced an average 90 eggs during a one day incubation, while those fed with high silica diatoms produced only 11 eggs per day. Similarly, the hatching success during a 3-day period was 82 ± 17% and 23 ± 36% for the low and high silica diatom treatments, respectively, with zero success observed in ~65% of the females feeding on high Si diatoms. Our findings have important ecological implications for the biological pump and may alter our previous view of the role of diatoms in planktonic food webs and the role of the degree of silicification in controlling amount of POC flux to deeper waters.

The diatom distribution in the surface sediments of the Eastern Arctic seas of Russia

The distribution features of diatoms in the surface sediments of the Laptev, East Siberian, and Chukchi seas were studied. The sediment diatom content varied widely, being lowest in the East Siberian Sea and highest in the Chukchi Sea. Cluster analysis revealed several diatom assemblages in the surface sediments of the studied region; their distribution depended on the hydrological conditions. A benthic Amphora libyca assemblage, a freshwater Aulacoseira subarctica one, and a brackish-water Thalassiosira hyperborea assemblage were identified in the Laptev Sea. A cold-water Th. antarctica assemblage was distinguished in the eastern part of the East Siberian Sea and in the northern Chukchi Sea; a highly productive Chaetoceros assemblage was noted in the Herald Canyon area; a sublittoral Odontella aurita assemblage occurred in sandy sediments of the Herald Shoal; a Paralia sulcata assemblage, which is an indicator of low salinity waters, was found in the eastern Chukchi Sea near Alaska; and ”sea-ice” Th. nordenskioeldii and Fragillariopsis oceanica assemblages occurred in the southern Chukchi Sea.

Fossil diatoms from endogangue of the Ypresian phosphatic pellets of the Gafsa-Metlaoui basin: implication on the origin of biogenic silica and depositional environment

This work deals with mineral and diatom contents of the lower Eocene (Ypresian) phosphatic pellets of the Gafsa-Metlaoui basin, using XRD and SEM method. Since, mineral composition and fossil diatoms are best indicators of the depositional environments and diatom content leads to understand the role of diatoms in the formation of siliceous rocks especially porcelanite of the interbedded facies. This study indicates that phosphate minerals (fluorapatite) are associated with opal CT, carbonate mineral (dolomite and calcite), pyrite, sphalerite, and clinoptilolite. This association corroborates with deposition of the Ypresian sediments of the Gafsa-Metlaoui basin in alkaline and anoxic to suboxic marine environments under sulfate-reducing conditions. On the other hand, the exogangue is roughly free from diatoms except some highly dissolved diatom frustules. Endogangue displays some preserved diatom frustules, which allow the determination of three species: Paralia sulcata, Stephanopyxis sp. and Aulacoseira sp. Aulacoseira sp occurs at the eastern part of the Gafsa-Metlaoui basin (M’Zinda section) and it is known as a freshwater diatom. Stephanopyxis sp. and P. sulcata are both indicative of warm shallow marine water. They occur at Metlaoui Table and Kef Eddour sections, respectively.