DISTRIBUTION OF INTERTIDAL DIATOMS ASSOCIATED WITH SEDIMENTS IN YAQUINA ESTUARY,OREGON1,2

Sediment samples and environmental data were collected from November 1973 to August 1974 to analyze the distribution of sediment-associated diatom assemblages relative to vertical, horizontal, and seasonal gradients in Yaquina Estuary, Oregon. The distribution of diatoms was regulated primarily by mean salinity and characteristics of the sediment, i.e., mean sediment size and percentage of organic carbon. Prominent taxa in the river above Yaquina Bay exhibited overlapping distributions along the salinity gradient to a location in brackish water where the mean salinity was approximately 5%_o. At this salinity, a relatively sharp discontinuity in the diatom flora existed which appeared to represent the biochemical and biophysical mechanisms involved in the osmotic regulation of fresh- and brackish-water diatoms. Relatively large disparities m the structure of diatom assemblages were found within relatively small areas of Yaquina Bay. These differences were attributed to properties of the sediment. Differences in diatom assemblages relative to variations in light intensity, water temperature and exposure to intertidal emergence were not apparent from the analysis of field data.     

Ecology and distribution of diatoms in Biscayne Bay,Florida (USA): Implications for bioassessment and paleoenvironmental studies

The spatial and temporal distribution of planktonic, sediment-associated and epiphytic diatoms among 58 sites in Biscayne Bay, Florida was examined in order to identify diatom taxa indicative of different salinity and water quality conditions, geographic locations and habitat types. Assessments were made in contrasting wet and dry seasons in order to develop robust assessment models for salinity and water quality for this region. We found that diatom assemblages differed between nearshore and offshore locations, especially during the wet season when salinity and nutrient gradients were steepest. In the dry season, habitat structure was primary determinant of diatom assemblage composition. Among a suite of physicochemical variables, water depth and sediment total phosphorus (STP) were most strongly associated with diatom assemblage composition in the dry season, while salinity and water total phosphorus (TP) were more important in the wet season. We used indicator species analysis (ISA) to identify taxa that were most abundant and frequent at nearshore and offshore locations, in planktonic, epiphytic and benthic habitats and in contrasting salinity and water quality regimes. Because surface water concentrations of salts, total phosphorus, nitrogen (TN) and organic carbon (TOC) are partly controlled by water management in this region, diatom-based models were produced to infer these variables in modern and retrospective assessments of management-driven changes. Weighted averaging (WA) and weighted averaging partial least squares (WA-PLS) regressions produced reliable estimates of salinity, TP, TN and TOC from diatoms (r² = 0.92, 0.77, 0.77 and 0.71, respectively). Because of their sensitivity to salinity, nutrient and TOC concentrations diatom assemblages should be useful in developing protective nutrient criteria for estuaries and coastal waters of Florida.     

Spatial and temporal distributions of epiphytic diatoms growing on Thalassia testudinum Banks ex König: relationships to water quality

The spatial and temporal distributions of the epiphytic diatom flora on Thalassia testudinum was described within the Florida Bay estuary and at one Atlantic site east of the Florida Keys over a 1-year period. Species of the genus Mastogloia dominated the epiphytic diatom flora (82 out of 332 total species). Nonmetric Multidimensional Scaling (NMDS) and Analysis of Similarity (ANOSIM) revealed four distinct spatial assemblages and two temporal assemblages. Eastern and western Florida Bay assemblages were identified within the estuary. The eastern diatom assemblage was characterized by high relative abundances of Brachysira aponina and Nitzschia liebetruthii, while the western assemblage was characterized by the abundance of Reimerothrix floridensis, particularly during summer. Two diverse and distinct marine assemblages, one located in the Gulf of Mexico along the western edge of Florida Bay and the other behind the Florida reef tract in the Atlantic Ocean, were also identified. Analysis of the spatial distribution of diatoms and water quality characteristics within Florida Bay suggest that these assemblages may be structured by salinity and nutrient availability, particularly P. The Gulf of Mexico and the western Florida Bay assemblages were associated with higher water column salinities and TP concentrations and lower DIN concentrations and TN:TP ratios relative to the eastern Florida Bay assemblage. The temporal variation in diatom assemblages was associated with water temperature, though temporal indicator species were few relative to the number of spatial indicators. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

A comparison of epiphytic diatom communities on <Emphasis Type="Italic">Plocamium cartilagineum</Emphasis> (Plocamiales,Florideophyceae) from two Antarctic areas

