Emigration and immigration can be important determinants of benthic diatom assemblages in streams

SUMMARY.

• 1 Interspecific differences in diatom abundances in stream drift (plankton), immigration, and natural benthic assemblages were compared to assess the importance of emigration and immigration in benthic diatom community dynamics. Water samples were collected throughout a 24-h period to measure diel changes in diatom drift abundances and to estimate benthic diatom emigration rates. Immigration was assessed with 24-h colonization of bare tiles.
• 2 Dissimilarity in species composition of drift, immigration, and natural substrate assemblages indicated differential emigration and immigration among diatom species.
• 3 A mathematical model indicated that reproduction by diatoms in the plankton could not account for diel drift peaks and that diel variation in drift was an informative measure of benthic diatom emigration.
• 4 Emigration and immigration of some species constituted substantial proportions of diatom abundances on natural substrata. We conclude that emigration into the drift and immigration onto substrata can be important processes that regulate benthic diatom species composition and standing crop in streams.

     

Phosphate limitation influences the sensitivity to copper in periphytic algae

1. To assess the influence of nutrient limitation on copper toxicity, periphitic communities from an oligotrophic stream were exposed to copper for six to 12 days with and without the supply of nutrients (mainly P). 2. In contrast to the hypothesis that nutrient cycling in mature biofilms would protect them from Cu toxicity, low and high biomass biofilms did not differ in their physiological response to copper after 6 days of exposure. 3. A clear influence of P‐limitation on copper toxicity was observed. Periphytic communities that were previously fertilised for 18 days were three times more tolerant than control communities indicating that P‐limitation enhanced Cu toxicity and tolerance induction were probably related to the higher P‐availability. In addition, a compensation of Cu toxicity after P‐addition was observed in the long‐term (after 12 days). 4. We conclude that periphyton from oligotrophic streams is more sensitive to copper than periphyton from fertilised streams, and that therefore a higher effect of chronic copper exposure is expected to occur in oligotrophic P‐limited fluvial systems. 5. Extrapolation of our results to the area of study (Catalonia, north‐east of Spain) indicates that while the levels of Cu commonly found in the zone may negatively affect the periphyton from oligotrophic streams, because of the interaction between Cu and P, they are not able to control the growth of nuisance algae which is common under high nutrient conditions.     

Transported biofilms and their influence on subsequent macrofouling colonization

Biofilm organisms such as diatoms are potential regulators of global macrofouling dispersal because they ubiquitously colonize submerged surfaces, resist antifouling efforts and frequently alter larval recruitment. Although ships continually deliver biofilms to foreign ports, it is unclear how transport shapes biofilm microbial structure and subsequent macrofouling colonization. This study demonstrates that different ship hull coatings and transport methods change diatom assemblage composition in transported coastal marine biofilms. Assemblages carried on the hull experienced significant cell losses and changes in composition through hydrodynamic stress, whereas those that underwent sheltered transport, even through freshwater, were largely unaltered. Coatings and their associated biofilms shaped distinct macrofouling communities and affected recruitment for one third of all species, while biofilms from different transport treatments had little effect on macrofouling colonization. These results demonstrate that transport conditions can shape diatom assemblages in biofilms carried by ships, but the properties of the underlying coatings are mainly responsible for subsequent macrofouling. The methods by which organisms colonize and are transferred by ships have implications for their distribution, establishment and invasion success.     

Changes in diatom-dominated biofilms during simulated improvements in water quality: implications for diatom-based monitoring in rivers

