Epilithic Algal Communities Research Articles

Convergent photophysiology and prokaryotic assemblage structure in epilithic cyanobacterial tufts and algal turf communities.

As global change spurs shifts in benthic community composition on coral reefs globally, a better understanding of the defining taxonomic and functional features that differentiate proliferating benthic taxa is needed to predict functional trajectories of reef degradation better. This is especially critical for algal groups, which feature dramatically on changing reefs. Limited attention has been given to characterizing the features that differentiate tufting epilithic cyanobacterial communities from ubiquitous turf algal assemblages. Here, we integrated an insitu assessment of photosynthetic yield with metabarcoding and shotgun metagenomic sequencing to explore photophysiology and prokaryotic assemblage structure within epilithic tufting benthic cyanobacterial communities and epilithic algal turf communities. Significant differences were not detected in the average quantum yield. However, variability in yield was significantly higher in cyanobacterial tufts. Neither prokaryotic assemblage diversity nor structure significantly differed between these functional groups. The sampled cyanobacterial tufts, predominantly built by Okeania sp., were co-dominated by members of the Proteobacteria, Firmicutes, and Bacteroidota, as were turf algal communities. Few detected ASVs were significantly differentially abundant between functional groups and consisted exclusively of taxa belonging to the phyla Proteobacteria and Firmicutes. Assessment of the distribution of recovered cyanobacterial amplicons demonstrated that alongside sample-specific cyanobacterial diversification, the dominant cyanobacterial members were conserved across tufting cyanobacterial and turf algal communities. Overall, these data suggest a convergence in taxonomic identity and mean photosynthetic potential between tufting epilithic cyanobacterial communities and algal turf communities, with numerous implications for consumer-resource dynamics on future reefs and trajectories of reef functional ecology.

Glacial stream ecosystems and epilithic algal communities under a warming climate

Climate change is accelerating the global loss of glaciers with potentially striking consequences for downstream ecosystems. However, there exists limited evidence of the ecological impacts of glacier loss in meltwater streams, particularly in those outside of North America and Europe. We provide a review of the abiotic conditions in glacial streams that are potential factors of their ecosystem function and biodiversity with an emphasis on their key primary producers, namely rock-attached algae or “epilithon”. Here, shrinking glaciers discharge over time less turbid melt waters, resulting in slower moving and more transparent stream conditions that are also warmer and more chemically dilute. We hypothesize that these environmental changes will stimulate epilithic algal growth while also shifting its community structure towards larger and less nutritious taxa. Although such an increase in algal growth may benefit the productive harvestable fish capacity of certain mountain streams, a potential negative trade-off involves the proliferation of nuisance algae (e.g., Didymosphenia geminata), which thrives under clear, nutrient-poor mountain conditions. We advocate the use of long-term ecological monitoring programs and experiments coordinated across global mountain ranges to better predict and understand the ecological consequences of loss of glaciers on mountain stream ecosystems.

Site mediates performance in a coral‐seeding trial

Coral seeding is a promising intervention being tested and applied in global reef‐restoration efforts. However, high mortality of newly settled corals, particularly in degraded environments, is one of several hurdles to overcome to up‐scale this technique. Incorporating design features that mitigate drivers of mortality could increase coral‐seeding effectiveness. Here we tested five ceramic seeding‐device designs that incorporated various features intended to act as coral microrefugia. Devices seeded with Acropora tenuis spat were deployed to three sites on a shallow mid‐shelf reef on the central Great Barrier Reef (GBR), and survival was assessed after 219 days. Average yield (device‐level survival) was moderate across the device designs (22%) and all devices performed comparably. However, there was a nearly threefold increase in survival at one site compared with the other, similar sites less than 100 m away. Assessment of the benthic community around each device suggested that the sites hosted similar communities, although multivariate analyses identified a weak but significant positive relationship between survival and the first principal component (only 17% of variance), characterized by higher cover of sponges and epilithic algal communities. These results suggest that within‐reef scale variations (10s of meters) in environmental conditions, or variations in community constituents not investigated here (e.g. grazing fishes, mobile invertebrates), may impact the success of coral seeding. Further investigations into the drivers of coral survival at fine spatial scales, particularly abiotic conditions, are required to guide the placement of coral‐seeding devices and to predict their effectiveness.

