Epiphytic Diatoms Research Articles

The Effects of Cattle Grazing on the Composition of Diatom Assemblages in the Peatland Pools of the Southeastern Alps (Italy, Adamello-Brenta Nature Park)

Mires are significant C-sinks and important habitats for biodiversity conservation. Particularly in the Alpine peatlands, grazing and trampling cause mires to degrade, causing changes in plant communities that increase bulk density, peat erosion, and nutrient excesses. We took sixteen samples of epipelic and epiphytic diatoms from mire pools subjected to varying degrees of grazing in the Adamello-Brenta Nature Park (Trento, Italy). We identified >100 diatom species (ca. 70% included in Red List threat categories). We used nMDS to identify groups of diatom species. Their statistical significance was checked with an ANOSIM and, to identify the species that contributed most to the difference between the two groups, a BEST-SIMPER procedure was carried out. The multivariate analyses allowed us to identify significant differences among the most and least grazed sites, and to select the species that contributed most to this distinction. We confirmed that some species were more frequent and abundant in the most grazed sites and behaved as opportunists in the presence of a greater nutrient input, to the detriment of rare and sensitive species, which were more numerous and abundant in the less grazed sites. We provided useful information on grazing effects, underlining the importance of managing and protecting habitats of unique environmental value.

Ecohydrological changes recorded by sedimentary diatoms in the Dajiuhu Wetland in Shennongjia over the past 40 years.

Anthropogenic hydrological regulation is profoundly altering the structure and function of wetland ecosystems. Due to the scarcity of long-term monitoring records, the responses of wetland ecosystems to anthropogenic hydrological regulation remain unclear. We reconstructed past ecohydrological changes in Dajiuhu Wetland during the last 40 years and explored the driving forces, based on multiproxy records of a 44-cm-length sediment core collected from Wuhaohu Lake of Dajiuhu Wetland in Shennongjia, Hubei. The results showed that the diatom community in Wuhaohu Lake had experienced three major stages, including the dominance of benthic diatoms between 1980 and 2008, the rapid increase in planktonic diatoms between 2008 and 2016, and the dominance of small-sized fragilarioid species after 2016. Results of redundancy analysis showed that change in diatom assemblage was significantly correlated with total organic carbon, total nitrogen and the ratios of Mn to Fe. Diatom floral changes after 2008 indicated the shift of Wuhaohu Lake from an early organic-rich peatland to a shallow lake, mainly in response to an increase in water table driven by damming. From 2016, the increases in benthic and epiphytic diatoms responded to the expansion of aquatic plants and improved light penetration after the relocation of local population. Sedimentary diatom records revealed the process of environmental changes, and hence would provide a scientific basis for the environmental protection of wetlands.

Cell-Death Metabolites from Cocconeis scutellum var. parva Identified by Integrating Bioactivity-Based Fractionation and Non-Targeted Metabolomic Approaches.

Epiphytic diatoms growing in Mediterranean seagrass meadows, particularly those of the genus Cocconeis, are abundant and ecologically significant, even in naturally acidified environments. One intriguing aspect of some benthic diatoms is their production of an unidentified cell-death-promoting compound, which induces destruction of the androgenic gland in Hippolyte inermis Leach, 1816, a shrimp exhibiting protandric hermaphroditism, principally under normal environmental pH levels. The consumption of Cocconeis spp. by this shrimp is vital for maintaining the stability of its natural populations. Although many attempts have been made to reveal the identity of the apoptotic compound, it is still unknown. In this study, we strategically integrated a bioactivity-based fractionation, a metabolomic approach, and two different experimental avenues to identify potential apoptotic metabolites from Cocconeis scutellum var. parva responsible for the sex reversal in H. inermis. Our integrated analysis uncovered two potential candidate metabolites, one putatively identified as a lysophosphatidylglycerol (LPG) (16:1) and the other classified as a fatty acid ester. This is the first time LPG (16:1) has been reported in C. scutellum var. parva and associated with cell-death processes. These candidate metabolites mark substantial progress in elucidating the factors responsible for triggering the removal of the androgenic gland in the early post-larval phases of H. inermis.

