Macroinvertebrate community patterns in relation to leaf-associated periphyton under contrasting light and nutrient conditions in headwater streams

1. Temperate headwater streams traditionally have been considered heterotrophic and brown food web dominated with little primary production. Recent work, however, suggests algae on leaves in these streams may play a greater role than previously thought through interactions with microbial decomposers like fungi. Algae also may be important for macroinvertebrates colonizing leaves in streams. Algae are a more nutritious food resource for shredders than fungi and bacteria and provide a food resource for non-shredder macroinvertebrates.
2. In a field experiment, we manipulated light in three low-nutrient and three high-nutrient streams using leaf bags filled with red maple leaves in winter and spring. After four weeks we measured algal and fungal biomass, leaf stoichiometry, and macroinvertebrate abundance and biomass associated with the leaf bags. We also identified the macroinvertebrate community and examined differences in functional feeding guilds and taxa under ambient- and shaded-light treatments and low- and high-nutrient concentrations in relation to measured leaf characteristics.
3. Algal biomass on leaves was greatest in high-nutrient streams and ambient-light treatments in both seasons. Fungal biomass on leaves was greatest in high-nutrient streams and showed a moderate marginally significant positive correlation with algae during the winter. Leaf C:N was negatively correlated to algae in winter and fungi in both seasons, while leaf N:P and C:P were negatively correlated to fungi in winter and algae in spring. Interactions between fungi and algae on leaves and the nutritional importance of each for macroinvertebrates likely change across seasons, potentially impacting macroinvertebrate community composition.
4. Macroinvertebrate diversity did not differ, but biomass was significantly greater in shaded-light treatments during spring. Abundance was highest in the high-nutrient ambient-light conditions in both seasons, corresponding to greatest algal biomass. Functional feeding guild biomass and abundance were related to different leaf characteristics by season and guild. Higher algal biomass was an important factor for colonization of certain macroinvertebrates (e.g., Ephemerella (Ephemeroptera: Ephemerellidae) and Stenonema (Ephemeroptera: Heptageniidae)), while others were more abundant under shaded treatments with lower algal biomass (e.g., Tipula (Diptera: Tipulidae)), indicating taxa-specific responses.
5. Leaf-associated algae may be an important factor mediating macroinvertebrate communities associated with leaves in temperate headwater streams. Our results demonstrate that green and brown food webs intersect within leaf packs, and they cannot be easily disentangled. We therefore should consider both autochthonous and allochthonous resources within headwater streams when examining their communities or developing water management strategies.

     

人工滩涂湖泊滴水湖浮游藻类群落特征

于2009年3月—2010年2月逐月对中国最大人工滩涂湖泊——滴水湖的浮游藻类群落特征进行研究。利用CANOCO4.5软件对浮游藻类数据和环境因子数据进行典范对应分析(CCA),以揭示浮游藻类对生态环境的响应。结果表明:全年共检测到浮游藻类186种及变种,隶属于8门92属,其中绿藻门种类最多,其次是蓝藻门和硅藻门;主要优势种为小席藻、微小平裂藻、银灰平裂藻、不定微囊藻、弱细颤藻、啮蚀隐藻、四尾栅藻、扁圆卵形藻;藻类的年均丰度和年均生物量分别为(4552.29±4591.33)×104cells·L-1和8.15±6.63mg·L-1,藻类现存量各月份间差异极显著(P<0.01),但站点间差异不显著;多样性分析显示,藻类物种多样性较好;典范对应分析表明,水温、总氮等是影响滴水湖藻类群落结构的主要因素。     

The influence of riparian vegetation on macroinvertebrate community structure and functional organization in six new Guinea streams