Characteristics of effluents from trout farms and their impact on water quality and benthic algal assemblages of the receiving stream

In this study, characteristics of effluents from three flow-through rainbow trout farms in Turkey and their impact on water quality and epilithic algal communities of the receiving stream were investigated. Water samples were taken monthly from both inlets and outlets of three fish farms, while both water and epilithic algae samples were collected from two stations (upstream and downstream) in the stream. A significant increase from inlets to outlets was observed for chemical oxygen demand (COD), soluble reactive phosphorus (SRP), total suspended solids (TSS), NH4–N and total phosphorus (TP) (p < 0.05) due to no effluent treatment processes and high FCR at the fish farms. The daily average total nitrogen (TN) and TP fluxes of the fish farms predicted with the nutritional method were found close to those measured with the hydrological method. Although there were significant increases in COD, TSS, NH4–N, TN, NO3–N, NO2–N, TP and SRP concentrations at the downstream station compared to the upstream station of the receiving stream (p < 0.05), water quality of the downstream station remained in Class I in terms of examined parameters. Trophic Diatomic Index and Biological Diatom Index values indicated that the upstream station had a better water quality than the downstream station. Also, filamentous algae such as Cladophora glomerata, Ulothrix zonata and Stigeoclonium lubricum were observed at the downstream station. In view of the above findings, several suggestions were put forward to protect the water quality of the receiving stream.

Dynamics of Epilithic Algae Communities and Their Relationship with Environmental Factors During Storage and Non-storage Periods in the Three Gorges Reservoir

In order to explore the composition of epiphytic algae and its related environmental factors, 12 sampling sites in the natural reaches and the backwater reaches (including perennial backwater sections and fluctuating backwater sections) were investigated among tributaries of the Caotang River, the Meixi River, and the Daxi River in the Fengjie district of the Chongqing section of the Three Gorges Reservoir under different hydrological regimes (i.e., storage and non-storage periods). Results showed that 103 species of epilithic algae belonging to 45 genera and 4 families are found in the 3 tributaries. This included 67 species belonging to 34 genus in the natural sections and 82 species (64 species in perennial backwater sections and 41 species in fluctuating backwater sections) belonging to 34 genera in the backwater sections. During the storage period, the dominant species in the natural sections were Melosira varians, Cocconeis placentula, Diatoma vulgure, Gyrosigma scalproides, and Oscillatoria tenuis, while the dominant species in the backwater sections were M. varians, Cymbella affinis,D. vulgure, Eucapsis alpina, and M. granulata. During the non-storage period, the dominant species in the natural sections were M. varians, C. affinis, and C. placentula, whereas the dominant species in the backwater sections were O. princeps, O. rupicola,O. formosa, Synedra acus, Ulothrix sp., Merismopedia elegans, and O. tenuis. These results suggested that the compositions of dominant species showed significant differences during the non-storage period, while little difference was found during the storage period. In addition, the dominant species did not show a significant change in the natural sections, but a marked difference was observed in the backwater sections. Similar dominant species were observed in both perennial and fluctuating backwater sections during the non-storage period, but significantly different dominant species were found during the storage period. Redundancy analysis suggested that the composition of epilithic algae was influenced by different environmental factors, such as temperature, electrical conductivity, pH, total nitrogen, and total phosphorus. Indeed, changes in the cell densities of dominant algae at the different sites were mainly affected by temperature and the concentrations of nitrogen and phosphorus. These results suggest that the different hydrological regimes had an important role not only on the reservoir water environment, but also the dynamics of epilithic algal communities.

Interactive effects of ocean acidification and warming on coral reef associated epilithic algal communities under past, present-day and future ocean conditions

We thank Jordan Hollarsmith, Emmett Clarkin, Camille Domy, Cassy Thompson, Patrick Buerger, Kathryn Berry, Laura Arthur and Caroline Assailly for their great help in maintaining the experimental system. Many thanks to the staff at the SeaSim facility and the AIMS workshop, Andrea Severati, Tom Barker, Paul Boyd, Craig Humphrey, Eneour Puill-Stephan, Grant Milton, Justin Hochen, Niall Jeeves, Michael Kebben and Gary Brinkman who contributed to the aquarium design, control systems and monitoring of the experimental conditions. Thanks to Lindsay Harrington for her help with the identification of CCA and epilithic organisms. Thanks to Michelle Liddy and Florita Flores for their help with the incubation experiments and general assistance. This study was funded by the Australian Institute of Marine Science, the Australian Government's National Environmental Research Program and a Super Science Fellowship Grant from the Australian Research Council.

