Development of filamentous green algae in the benthic algal community in a littoral sand-beach zone of Lake Biwa

Temporal changes of biomass and dominant species in benthic algal communities were investigated in a littoral sand-beach zone in the north basin of Lake Biwa from December 1999 to September 2000. Chlorophyll-a amounts of benthic algal communities per unit area of the sandy sediments rapidly increased from late April to June. Increases in biomass of the benthic algal communities are considered to result from the propagation of filamentous green algae Oedogonium sp. and Spirogyra sp. The cell numbers of filamentous green algae and chlorophyll-a amounts of benthic algal communities at depths of 30 and 50cm at a station protected by a breakwater in May were significantly higher than those of a station exposed directly to wave activity. Thus, the biomass accumulation of the benthic algal communities seems to be regulated strongly by wave disturbance. The development of filamentous green algae may contribute to the increase in biomass of the benthic algal community and to the changes in seasonal patterns of biomass in the sand-beach zone of Lake Biwa. We consider that the development of the filamentous green algal community in the littoral zone of Lake Biwa is the result of eutrophication.     

The independent and interactive effects of snail grazing and nutrient enrichment on structuring periphyton communities

We investigated the independent and interactive effects of nutrient enrichment and snail grazing on structuring periphyton communities in a northern temperate lake. Nutrient releasing substrates and grazer enclosures were used to simultaneously manipulate nutrient availability and herbivory. Periphyton was allowed 18 days to accrue before grazers (Elimia livescens = Goniobasis livescens) were introduced.Addition of nitrogen and phosphorus caused a significant increase in biovolume (p < 0.001), whereas grazing had no significant effect on biovolume but resulted in a shift in species composition. Four taxa were largely responsible for the increase in biovolume on the nutrient enriched substrates: Oedogonium sp, Stigeoclonium tenue, Navicula radiosa var. radiosa and Navicula radiosa var. tenella. By the 28th day, nutrient enrichment caused a shift from a community dominated by diatoms (Bacillariophyceae) to a community dominated by green algae (Chlorophyceae). Blue green algae (Myxophyceae) maintained an equal proportion in high and low-nutrient regimes.Grazing had a more pronounced effect on altering community composition on the nutrient enriched substrates than on the unenriched substrates. Grazing caused a decrease in diversity and an increase in dominance by green algae on the nutrient enriched substrates. The relative biovolume of green algae increased from 64% to 93% on grazed substrates, due to the significant increase in relative abundance of Stigeoclonium tenue. This taxon has both prostate basal cells and erect filamentous cells. The ratio of basal: filamentous cells increased from 4.7 to 5.2 with grazing, suggesting that the heretotrichous growth form of Stigeoclonium tenue is adapted to grazing by virtue of the basal cells which are able to adhere to the substratum and resist being grazed.     

Characteristics of softwater streams in Rhode Island II. Composition and seasonal dynamics of macroalgal communities

Forty stream segments in Rhode Island, U.S.A., were examined seasonally from June 1979 to March 1982. Thirty-nine species of macroalgae were collected, respresenting 25 genera. The composition of the lotic flora was 54% green algae, 31% red algae, 5% blue-green algae, 5% xanthophytes, 3% chrysophytes and 3% diatoms. The majority of these taxa (85%) were filamentous. From a biweekly examination of five stream segments, macroalgal communities could be grouped according to light regime. Species in unshaded streams exhibited little seasonality, whereas in streams shaded by one or more layers of riparian canopy, maxima in species numbers and abundance occurred during colder seasons. The most widespread and abundant species were the blue-green alga Phormidium retzii, the green alga Draparnaldia acuta, and the diatom Eunotia pectinalis. P. retzii and E. pectinalis were aseasonal annuals, while D. acuta was primarily a winter-spring form. It appears that pH is a major factor affecting broad geographic distribution patterns of stream macroalgae, whereas the light regime established by overhanging canopy is an important factor which influences localized abundance and seasonality of lotic macroalgal communities. Niche pre-emption appears to be a common mode of resource space division among stream macroalgae in Rhode Island. E. pectinalis is the strongly developed dominant in this drainage system.     