Although benthic diatoms are used to assess river water quality, there are few data on the rate at which diatom assemblages react to changes in water quality. The aim of this study was to assess the reaction time of diatoms and to discuss the changes occurring during water quality improvement on the basis of their autecological characteristics. In order to simulate this improvement, diatom-dominated biofilms grown on artificial sandstone substrata were transferred from several polluted rivers to an unpolluted river. They were sampled three times: before transfer and 1 and 2 months after transfer. The ecology and growth-forms of the taxa explained most of the changes in species composition observed during the experiment. Adnate diatoms gradually replaced motile and stalked taxa. Gomphonema parvulum, a stalked diatom positioned vertically in the biofilm, is adapted for light and space competition in high-density algal biofilms. When transferred to an unpolluted site, this growth-form is less competitive and does not tolerate the high grazing pressure. Fistulifera saprophila is a single celled motile diatom, living in organic matrices. When the artificial substrata were transferred to the unpolluted site, this particular ecological niche disappeared quickly. On the other hand, Achnanthidium minutissimum, which is considered to be cosmopolitan and an early colonizer, increased during the first month of transfer and then decreased. It was gradually replaced by A. biasolettianum, which was the taxon best suited to this pristine stream. The changes observed differed between treatments depending on the species composition and architecture of the biofilms. In particular, biofilms dominated by stalked and motile diatoms were more quickly modified than those dominated by small motile diatoms. The diatom index reflects these changes, and its values showed that about 60 days following a water quality improvement were necessary for transferred diatom assemblages to reach diatom index values similar as those at the unpolluted river.     

Mechanisms of benthic algal recovery following spates: comparison of simulated and natural events

We conducted a manipulative field experiment to examine individual and interactive effects of scour and short-term nutrient enrichment (4 h exposure) on postspate recovery of benthic algae in a desert stream. We then compared recovery from these simulated-spate conditions to algal recovery patterns following a natural spate that increased water-column nutrient levels for 2 weeks. That event differentially scoured communities on artificial substrata in place for a long-term experiment, significantly reducing biomass in 49-day-old communities but causing no significant reduction of biomass in older, 133-day-old communities. Thus, we were able to examine recovery of scoured and non-scoured benthic algal communities under natural post-spate conditions. Both natural and simulated spates reduced actual and relative abundances of diatoms within communities. In the manipulative experiment, scoured communities accrued biomass more rapidly than those not subjected to scour, but short-term enrichment had not effect. Accrual of diatoms and green algae was stimulated by the scour manipulations, while cyanobacteria maintained equal rates of growth in all treatments. Following the natural spate, diatom and green-algal densities increased in scoured communities, but recovery of algal biomass was slow on both scoured and non-scoured substrata, primarily because cyanobacteria, the dominant algal group on all tiles, did not increase under exposure to highly nitrate-enriched waters. Rates of algal cell accrual were inversely correlated with the amount of algal biomass present at the start of a recovery sequence. Algal immigration rates measured immediately after the natural spate and during an interflood period in the same season did not differ, indicating that the algal drift pool was not augmented by disturbance. Benthic algal recovery following spates is strongly influenced by the degree of scour generated by the event, but recovery patterns are also affected by the length of post-spate enrichment and the taxonomic composition of the affected community.     

Response of diatom indices to simulated water quality improvements in a river

Various diatom indices are routinely used in European countries to monitor water quality in waterways. In order to assess their sensitivities and their integration interval after a sudden and lasting environmental change, epilithic diatom biofilms were transferred from several polluted rivers to an unpolluted stream. To monitor the changes of the index values, the biofilms were sampled in a first experiment 20 and 40 days after transfer, and in a second experiment 30 and 60 days after transfer. Sensitivities of the indices to the water quality improvement were assessed calculating the differences between the index values of the reference and the transferred assemblages. Some indices have intermediate sensitivities (BDI, GDI, ILM, SLA), others higher sensitivities (CEE, EPI, ROT, SPI, TDI). The integration interval of these indices was 40–60 days. Some differences were observed between the indices, but their results were homogeneous when compared to those obtained with other metrics such as Bray-Curtis or Chord distances, used to assess the difference between the transferred and the reference diatom assemblages. These other metrics showed that even after 60 days, the transferred assemblages still differed from the reference. This underlines that metrics do not have the same integration intervals and do not assess the same stresses; the choice of the metric used to assess water quality is of prime importance.     

