A multi-lake comparison of epilithic diatom communities on natural and artificial substrates

In a multi-season, multi-lake study of epilithic diatom communities, glass slide artificial substrate samplers provided poor representation of communities on natural substrates. Percent similarities between the two communities averaged only 37 over the course of the study. Overall, natural substrates exhibited greater species richness than artificial samplers, particularly during the summer, although this difference was slight. Patterns of selection and inhibition by artificial substrates of individual diatom species varied by both season and lake. Members of the genus Cymbella, particularly C. microcephala, appeared to be the most consistently inhibited, while Achnanthes minutissima was often selected for. In spite of the great differences between the two substrate types, replicability of artificial substrates was very high, and could prove to be a more important quality in monitoring applications than accurate representation of the natural community.     

EFFECTS OF LIGHT AND SUBSTRATE ON THE BENTHIC DIATOMS IN AN OLIGOTROPHIC LAKE: A COMPARISON BETWEEN NATURAL AND ARTIFICIAL SUBSTRATES1

Benthic diatoms form a particularly important community in oligotrophic lakes, but factors influencing their distribution are not well known. This study reports the depth distribution of living motile and total diatoms (living plus dead diatoms) on both natural (from sand to fine organic mud) and artificial substrates in an oligotrophic lake. On artificial substrates, motile diatom densities peaked in abundance (24–30 cells · mm^?2) between 0.6 and 1.9 m depth; on natural sediment surfaces, motile diatoms were generally more numerous and peaked in abundance (925 cells · mm^?2) at 1.3 m depth. Total diatom densities on artificial substrates were highest (1260 valves · mm^?2) at 0.6 m depth, with very low values below 3 m depth; on natural sediment surfaces, total diatom abundances were generally much higher (21600 valves · mm^?2) at 3 m depth and declined gradually with depth. Significant relationships were found between light and diatom densities on the artificial substrate. Ordination analysis indicated that substrate type significantly correlated with the variation of diatom composition on artificial and natural substrates. Our results suggest that in oligotrophic lakes, light influences benthic diatom abundance, whereas substrate type has more influence on benthic diatom composition.     

Early Colonization Patterns of Diatoms and Protozoa in Fourteen Fresh-water Lakes1

ABSTRACT. Polyurethane substrates were anchored near the surface of 14 lakes in the northern tip of the lower peninsula of Michigan. I wo substrates were removed from each take and taken to the laboratory after 1, 3, 6, 15, and 21 days of exposure. At the laboratory, one substrate was used for determining the number of species of diatoms and the other for protozoa. A cluster analysis of the matrix of Jaccard's coefficients for all diatom samples from all lakes showed that virtually all samples from any given lake consistently clustered together. This indicates that, with respect to species occurrence, distinct and compositionally stable diatom assemblages formed on the substrates in fewer than 21 days. Analysis of all protozoan samples from all lakes did not show such clustering, however, and the correspondence of clusters for protozoan and diatom communities for the 14 lakes was not particularly good. This suggests that the link between the two groups at the species level is not particularly strong during the early phases of artificial substrate colonization.     