Food Limitation Affects Algivory and Grazer Performance for New Zealand Stream Macroinvertebrates

We studied herbivory and grazer performance (i.e., fitness correlates) for the hydrobiid snail Potamopyrgus antipodarum, the leptophlebiid mayfly Deleatidium spp., and the conoesucid caddisfly Pycnocentrodes aeris, common, co-occurring algivores in many New Zealand streams. Grazing effects and costs of coexisting differed among these taxa reared at ambient densities in different combinations in microcosms with algal food conditions (on clay tiles) characteristic of heavily grazed streams. The prostrate diatoms Staurosirella leptostauron, Cymbella novazealandia, and Achnanthidium minutissimum were the dominant algal species on pre- and post-grazed tiles. The relative abundance of erect physiognomic forms, dominated by Synedra ulna and Fragilaria vaucheriae, were 2–3× higher in ungrazed controls and in snail alone treatments than in other grazer treatments. The green filamentous algae Mougeotia sp. and Stigeoclonium lubricum, and the cyanophyte Merismopedia glauca were present only in ungrazed controls. Grazers significantly reduced algal community biomass in treatments by 26–52% relative to controls, except snails alone. Snails (15–30%) burrowed into surrounding sand substrates, dampening their grazing impact on tiles. Caddisflies were more effective than mayflies or snails at removing algae because of higher foraging rates, a larger body size, and an abrasive sand-grained case. Algal biomass reductions did not affect grazer growth. However, pre-pupation rates of caddisflies and emergence rates of subimago mayflies were significantly higher in caddisfly-alone and mayfly-alone treatments, respectively, than in combined-species treatments. These results imply that a limited periphytic food supply ( < 0.3 mg AFDM cm⁻²) even over a relatively brief period ( ≤ 16 d) may have population-scale consequences for co-existing P. aeris and Deleatidium spp.     

DISTURBANCE OF STREAM PERIPHYTON BY PERTURBATIONS IN SHEAR STRESS: TIME TO STRUCTURAL FAILURE AND DIFFERENCES IN COMMUNITY RESISTANCE1

The resistance of stream periphyton to structural disturbance by increases in shear stress (simulating a spate) was investigated in a laboratory flow tank. We monitored loss of biomass from a filamentous community (dominated by Melosira varians) under four different levels of shear stress. In each case, any loss that was going to occur did so within 10 min for this community. In a second experiment, we tested the resistance of four different communities (two dominated by nonfilamentous diatoms and two dominated by filamentous green algae/diatoms) to increases in shear stress. Nine different levels of shear stress were used, ranging from 1- to 70-fold higher than the conditions to which the communities were acclimated. All communities were 14 days old, but some differences in initial biomass occurred that influenced the degree of resistance independently of species composition. Overall, the nonfilamentous diatom communities were the most resistant, and the filamentous communities were the least resistant. The kinetics of the sloughing process varied among community types, with a community dominated by Melosira varians/Gom-phonema parvulum losing 50% of its biomass with only a 3-fold increase in shear stress. In contrast, a community dominated by the nonfilamentous diatoms Fragilaria vaucheriae/Cymbella minuta lost <50% of its biomass after a 70-fold increase in shear stress. Shear stresses required for 50% loss of biomass for the different communities were as follows: 3.6 Newtons.m^?2 for the Melosira varians/Gomphonema parvulum community, 10.0 N.m^?2 for the Spirogyra sp./Gomphoneis her-culeana/Ulothrix zonata community, 50.6 N.m^?2 for the Fragilaria construens/Cymbella minuta/Ach-nanthes minutissima community, and >90.0 N.m^?2for the Fragilaria vaucheriae/Cymbella minuta community. These results show that spates without bedload movement can potentially have widely differing disturbance effects on periphyton loss among streams depending on the initial taxonomic composition of resident communities. These results have important implications for stream ecosystem analysis and modeling.     