Dietary variation and food selection by mayfly grazers in a subtropical mountain stream

Abstract Background The classification of functional feeding groups of aquatic insects is often misleading in tropical/subtropical streams because their feeding habits are assumed to be the same as their temperate counterparts according to the mouthpart structure and foraging behavior. This study aimed to examine the diets and preferences of mayfly grazers (Baetis spp. and Rhithrogena ampla) in a subtropical mountain stream in the dry and wet seasons. Results In the stream, epilithic algal communities on insect-excluded bricks (as a grazer-excluded control) were dominated by small adnate diatoms, most likely due to the high current velocity. Both grazers preferred understory and small adnate diatoms, Achnanthes spp. and Achnanthidium pyrenaicum, in both seasons. However, the stalked diatoms Gomphonema spp. were preferred only by Baetis, but not by Rhithrogena, in the dry season when the current velocity became relatively slower. The results of pairwise tests further showed that the algal compositions on the insect-excluded bricks coincided with the diets of both grazers in the wet season but were distinct from those on the bricks in the dry season. Seasonal variations in the algal compositions of the diets of Rhithrogena and on the insect-excluded bricks were apparent, but not in the diets of Baetis. Conclusions The algal physiognomy was most likely attributed to the impact of the high current velocity in the stream. Our results suggest that the diet preference by mayfly grazers in the stream is potentially influenced by algal availability.

Dietary variation and food selection by mayfly grazers in a subtropical mountain stream

The classification of functional feeding groups of aquatic insects is often misleading in tropical/subtropical streams because their feeding habits are assumed to be the same as their temperate counterparts according to the mouthpart structure and foraging behavior. This study aimed to examine the diets and preferences of mayfly grazers (Baetis spp. and Rhithrogena ampla) in a subtropical mountain stream in the dry and wet seasons. In the stream, epilithic algal communities on insect-excluded bricks (as a grazer-excluded control) were dominated by small adnate diatoms, most likely due to the high current velocity. Both grazers preferred understory and small adnate diatoms, Achnanthes spp. and Achnanthidium pyrenaicum, in both seasons. However, the stalked diatoms Gomphonema spp. were preferred only by Baetis, but not by Rhithrogena, in the dry season when the current velocity became relatively slower. The results of pairwise tests further showed that the algal compositions on the insect-excluded bricks coincided with the diets of both grazers in the wet season but were distinct from those on the bricks in the dry season. Seasonal variations in the algal compositions of the diets of Rhithrogena and on the insect-excluded bricks were apparent, but not in the diets of Baetis. The algal physiognomy was most likely attributed to the impact of the high current velocity in the stream. Our results suggest that the diet preference by mayfly grazers in the stream is potentially influenced by algal availability.

Effect of a dam on epilithic algal communities of a mountain stream: before-after dam construction comparison

In this study we evaluated the effect of a dam on epilithic algal communities by analyzing community response after dam construction and by comparing community composition, structure and biomass upstream and downstream of the dam. Samples of epilithic algae and environmental data were collected at each site during high and low water periods before and after dam construction in Achiras Stream (Córdoba, Argentina). Ordinations showed modifications in algal assemblages after dam construction and downstream of the dam. Ordinations also suggested a loss of seasonality at the downstream site since the assemblages were similar between hydrological periods after dam construction. Indicator species, obtained by the Indicator Value method, showed that, after dam construction, there could have been an increase in nutrient concentration and a release of plankton from the impoundment. Abundance, richness and diversity were altered after dam construction as assessed by ANOVAs derived from a modified BACI Design. Proportion of early-successional species was higher at the upstream site while late-successional species were dominant at the downstream site, as predicted. Lower fluctuations in discharge downstream of the dam may have helped succession advance, whereas at the upstream site, mainly during the high water period, floods could have caused sloughing of life forms from the outer layers of the biofilm, resetting the algal community to early successional stages. It may be concluded that the dam affected algal community and favored succession advance mainly by reducing current velocity and flow fluctuations.