Studies on Plover Cove Reservoir, Hong Kong

The species composition and year-month frequency together with the abundance of the four periphytic communities of Plover Cove Reservoir (the epiphyton, epilithon, epipelon and epipsammon) were compared both in terms of all species present and in terms of major (dominant/frequent) species using the ‘circle’ method. All four communities were similar in terms of overall species composition but the richest variety of species occurred in the epiphyton. The diatom floras on wood and rock surfaces closely resembled each other as did the two sand grain floras. The former floras were, however, much more diversified than the latter floras and stood distinctly apart from them. In terms of their dominant/frequent species, the epipelic/epipsammic communities and the epiphytic/epilithic communities had the same number of common taxa (three), a further indication of the closeness between the two communities in each combination. On the other hand, the fact that the three common taxa were different for each combination again reveals the distinct differences between the two combinations. Investigations concerning the effect of the nature of the substrate on diatom growth revealed that it had little effect in qualitative terms. Quantitatively there would appear to be some effect, since differences in abundance and frequency and thus in the seasonal cycle of diatoms growing on different substrates were observed. The conditions in the microhabitats of each substrate undoubtedly determined the dominance and abundance of the flora. However, the effect of the nature of the various substrates on diatom growth varied from species to species and in general, the substrates showed little qualitative selectivity. Thus, no truly differential species were found to any great extent on any of the four substrates. The relationships between the growth of these four periphytic diatom communities and the physical and chemical conditions have also been investigated in terms of cell number and chlorophyll content. Both graphical and statistical analyses of the results are discussed, and it is suggested that fluctuations in water level, temperature and nutrients (especially silica, nitrate and phosphate) are the major factors governing the seasonal patterns of variation in periphyton standing crop. Thus, diatom growth is maximum when nutrient concentrations and water level are high and when water temperature is low, and as temperature increases and nutrients decrease so diatom growth falls. It is probable that an interplay of these factors, together with the detrimental effects of heavy rainfall and typhoons during summer, is responsible for the seasonal changes in periphyton in Plover Cove Reservoir exhibiting a winter peak as opposed to the commonly occurring spring and autumn growth peaks.     

Microbial transformation of distinct exogenous substrates into analogous composition of recalcitrant dissolved organic matter

Oceanic dissolved organic matter (DOM) comprises a complex molecular mixture which is typically refractory and homogenous in the deep layers of the ocean. Though the refractory nature of deep-sea DOM is increasingly attributed to microbial metabolism, it remains unexplored whether ubiquitous microbial metabolism of distinct carbon substrates could lead to similar molecular composition of refractory DOM. Here, we conducted microbial incubation experiments using four typically bioavailable substrates (L-alanine, trehalose, sediment DOM extract, and diatom lysate) to investigate how exogenous substrates are transformed by a natural microbial assemblage. The results showed that although each-substrate-amendment induced different changes in the initial microbial assemblage and the amended substrates were almost depleted after 90 days of dark incubation, the bacterial community compositions became similar in all incubations on day 90. Correspondingly, revealed by ultra-high resolution mass spectrometry, molecular composition of DOM in all incubations became compositionally consistent with recalcitrant DOM and similar toward that of DOM from the deep-sea. These results indicate that while the composition of natural microbial communities can shift with substrate exposures, long-term microbial transformation of distinct substrates can ultimately lead to a similar refractory DOM composition. These findings provide an explanation for the homogeneous and refractory features of deep-sea DOM.     

A comparison of diatom community structure on natural and artificial substrata

Artificial substrata have been used in diatom studies for almost 100 years. However, concern still exists over whether diatom communities developing on artificial substrata accurately represent communities developing on natural substrata. This study compares the diatom communities colonising glass slides and clay tiles in two coastal dune lakes, and compares these communities to the naturally occurring communities in the epipelon, epilithon, and epiphyton. Both glass microslides and clay tiles, incubated for three separate periods ranging from 29 to 68 days, resulted in replicate substratum samples supporting similar diatom community compositions at each site. The degree of variation between artificial substrata communities at different sites, and between the two artificial substrata types, was generally no more than the degree of variation between communities on different types of natural substrata. Additionally, the composition of the diatom communities on the artificial substrata was representative of the community composition on the natural substrata. The effects of incubation period and siting are discussed.     

Do artificial substrates favor nonindigenous fouling species over native species?

Exotic species are prominent constituents of fouling communities. If exotic fouling organisms colonize or compete better on a wider range of substrate types than native species, this may partially account for their high abundance in estuaries and bays. We used four artificial and four naturally occurring substrate types to compare initial settlement and percent cover of native and exotic fouling species through six months of community development. Both the identity of common taxa and the total number of species colonizing artificial versus natural substrate types were similar. Despite the similarities in species richness, relative abundance patterns between natural and artificial substrate types varied, particularly as the communities developed. Native species were initially in equal abundance on natural and artificial substrate types. Initially, the two most common exotic species, the colonial tunicates, Botrylloides violaceus Ritter and Forsyth and Botryllus schlosseri (Pallas), were also in similar, but low, abundance on artificial and natural substrates. As the communities developed, there was little change in abundance of exotic or native species on natural substrates. However, on artificial substrates the exotic tunicates increased dramatically and native species declined in abundance. Artificial surfaces may provide a novel context for competitive interactions giving exotic species a more “level playing field” in an environment for which they otherwise might not be as well adapted compared to long-resident native species. Additions of artificial substrates to nearshore environments may disproportionately favor exotic species by increasing local sources of exotic propagules to colonize all types of substrates.     