Recent increase of filamentous algae in shallow Swedish bays: Effects on the community structure of epibenthic fauna and fish

A summary is presented of estimates of distribution and growth of filamentous algae and its effect on the structure and functioning of epibenthic fauna and fish communities in shallow bays on the Swedish west coast. As a consequence of coastal eutrophication vegetation cover has gradually increased during the last decade, and during 1990's most bays in the Skagerrak-Kattegat area were variously covered with filamentous algae during spring and summer (May–July). In some areas filamentous algae (mainlyCladophora andEnteromorpha) completely covered the bottom. In field studies it was demonstrated that increased cover and dominance of filamentous algae result in structural changes of the epibenthic fauna community. Field studies showed that species richness and biomass of epibenthic fauna increased in a sandy bay with a moderate increase (30 to 50%) of filamentous algae cover. At higher cover (90%), biomass of epibenthic fauna was reduced, however, to the same level as for the sandy habitat, although the dominant epibenthic species were different. Heavy growth of epiphytic filamentous algae on eelgrass resulted in reduced biomass and a shift in the species composition of the epibenthic fauna community. Fish assemblage structure was also related to changes in vegetation. In eelgrass beds, fish species numbers were reduced with increasing cover of epiphytic filamentous algae, and at rocky bottoms with kelp algae (dominated byFucus), fish biomass decreased with increasing cover of attached filamentous algae. Further, foraging efficiency of juvenile cod and settling success of plaice were reduced as a response to increasing dominance of filamentous algae.     

The influence of macrophytes on a phytoplankton community in experimental conditions

The impact of submerged macrophytes or their extracts on planktonic algae was studied under experimental conditions. Live Ceratophyllum demersum L., its extract, and extracts of four other plant species induced modifications in the phytoplankton dominance structure. These modifications were: a decline in the number of Oscillatoria limnetica Lemm., which was the most numerous cyanobacterian species, and a decline in biomass and percentage contribution of all cyanobacteria to total algal biomass. This was accompanied by an increase in biomass and percentage contribution of green algae, especially Chlorella sp. and Chlamydomonas sp. Also, there was an increase in biomass and percentage contribution of nanoplankton (under 50 µm) to total phytoplankton biomass.The isolation of planktonic algae from direct influence of C. demersum by means of dialysis membranes caused an increase in number, biomass and percentage contribution of cyanobacteria. Release of organic compounds of over 3000 daltons by macrophytes apparently contributed to a decline of cyanobacteria by changing the phytoplankton dominance structure.     

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.     

SOME FACTORS IN THE COMPETITION OR ANTAGONISM AMONG BACTERIA, ALGAE, AND AQUATIC WEEDS

Field observations of changes in the populations of aquatic weeds and phytoplankton have confirmed that aquatic weeds have antagonistic activity toward phytoplankton. Nutritional studies in the laboratory indicate that cultures of the aquatic weeds, Myriophyllum sp., Ceratophyllum sp., and duckweed (Lemma minor L.); liquid cultures of barley (Hordeum vulgare L., Dickson variety); and cultures of the filamentous green algae, Cladophora sp. and Pithophora oedogonium (Mont.) Withrock, will remain relatively free of epiphytes or competing phytoplankton if the cultures are nitrogen-limited. Field observations of Cladophora sp. have confirmed that the growth of epiphytes on the Cladophora is related to conditions of surplus available nitrogen compounds. It is proposed that this antagonistic activity may be due to a “nitrogen sink” effect in which the aquatic weeds or filamentous green algae prevent the growth of contaminating algae by competition for the limited nitrogen compounds available. However, the presence of bacteria-sized organisms which have selective toxicity to certain algae indicates that perhaps multiple factors exist. Discussed are the ecological implications of associations of certain algae with bacteria that have selective toxicities for other species of algae under certain environmental conditions such as nitrogen-limited growth.     

Winter phytoplankton communities in different depths of three mesotrophic lakes (Łęczna-Włodawa Lakeland, Eastern Poland)

Phytoplankton samples were collected from three mesotrophic lakes: Piaseczno, Rogóźno and Krasne during winter seasons (from January to March). The samples were analyzed for species analysis and abundance of planktonic algae in relation to different depths of water column (0–7 m). Selected water physical-chemical parameters were also measured. Abundance of phytoplankton depended strongly on the thickness of snow and ice cover or mixing conditions. The maximal phytoplankton total number reached about 5 × 10⁶ ind. L⁻¹ beneath the clear ice in the Krasne Lake, minimal numbers were recorded under the thick snow and ice layers in the Piaseczno Lake (2 × 10³ ind. L⁻¹). The winter phytoplankton communities were dominated by flagellates principally cryptomonads (Cryptomonas spp. Rhodomonas minuta), euglenophytes (Trachelomonas volvocina, T. volvocinopsis), dinoflagellates (Peridinium bipes, Gymnodinium helveticum) and chrysophytes (Mallomonas elongata, M. akrokomos, Dinobryon sociale) or non-motile small species of blue-green algae (e.g. Rhabdoderma lineare, Limnothrix redekei), diatoms (Stephanodiscus spp., Asterionella formosa), and green algae (e.g. Scenedesmus spp., Monoraphidium spp.). Phytoplankton abundance and structure showed differentiation during the winter season and along the water column as well.     