Fringing Reefs of Reunion Island and Eutrophication Effects - Part 2: Long-Term Monitoring of Primary Producers

Studies on the reef flat of Saint-Gilles La Saline between 1987 and 2009 compared spatio-temporal variations of primary producers on two sites, Toboggan and Planch'Alizes. Toboggan (Site-T) is an oligotrophic site characterized by Acropora corals, abundant sea urchins and few primary producers. Planch'Alizes (Site-P) is a heterotrophic site, characterized by massive corals, abundant primary producers and occasional sea urchins. From shore to outer reef front, the reef flat comprises three parts: the back reef (B), the coral zone with Large coral strips (L) and the coral zone with Narrow coral strips (N). This paper (which is Part 2 in a three part series) is divided into four sections. The first (1993, 1996, and 2002) focuses on four groups of primary producers: cyanophytes; turfs (including Stegastes epilithic algal communities); encrusting coralline algae; macroalgae. Their abundance and dominant species were recorded in the three subzones, B, L and N, using 50m-line intercept transects (LITs). The second section (1998 to 2009 inclusive, on the two same sites), reports on annually monitored turfs, encrusting coralline and macroalgae on two permanent 20m LITs. These annual records extend periodic records from these same LITs from 1987, 1993, 1996 and 2002. The third section describes species richness of primary producers at the infracentimetric level in zones B, L and N in 1994. In the final section, seasonal variability is documented as changes in the biomass of dominant macroalgae reported monthly over a period of seven months (1993-94). In 1993-2002, primary producers were dominant at P (average ~ 60%) but inconspicuous at T (~5%). In terms of relative cover, turfs and macroalgae were the dominant forms at both sites (75% turfs, 10% macroalgae at T ; 24% t. and 52% m. at P). On both sites, cyanophytes significantly decreased over time. Among turfs, fine filamentous turfs were prevalent on the back reef on both sites, and also on the narrow outer coral zone at P. Stegastes turf territories dominated both coral zones at Site-T (L and N), but only the L coral zone at Site-P. Encrusting coralline algae were sparse at Site-T but locally abundant at Site-P, where they increased significantly from 1993 to 1996 in both coral zones. There was a major decrease in macroalgae between 1993 and 2002 at P. There were marked differences in the trajectories of decline of the dominant soft macroalgae (Hypnea valentiae, Padina spp, Dictyota spp, Turbinaria ornata and Gracilaria canaliculata). Seventy six primary producer species were recorded in the infracentimetric study (52 species at T and 67 at P). Different algae dominated different areas at both sites. At Toboggan, locally dominant species were the small Gelidium pusillum, an unidentified Melobesiae, Jania adhaerens, the encrusting corallines Hydrolithon onkondes and Lobophora variegata, the turfs Polysiphonia mollis and Anotrichium tenue (mainly in Stegastes territories), Jania adhaerens and Dictyosphaeria verluysii. At P, the dominants were Mesophyllum erubescens encrusting dead hard substrates and decimetric bioclasts in the back reef (B), where they form numerous rhodoliths. In the P coral zones, the dominant taxa were Lyngbya majuscula (cyanobacteria) followed by Hydrolithon onkodes, Blennothrix cantharidosma and Lithophyllum kotschyanum. Jania adhaerens, Hydrolithon onkodes and Gelidiella acerosa were dominant in the narrow coral zone (N). The local composition of the algal community appears to be more related to geomorphological zones and the presence or absence of the territorial Stegastes fish than to environmental differences between T and P. There was strong seasonal change in macroalgae biomass in 1993-4. On the back reef of both sites, peak biomass was due to Hypnea valentiae in February, when it is significantly greater than it was in January. Dictyosphaeria verluysii was dominant and highly visible at Site-T, but extremely rare and hidden below the Hypnea valentiae at P. On the outer coral zone (N), biomass was significantly different between most months on both sites. At Site-T in summer (December to March) the peak biomass was due to the sponge seaweed Hydroclathrus clathratus (Phaeophyceae) which exploded in December, declined in January and disappeared in February. At Site-P, H.clathratus was almost absent, and instead, Gracilaria canaliculata dominated the community throughout the year. Dictyosphaearia verluysii and D. cavernosa were prevalent in winter, the former preferring intertidal locations. In autumn (April - June), Turbinaria ornata invaded the subtidal substrates on the outer N-zones. To conclude this Part 2 of the Reunion Island Fringing Reef series, we discuss the influence of nutrients and herbivores (especially sea urchins and the territorial damselfish Stegastes) on the abundance and distribution of primary producers.