Information on the ecology of New Guinea streams is meagre, and data are needed on the trophic basis of aquatic production in rivers such as the Sepik in Papua New Guinea which have low fish yields. This study investigates the relationship between riparian shading (from savanna grassland to primary rainforest), algal and detrital food, and macroinvertebrate abundance and community structure in 6 Sepik River tributary streams. A particular aim was to elucidate macroinvertebrate community responses to changes in riparian conditions. All streams supported diverse benthic communities, but morphospecies richness (overall total 64) was less than in streams on the tropical Asian mainland; population densities of benthic invertebrates, by contrast, were similar to those recorded elsewhere. Low diversity could reflect limited taxonomic penetration, but may result from the absence of major groups (Plecoptera, Heptageniidae, Ephemerellidae, Psephenidae, Megaloptera, etc.) which occur on the Asian mainland. Population densities of all 19 of the most abundant macroinvertebrate taxa varied significantly among the 6 study streams, but community composition in each was broadly similar with dominance by Baetidae and (in order of decreasing importance), Leptophlebiidae, Orthocladiinae, Elmidae and Hydropsychidae. Principal components analysis (PCA) undertaken on counts of abundant macroinvertebrate taxa clearly separated samples taken in two streams from the rest. Both streams contained high detrital standing stocks and one was completely shaded by rainforest. Stepwise multiple-regression analysis indicated that population densities of the majority of abundant taxa (11 out of 19) across streams (10 samples per stream; n = 60) were influenced by algae and/or detritus, although standing stocks of these variables were not clearly related to riparian conditions. When regression analysis was repeated on mean counts of taxa per stream (dependent variables) versus features of each stream as a whole (thus n = 6), % shading and detritus were the independent variables yielding significant regression models most frequently, but pH, total-nitrogen loads and algae were also significant predictors of faunal abundance. Further regression analysis, undertaken separately on samples (n = 10) from each stream, confirmed the ability of algae and detritus to account for significant portions of the variance in macroinvertebrate abundance, but the significance of these variables varied among streams with the consequence that responses of individual taxa to algae or detritus was site-specific.Community functional organization — revealed by investigation of macroinvertebrate functional feeding groups (FFGs) — was rather conservative, and streams were codominated by collector-gatherers (mean across 6 streams = 43%) and grazers (36%), followed by filter-feeders (15%) and predators (7%). The shredder FFG was species-poor and comprised only 0.4% of total macroinvertebrate populations; shredders did not exceed 2% of benthic populations in any stream. PCA of FFG abundance data was characterized by poor separation among streams, although there was some evidence of clustering of samples from unshaded sites. The first 2 PCA axes accounted for 84% of the variation in the data suggesting that the poor separation resulted from the general similarity of FFG representation among streams. Although stepwise multiple-regression analysis indicated that algae and detritus accounted for significant proportions of the variations in population density and relative abundance of some FFGs, the response of community functional organization to changes in riparian conditions and algal and detrital food base was weak — unlike the deterministic responses that may be typical of north-temperate streams.     

Correlates of habitat favourability for benthic macroinvertebrates at five stream sites in an Appalachian Mountain drainage basin, U.S.A.

SUMMARY.

• 1 Based on monthly samples taken over a 1-year period, average density (individuals m^-2). average standing biomass and annual production of benthic macroinvertebrates were estimated at five sites within an Appalachian Mountain drainage basin. Two sites were on first order streams and differed from the three second order sites: they were smaller and more shallow and they were depressed in pH and chemical richness.
• 2 Patterns of abundance of individual taxa, of higher taxonomic groups and of functional (feeding) groups differed according to whether abundance was measured as density, as standing biomass or as annual production. Standing biomass was chosen as the measure of macroinvertebrate abundance because available evidence indicates that only standing biomass is consistently, positively correlated with survivorship, and thus with habitat favourability.
• 3 Two non-insect taxa (the crayfish Cambarus and the snail Leptoxis carinata) dominated standing biomass at each site. Consequently, differences among sites in total macroinvertebrate standing biomass and differences within and among sites in standing biomass of functional groups were determined by differences in estimated standing biomass of these two taxa. Differences in estimates of crayfish standing biomass were consistent with an explanation based on the availability of refuges created by large substrate particles. The abundance of L. carinata appeared to be controlled primarily by water chemistry and possibly secondarily by predators. A number of insect taxa exhibited patterns of standing biomass consistent with hypotheses based on effects of annual depth-flow regimes. Hypotheses based on differences in food resource and on competition appeared, in general, to be inconsistent with observed patterns of macroinvertebrate abundance.
• 4 Contrary to predictions of the River Continuum Concept, the shredder functional group in the Guys Run drainage and in other temperate woodland streams was found to be a minor part of total macroinvertebrate standing biomass. Further, in a majority of small forested stream sites studied to date, standing biomass of grazers has been determined to be greater than that of shredders.

     

A manipulative study of macroinvertebrate grazers in Hong Kong streams: do snails compete with insects?