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.     

Natural succession of macroalgal-dominated epibenthic assemblages at different water depths and after transplantation from deep to shallow water on Spitsbergen

In the current study, we investigated the primary succession of seaweeds over different time periods at different water depths. Furthermore, we followed the succession of field-grown benthic communities of different successional age, developing on ceramic tiles, prior to and after transplantation from 8 to 0.5 m water depth. The transplantation simulated changes associated with the break up of sea-ice cover, e.g. light regime or wave exposure. For this purpose, we transplanted 12 and 21-month old communities, grown at 8 m water depth, together with a set of sterile tiles, onto rafts, floating in 0.5 m water depth. Our results describe for the first time the succession of macroalgal communities in the Arctic and give important insights into the effect of disturbance of differently aged communities. The primary succession at 0.5 m water depth was mainly driven by Bacillariophyta and filamentous green algae like Urospora sp. and Ulothrix implexa. Twelve-month old communities at 8 m water depth are dominated by members of the Ectocarpales (Phaeophyceae), like Pylaiella littoralis, P. varia, and Ectocarpus siliculosus and the green alga U. implexa, whereas the 21-month old community showed a higher cover of the green algal class Ulvophyceae and sessile invertebrates. After transplantation to near surface conditions, species composition of the communities changed, but this effect was differently strong between communities of different age.     

金沙江上段浮游藻类和着生藻类群落格局及其与环境因子的关系比较研究

比较河流浮游藻类和着生藻类群落的时空格局及其与环境因子关系的差异,有助于了解两类藻的区别与联系。然而,目前这方面的研究还不多。基于2019年秋季和2020年夏季金沙江上段干流17个样点藻类及水体理化指标的调查数据,分析了不同季节浮游藻类和着生藻类群落结构及其主要环境驱动因子,比较了两类藻的多样性格局及其与环境关系的异同。结果发现,调查河段的浮游藻类和着生藻类均以硅藻为主,其中浮游藻类以极小曲壳藻(Achnanthes minutissima)、钝脆杆藻(Fragilaria capucina)、适中舟形藻(Navicula accomoda)为主要优势种,着生藻类以极小曲壳藻(Achnanthes minutissima)、扁圆卵形藻(Cocconeis placentula)、橄榄绿色异极藻(Gomphonema olivaceum)为主要优势种。浮游藻类和着生藻类秋季平均密度分别为:2.41×10~5个/L、9.43×10~3个/cm~2,均明显高于夏季的平均密度(4.84×10~4个/L、4.84×10~3个/cm~2)。两类藻的群落格局表现出明显的季节变化,但只有着生藻分类单元...     

Diet,food preference,and algal availability for fishes and crabs on intertidal reef communities in southern California