Micro-environmental characteristics of filamentous algal communities in flowing freshwaters

SUMMARY. 1. Filamentous algae in flowing freshwaters can represent a spatially and temporally distinct sub-habitat for epiphytic diatom communities. This sub-habitat is described in a low discharge, spring-fed stream with extensive filamentous green algal mats, and in a tuft of Cladophora glomerata (L.) Kützing from a large river.
2. Oxygen micro-electrodes, a thermistor current velocity probe, a standard pH probe and water chemistry were employed to assess spatial heterogeneity. Temporal patterns of epiphyte colonization were evaluated on filamentous artificial substrates.
3. There were steep spatial gradients in the low discharge stream. At mid-day, O₂ ranged from 0–1.5 times air-saturated O₂ concentrations, pH varied from 7.25–8.0, and current velocity spanned 0–0.5 m s⁻¹. Areas near the surface of algal mats had high O₂, pH and current velocity. These patterns were correlated with epiphyte community structure.
4. In the interior of C. glomerata tufts O₂ concentration was raised and current velocity depressed compared to the surrounding water, even when external current velocity was as high as 0.4 m s⁻¹.
5. After thirty-five days of colonization of artificial substrate in the low discharge environment, epiphyte communities were similar to those on filamentous atgae. Epiphyte diversity on artificial substrates subsequently decreased compared to natural substrates as did the similarity between the types on substrates, suggesting that microscale renewal of epiphyte habitat (growth of filamentous algae) maintains high epiphytic diversity.     

SHORT-TERM STANDING CROP AND DIVERSITY OF PERIPHYTIC DIATOMS IN A EUTROPHIC RESERVOIR1

Adverse weather and resultant turbulence caused sloughing of attached diatom communities during the first two weeks of colonization on artificial substrates. In contrast to Pacific macroalgal systems, older communities (8–12 d) were the most affected by wave action. Ash-free dry weight of the periphyton and diatom cell density generally increased, except following periods of high turbulence when losses of up to 80% occurred. The maximum cell density (4 × 10⁵ diatoms · cm^?2) and ash-free dry weight (2.9 mg · cm^?2) are among the highest reported for similar conditions. Percent transmittance through the growth layer correlated significantly with cell density and ash-free dry weight and is recommended as a rapid method for measuring the relative accumulation of periphyton. Diatom diversity generally increased throughout the study period and did not clearly reflect the effects of disturbance as did standing crop. Comparisons of diatom diversity and community composition indicated that the three overlapping growth series were not significantly different and samples collected on the same date were not more similar than those of identical age. Combined with previous evidence, the present study indicates that the first two weeks of substrate exposure in the summer represented a colonization phase followed by rapid microsuccession.     

COMPARISON OF ATTACHED DIATOM COMMUNITIES ON NATURAL AND ARTIFICIAL SUBSTRATES1

A study of attached diatom communities on artificial and natural substrates was conducted in Wheelwright Pond, New Hampshire, during 1975. There were differences in the species composition growing on artificial glass slides and natural substrates. The slides favored the accumulation of Achnanthes minutissima Kütz. and decreased the relative abundance of Eunotia incisa W. Sm. ex. Greg. and Cocconeis placentula v. euglypta (Ehr.) Cleve. Large growths of planktonic species were also noted on the slides. Compositional differences between slides positioned at 15–30 cm (upper) and 1 m (lower) from the surface of the water were minimal. A similar community composition of periphytic diatoms was found on five aquatic macrophytes.     