Assessing long-term diatom changes in sub-Arctic ponds receiving high fluxes of seabird nutrients.

Algal bioindicators, such as diatoms, often show subdued responses to eutrophication in Arctic lakes because climate-related changes (e.g., ice cover) tend to be the overriding factors influencing assemblage composition. Here, we examined how sub-Arctic ponds historically receiving high nutrient inputs from nesting seabirds have responded to recent climate change. We present diatom data obtained from 12 sediment cores in seaduck-affected ponds located on islands through Hudson Strait, Canada. All study cores show consistently elevated values of sedimentary ẟ15N, an established proxy for tracking marine-derived nutrients, indicating seabirds have been present on these islands for at least the duration of the sediment records (~100 to 400 years). We document diverse epiphytic diatom assemblages to the base of all sediment cores, which is in marked contrast to seabird-free Arctic ponds-these oligotrophic sites typically record epilithic diatom flora prior to recent warming. Diatoms are likely responding indirectly to seabird nutrients via habitat as nutrients promote the growth of mosses supporting epiphytic diatom communities. This masks the typical diatom response to increased warming in the Arctic, which also results in habitat changes and the growth of mosses around the pond edges. Changes in sedimentary chlorophyll a were not consistently synchronous with large changes in ẟ15N values, suggesting that primary production in ponds is not responding linearly to changes in seabird-derived nitrogen. Across all ponds, we recorded shifts in diatom epiphytic assemblages (e.g., increases in % relative abundance of many Nitzschia species) that often align with increases in chlorophyll a. The changes in diatoms and chlorophyll a, although variable, are most likely driven by climate change as they are generally consistent with longer ice-free conditions and growing seasons. Together, our results show that to effectively use diatoms in animal population reconstructions across the sub-Arctic and Arctic, a strong understanding of eutrophication and climate change, based on supplementary proxies, is also required.

Combined application of nitrogen, phosphorus, iron, and silicon improves growth and fatty acid composition in marine epiphytic diatoms

IntroductionMarine epiphytic diatoms are natural diets for multiple marine invertebrates, including sea cucumbers, sea urchins, etc. They also act as bioindicators in marine waters to assess water quality of coastal ecosystems. Material and methodsWe isolated three strains of Navicula and two strains of Nitzschia from macroalgal epiphytes. Combined concentrations of four macroelements, five trace metals, and three vitamins in f/2 medium were optimized for these diatoms using single-factor and orthogonal tests. Results and discussionThe biomass productivities for 4-L enlarged cultures of the five isolated diatoms in their exclusively optimized f/2 media all increased by nearly 10-fold relative to f/2 medium, and that of Navicula-1 and Nitzschia-2 reached the highest, i.e., 29.52 ± 1.98 and 30.68 ± 2.84 g m-2 d-1, respectively. Moreover, the relative abundance of C20:5n3 in the exclusively optimized f/2 medium-cultured Navicula-1 notably rose by 24%, and that in Nitzschia-2 held stable at > 25%. Thus, Navicula-1 and Nitzschia-2 were screened out with outstanding growth traits and improved fatty acid compositions at high levels of combined nitrogen, phosphorus, iron, and silicon. The two diatoms have potential for becoming quality diets for marine aquaculture, and ideal candidates for effective nutrient removal.

Particulate matter from water moss of a large Siberian river: Morphometric, mineral, elemental and radionuclide composition

Particulate matter trapped by tufts of water moss Fontinalis antipyretica inhabiting fast flowing waters of the Yenisei River (Siberia, Russia) contaminated with artificial radionuclides has been studied as a potential monitor of radioactive releases to the river. Particulate matter, which was removed from wet tufts of water moss of the Yenisei by rinsing them in water, constituted at least 38% of bulk dry weight of the moss biomass sample and was similar in the contents of chemical elements, minerals, organic matter, and artificial radionuclides to bottom sediments of the Yenisei. Considerable bulk percentages of artificial radionuclides in the sample of water moss, 77% of 137Cs, 44% of 60Co, 41% of 152Eu, 55% of 154Eu, 66% of 241Am, and 34–36% of plutonium were associated with extracellular particles. The comparative study and correlation analysis suggested that 137Cs was mainly associated with mineral particles trapped by moss and that organic matter was responsible for binding plutonium in samples of water moss. Consequently, analysis of extracellular particles of water moss can provide data on contents and speciation of radionuclides transported by water current. Although a considerably high proportion of particulate matter had been washed out from tufts of water moss, some extracellular mineral particulate material and a large number of epiphytic diatoms remained attached to leaves of water moss. Our study proves that particulate matter trapped by water moss can be used as an informative monitor to trace radioactive pollutants transported by water current in running waters deficient in bottom sediments and potential biomonitors.