Responses and structural recovery of periphytic diatom communities after short-term disturbance in some rivers (Hanoi, Vietnam)

Field transfer experiments of periphytic diatom assemblages developed on artificial substrates were set up to assess the responses of those communities to environmental disturbances. The glass slides were positioned for colonization at the relatively unpolluted site (Red, in the Red River) and at the heavily polluted site (TL, in the To Lich River) in the beginning of the experiment. After a period of 2?weeks, the colonized glass slides were concomitantly transferred from the unpolluted Red site to the heavily polluted TL site and to the moderate polluted site (NT₂, in the Nhue River) and, conversely, from the TL site to the Red site, and then to the NT₂ site. The responses and the adapting capacity of periphytic diatom communities to environmental changes were assessed through the cell density, diversity index, species richness, taxonomic composition, and diatom indices after 2 and 4?weeks of transfer periods. For all transfers except for the transfer from the Red to the TL site in which the growth inhibition of diatom cells was found, the diatom density significantly increased until the end of the experiment. Thus, the diatom communities have expressed their pollution tolerance or sensitivities by changing their composition to adapt themselves to environmental changes. Characteristic species of the Red site (Gyrosigma scalproides, Navicula recens) were replaced by Nitzschia palea, Nitzschia umbonata, Aulacoseira granulate typical species of the NT₂ site, in the biofilm transferred from the Red site to the NT₂ site. The relative abundances of typical diatom species of the Red site proliferated in the biofilm transferred from the TL site to the Red site. The replacement of periphytic diatom communities appeared after the transfer from the second week at the different sites. The slow shift of the species towards the typical species at the TL site could result from the organized structure of diatoms within biofilm before the transfer from the Red site to the TL site. The shifts in values of the Index of Specific Polluosensitivity and Diatom Assemblage Index to organic pollution throughout the experiment indicated the clear sensitivity of these indices to water quality changes.     

The potential effects of energy related activities on the seasonal trajectories of epiphytic marine diatoms

Seasonal successional trajectories of transplanted and experimental diatom communities were studied during the summer of 1973. Manipulation of these diatom assemblages was accomplished through the development of an in situ experimental apparatus capable of incubating these organisms without doing violence to the community itself.In one set of experiments the effects of water quality were tested on the development of inocula from grossly similar but fairly distant locations. In another set the native inoculum was incubated in the continual presence of Fe, Cu, Cr, Pb, Zn and crude oil. Seasonal succession took place in all of the control and experimental communities. During the course of succession the trajectories of assemblages under some conditions converged while others diverged. Since the random fluctuations in the environment were constant for all assemblages, the abundances of individual species were due to niche packing and interspecific restraints on the biotic potential of selected diatom species as well as the changes in water quality. The most diverse community was an experimentally mixed one. The high diversity of this community was probably due to niche packing a phenomenon which restricted the realized niches of many species and hindered their blooming. Paradoxically twice as many species (40%) had their greatest niche breadth in the mixed community as did species in the transplanted (20%) or native controls (17%). Enrichment of the incubation medium with heavy metals and oil altered the community structure and diversity of most experimental vessels. Growth of some species was depressed while that of others was enhanced. The trajectories of the communities enriched with oil and Pb were quite similar throughout the summer. The Cu and Cr assemblages initially followed the trajectory of oil and Pb but later diverged. Greatest species diversity was consistantly found in the community incubated in the presence of Cu. The Fe enriched community generally diverged from all the others. Recurrent group analysis identified distinctive groups of species for each of the experimental assemblages as well as controls.The response of these diatom communities incubated under natural conditions were characteristic of resilient communities in which populations with different structures were quickly established.Supported by ERDA Contract E (11-1) 3254, Reference Number (COO) 3254-28. The authors would like to acknowledge Dr. Howard Rubin for his assistance in writing the many computer programs used in this investigation.This paper represents a revised expansion of a thesis project accepted by the CCNY Biology Faculty in partial fulfillment of the requirements of the M.A. degree in September 1976.     