Experimental demonstration of the roles of bacteria and bacterivorous protozoa in plankton nutrient cycles

We have used a model food chain composed of a natural bacterial assemblage, a pennate diatom and a bacterivorous microflagellate to investigate the factors controlling the relative importance of bacteria and protozoa as sources for regenerated nitrogen in plankton communities. In bacterized diatom cultures in which diatom growth was nitrogen-limited, the carbon:nitrogen (C:N) ratio of the bacterial substrate greatly affected which population was responsible for the uptake of nitrogen. When nitrogen was added as NH ₄ ⁺ and the cultures were supplemented with glucose, the bacteria competed successfully with the algae for NH ₄ ⁺ and prevented the growth of algae by rapidly assimilating all NH ₄ ⁺ in the cultures. Bacterivorous protozoa inoculated into these cultures grazed the bacterial population and remineralized NH ₄ ⁺ , thus relieving the nitrogen limitation of algal growth and allowing an increase in algal biomass. In contrast, bacteria in cultures supplemented with the amino acid glycine (C:N = 2) were major remineralizers of nitrogen, and the influence of protozoan grazing was minimal. We conclude that the relative importance of bacteria and protozoa as nutrient regenerators in the detrital food loop is dependent largely on the overall carbon:nutrient ratio of the bacterial substrate. The role of bacterivorous protozoa as remineralizers of a growth-limiting nutrient is maximal in situations where the carbon:nutrient ratio of the bacterial substrate is high.     

Analysis of Factors Affecting the Accuracy, Reproducibility, and Interpretation of Microbial Community Carbon Source Utilization Patterns

We determined factors that affect responses of bacterial isolates and model bacterial communities to the 95 carbon substrates in Biolog microtiter plates. For isolates and communities of three to six bacterial strains, substrate oxidation rates were typically nonlinear and were delayed by dilution of the inoculum. When inoculum density was controlled, patterns of positive and negative responses exhibited by microbial communities to each of the carbon sources were reproducible. Rates and extents of substrate oxidation by the communities were also reproducible but were not simply the sum of those exhibited by community members when tested separately. Replicates of the same model community clustered when analyzed by principal-components analysis (PCA), and model communities with different compositions were clearly separated on the first PCA axis, which accounted for >60% of the dataset variation. PCA discrimination among different model communities depended on the extent to which specific substrates were oxidized. However, the substrates interpreted by PCA to be most significant in distinguishing the communities changed with reading time, reflecting the nonlinearity of substrate oxidation rates. Although whole-community substrate utilization profiles were reproducible signatures for a given community, the extent of oxidation of specific substrates and the numbers or activities of microorganisms using those substrates in a given community were not correlated. Replicate soil samples varied significantly in the rate and extent of oxidation of seven tested substrates, suggesting microscale heterogeneity in composition of the soil microbial community.     

SYSTEMATICS OF PRASIOLA AND PHYLOGENETIC POSITIONING OF THE PRASIOLALES (CHLOROPHYTA)

Sellman, S. M., Johansen, J. R. & Coburn, M. M. Department of Biology, John Carroll University, University Heights, OH 44118 USA The diatom composition of natural substrates at a single site were compared with that of the gut contents of three species of fish: stoneroller minnows, bluntnose minnows, and common shiners. Seven samples of each type were collected on a single day from a single pool in a headwater stream. Cluster analysis showed that diatom species composition clustered by fish species, with common shiners being a totally exclusive cluster, while natural substrates were scattered within the stoneroller and bluntnose clusters. Both richness and Shannon diversity were higher in fish gut samples than in the samples collected by humans, with stonerollers having the greatest diversity. When water quality indices calculated from the diatom floras recovered in these samples were compared, it was surprising to see that these indices consistently were better in fish gut samples than in samples collected by researchers. Common shiners particularly differed, a result possibly due to the fact that they apparently fed off of Cladophora and the highly oxygenated rock wall where the stream cascaded into the pool. In no case was the difference between stonerollers and natural substrates significantly different. Furthermore, samples from natural substrates had an internal similarity not significantly different from their similarity to samples in stoneroller and bluntnose guts. Our data thus consistently indicate that stoneroller minnows are excellent samplers that efficiently collect diverse, representative diatom samples.     