Relationship of epilithic diatom communities to environmental variables in Homa lagoon (Izmir, Turkey)

Spatio-temporal changes in taxonomic composition and structure of a diatom com- munity were assessed between June 2006 and June 2007 at the intertidal zone of Homa lagoon, Izmir, Turkey. The communities were composed of a mixture of epilithic, epiphytic, epipsammic, and occasionally some pelagic diatoms. In total, 87 taxa belonging to 39 genera were identified, of which 39 were used as active taxa in the numerical analysis. The Shannon-Wiener diversity index (H') values were quite variable, varying between 1.00 and 3.39 and correlated with both species richness (r = 0.93) and evenness (J'; r = 0.38). Cylindrotheca closterium, Halamphora veneta, Lic- mophora gracilis, L. lyngbyei, Navicula cryptocephala, N. cincta, and N. ramosissima var. mollis were the overall most abundant taxa throughout the sampling. The relationship between epilithic algal communities and 10 environmental variables was explored using canonical correspondence analysis. According to a Monte Carlo unrestricted permutation test, the silicate and ammonium concentrations were the most important variables in accounting for species distribution.

Photosynthetic activity of epilithic algal communities in sections of the Torna stream (Hungary) with natural and modified riparian shading

The photosynthetic activity of epilithon grown in the Torna-stream (Hungary) was studied. Samples were collected from natural sections with closed canopy and natural stream bed and from modified sections with trapezoid river bed and shores lacking riparian vegetation. We assumed that human modifications would have a significant impact on epilithic photosynthesis, and therefore expected to observe corresponding changes in photosynthesis–irradiance (P–I) parametric. The laboratory P–I measurements were carried out monthly between April 2008 and September 2009 with epilithon after 3 weeks of in situ colonization. The maximum rate of the photosynthesis (Pmax) correlated positively with the chlorophyll a content of the samples. Natural sites had lower biomass and Pmax values than modified sites, and the biomass differed substantially in spring and summer, the Pmax differed significantly only in spring. Natural sections had higher biomass-specific photosynthesis values than modified sections in all seasons, but the difference was significant only in summer–autumn: in summer the samples from the natural sections had significantly higher photosynthetic efficiency. In spring and summer, the photoadaptation parameters (Ik) of communities grown in modified sections were substantially higher than in natural sections. Light availability appeared to be the major factor regulating the seasonal photosynthetic activity of epilithic communities.

Effects of Residual Chlorine on Epilithic Algal Communities in Lotic Systems

Effects of Residual Chlorine on Epilithic Algal Communities in Lotic Systems

Seasonal variations of metal concentrations in periphyton and taxonomic composition of the algal community at a Yenisei River littoral site

AbstractThe concentrations of metals K, Na, Ca, Mg, Fe, Mn, Zn, Cu, Ni, Pb, Co and Cr, in the water and periphyton (epilithic algal communities) were studied at a site in the middle stream of the Yenisei River (Siberia, Russia) during three years using monthly sampling frequencies. Despite considerable seasonal variations in aquatic concentrations of some metals, there was no correlation between metal contents in the water and in periphyton. Seasonal concentration variations of some metals in periphyton were related to the species (taxonomic) composition of periphytic microalgae and cyanobacteria. Enhanced levels of Ni and Co in periphyton in late autumn, winter, and early spring were likely caused by the predominance of cyanobacteria in the periphytic community, and annual maximum levels of K in periphyton in late spring and early summer were attributed to the domination of Chlorophyta, primarily Ulothrix zonata.

δ13C and δ15N in tissue of coral polyps and epilithic algae inhabiting damaged coral colonies under the influence of different light intensities