Our understanding of diatoms, one of the most important Antarctic primary producers, is based mostly on investigations of plankton, sea-ice, and sediment samples. Herein, we contribute to the limited research devoted to benthic Antarctic diatoms by presenting a study on epiphytic diatom communities sampled in two remote Antarctic regions: Admiralty Bay (maritime Antarctica, Antarctic Peninsula) and Terra Nova Bay (Ross Sea). Recent studies have demonstrated that the most critical factor for the local epiphytic diatom communities was the nature of the substrate. In order to eliminate this factor so we could evaluate other potential controls, we sampled epiphytic diatoms from only one substrate that is common to both regions: the macroalgae Plocamium cartilagineum (L.) Dixon. Thalli of P. cartilagineum and their associated microalgal community was collected in January 2011 (Admiralty Bay) and 2012 (Terra Nova Bay) from a water depth of 5–25 m. Dehydrated macroalgal pieces were placed on stubs and sputter-coated, which allowed observation of diatoms attached to the substrate in their original position using scanning electron microscopy. A total of 72 taxa were observed, of which 31 taxa were common to both regions. Cell abundance and diatom growth form dominance were significantly different in Admiralty Bay and Terra Nova Bay samples. Total diatom abundance was higher in Admiralty Bay samples, dominated by adnate diatoms (Cocconeis spp.), but the number of taxa found as well as the values of ecological indices were higher for samples from the Ross Sea, where motile forms were dominant (Navicula spp.). Our results suggest that Antarctic shallow-water benthic habitats may present a high degree of microniche heterogeneity and highlight the need of fine-scale analyses in microbial studies. We also suggest grazers as a factor that contributes greatly to the observed differences.     

Benthic diatoms of the Vistula River estuary (Northern Poland): Seasonality,substrata preferences,and the influence of water chemistry

Seasonal studies of water bodies in separate branches of the Vistula River estuary in Northern Poland were conducted over 30 months from May 2005 to October 2007. Diatom samples were collected from different substrata from two sites located in the river mouth, which has physical characteristics as a result of a complex interplay of natural and human influences that have taken place over the last 100+ years. The diatom flora growing on hard surfaces near the river banks such as sand, muddy sand, rocks, macroscopic green algae and/or vascular aquatic plants was recorded. All diatom taxa collected were distinguished based on their morphological features using light (LM) and scanning electron microscopy (SEM). A total of 187 species belonging to 61 genera were identified. A canonical correspondence analysis indicated that the diatom assemblages were definitely associated with salinity as well as nutrient concentrations and substratum type. During the study, malformations of diatom valves were observed in 48% of the microphytobenthos samples. Abnormal outline morphology and ornamentation deformities in several individuals of nine different species were recorded, which were mainly in epilithic and epiphytic communities collected from spring to autumn.     

DIATOM PALEOLIMNOLOGY OF TWO FLUVIAL LAKES IN THE ST. LAWRENCE RIVER: A RECONSTRUCTION OF ENVIRONMENTAL CHANGES DURING THE LAST CENTURY

Water quality degradation is a serious concern for the St. Lawrence River. While some environmental data are available for the St. Lawrence ecosystem, long-term monitoring data are generally lacking. To infer past environmental changes, we undertook a paleolimnological assessment of diatom assemblages preserved in four ²¹⁰Pb- and ¹³⁷Cs-dated sediment cores from two fluvial lakes in the river, and used diatom transfer functions to infer past shoreline habitat characteristics. At sites in Lake Saint-François, a fluvial lake downstream from Cornwall, water quality decreased this century in response to human impacts (e.g. macrophyte density and nutrient levels increased). These trends were apparent from an increase in epiphytic diatom taxa, followed by an increase in eutrophic planktonic taxa. Water quality, however, appears to have improved somewhat in response to rehabilitation measures during the last two decades. From a sediment core near Montréal (Lake Saint-Louis), we also noted a large proportion of eutrophic and epiphytic taxa, but less evidence was recorded of a recent improvement in water quality. The diatom-based inference model for habitat characteristics appeared to reconstruct environmental conditions in the St. Lawrence River during the last century. The most notable shift has been an increase in diatom taxa commonly associated with macrophyte substrates. Trends in some of the planktonic diatoms were similar to those recorded in paleolimnological investigations from Lake Ontario, but cores from the river also may be reflecting local environments. This study shows that diatom-based paleolimnological studies are possible in large river systems, if coring sites (e.g. fluvial lakes) are carefully selected.     