EPIPHYTIC DIATOMS IN ENVIRONMENTAL BIOINDICATION: A CASE STUDY OF A SIGNIFICANT NATURAL LAKE IN THE NORTHWEST OF TURKEY

Aim of the study: The Gala Lake, which has a status of National Park and is an under-protection area, is the one of the most important natural stagnant water bodies in the Marmara Region of Türkiye. However, it is under effect of a significant agricultural stress sourced by mainly paddy cultivation. In this research, the epiphytic diatoms of Gala Lake were investigated, and the trophic status of the lake was assessed by applying the Biological Diatom Index (BDI). Material and methods: Epiphytic diatom samples were collected from the submerged macrophytes from 5 selected locations on the lake (G1–G5) with different ecological characters observed to be exposed to different pollution pressures. Results and conclusions: As a result of taxonomic data, 37 diatom species were recorded by identifying a total of 2095 valves, and Cyclotella meneghiniana, Bacillaria paxillifera, and Navicula recens were found as the most dominant species for the Gala Lake. According to the results of bioindication data, Gala Lake was found to be in a "eutrophic state"—"having poor water quality" in terms of applied BDI.

Biological and Ecological Monitoring Using Epiphytic Diatoms on Two Aquatic Plants to Estimate the Water Quality of Habbaniyah Lake, Western Iraq

The current study was conducted in Habbaniyah Lake in Anbar Governorate - western Iraq, starting from February 2022 tol July 2022. Five sites were chosen to collect water samples and epiphytic diatoms attached to two aquatic plants, Phragmites australlis (Cav.) Trin. and Ceratophylum demsrsam L.. The current study aims to employ the quality and quantity of the epiphytic diatoms community attached to the host aquatic plants to estimate the quality of the lake water, by conducting a set of environmental indicators that included biological indicators. 102 species of Bacillariophyceae class were identified. Where 84 species were diagnosed on the Ceratophyllum, while 61 species were diagnosed on the Phragmites In the current study, a set of ecological indices was conducted to characterize the water quality of Habbaniyah Lake, which included three biological indices: the Tolerance Pollution Index (PTI), where the lake was described as moderately polluted, to record values whose averages ranged (1.65-2.35), and Trophic Diatomic Index (TDI), whose average values ranged from (55.62 - 58.72), where the lake was described as mesotrophic and Shannon Diversity Index, where the waters of Lake Habbaniyah were described as having medium biodiversity, recording average values (2.22 - 2.50). An environmental index was conducted, which is the Canadian Water Quality Index (CCME), where it recorded values that ranged from (76.59 - 78.66), where the lake water was described as of moderate (Fair) quality and often threatened or weak from time to time, and the water condition deviates from the required level. or desired.

Diversity and Abundance of Epiphytic Diatoms on Seagrass Leaves (Enhalus acoroides) in Poncan Gadang Island Sibolga City, North Sumatra