Synopsis Herbivory by wide-ranging fishes is common over tropical reefs, but rare in temperate latitudes where the effects of herbivorous fishes are thought to be minimal. Along the west coast of North America, herbivory by fishes on nearshore reefs is largely restricted to a few members of the Kyphosidae, distributed south of Pt. Conception. This paper presents information on natural diets and results from feeding choice experiments for two abundant kyphosids from intertidal habitats in San Diego, California —Girella nigricans andHermosilla azurea, and similar data for the lined shore crab,Pachygrapsus crassipes, which also forages over intertidal reefs. These results are compared with the availability of algae in intertidal habitats measured during summer and winter, on both disturbed and undisturbed habitats. The diets of juveniles ofG. nigricans andH. azurea collected from nearshore habitats were dominated by animal prey (mainly amphipods), but adults of these fishes, andP. crassipes, consumed algae nearly exclusively, with 26, 10, and 14 taxa of algae identified fromG. nigricans, H. azurea, andP. crassipes, respectively. Algae with sheet-like morphologies (e.g.Ulva sp.,Enteromorpha sp., members of the Delesseriaceae) were the principal algae in the diets of the fishes, and calcareous algae (e.g.Corallina sp.,Lithothrix aspergillum) and sheet-like algae (Enteromorpha sp.) comprised the greatest identifiable portion of the shore crab's diet. Feeding choice experiments indicated that the fishes preferred filamentous algae (e.g.Centroceras clavulatum, Polysiphonia sp.,Chondria californica) and sheet-like algae (e.g.Enteromorpha sp.,Ulva sp.,Cryptopleura crispa) over other algal morphologies, whereas the shore crab chose jointed calcareous algae (e.g.Lithothrix aspergillum, Corallina vancouveriensis, Jania sp.) most frequently. The diets and preferences for algae by the fishes were generally most similar to the assemblage of algae available in early successional (disturbed) habitats during summer when sheet-like and filamentous algae are abundant. The shore crab exhibited the opposite trend with a diet more similar to late successional (undisturbed) habitats.     

空间层次及人工基质对着生藻类建群特性的影响

为全面了解着生藻类在建群中群落变化的生态学特性,揭示着生藻类的建群规律,在以丝状藻类为优势藻的生态塘中,采用花岗岩和瓷砖为附着材料,设置水体底部和中部为附着位点,进行频次为10d的采样分析。结果表明,生态塘中共检出8门73属117种着生藻类,其中以硅藻、蓝藻、绿藻为优势类群。同时不同人工基质和不同空间层次条件下着生藻类的建群特征较一致,早期以单细胞硅藻如舟形藻(Navicula sp.)、脆杆藻(Fragilaria sp.)、曲壳藻(Achnanthes sp.)等为优势,后期以丝状藻类如鞘丝藻(Lyngbya sp.)、颤藻(Oscillatoria sp.)、伪鱼腥藻(Pseudanabaena sp.)等为优势;研究结果发现不同人工基质(花岗岩和瓷砖)对着生藻类的种类组成、细胞密度、生物量和藻类多样性无显著影响,花岗岩和瓷砖上附着的着生藻类具有较高的相似性;但不同的空间层次对着生藻类建群特征影响明显,水体底部具有更多的硅藻种类数,中部具有更多的绿藻,随着建群时间的发展,蓝藻比例不断增加;就生物量而言,底部的着生藻类叶绿素a显著高于水体中部,但两者的细胞密度无显著性差异;随着建群过程的发展,水体底部的着生藻类生物量达峰值所需的时间比中部更长。通过相关性分析,生态塘中着生藻类的生长主要受总磷的影响。     

Microbial Biofilms on the Sandstone Monuments of the Angkor Wat Complex,Cambodia

Discoloring biofilms from Cambodian temples Angkor Wat, Preah Khan, and the Bayon and West Prasat in Angkor Thom contained a microbial community dominated by coccoid cyanobacteria. Molecular analysis identified Chroococcidiopsis as major colonizer, but low similarity values (<95%) suggested a similar genus or species not present in the databases. In only two of the six sites sampled were filamentous cyanobacteria, Microcoleus, Leptolyngbya, and Scytonema, found; the first two detected by sequencing of 16S rRNA gene library clones from samples of a moist green biofilm on internal walls in Preah Khan, where Lyngbya (possibly synonymous with Microcoleus) was seen by direct microscopy as major colonizer. Scytonema was detected also by microscopy on an internal wall in the Bayon. This suggests that filamentous cyanobacteria are more prevalent in internal (high moisture) areas. Heterotrophic bacteria were found in all samples. DNA sequencing of bands from DGGE gels identified Proteobacteria (Stenotrophomonas maltophilia and Methylobacterium radiotolerans) and Firmicutes (Bacillus sp., Bacillus niacini, Bacillus sporothermodurans, Lysinibacillus fusiformis, Paenibacillus sp., Paenibacillus panacisoli, and Paenibacillus zanthoxyli). Some of these bacteria produce organic acids, potentially degrading stone. Actinobacteria, mainly streptomycetes, were present in most samples; algae and fungi were rare. A dark-pigmented filamentous fungus was detected in internal and external Preah Khan samples, while the alga Trentepohlia was found only in samples taken from external, pink-stained stone at Preah Khan. Results show that these microbial biofilms are mature communities whose major constituents are resistant to dehydration and high levels of irradiation and can be involved in deterioration of sandstone. Such analyses are important prerequisites to the application of control strategies.     