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Structure of the Phytoplankton Community and Its Relationship to Water Quality in Donghu Lake, Wuhan, China

The phytoplankton community structure, in terms of species composition, total standing crop,and abundance of the dominant algal species, at four stations in Donghu Lake, Wuhan, China, was investigated monthly from January 1994 to December 1996. A total of 260 taxa was observed, of which Chlorophyta (106 taxa) contributed the highest portion of the total number of taxa, followed by Bacillariophyta (82 taxa)and Cyanophyta (32 taxa). The total standing crop measured by means of chlorophyll a content, cell density,and cell biovolume, as well as the abundance of the dominant species, declined in the order of Station I to Station Ⅳ. Seasonal changes of the standing crop varied greatly among the four stations. Although the cell density at the four stations showed a single peak within a year, the peak density varied from July to November, dependent on the sampling year and the station. For chlorophyll a content and cell biovolume,multiple peaks were observed at Stations Ⅰ and Ⅱ, but a single peak was found at Stations Ⅲ and Ⅳ. The phytoplankton community structure indicated that the trophic status was the highest at Station Ⅰ (most eutrophic), followed by Station Ⅱ; Stations Ⅲ and Ⅳ were the least trophic areas. The long-term changes in phytoplankton community structure further suggested that changes in phytoplankton community structure were correlated with water quality, and eutrophication of Donghu Lake had been aggravated since the 1950s.     

Structure of the Phytoplankton Community and Its Relationship to Water Quality in Donghu Lake, Wuhan, China

The phytoplankton community structure, in terms of species composition, total standing crop,and abundance of the dominant algal species, at four stations in Donghu Lake, Wuhan, China, was investigated monthly from January 1994 to December 1996. A total of 260 taxa was observed, of which Chlorophyta (106 taxa) contributed the highest portion of the total number of taxa, followed by Bacillariophyta (82 taxa) and Cyanophyta (32 taxa). The total standing crop measured by means of chlorophyll a content, cell density,and cell biovolume, as well as the abundance of the dominant species, declined in the order of Station I to Station IV. Seasonal changes of the standing crop varied greatly among the four stations. Although the cell density at the four stations showed a single peak within a year, the peak density varied from July to November, dependent on the sampling year and the station. For chlorophyll a content and cell biovolume,multiple peaks were observed at Stations I and II, but a single peak was found at Stations III and IV. The phytoplankton community structure indicated that the trophic status was the highest at Station I (most eutrophic), followed by Station II; Stations III and IV were the least trophic areas. The long-term changes in phytoplankton community structure further suggested that changes in phytoplankton community structure were correlated with water quality, and eutrophication of Donghu Lake had been aggravated since the 1950s.     

Effects of a forest disturbance on shredder production in southern Appalachian headwater streams

• 1 The effects of a forest disturbance were investigated by comparing production of leaf-shredding aquatic insects in three streams draining a mature hardwood forest and three streams draining an 11-year-old, cable-logged clearcut.
• 2 Reference streams contained significantly greater mean annual standing crop of leaf material and significantly more slow-processing leaf material than disturbed streams. Disturbed streams had a significantly higher mean annual standing crop of fast-processing leaf material than the reference streams.
• 3 Leaf-shredding cranefly (Tipula abdominalis), caddisfly (Pycnopsyche gentilis), and stonefly (Tallaperla maria) larvae comprised over 95% of shredder biomass in all streams. Total shredder production was significantly greater (P<0.05) in disturbed versus reference streams, but individual production rates were not significantly different between stream types.
• 4 Pycnopsyche gentilis larvae were present at higher densities and achieved significantly greater annual biomass in disturbed versus references streams, Biomass of P. gentilis was significantly correlated with the standing crop of fast-processing, early successional leaf material in samples, whereas biomass of other shredders was correlated significantly with medium or slow-processing leaf species characteristic of later stages of forest succession.

     

An experimental study of the influence of periphytic algae on invertebrate abundance in a Hong Kong stream