The seagrass ecosystem is one of the marine ecosystems that has an important role, namely as a source of life for organisms in the sea. Diatoms are microalgae widely distributed throughout the aquatic environment and are even found in plants, including seagrass leaves. Diatoms greatly influence life in the waters because they play an essential role as a food source for various marine organisms and play a role in the transfer of carbon, nitrogen, and phosphate. This research was conducted in February 2023 on Poncan Gadang Island, Sibolga City, North Sumatra. The study aims to determine the density, relative abundance, abundance, and diversity of epiphytic diatom species on seagrass (Enhalus acoroides) leaves in Poncan Gadang Island. The method used is the survey method, using three stations to take samples. The determination of 3 stations is based on the density of the seagrass beds ecosystem. Sampling of diatoms was carried out by brushing the surface of seagrass leaves about 5x2 cm on the front and back of the leaves. The samples obtained were then analyzed in the laboratory. There were 12 types of diatoms found, consisting of Cocconeis sp., Rhizosolenia sp., Biddulphia sp., Amphipluera sp., Thalassiotrix sp., Nitzchia sp., Synedra sp., Melosira sp., Pleurogosigma sp., Skeletonema sp., Licmiphora sp., and Thalassionema sp. the average value of epiphytic diatom abundance in seagrass leaves ranged from 2160.85 – 4649.94 ind/cm². The epiphytic diatom diversity (H') values ranged from 2.53 to 2.72

Environmental drivers of genetic variability in common diatom genera: Implications for shallow lake biomonitoring

Diatoms are microalgae, known to present several characteristics that make them excellent bioindicators. In this study, we analyzed the epiphytic diatom communities of ponds, with the aim of exploring the genetic variability explained by physical, chemical or geographical variables. We selected 77 lakes within the Spanish part of the Duero River Basin characterized by wide chemical variability. In each lake, physical parameters were measured in situ and water samples were taken to determine nutrient levels in the laboratory. Diatom communities were collected and identified by DNA-metabarcoding, amplifying a genetic barcode of rbcL gene. We analyzed the phylogenetic signal for several environmental parameters at the genus level for the three most representative genera of these lakes. Our results indicate significant phylogenetic signals that differ from a genus to another. Processes related to spatial scales appear to be the main predictors controlling the genetic diversity of diatom communities in these ponds, with genetic variants differing among geographical areas for a given species. These molecular studies confirm the enormous diversity present in the diatom communities that inhabit these ecosystems, but further research is needed to apply diatom-based techniques in ponds monitoring or conservation programs. Our results reinforce the view that considering not only morphological but also molecular and ecological characters are necessary to describe new living diatom species, whenever possible, especially given the high number of species described each year.

Use of Epiphytic Diatoms in Cyperus Papyrus L. As Bioindicators in the Assessment of the Health of the Upper Euphrates River Between the Haditha Dam and Al-Baghdadi, Iraq

The aim of this study is to use epiphytic diatoms in Cyperus papyrus L. plant as biological indicators for estimating the water quality of the upper Euphrates River between Haditha Dam and Al-Baghdadi. Biodiversity and biological indicators for water quality estimation, along with the Canadian Water Quality Index. The study showed that the water of the upper Euphrates River is warm, light alkaline, the electrical conductivity and the total dissolved soled of water affected by agricultural land water and human activities, turbidity, total hardness and the biological oxygen demand, chloride and sodium did not exceed the permissible limits, while the values of calcium, nitrate and phosphate exceeded the permissible limits. And that the calcium values have exceeded the magnesium values, and that the water in the river is well ventilated. We have identified 130 species of epiphytic diatoms in Cyperus papyrus L. plant, including 6 species (5%) belonging to the centrales diatoms and 124 species (95%) belonging to the pennales diatoms, and the highest total number of cells of the epiphytic diatoms was recorded as 1322.3 cells x 103 / gm in site I. The values of physical and chemical factors, ecological indices, and water quality index agreed that the water of the upper Euphrates River is of moderate pollution, medium biodiversity, mesotrophic, and homogeneous in the presence of species.

Interactions of hydrology, geochemistry, and biodiversity in woodland ponds located in riverine floodplains: case study from Scotland