Studies were performed of the carbon and nitrogen stable isotope (δ13C and δ15N) composition (δ13C and δ15N) of the corals Porites cylindrica and P. lutea (5 years after damaging the colonies by the bleaching events) and of epilithic algae settled onto damaged areas of coral colonies. Coral polyps and three epilithic algal communities (‘red algal turf, green algal turf and red calcified crusts’) were sampled along the boundary between communities of coral polyps and algal colonizers from differently illuminated habitats from 2 to 90% of incident surface photosynthetically active radiation (PAR0). It was found that communities with a predominance of red algae significantly differed from communities with a predominance of green algae in δ13C but not in δ15N values. An influence of habitat irradiance was found only for communities of coral polyps for δ13C and δ15N values: under bright light (70–90% PAR0) polyp tissues of both coral species were significantly enriched in heavy carbon isotopes and insignificantly in nitrogen isotopes (δ13C values difference ~4‰) relative to tissues of corals under lower light 15–50% PAR0. On the basis of these results we assumed that differences in light intensities in the habitat ranging from 15 to 90% PAR0 do not influence on accessibility of the main carbon and nitrogen sources for corals and algae, and exchange by these elements between organisms. We also assumed that the relative enrichment in the heavy carbon isotopes of coral tissues in high light is a result of decreased isotope fractionation (or the absence of fractionation in photosynthesis of their zooxanthellae).

δ13C and δ15N values in reef corals Porites lutea and P. cylindrica and in their epilithic and endolithic algae

In summer 1998, shallow water corals at Sesoko Island, Japan (26°38′N, 127°52′E) were damaged by bleaching. In August 2003, partially damaged colonies of the massive Porites lutea and the branching P. cylindrica were collected at depths of 1.0–2.5 m. The species composition of epilithic algal communities on dead skeletal surfaces of the colonies (‘red turfs’, ‘green turfs’, ‘red crusts’) and the endolithic algae (living in coral skeletons) growing close to and away from living coral polyps was determined. Carbon and nitrogen stable isotope values of organic matter (δ13C and δ15N) from all six of these biological entities were determined. There were no significant differences in the isotope composition of coral tissues of the two corals, with P. lutea having δ13C of −15.3 to −9.6‰ and δ15N of 4.7–6.1‰ and P. cylindrica having similar values. Polyps in both species living close to an interface with epilithic algae had similar isotope values to polyps distant from such an interface. Despite differences in the relative abundance of the algal species in red turfs and crusts, their δ13C and δ15N values were not significantly different from each other (−18.2 to −13.9, −20.6 to −16.2, 1.1–4.3, and 3.3 to 4.9‰, respectively). The green algal turf had significantly higher δ13C values (−14.9 to −9.3‰) than that of red turfs and crusts but similar δ15N (1.2–4.1‰) to the red algae. The data do not suggest that adjoining associations of epilithic algae and coral polyps exchange carbon- and nitrogen-containing metabolites to a significant extent. The endolithic algae in the coral skeletons had δ13C values of −14.8 to −12.3‰ and δ15N of 4.0–5.4‰. Thus they did not differ significantly from the coral polyps in their carbon and nitrogen isotope values. The similarity in carbon isotope values between the coral polyps and endolithic algae may be attributed to a common source of CO2 for zooxanthellae and endolithic algae, namely, from respiration by the coral host. While it is difficult to fully interpret similarity in the nitrogen isotope composition of coral tissue and of green endolithic algae and the difference in δ15N between green epilithic and endolithic algae, the data are consistent with nitrogen-containing metabolites from the scleractinian coral serving as a significant source of nitrogen for the endolithic algae.

Indirect effects of brook trout (Salvelinus fontinalis) on the structure of epilithic algal communities in an oligotrophic boreal forest stream

The impact of fish on epilithic algae community structure was studied in a replicated series of artificial outdoor channels fed by a boreal forest stream (Canada) to test the hypotheses that brook trout (Salvelinus fontinalis) induce a three-trophic chain top-down change in epilithic community structure, at both taxonomic and physiognomic levels. Fish were introduced into five of ten channels and the epilithic algae growing on tiles were sampled four times during summer to determine biomass, algal physiognomy and species composition in relation to presence of fish and invertebrate community structure. Diatom biomass showed distinctive development patterns, increasing at the beginning of fish introduction and decreasing towards the end of the experiment. The responses were the reverse in the absence of fish. Chrysophyceae increased in the absence of fish, particularly at the end of the experiment. From the seven algal physiognomic types considered, epilithon overstory, attached erected algae and loosely attached algae were generally more abundant in the presence of fish. Species' biomass was markedly different in both treatments and followed contrasted temporal patterns. In the presence of fish, attached erected diatoms species rapidly reached a complex spatial overstory structure, while in the absence of fish the epilithic community remained at a younger successional stage. Partial redundancy analysis showed that those changes were mediated by large grazing invertebrates, which had lower abundance over the bottom surfaces in the presence of fish. Variance partitioning analysis reinforced the hypothesis that most of the variability in epilithic community structure was explained by fish-invertebrate interactions and that the effect of fish presence alone was not significant. The results show that reduction in total epilithic algal biomass was a transient top-down effect, but the three-trophic level control on major taxa, species composition and community physiognomy remained along the summer experiment.