1. Small cages (294cm²) containing unglazed clay quarry tiles were used to investigate the influence of periphytic algae on macroinvertebrate abundance in a Hong Kong stream. Algal biomass was manipulated by shading cages with plastic sheets. Individual cages were assigned to one of three treatment groups: unshaded, shaded and deeply shaded. Invertebrate densities and algal biomass within cages were monitored after 23, 37 and 65 days. 2. Multiple-regression analysis revealed that algal biomass, invertebrate morphospecies richness and total abundance declined with greater shading intensity. The responses of individual invertebrate taxa varied: some (especially Trichoptera) were unaffected by shading, whereas grazers (Baetidae, Psephenidae and Elmidae) declined as shading increased. 3. Significant regressions of the densities of individual taxa upon algal and detrital standing stocks in cages had positive slopes, but algal biomass increased during the study while detrital standing stocks declined. Abundance of invertebrates declined or remained rather stable over time. Density increases resulting from a positive association with algae were apparently offset by declines in abundance correlated with reductions in detritus. 4. Declines in algal biomass were associated with greater shading to which animals may respond directly. To uncouple the link between scarcity of algae and reduction of light intensity, the plastic covers on two groups of cages (deeply shaded and unshaded) which had been placed in the stream for 28 days were reversed so that cages which had been shaded became unshaded and vice versa. The cages were recovered on day 33, Only Coleoptera demonstrated a positive association with atgae inside cages; no relationship between population densities and algal biomass or light intensity was apparent for other taxa. However, the design may have been confounded by deposition of sediment in the cages (due to declining stream discharge) which reduced population densities of colonizers. 5. This study documents changes in invertebrate abundance and morphospecies richness in response periphyton and detritus standing stocks within patches. Summation of such responses may account for observed variations in benthic communities among Hong Kong streams which differ in the extent of shading by riparian vegetation.     

Invasive willows drive instream community structure

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Structural characteristics of algal communities in thermally altered artificial streams

Algal community structure on natural substrates of thermally altered artificial streams was studied for one year. The streams were fed by a natural blackwater stream near Aiken, South Carolina. Temperature-related shifts in the abundance of major species were demonstrated. Red algae were absent from a stream heated 12·5°C above ambient, but remained abundant in streams heated 7·5°C or less. Water temperatures above 30°C produced blue-green algal dominance and eliminated several indigenous species. Substrate specificity was exhibited by all major taxa. Several taxa were abundant only on the bottom sediments and some showed a distinct affinity for either sand or silt, the principal bottom types.     

Filamentous green algae in freshwater streams on Signy Island,Antarctica

The streams of Signy Island are varied and extremely seasonal environments. Water flows from November/December to March/April; streams are frozen for the rest of the year. Streams usually flow through small, barren catchments and are nutrient poor, though they may be enriched by dense summer populations of seabirds and seals. Temperatures are consistently low. Stream depth is maximal during the spring melt period, declining over the course of the summer. Vegetation is exclusively algal, and filamentous chlorophytes from a particularly conspicuous component. Small numbers of vegetative cells survive the long frozen period in situ. A steady increase in standing crop results in a maximum 2 to 3 months after flow begins. Sloughing is the major loss mechanism and grazers are effectively absent. Three taxa of filamentous algae are common in Signy streams, species of Zygnema, Mougeotia and Klebsormidium. The distributions of these algae are described and related to physical and chemical features of their environment.     

Responses of benthic algae to nutrient enrichment in a shallow lake: Linking community production,biomass, and composition

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The survival of <Emphasis Type="Italic">Sicyopterus stimpsoni</Emphasis>, an endemic amphidromous Hawaiian gobiid fish,relies on the hydrological cycles of streams: evidence from changes in algal composition of diet through growth stages fish

Gut contents of larval, juvenile, and adult specimens of the Hawaiian gobiid fish Sicyopterus stimpsoni were examined to catalog the algal flora ingested by this species. The developmental stages of S. stimpsoni examined represented hallmark points in the fish’s life cycle corresponding with major migratory and metamorphic transitions. The algal flora was dominated by diatom species and shifted from taxa representative of a marine, planktonic community in larval fish to a freshwater, benthic community in juvenile and adult fish. This change in diet corresponds with the migration of larval fish to freshwater streams just prior to juvenile development in which rapid modification in mouth anatomy makes ingestion of planktonic algal species difficult. Benthic diatoms from juvenile and adult fish assemblages represented multiple genera that live in a narrow set of environmental conditions. These algae grow during a specific period in the development of the benthic algal community in Hawaiian streams. This suggests a highly specialized dietary behavior that depends heavily on continually restarting the benthic algal successional pattern, which appears to be regulated by the hydrological cycles of streams on the island.     