Diatom flora of surface sediments of the Amur River Estuary and adjacent areas of the Sea of Japan and the Sea of Okhotsk

Results of the study of the diatom flora from surface sediments of the Amur River Estuary and adjacent areas of the Sea of Japan and the Sea of Okhotsk are presented for the first time. This study revealed high species diversity of diatoms: 287 diatom taxa belonging to 80 genera were identified in 35 surface sediment samples. The ecological composition of diatom assemblages allowed us to evaluate the influence of the Amur River runoff on adjacent areas of the seas.     

PATTERNS OF DISTRIBUTION OF DIATOM ASSEMBLAGES ALONG ENVIRONMENTAL GRADIENTS IN THE SEVERN RIVER ESTUARY,CHESAPEAKE BAY,MARYLAND1

Distribution patterns of diatoms from natural substrates and surface waters of the Severn River, Maryland, are related to salinity and seasonal gradients through time and space by minimum spanning tree cluster analysis and principal components analysis. Assemblages were found to be distributed in a complex but orderly fashion, with primary discontinuties occurring between seasons, and between planktonic and attached forms. Within seasons, benthic groupings are distributed as continua along a horizontal salinity gradient, with one discontinuity at a location with a mean salinity of approximately 7%o. Downstream from this discontinuity, most species do not follow the changing salinity patterns from season to season, and are considered euryhaline for a salinity range of 8–16%o. Upstream from this discontinuity there is a relatively distinct and persistent assemblage of oligohaline indicators. Evidence derived by comparing this study with similar studies from Oregon estuaries indicates that similar distribution patterns, community structures and taxa can be expected to occur in estuaries on the east and west coasts of North America.     

PATTERNS OF DISTRIBUTION OF DIATOM ASSEMBLAGES ALONG ENVIRONMENTAL GRADIENTS IN THE SEVERN RIVER ESTUARY,CHESAPEAKE BAY,MARYLAND1

Distribution patterns of diatoms from natural substrates and surface waters of the Severn River, Maryland, are related to salinity and seasonal gradients through time and spare by minimum spanning tree cluster analysis and principal components analysis. Assemblages were found to be distributed in a complex but orderly fashion, with primary discontinuities occurring between seasons, and between planktonic and attached forms. Within seasons, benthic groupings are distributed as continua along a horizontal salinity gradient, with one discontinuity at a location with a mean salinity of approximately 7‰, Downstream from this discontinuity, most species do not follow the changing salinity patterns from season to season, and are considered euryhaline for a salinity range of 8–16‰. Upstream from this discontinuity there is a relatively distinct and persistent assemblage of oligohaline indicators. Evidence derived by comparing this study with similar studies from Oregon estuaries indicates that similar distribution patterns, community structures and taxa can be expected to occur in estuaries on the east and west coasts of North America.     

PERIPHYTIC DIATOM ASSEMBLAGES FROM HIGH ARCTIC PONDS1

Epiphytic, epilithic, and surface sediment diatom assemblages were identified and enumerated from 35 study ponds on CapeHerschel (78°37″N, 74°42″W), east-central Ellesmere Island, Canada. All the sites are shallow (maximum depth <2 m), clear, oligotrophic, and freshwater. The ponds freeze completely for 10 months of the year. Major ion concentrations are relatively similar among the 35 sites, although environmental gradients exist. Over 130 diatom taxa from 28 genera were identified in the periphyton samples. Marked differences in species composition were evident among the ponds. Moreover, many of the diatoms exhibited varying degrees of microhabitat specificity. Variance partitioning by canonical correspondence analysis showed that 26% of the total variance exhibited by diatom species composition could be accounted for by the measured environmental variables (i.e. 10.2% by habitat and 15.8% by water chemistry). Pondwater alkalinity best explained the distribution of taxa, and weighted averaging regression and calibration were used to develop a transfer function to infer pondwater alkalinity from the diatom assemblages. Other important environmental variables included [Na⁺] for the epilithic and [SiO₂] for the epiphytic assemblages.     