Simultaneous ammonium-nitrogen and copper removal, and copper recovery using nitrifying biofilm from the ultra-compact biofilm reactor

Simultaneous ammonium-nitrogen (NH(4)(+)-N) and copper removal, and copper recovery in synthetic wastewater using nitrifying biofilm from an ultra-compact biofilm reactor (UCBR) was demonstrated in batch studies, which consisted of three phases: Phase 1 for NH(4)(+)-N and copper removals, Phase 2 for copper recovery, and Phase 3 for NH(4)(+)-N removal. The results showed that more than 96.3% of copper was removed within 60min, while 60.1% of the adsorbed copper was recovered through rinsing the biofilms with 0.1mM of ethylenediaminetetraacetic acid (EDTA). The nitrifying biofilm was able to adsorb 0.245mg of copper/g of biofilms. After recovery treatment, 29.4% of copper remained bound within the nitrifying biofilms. No significant inhibitory effects towards NH(4)(+)-N removal in the presence of 0.92mg copper/L was noted in Phase 1 compared with the control test. However, lower initial pH condition in the recovery process and the accumulation of copper on the biofilm led to 50% inhibition on NH(4)(+)-N removal efficiency in the subsequent phase.     

Ecology of the Major Periphytic Diatom Communities from the Mesta River,Bulgaria

Epilithon, epiphyton, epipelon, epipsammon and plocon diatom samples and water chemistry samples were collected bimonthly from 11 stations along the Mesta River, Bulgaria between December 1989 and April 1991. Principal component analysis (PCA), correlation, and dominance analysis were employed for describing the seasonal dynamics of diatom assemblages and estimating the correlation between diatom distribution and the physico-chemical parameters. All periphytic communities were compared by PCA, MANOVA and Fisher's LSD multiple comparison test. Ionic strength and eutrophication were the major abiotic factors affecting diatom distribution in the epilithon, epiphyton, epipelon and epipsammon. Current velocity had an important influence on the diatom assemblages from the epilithon and epiphyton. Epilithon showed the lowest correlation with most of the environmental factors and had significantly lower species diversity than epiphyton, epipelon and epipsammon. Multivariate analysis of the diatom data suggested that in all benthic habitats of the Mesta River seasonal replacement of diatom assemblages was controlled by the water chemistry rather than substratum, current velocity or discharge. The oligotrophic, mesotrophic and eutrophic diatom communities in the Mesta River comprised early-, mid- and late-successional colonizers respectively. Multiple comparisons of all periphytic communities showed that habitat specificity was positively correlated with current velocity.     

Effect of chlorination on the development of marine biofilms dominated by diatoms

This study addressed the antifouling efficiency of commercially available chlorine at different concentrations (0.5%, 1%, and 2%) and exposure times (0.5?min, 1?min, 5?min, and 15 min). The rapid and non-destructive FIRe (fluorescence induction and relaxation) technique was used to evaluate the effects of the biocide on diatom dominated biofilms. The efficiency of chlorine in removing diatoms from the developed biofilms increased with an increase in concentration and exposure time. The fluorescence measurements revealed low F(v)/F(m) and high σ(PSII) values for chlorine-treated Navicula and Amphora biofilms indicating that chlorination was efficient in damaging the photosystem-II reaction centers. Chlorination also caused mortality of diatom cells by damaging the cell body. In natural biofilms, the biocidal effect of chlorine was species specific; species of Amphiphrora, Navicula, Cylindrotheca, and Coscinodiscus showed an increase in the density of the population, but species of Pleurosigma, Amphora, and Thalassionema did not increase in density after chlorine treatment. It was also demonstrated that diatoms can colonize, grow and photosynthesize on chlorine-treated surfaces. Under pulse chlorination (treatment every 6 h), irrespective of chlorine concentration, the development of biofouling decreased with an increase in exposure time. Differences between exposure times of 1 to 15?min were not significant. Additionally, transmission levels of the control (non-chlorine-treated) fouled coupons reduced significantly (～20%) compared to the chlorine-treated fouled coupons (<2%). These results suggest that chlorine can be used as a biocide to control the development of diatom biofilms.     

VARIATION IN BENTHIC DIATOM (BACILLARIOPHYCEAE) IMMIGRATION WITH HABITAT CHARACTERISTICS AND CELL MORPHOLOGY1

We studied the hypothesis that diatom immigration abilities are related to their fitness for colonizing stream substrates. Diatom abundances on artificial substrates exposed for 24 h (the measure of immigration rate) and abundances of stream plankton were determined in six habitats. Diatom immigration varied among habitats from 50–2500 cells·cm^?2·d^?1. Immigration rates decreased 10-fold with increases in current from 10 to 30 cm·s^?1 but changed little during a 40-d summer period. Immigration abilities of diatom taxa were characterized as ratios of either their abundances or relative abundances in immigration assemblages versus in the plankton. Immigration abilities varied over 100-fold among different species. Immigration of some species could be characterized as slower than others in different streams; however, variation in immigration abilities of other species among streams indicated that environment also affected immigration. Diurnal variation in abundance and species composition of the immigration pool (stream plankton) can be important in assessing immigration abilities. Immigration ability may affect benthic diatom fitness. Monoraphid diatoms had a lower probability of immigrating from the plankton than araphid diatoms.     