Growth form analysis of epiphytic diatom communities of Terra Nova Bay (Ross Sea, Antarctica)

Diatoms have been long collected from the Southern Ocean but almost no data exist for epiphytic communities, despite their high ecological significance as an important food source in Antarctic coastal food chains. Here, we present a first growth form analysis of diatoms associated with rhodophyte hosts from Terra Nova Bay, Ross Sea, Antarctica. We performed this study to gather baseline information on the species composition of epiphytic diatom communities, determine the influence of some environmental variables on the diatom distribution patterns, and assess the caveats that must be taken into account in terms of sampling design. Macroalgal material was collected during the Italian Antarctic expeditions between 1990 and 2004. Epiphytic diatoms were studied by means of scanning electron microscopy. In terms of growth forms, there were no significant differences between the diatom communities on the different macroalgal host species. Motile (mainly small-celled Navicula perminuta and other Navicula spp.) and adnate (Cocconeis spp.) diatoms dominated the community throughout the study period. Many of the macroalgal blades examined were also covered by epiphytic animals (calcareous bryozoans, hydroids) over most of their surface, with a significant effect on the associated diatom community structure. Our findings suggest that the bio-physicochemical characteristics of each sampling site affected the epiphytic diatom communities more than the substrate type provided by the macroalgal host or the sampling depth.     

Cadmium and lead toxicity on tropical freshwater periphyton communities under laboratory-based mesocosm experiments

Periphyton constitutes an important community that is useful for assessment of ecological conditions in lotic systems. The objective of this study was to assess the effects of different mixtures of Cd and Pb on periphyton growth as well as Cd and Pb mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural periphyton community sampled from the Monjolinho River (South of Brazil) was inoculated into five experimental systems containing clean glass substrates for periphyton colonization. The communities were exposed to mixtures of dissolved Cd and Pb concentrations of 0.01 and 0.1 mg l⁻¹ Cd and 0.033 and 0.1 mg l⁻¹ Pb. Periphyton ash-free dry weight, growth rate, diatom cell density and diatom community composition were analyzed on samples collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg l⁻¹) has negative effects on periphyton growth while high concentration of Pb (0.1 mg l⁻¹) decreased the toxic effects of Cd on periphyton growth. Shifts in species composition (development of more resistant species like Achnanthidium minutissimum and reduction of sensitive ones like Cymbopleura naviculiformis, Fragilaria capucina, Navicula cryptocephala, Encyonema silesiacum, Eunotia bilunaris, and Gomphonema parvulum), decreases in species diversity of diatom communities with increasing Cd and Pb concentrations and exposure duration have been demonstrated in this study making diatom communities appropriate monitors of metal mixtures in aquatic systems.     

Influence of easily degradable naturally occurring carbon substrates on biodegradation of monosubstituted phenols by aquatic bacteria

The influence of readily degradable, naturally occurring carbon substrates on the biodegradation of several monosubstitued phenols (m-cresol, m-aminophenol, p-chlorophenol) was examined. The natural substrate classes used were amino acids, carbohydrates, and fatty acids. Samples of the microbial community from Lake Michie, a mesotrophic reservoir, were adapted to different levels of representatives from each natural substrate class in chemostats. After an extended adaptation period, the ability of the microbial community to degrade the monosubstituted phenols was determined by using a radiolabeled substrate uptake and mineralization method. Several microbiological characteristics of the communities were also measured. Adaptation to increasing concentrations of amino acids, carbohydrates, or fatty acids enhanced the ability of the microbial community to degrade all three phenols. The stimulation was largest for m-cresol and m-aminophenol. The mechanism responsible for the enhancement of monosubstituted phenol metabolism was not clearly identified, but the observation that adaptation to amino acids also increased the biodegradation of glucose and, to a lesser extent, naphthalene suggests a general stimulation of microbial metabolism. This study demonstrates that prior exposure to labile, natural substrates can significantly enhance the ability of aquatic microbial communities to respond to xenobiotics.     