Diatom (Bacillariophyceae) assemblages in tidal environments of Vancouver Island,British Columbia,Canada

To understand distributions of coastal diatoms along Vancouver Island, British Columbia, Canada, this paper describes diatom assemblages observed in 47 surface sediment samples from intertidal environments. One hundred and eighty-four diatom taxa were identified from five transects crossing tidal flats, salt marshes, and freshwater forests in Tofino, Ucluelet, and Port Alberni. Distributions of the diatom assemblages were consistent with those reported elsewhere in the Pacific Northwest, but a few diatom taxa show different trends in their distributions. For example, one benthic species Denticula subtilis shows widespread distributions along the transect in Tofino. An ordination shown by Detrended Correspondence Analysis (DCA) using a combined dataset indicated overlapped scatter plots of diatom assemblages, suggesting that assemblages with similar species compositions are observed in more than one location. Hierarchical and k-means clustering analyses using Euclidean distance recognized unique small groups along each transect. Rank abundance curves show different trends for richness and evenness of diatom assemblages among the five transects.     

The Foram Stress Index: A new tool for environmental assessment of soft-bottom environments using benthic foraminifera. A case study from the Saronikos Gulf,Greece, Eastern Mediterranean

Saronikos Gulf, including the industrial zone of Elefsis Bay and the Port of Piraeus, is one of the most anthropogenically impacted coastal regions of Greece. Distinct assemblages of benthic foraminifers in sediment samples, collected from this gulf in February 2012, defined three zones that reflect abiotic parameters of the sediments (e.g., organic carbon, metal content). A low-diversity assemblage, dominated by stress-tolerant Ammonia tepida and Bulimina spp., was characteristic of samples from Elefsis Bay. Samples from the western and central part of Saronikos Gulf were the most variable with respect to both abiotic parameters and the foraminiferal assemblage, characterized by a mix of stress-tolerant and more sensitive taxa, especially Bolivina spp. and Nonion fabum. Samples from the coast of Salamis and at the eastern sector of the gulf were characterized by a diverse assemblage that included Peneroplis pertusus, miliolids, and a variety of small, epiphytic rotaliid taxa. A new biotic index, the Foram Stress Index (FSI), is based on the relative percentages of two ecological groups of benthic foraminiferal species, grouped according to their tolerance/sensitivity to organic matter enrichment and weighted proportionately to obtain a formula to define five ecological-status classes. The FSI produced three rankings for these samples (Poor, Moderate and Good), that strongly correlate with the macroinvertebrate-classification tool known as the BENTIX Index. The FSI provides a new tool to assess sediment or substrata quality based upon the benthic foraminiferal assemblages, which are a significant component of living meiobenthic communities that are generally not considered in most biotic benthic indices.     

DISTRIBUTION OF DIATOMS IN THE PLANKTON OF YAQUINA ESTUARY,OREGON1

The distributional patterns of diatoms in the plankton of the Yaqnina Estuary, Oregon, were, investigated and related to selected climatic and hydrographic factors. Distribution was strongly influenced by seasonal patterns of rainfall resulting in the introduction of a large volume of fresh water into the estuary during fall and winter. Plankton assemblages in spring, summer and fall had fewer diatom species and exhibited a more rapid rate of change in species composition than in winter. Winter assemblages were further characterized by many pennate diatoms, apparently dislodged from the benthos during periods of high freshwater discharge and silt loads. A statistical measure of community difference indicated an increase in taxonomic homogeneity among assemblages throughout the estuary with the onset of the rainy season in late fall and a gradual transition to a more heterogeneous system again during late spring. Canonical correlation ordered 20 prominent diatom taxa along the salinity gradient and identified possible relationships among certain taxa and selected environmental variables, namely visible light energy and temperature. Redundancy in the species data given the environmental data was only 40%, emphasizing the difficulty in demonstrating a quantitive relationship between plankton dynamics in the field and concurrent measurements of chemical and physical variables.     

Algal Assemblages in Multiple Habitats of Restored and Extant Wetlands

The functional and structural attributes of algal assemblages were studied in 25 restored and 20 extant depressional wetlands in southern central Michigan. Environmental conditions and algal assemblages were compared between restored and extant wetlands and among habitats within wetlands. Restored marshes generally had lower shading by macrophytes, nutrient concentrations, and sediment organic matter. Relative biovolume of non-diatom algae was significantly different among plankton, macrophyte and sediment habitats in restored wetlands, but did not differ between macrophytes and sediments in extant wetlands. Species composition of diatom assemblages was not significantly different between plants and sediments in both restored and extant wetlands. The observed differences in non-diatom algae could not be attributed to any measured environmental variable; however, diatom assemblage differences between habitats increased with light irradiance. Differences in sediment diatom assemblages were observed between restored and extant wetlands and were related to differences in nutrients, pH, and canopy cover. Differences were also observed between epiphytic diatom assemblages in restored and extant wetlands and they were related to light and dissolved oxygen. In summary, differences in light and nutrient availability were the main environmental factors differentiating algal communities in wetlands.     