Effects of cadmium stress on periphytic diatom communities in indoor artificial streams

SUMMARY 1. Two experiments were performed with periphytic diatoms originating from the River Lot (France) and allowed to grow on clean substrata within indoor artificial streams. Three cadmium (Cd) levels (control, low Cd=10 μg L⁻¹ and high Cd=100 μg L⁻¹) were used to test the effects of Cd on (i) the settlement and development of diatom communities (Experiment 1, 4 weeks Cd exposure) and (ii) predeveloped communities grown over a 2-week period without contamination (Experiment 2, 2 weeks Cd exposure).
2. Experiment 1 revealed that growth and taxonomic composition of diatom communities clearly differed with Cd exposure. Biofilms were more adpressed to substrata under low Cd concentration, and were thinner and patchy under high Cd concentration.
3. Exposure of developed diatom communities (Experiment 2) to Cd revealed only minor variations in taxonomic composition, possibly linked to the protective role of the developed organic matrix against metal stress.
4. These results support the validity of periphytic diatom communities as indicators of metal pollution, although significant structural changes would take longer within developed communities.     

Importance of scalar and riparian habitat effects for assessment of ecological status using littoral diatoms

The classification of waterbodies under the Water Framework Directive is dependent on the ability of monitoring programmes to reflect habitat quality using biotic elements including benthic diatom communities. This study investigated the influence of specific riparian habitats, of mixed woodland, grassland and lake artificial structures such as jetties and slipways, on benthic diatom assemblages in nine lakes across gradients of total phosphorus, alkalinity and in the presence or absence of Dreissena polymorpha. The heterogeneity of the benthic diatom assemblages at riparian and lake scale was assessed by taking three replicates per site category per lake, following standard European Union protocols. Canonical correspondence analysis (CCA) and mixed effect modelling was used to investigate the main environmental controls on assemblage structure. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in assemblage structure. No single environmental gradient was found to control benthic diatom composition, with differences among assemblages influenced both by riparian habitat type within lakes and interaction of multiple environment gradients, including presence of D. polymorpha. Greater control was exerted on community structure at the lake than local riparian scale. The influence of scalar factors on diatom assemblages increased with increasing scale. We recommend that for effective monitoring and assessment of ecological status, standard sampling protocols should include localised littoral habitats with individual samples pooled across riparian habitat types, thereby accounting for both multiple environmental and spatial controls on community structure.     

Dynamics of grazing protozoa follow that of microalgae in natural biofilm communities

This study investigates the dynamics of protozoan community in biofilms formed on inert artificial surfaces suspended in various freshwater environments. The results also test the hypothesis that the dynamics of protozoan and microalgal communities in biofilms are interdependent because the latter form one of the major food items of benthic protozoa. Cleaned glass slides were suspended in surface waters at four sampling locations to collect biofilm communities. The glass slides after retrieval were observed under a microscope for diatom and protozoan density and their generic composition. Members of protozoa belonging to phylum Sarcomastigophora dominated the protozoan community followed by phylum Ciliophora in all sampling locations. The variation of protozoan feeding groups showed an initial abundance of autotrophs/holophytes which gave way to heterotrophs, predators, and bacterivores towards the end of the study. The density and generic composition of protozoa varied significantly with the age of biofilm and sampling location. The density variation of protozoa followed that of diatoms in all four sampling locations and this has resulted in a significant positive correlation between diatom and protozoan densities. This suggests the dependency and/or food web connectedness of these two communities in natural biofilms.     