Acidity status and phytoplankton species richness,standing crop,and community composition in Adirondack,New York,U.S.A. lakes

The mid-summer phytoplankton communities of more than 100 Adirondack lakes ranging in pH from 4.0 to 7.2 were characterized in relation to 25 physical-chemical parameters. Phytoplankton species richness declined significantly with increasing acidity. Acidic lakes (pH < 5.0) averaged fewer than 20 species while more circumneutral waters (pH > 6.5) averaged more than 33 species. Phytoplankton abundance was not significantly correlated with any of the measured physical-chemical parameters, but standing crop parameters, i.e., chlorophyll a and phytoplankton biovolume, did correlate significantly with several parameters. Midsummer standing crop correlated best with total phosphorus concentration but acidity status affected the standing crop-phosphorus relationship. Circumneutral waters of low phosphorus content, i.e. < 10 µg·1^–1 TP, averaged 3.62 µg·1^–1 chlorophyll a whereas acidic lakes of the same phosphorus content averaged only 1.96 µg·1^–1 chlorophyll a. The midsummer chlorophyll content of lakes of high phosphorus content, i.e. > 10 µg·1^–1 TP, was not significantly affected by acidity status.Adirondack phytoplankton community composition changes with increasing acidity. The numbers of species in midsummer collections within all major taxonomic groups of algae are reduced with increasing acidity. The midsummer phytoplankton communities of acidic Adirondack lakes can generally be characterized into four broad types; 1) the depauperate clear water acid lake assemblage dominated by dinoflagellates, 2) the more diverse oligotrophic acid lake community dominated by cryptomonads, green algae, and chrysophytes, 3) the productive acid lake assemblage dominated by green algae, and 4) the chrysophyte dominated community. The major phytoplankton community types of acid lakes are associated with different levels of nutrients, aluminum concentrations, and humic influences.     

Relationships between macroinvertebrate communities and environmental variables in metal-contaminated streams in south-west England

1. Macroinvertebrate species and information on thirty-nine variables were recorded at forty-six sites on twelve Cornish streams affected to varying extents by past metalliferous mining. 2. Relationships between macroinvertebrate communities and environmental variables were examined using canonical correspondence analysis (CCA). Copper was the strongest correlate with Axis 1 of the analysis, suggesting that it may have a major role in determining community structure. There were also strong correlations between Axis 1 and aluminium, alkalinity, pH, dissolved organic matter and algal cover, and between Axis 2 and discharge. 3. CCA distinguished four site groupings. In spite of seasonal changes in position on the ordination, as revealed through CCA and detrended correspondence analysis (DCA), sites retained their group membership. There were differences in the proportions of the major taxa within the four CCA-derived groups. In the group with the highest copper concentration, Ephemeroptera were absent, but triclads and chironomids were abundant, with Orthocladiinae the dominant group. 4. Changes in the occurrence of species along the metal gradient reflected changes in sensitivity. Tolerance' plots of selected species based on the CCA site ordination diagram were used to identify environmental thresholds. 5. As well as direct toxic effects of copper and aluminium on invertebrate communities, co-precipitation of these two metals could be an important physical factor. Further modifying influences resulting from interactions between toxic metals and pH, alkalinity, hardness and dissolved organic matter contributed to the complexity of conditions affecting the faunal community in metal-contaminated streams. 6. The most severely contaminated sites, with mean copper concentration exceeding 500 μgl^?1, were all characterized by a reduced community dominated by the flatworm Phagocata vitta, the chironomids Chaetodadius melaleucus and Eukiefferiella claripennis and the net-spinning caddis Plectrocnemia conspersa. The necessity for species identification is demonstrated in relation to variation in metal tolerance.     

A comparison of algal,macroinvertebrate, and fish assemblage indices for assessing low-level nutrient enrichment in wadeable Ozark streams

Biotic indices for algae, macroinvertebrates, and fish assemblages can be effective for monitoring stream enrichment, but little is known regarding the value of the three assemblages for detecting perturbance as a consequence of low-level nutrient enrichment. In the summer of 2006, we collected nutrient and biotic samples from 30 wadeable Ozark streams that spanned a nutrient-concentration gradient from reference to moderately enriched conditions. Seventy-three algal metrics, 62 macroinvertebrate metrics, and 60 fish metrics were evaluated for each of the three biotic indices. After a group of candidate metrics had been identified with multivariate analysis, correlation procedures and scatter plots were used to identify the four metrics having strongest relations to a nutrient index calculated from log transformed and normalized total nitrogen and total phosphorus concentrations. The four metrics selected for each of the three biotic indices were: algae—the relative abundance of most tolerant diatoms, the combined relative abundance of three species of Cymbella, mesosaprobic algae percent taxa richness, and the relative abundance of diatoms that are obligate nitrogen heterotrophs; macroinvertebrate—the relative abundance of intolerant organisms, Baetidae relative abundance, moderately tolerant taxa richness, and insect biomass; fish—herbivore and detritivore taxa richness, pool species relative abundance, fish catch per unit effort, and black bass (Micropterus spp.) relative abundance.All three biotic indices were negatively correlated to nutrient concentrations but the algal index had a higher correlation (rho = ?0.89) than did the macroinvertebrate and fish indices (rho = ?0.63 and ?0.58, respectively). Biotic index scores were lowest and nutrient concentrations were highest for streams with basins having the highest poultry and cattle production. Because of the availability of litter for fertilizer and associated increases in grass and hay production, cattle feeding capacity increases with poultry production. Studies are needed that address the synergistic effect of poultry and cattle production on Ozark streams in high production areas before ecological risks can be adequately addressed.     