Reattachment of certain species of mytilid bivalves to various substrates

Reattachment to various substrates (concrete, wood, and iron) was studied in three species of Mytilidae in the laboratory. Each of the investigated species exhibited substrate selectivity. The most successful substrate colonization occurred on concrete, which, owing to its physicochemical properties, proved to be more appropriate for rapid and firm anchorage of the mollusks. Mytilid response to any specific substrate, judged from the reattachment rate and substrate preference, may indirectly indicate the possibile existence of natural communities of organisms associated with a corresponding biotope.     

Effects of physical disturbance and canopy cover on attached diatom community structure in an Idaho stream

A field experiment was conducted to determine the effect of disturbance frequency on diatom communities established on artificial substrates within an open canopy site and a closed canopy site of a 3rd order stream. The open canopy site (OCS) had a total of 80 diatom taxa colonizing the substrates, while the closed canopy site (CCS) had only 55 taxa. Cluster analysis revealed that the two sites had distinct diatom communities, although the most common species were similar between sites. There was no effect of disturbance frequency on species diversity (H') at OCS, however species diversity significantly decreased as disturbance frequency increased at CCS. At OCS, Amphora perpusilla increased in abundance as disturbance frequency increased, while Navicula lanceolata abundance decreased as disturbance increased. At CCS, Cocconeis placentula v. euglypta remained dominant regardless of disturbance frequency. The results suggest that some diatom species may be shade adapted, which may explain the site-specific responses. In addition, diatom growth-forms may explain the within site taxon-specific responses to disturbance. For example, Achnanthes sp. and Cocconeis sp., small horizontal forms, were predominant on the high disturbance substrates. Vertical or large horizontal forms may be mechanically removed by frequent physical disturbance allowing such small horizontal forms to become abundant. Frequent disturbance, by maintaining the community in an early stage of development, directly influences the diatom assemblage on rocks in streams.     

Effects of nutrient (N,P, C) enrichment upon the littoral diatom community of an oligotrophic high-mountain lake

The effects of nutrient additions upon the epilithic diatom communities and the algal standing crop were investigated in the oligotrophic, softwater Lake Piccolo Naret, situated in the Swiss alps. Nutrient-diffusing flower pot substrates were filled with either N (0.15 mol NaNO₃), P (0.015 mol Na₂HPO₄) or C (0.15 mol NaHCO₃) or combinations of them. Twenty-five pots representing eight treatments were placed into the lake in July 1991 and sampled after 42 days of exposure.On the surfaces of all pots containing P we measured higher algal biomasses as on the control pots. The chlorophyll-a maximum of 12.9 µg cm^{– 2} was obtained on NPC pots (0.47 µg cm^{– 2} on control pots). On pots with P, NP or NPC supply high amounts of green algae were detected, also reflected in an increased chl-b/chl-c ratio related to the controls which showed algal communities dominated by diatoms.The diatom communities on the control pots as well as on the pots with N, P and NP had a structure similar to the epilithic community in Lake Piccolo Naret (dominance identity > 58 %). However, the community structures of the diatoms from pots with C addition (C, NC, PC and NPC) differed considerably. This is discussed in view of the cell densities of dominant diatom species. For further comparisons the results of two additional high-mountain lakes are used. By means of a cluster analysis it could be shown that epilithic diatom communities were considerably influenced by C addition, while N and P supply were of minor importance.     

Epilithic and epipelic diatoms in the Sandusky River,with emphasis on species diversity and water pollution

Benthic diatom communities were collected seasonally from silty and rocky substrates to survey the water quality of the Sandusky River. Even though species composition was highly variable along the river, recurrent changes in relative abundance of specific diatom taxa and changes in overall community composition delineated areas where discharge of treated sewage affected water quality of the river. Changes in species diversity (Shannon formula), not decreases in diversity, marked the site where greatest pollution had occurred. Problems with using species diversity indices to indicate pollution tend to be related to predicting decreases in diversity in response to decreases in water quality. Evidence in the Sandusky River and the theories of diatom community dynamics suggest that species diversity can be greater in polluted areas than less polluted areas.