Effect of copper on multiple successional stages of a marine fouling assemblage

Copper based paints are used to prevent fouling on the hulls of ships. The widely documented effect of copper on hull assemblages may be primarily due to direct effects on the invertebrates themselves or indirect effects from copper absorbed into the microbial biofilm before settlement has commenced. Artificial units of habitat were exposed to varied regimes of copper to examine (1) the photosynthetic efficiency and pigments of early-colonising biofilms, and (2) subsequent macroinvertebrate assemblage change in response to the different regimes of copper. Macroinvertebrate assemblages were found to be less sensitive to the direct effects of copper than indirect effects as delivered through biofilms that have been historically exposed to copper, with some species more tolerant than others. This raises further concern for the efficacy of copper as a universal antifoulant on the hulls of ships, which may continue to assist the invasion of copper-tolerant invertebrate species.     

Biotic Disturbance,Recolonization, and Early Succession of Bacterial Assemblages in Intertidal Sediments

The role of disturbance in structuring natural microbial communities has been largely unexplored. Disturbance associated with invertebrate ingestion can reduce bacterial biomass and alter metabolic activities and compositions of bacterial assemblages in marine sediments. The primary objectives of the research presented here were to test whether ingestion by a taxonomically diverse group of deposit feeders constituted a disturbance, and to determine the mechanisms by which bacterial assemblages recover following deposit-feeder ingestion. To test the question of disturbance, we compared fresh egesta vs surficial sediments with respect to bacterial assemblage structure. In emersed intertidal sediments, microbial recovery could be due to regrowth of bacterial populations surviving gut passage or to immigration from adjacent sediments. To differentiate between these modes of recolonization we used field manipulative experiments to exclude migration by isolating freshly extruded fecal coils of three deposit-feeding species from surrounding sediments. We then followed the quantitative and qualitative recovery in egesta and sediments through time using epifluorescence microscopy and PCR-DGGE analysis of 16S rDNA. Our findings indicate that (1) the degree and nature of the disturbance to bacterial assemblages from deposit feeding varies among invertebrate taxa, (2) recovery was significant but incomplete over 3 h, and (3) recolonization of biotically disturbed sediments is dominated by immigration.This revised version was published online in November 2004 with corrections to Volume 48.     

PHOTO‐ACCLIMATION RESPONSE OF BENTHIC STREAM ALGAE ACROSS EXPERIMENTALLY MANIPULATED LIGHT GRADIENTS: A COMPARISON OF GROWTH RATES AND NET PRIMARY PRODUCTIVITY1

The objective of this study was to measure the photo‐acclimation response of stream algae inhabiting thin biofilms across a range of light treatments comparing both growth rates and net primary productivity (NPP). Algae were grown on clay tiles incubated in artificial stream channels where light levels were manipulated by layering a neutral‐density shade cloth over each channel. We measured NPP and algal growth rates in the early stages of community development and compared assemblages that were either acclimated or unacclimated to a given light treatment. Algal growth rates did acclimate to light treatment, with saturation occurring at light levels that were substantially lower for the acclimated communities. Growth efficiency calculated from algal biovolume increased by a factor of 3. However, algal NPP showed a weaker photo‐acclimation response, with only a 30% increase in photosynthetic efficiency. Our results indicate that diatom‐dominated periphyton in thin biofilms are probably not light limited in many shaded streams with respect to growth rates, but are light limited with respect to NPP.     

Novel techniques for field assessment of copper toxicity on fouling assemblages

Laboratory toxicity tests generally expose organisms to a constant concentration of a toxicant in a uniform environment. The two techniques outlined in this paper assess the impact of a model toxicant, copper, on marine fouling assemblages in the field. These techniques allow natural assemblages to develop under a regime of toxicant dosing. The experiments were conducted using both techniques over time frames ranging from 2 weeks to 6 months. Short term experiments using the techniques assess the effects of toxicant exposure on recruitment. The longer term experiments enabled detection of certain indirect impacts of pollution. These include effects due to competition for space and variations in the susceptibility of organisms with age. Over the course of the experiments, a range of responses to copper was observed for different taxa. Both techniques have the potential to be used for testing the impact of other toxicants. Approaches such as those described are necessary in order to understand how communities react to toxicants in real world situations.