The Gore Glen pond is located in the forested floodplain of the Gore River, in the Mid-Lothian region near Edinburgh, Scotland. This work has considered in detail the hydrology, hydrochemistry, and biodiversity of the pond together with all their interactions and in addition interactions with the adjacent Gore River. It is important as it is one of few studies considering all these issues for a pond located in a riverine floodplain. This work shows the pond is connected to the Gore River for discharge events in the river larger than a 1 in 5-year return period. For these events, the pond acts as an online storage feature and will attenuate the flow, thus contributing towards the mitigation of downstream flooding. These large events are also a potential source of the large amount of sediments, as well as adsorbed chemicals, accumulated in the pond. The open water surface of the pond is covered by duckweed, Lemna minor, for most of the year, and that has profound implications for the hydrobiological community and biogeochemical cycling. The system is characterised by nutrient release from sediments due to the extensive hypolimnion anoxia in the summer/autumn period caused by the decomposition of organic matter. Algae are mostly represented by epiphytic diatoms and the cyanobacterium Microcystis, but their development appears to be constrained by light penetration. The eutrophic conditions are also conducive for the population of Difflugia (Protozoa, Rhizopoda). This work improves our understanding of the ecological relations of testate amoebae—an important group which has recently been used as biological indicators for the analysis of paleoecological relationships and paleogeographical reconstructions.

Epiphytic Diatoms from the Central Region of the Gulf of California: Floristics and Biogeographic Remarks

The ecological significance of benthic diatom taxocoenoses in marine ecosystems renders them a suitable reference when making decisions on conservation, as well as ecological and biogeographical issues. This study focuses on floristics of epiphytic diatoms of macroalgae from the central region of the Gulf of California and their biogeographical affinities. Based on current floristics for benthic diatoms of the Mexican NW, it was hypothesized that species richness would be higher for the central gulf (transitional) than for the tropical Revillagigedo Archipelago. Additionally, it was hypothesized that it would be composed mainly of common taxa of the region, with tropical and temperate components. Likewise, it was hypothesized that Mastogloia (tropical) would include less taxa and Lyrella would include more taxa in the transitional central gulf. The diatom flora yielded 333 taxa and 101 genera, and out of which the best represented were Navicula with 29 taxa, Amphora (27), Cocconeis (25), Nitzschia (24), Diploneis (19), Achnanthes (13), Halamphora (14), Fallacia (10), Lyrella (9), and Mastogloia (8), adding up to 53% of the total. The inspected diatom taxocoenosis included mostly taxa commonly distributed in the Mexican NW, albeit with 16 new records. This, plus the high species richness, as well as the proportions of selected taxa depicting this diatom taxocoenosis as being of transitional biogeographical affinity, back the posed hypotheses.

Diatomological Profile at Discrete Depths of Powai Lake, Mumbai for Medico-Legal Purposes

Diatoms are photosynthetic microorganisms that play important role in forensic diatomology in the diagnosis of drowning deaths. In the present study, the Diatomological profile of Powai lake was prepared for medico-legal purposes using the Shannon-Wiener index. Powai lake (19.1266° N, 72.9062° E) is a large artificial lake situated in a northern suburb of Mumbai. Diatoms sampling was conducted in February 2017 from this lake. This study aimed to identify the various genera of diatoms and to determine the relative abundance, generic counting, and diversity index of diatoms for the medico-legal purposes. Littoral benthic diatoms of five locations were sampled from this lake. Diatoms slides were prepared by scraping the rock surface with an area of 3x3 cm, diluting in 50 ml distilled water, and identification under the microscope with 1000 magnification. Identification of 17 genera of diatoms was done using the web-based visual guide ‘Diatoms of the United States’. Diatoms belong to both the orders Centrales and Pennales. The pH of the lake water was found to be 7.64 i.e. slightly alkaline and the temperature was 27°C. Water quality parameters showed a fairly good value for the growth of diatoms. Samples were dominated by class Bacillariophyceae, which included 9 genera followed by Coscinodiscophyceae, with 6 genera, and Fragilariophyceae, with 2 genera. Generic counts of diatoms were obtained by using the ‘Neubauer’ Counting chamber. The Shannon-Wiener diversity index (H') ranges from 1.042 in Epipelic to 0.454 in Emerged Epiphytic diatoms. The purpose of this study was to prepare a diatomological profile of diatoms at discrete depths for medico-legal purposes.