The role of ultraviolet radiation in structuring epilithic algal communities in Rocky Mountain montane lakes: evidence from pigments and taxonomy

We investigated changes in the community structure of epilithic (rock-dwelling) algae brought about by ultraviolet-A and -B radiation (UV-A and UV-B, respectively), using measurements of biovolume of individual taxa, and taxonomically diagnostic photosynthetic pigments. We undertook our study in four Canadian Rocky Mountain montane lakes, where downwelling ultraviolet radiation (UVR) can be intense. Although taxonomic counts revealed significant decreases in algal community diversity under UV-A and UV-B exposure, they revealed no other significant trends in algal community composition. Instead, redundancy analysis using these counts suggested that variations in nutrient concentrations were most important in structuring these communities. Photosynthetic pigments decreased significantly under UV-A and UV-B exposure. This decrease was much more striking for carotenoid than for chlorophyll concentrations, despite the photoprotective properties of many carotenoid pigments. Grazed carotenoids have been shown to be more resistant to degradation than grazed chlorophylls. We suggest that an observed increase in grazing pressure in our UVR-shielded communities counteracted increases in algal growth, but that increased algal growth rates were reflected by increased concentrations of slowly degrading carotenoids. Our study suggests that other factors, such as nutrients and grazers, are more important than UVR for structuring epilithic algal communities in our study lakes.

Ecological Studies on Togyo Reservoir in Chulwon, Korea. 8. The Epilithic Algal Community after the Experimental Acidification on the Artificial Substrata (Tiles) at Mesocosm

The epilithic algal communities on the artificial substrata (unglazed ceramic tiles) were investigated from 5th July to 24th July 1999 with two or three days intervals for elucidating the effects of the experimental acidification. They were harvested inside the mesocosm with and without the acid treatment on Togyo reservoir within the Civilian Passage Restriction Line near Demilitarized Zone (DMZ) in Korea. After the colonization of epilithic algal community, their standing crops revealed different patterns outside and inside the mesocosm. However the time lapse of 5 days was observed on the inside with acid treatment. The dominant species were different: Achnanthes minutissima was outside but Coenochloris polycocca was inside and inside with acid treatment. The differences in floral composition were also found. Achnanthes minutissima which has been the most important species in the colonization by the epilithic algal community of the mesocosm was less important at the lower pH. Coenochloris polycocca is a species well adapted to low pH.

USING EPILITHIC ALGAL COMMUNITIES TO ASSESS TROPHIC STATUS IN IRISH LAKES1

Relationships between taxonomic composition of shallow epilithic algal communities and nine environmental variables in 32 lakes of different trophic states in Ireland were explored using gradient analysis. A canonical correspondence analysis using four representative environmental variables, alkalinity (correlated with pH and conductivity), maximum phytoplankton chl a (CHLmax) (correlated with total P, total N, and chl), turbidity, and water color explained 21% of the variance in taxa distributions. The first two axes were significant and accounted for 77% of the variance in the periphyton–environmental relationship. The first axis was strongly related to alkalinity and color, which reflected geology and land use in the watersheds. The second axis was most correlated with CHLmax, and separation of lakes corresponded to their Organization for Economic Cooperation and Development (OECD) trophic classification based on water chemistry. Eutrophic lakes were characterized by cyanobacteria taxa and Stigeoclonium sp. Diatoms and desmids were generally more abundant in oligotrophic and mesotrophic lakes. Values for diatom trophic indices were poor indicators of trophic state. Weighted averaging regression and calibration techniques were used to develop transfer functions between 84 taxa and total P, total N, and CHLmax. The total P inference model predicted OECD trophic classification correctly for 84% of the lakes. Values for taxa preferences resulting from such models can provide the foundation for biomonitoring schemes using extant periphyton communities. The turnover time of periphyton taxa should integrate changes in environmental conditions at a temporal scale intermediate to surface‐sediment fossil diatom assemblages and water column variables, which may be more appropriate for detecting annual changes.