Algae, macrofaunal assemblages and temperature: a quantitative approach to intertidal ecosystems of Iceland

Algae and the associated macrofauna in two Icelandic intertidal ecosystems under cold and warm influence, respectively, were studied with respect to algae-macrofauna relationships and a possible effect of temperature on community structure. Two sites in Iceland were selected, Sandgerdi ligthhouse (64°8′N 22°40′W) on the southwestern coast, and Grimsey Island (66°33′N 18°04′W), in the north, on the Arctic Circle, where sea temperature is considerably lower (5° approximately). The biomass of algae and the number of species of algae and macrofauna were higher in Sandgerdi than in Grimsey, and the patterns of diversity, evenness, biomass and abundance also differed between the sites. In the intertidal zone of Sandgerdi, a total of 28 species of algae and 45 species of macrofauna were identified whereas only 16 algal species and 27 macrofaunal species were found in Grimsey. Canonical correspondence analysis (CCA) using algal biomass as the environmental variable were conducted, and revealed significant relationships between algae composition and the associated macrofauna; some macrofauna taxa showed specific trophic or refuge relationships with algal species. According to the CCA, Corallina officinalis showed the highest correlation with macrofaunal assemblages in both study sites. However, correlations between macrofauna and other algae differed between Grimsey and Sandgerdi. The present study, together with additional observations in Greenland waters, shows a general decrease of species richness and diversity towards the north which may primarily be due to the temperature regime.     

Benthic invertebrate communities in six Danish forest streams: Impact of forest type on structure and function

I investigated the impact of riparian vegetation type on stream invertebrate communities in SIX Danish forest streams during the period 1992–1993 Two of the streams ran through beech forest Fagus sylvatica , two through mixed, mainly deciduous forest, and two through conifer plantations Algal biomass and detritus standing stock differed significantly depending on forest type In mixed deciduous forest streams algal biomass was higher and detritus standing stock lower than in beech and conifer forest streams Benthic invertebrate community composition was functionally similar in all streams, with detritivores comprising >80% by numbers of the community Grazer abundance was low in all streams Shredder abundance in the four deciduous streams was significantly correlated to coarse detritus standing stock When taking into account both quantitative and qualitative POM parameters for all six streams combined, shredder abundance correlated significantly to the amount of CPOM There were significantly more invertebrates with a ≥ 2 yr life cycle in the conifer and beech forest streams than m the mixed forest streams, probably reflecting the larger and more stable food resource For all streams combined there was a significant correlation between predator abundance and the abundance of potential prey My findings suggest that Danish forest streams are regulated by "bottom-up control" at all trophic levels within the invertebrate community, and hence that forest type can structure benthic communities in forest streams     

A quantitative study of calcareous stream and Tintenstriche algae from the Malham district,Northern England

The algal floras of two limestone streams and two calcareous Tintenstrichen are described and compared. The most important factor governing the distribution and abundance of species was the availability of water. Permanently wet stands, dominated by filamentous blue-green algae (Schizothrix calcicola and Phormidium incrustatum) had a greater species diversity than stands subject to frequent drying which were dominated by coccoid blue-green algae (Gloeocapsa spp.).

Significant correlations were found between S. calcicola and water pH (+ve), total species numbers and pH (+ve), filamentous blue-green algae and aufwuchs thickness (+ve) and Calothrix numbers and rock mass colonized (+ve).

The algal flora of the Tintenstrichen and the streams differed, although both developed upon the same limestone formation. The results are discussed with reference to previous work, substratum stability, aufwuchs structure, water chemistry, light and temperature.