Epiphytic diatom production on the seagrass Thalassia testudinum in northern Gulf of Mexico

Epiphytic diatom production on the seagrass Thalassia testudinum in northern Gulf of Mexico

FTIR autecological analysis of bottom-ice diatom taxa across a tidal strait in the Canadian Arctic

A recent study demonstrated that an Arctic tidal strait, where a shoaled and constricted waterway increases tidally driven sub-ice currents and turbulence, represents a “hotspot” for ice algal production due to a hypothesized enhanced ocean-ice nutrient supply. Based on these findings, we sampled the bottom-ice algal community across the same tidal strait between the Finlayson Islands within Dease Strait, Nunavut, Canada, in spring 2017. Our objective was to examine cellular responses of sea-ice diatoms to two expected nutrient supply gradients in their natural environment: (1) a horizontal gradient across the tidal strait and (2) a vertical gradient in the bottom-ice matrix. Two diatom taxa, Nitzschia frigida and Attheya spp. in bottom-ice sections (0–2, 2–5, and 5–10 cm) under thin snow cover (<5 cm), were selected for Fourier Transform Infrared (FTIR) spectrochemical analysis for lipid and protein content. Results from the FTIR technique strongly supported the existence of a horizontal nutrient gradient across the tidal strait of the Finlayson Islands, while estimates of particulate organic carbon and chlorophyll a concentrations were difficult to interpret. The larger N. frigida cells appeared to be more sensitive to the suspected horizontal nutrient gradient, significantly increasing in lipid content relative to protein beyond the tidal strait. In contrast, the epiphytic diatoms, Attheya spp., were more sensitive to the vertical gradient: above 2 cm in the bottom-ice matrix, the non-motile cells appeared to be trapped with a depleted nutrient inventory and evidence of a post-bloom state. Application of the FTIR technique to estimate biomolecular composition of algal cells provided new insights on the response of the bottom-ice algal community to the examined spatial gradients that could not be obtained from conventional bulk measurements alone. Future studies of sea ice and associated environments are thus encouraged to employ this technique.

Thermogravimetric Analysis of Marine Macroalgae Waste Biomass as Bio-Renewable Fuel

Macroalgae are considered as the 3rd generation of biofuels and a future feedstock for biorefinery. This research aims to provide simple and dependable analytical techniques for measuring the thermal characteristics of dried seaweed. The main objective was to investigate the thermal characteristics of four seaweed species utilizing a thermogravimetric analyzer. The seaweeds Gracilaria fisheri, Caulerpa lentillifera, Ceramium rubrum, and Eucheuma cottonii were collected from the Pahang state of Peninsular Malaysia. The calorific value of the samples was revealed by using a calorimeter. Ceramium rubrum showed the highest calorific value, while Gracilaria fisheri had the most negligible calorific value among the selected samples. The thermogravimetric analysis (TGA) data revealed that the most significant weight loss for this biomass occurred between 160 and 300° for the selected species. Gracilaria fisheri has shown the highest decomposition with the minor residue at 30.26%, whereas Caulerpa lentillifera has a slow weight loss rate in the mentioned range. SEM analysis has been used to perform the morphology of samples, which shows differences in the concentration of epiphytic diatoms with different structural shapes. Based on the results, macroalgae is a promising sustainable biomass feedstock for biofuel application.

Diversity and Variation of Epiphytic Diatoms on Ruppia maritima L., Related to Anthropogenic Impact in an Estuary in Southern Brazil

Knowledge about the diversity and spatiotemporal variability of epiphytic diatom communities in estuarine meadows has great relevance for coastal ecology and, thus, contributes to understanding the impact of natural and anthropogenic changes on seagrass meadows. The community of epiphytic diatoms in Ruppia maritima L. meadows was investigated in two environments with different levels of anthropogenic impact and nutrient loads. Both impacted and non-impacted meadows had similar conditions in terms of water depth, temperature and transparency but distinct nutrient loads and salinity ranges. A total of 159 diatom taxa were found on Ruppia maritima leaves during the monitoring period, including freshwater (30.8%), marine (25.1%), brackish (9.4%) and cosmopolitan (8.8%) taxa. The most abundant species were C. placentula, T. tabulata, M. pumila and T. fasciculata, in addition to A. tenuissimus, C. adhaerens and M. moniliformis. Although present in both sites, C. placentula and T. tabulata were the dominant species in the impacted site. We found that 32% of the taxa were exclusive to the non-impacted site, 23% to the impacted site and 45% were common to both sites. The study sites showed marked differences in community attributes; i.e., higher richness, diversity and equitability and lower dominance were found in the non-impacted site, which is distant from anthropogenic sources of domestic and industrial sewage and has low concentrations of dissolved N and P in water and low values of sediment organic matter. Nutrient concentration and salinity were the main factors behind the spatial and temporal variability in the structure of the epiphytic community when all other environmental variables were similar (water depth, temperature, transparency and host plant). The influence of temperature and salinity on community structure was site-dependent. This study revealed the high richness and diversity of epiphytic diatoms in the meadows of the Patos Lagoon estuary (PLE) and the high spatial and temporal heterogeneity of the communities, and it shows the potential of epiphytic community studies for the assessment of environmental quality in seagrass meadow habitats.