Diatom assemblages in superficial sediments from the Gulf of Riga,eastern Baltic Sea

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.The results seem to imply that the number of taxa and the abundance of the frustules are affected by runoff from rivers and the degree of eutrophication in different parts of the Gulf. Areas with high eutrophication, e.g. the river estuaries, have diatom assemblages of varying composition, while in areas with moderate eutrophication the composition is almost constant and the influx of freshwater diatoms and littoral periphyton small. The high abundance and low diversity of brackish-marine and brackish, planktonic diatoms seem to be a result of an influx of nutrients and pollutants in the water and bottom sediments. The sea ice diatoms occurring in the Baltic waters and also in the Gulf of Riga tend to be resistant to eutrophication or are even favoured by it.     

Seasonal and microhabitat influences on diatom assemblages and their representation in sediment traps and surface sediments from adjacent High Arctic lakes: Cape Bounty,Melville Island,Nunavut

The spatial (i.e. microhabitat) and temporal (i.e. seasonal) characteristics of diatom assemblages in adjacent High Arctic lakes were studied intensively June–August 2004. These baseline data are used to improve understanding of modern diatom community dynamics, as well to inform paleoenvironmental reconstructions. Diatoms were collected approximately weekly through the melt season from each principal benthic substrate (moss/macrophyte, rock scrapes, littoral sediment), plankton, and sediment traps, and were compared to the uppermost 0.5 cm of a surface core obtained from the deepest part of the lake where sediment cores are routinely collected. Water samples were collected concurrently with diatom samples to investigate species–environment relationships. The lakes share approximately half of their common taxa, the most abundant overall in both lakes being small Cyclotella species. Results of detrended correspondence analysis (DCA) indicate that the largest gradient in species turnover existed between benthic and planktonic communities in both lakes, and that sediment trap and the surface core top samples most closely resemble the planktonic assemblage, with an additional contribution from the lotic environment. Our results indicate clear micro-spatial controls on species assemblages and a degree of disconnection between the benthos and deep lake sediments that manifests as an under-representation of benthic taxa in deep lake surface sediments. These findings are particularly relevant in the context of interpreting the paleoenvironmental record and assessing ecosystem sensitivity to continued climate change.     

Physical microhabitat requirements of freshwater pearl mussels,Margaritifera margaritifera (L.)

Surface sediment diatoms from the east coast of Lake Tanganyika were analysed using ordination and classification techniques, and compared with assemblages previously described from the northern part of the lake. Grain-size analyses were performed on subsamples. Four groups of diatom assemblages were recognised. The first group clusters samples taken in the north, far from the Rusizi river mouth. The second group comprises samples taken on silty sediment along the Tanzanian coast, including one sample taken near the mouth of the Malagarazi river and those from the northernmost part of the lake. The third group comprises surface sediments along the Burundian coast (near Ramba and Magara), and the fourth is characterised by epipsammic taxa. A sample taken near the central arm of the Malagarazi river is included in the latter group. The impact of small rivers on the diatom assemblages in the surface sediments is restricted to the mouth area.     

Incidence of Vibrio cholerae from estuaries of the United States West Coast.

The incidence of Vibrio cholerae in shellfish, sediment, and waters of California, Oregon, and Washington was determined during the summer of 1984. Samples from 24 distinct estuaries were analyzed qualitatively. V. cholerae non-O1 was found in 23 estuaries and in 44.6% of the 529 samples examined. V. cholerae O1 Inaba was isolated from water samples in Morro Bay, Calif. Vibrio mimicus was found in 2.3% of the samples. Cholera enterotoxin was not found in cell-free filtrates of the 100 isolates tested in the Y-1 mouse adrenal cell assay, but heat-labile cytotoxic activity was observed with 3% of the isolates.     

Incidence of Vibrio cholerae from estuaries of the United States West Coast

The incidence of Vibrio cholerae in shellfish, sediment, and waters of California, Oregon, and Washington was determined during the summer of 1984. Samples from 24 distinct estuaries were analyzed qualitatively. V. cholerae non-O1 was found in 23 estuaries and in 44.6% of the 529 samples examined. V. cholerae O1 Inaba was isolated from water samples in Morro Bay, Calif. Vibrio mimicus was found in 2.3% of the samples. Cholera enterotoxin was not found in cell-free filtrates of the 100 isolates tested in the Y-1 mouse adrenal cell assay, but heat-labile cytotoxic activity was observed with 3% of the isolates.