Paleoenvironmental changes of the last 16,000 years based on diatom and geochemical stratigraphies from the varved sediment of Holzmaar (West-Eifel Volcanic Field, Germany)

Lacustrine environmental archives with annually laminated (varved) sediments allow a calendar-year chronology and the calculation of precise sediment accumulation rates. We present multiproxy analyses of a varved sediment record from Holzmaar (West-Eifel Volcanic Field, Germany) for the last 16,000 years providing a continuous diatom stratigraphy supported by physical and chemical variables with a centennial resolution. Patterns of diatom assemblages infer the trophic history of Holzmaar. There is a distinct variation at the Pleistocene/Lateglacial transition characterized by the replacement of Staurosira construens with Stephanodiscus minutulus, increases of Ca/Ti, total organic carbon/total nitrogen (TOC/TN) ratios and biogenic silica, together suggesting an increase in lacustrine productivity and a shift of the lake's trophic status from oligotrophic to mesotrophic. These conditions remain during the Bölling/Alleröd interstadial. During the Younger Dryas stadial, there is a decrease in organic productivity as reflected by TOC, a subtle increase in benthic and epiphytic diatoms indicating colder and dry conditions, and S. minutulus remains dominant suggesting increased winds. The Postglacial is dominated by Lindavia radiosa, S. minutulus and Nitzschia paleacea. The latter occurs between 9000 and 6000 cal yr BP together with an increase of TOC/TN and total sulphur (TS) suggesting eutrophication with periodic anoxia during the Holocene Thermal Maximum. After 2200 cal yr BP, L. radiosa and Pantocsekiella comensis are dominant suggesting warmer conditions (especially during the Medieval Climate Anomaly) and thermal stability. Increased surface runoff is reflected by higher values of Ti and magnetic susceptibility, suggesting more humidity and enhanced anthropogenic disturbance. Moreover, the appearance of Aulacoseira subarctica is related to a cold and wet period coinciding with the Little Ice Age. In addition to environmental changes, our multiproxy analyses track human impact since the Middle Neolithic.

Additions to the Mastogloia (Bacillariophyceae: Mastogloiales) of the Revillagigedo Archipelago, Mexico

Certain diatom species, mainly those that are conspicuous within an assemblage, may constitute useful references while addressing various ecological and biogeographical issues. This may well be the case with Mastogloia species which are frequently the most diverse diatom taxa in benthic marine assemblages from warm seas. Twenty three new records of Mastogloia taxa collected from several thalli of red and brown macroalgae are here added to the epiphytic diatom floristics of the Revillagigedo Archipelago, summing a total of 51 Mastogloia taxa. Most conspicuous forms were frequent, and several taxa seemed to dominate the assemblages, e.g., Mastogloia binotata, M. cocconeiformis, M. cuneata, M. fimbriata, M. inaequalis, M. ovum-paschale, and M. punctatissima, as well as others recorded earlier. Of the new records, M. asperuloides, M. graciloides, M. peragalloi, and M. mauritiana also appeared frequently. The list includes 8 new records for Mexican waters, although no new taxa for this genus were found. However, because of the few macroalgae thalli inspected, it is expected that further inspection of surfaces of other species of macroalgae, and other substrates, will increase the species richness of Mastogloia recorded for the archipelago.