Environmental Factors Associated with the Eukaryotic Microbial Community and Microalgal Groups in the Mountain Marshes of South Korea

The diversity indices of eukaryotic microalgal groups in the Jeonglyeongchi, Waegok, and Wangdeungjae marshes of Mount Jiri, Korea, were measured using Illumina MiSeq and culture-based analyses. Waegok marsh had the highest species richness, with a Chao1 value of 828.00, and the highest levels of species diversity, with Shannon and Simpson index values of 6.36 and 0.94, respectively, while Wangdeungjae marsh had the lowest values at 2.97 and 0.75, respectively. The predominant species in all communities were Phagocata sibirica (Jeonglyeongchi, 68.64%), Aedes albopictus (Waegok, 34.77%), Chaetonotus cf. (Waegok, 24.43%), Eimeria sp. (Wangdeungjae, 26.17%), and Eumonhystera cf. (Wangdeungjae, 22.27%). Relative abundances of the microalgal groups Bacillariophyta (diatoms) and Chlorophyta (green algae) in each marsh were respectively: Jeonglyeongchi 1.38% and 0.49%, Waegok 7.0% and 0.3%, and Wangdeungjae 10.41% and 4.72%. Illumina MiSeq analyses revealed 34 types of diatoms and 13 types of green algae. Only one diatom (Nitzschia dissipata) and five green algae (Neochloris sp., Chlamydomonas sp., Chlorococcum sp., Chlorella vulgaris, Scenedesmus sp.) were identified by a culture-based analysis. Thus, Illumina MiSeq analysis can be considered an efficient tool for analyzing microbial communities. Overall, our results described the environmental factors associated with geographically isolated mountain marshes and their respective microbial and microalgal communities.     

The Effects of pH on a Periphyton Community in an Acidic Wetland, USA

Despite the importance of peatlands, the algal ecology of peatlands and the periphyton communities which are abundant in these habitats are relatively understudied. We performed an in situ manipulation of pH in an intermediate fen in northern lower Michigan in order to examine how hydrogen ion concentrations structure an epiphytic algal community. Levels of pH were manipulated in enclosures from the control level (pH = 5) to an acid treatment (pH = 4) by adding H₂SO₄ and a neutral treatment (pH = 7) by adding NaOH. Algal communities growing on sections of Chamaedaphne calyculata (L.) Moench stems were examined after 22 days of colonization. Chlorophyll a concentration was significantly greater only in the acid treatment (~5.5 mg m⁻²) relative to the control (~3.5 mg m⁻²). Taxa richness was lower in the acid treatment. The algal assemblages were dominated by filamentous green algae and a filamentous taxon, Mougeotia spp., was significantly greater in the acid treatment relative to the control. Increases in Zygnemataceae and Oedogonium spp. most likely account for the higher chlorophyll a in the acid treatment. Most treatment differences were detected in the neutral treatment, including increased abundances of Closterium polystichum Nygaard, Cosmarium sp., Peridinium inconspicuum Lemmermann, and Synedra acus Kütz. Unexpectedly, there was no strong response of the desmid community. These data can be informative in the development of algal monitoring programs in peatlands when assessment of acidification is desired.     

How will increased temperature and nutrient enrichment affect primary producers in sub‐Arctic streams?

1. Spring‐fed streams, with temperatures ranging from 7.1 to 21.6 °C, in an alpine geothermal area in SW Iceland were chosen to test hypotheses on the effects of nutrients and temperature on stream primary producers. Ammonium nitrate was dripped into the lower reaches of eight streams, with higher reaches being used as controls, during the summers of 2006 and 2007. Dry mass of larger primary producers, epilithic chlorophyll a and biovolumes of epilithic algae were measured. 2. Bryophyte communities were dominated by Fontinalis antipyretica, and biomass was greatest in the warmest streams. Jungermannia exsertifolia, a liverwort, was found in low densities in few samples from cold streams but this species was absent from the warmest streams. 3. Nutrient enrichment increased the biomass of bryophytes significantly in warm streams. No effects of the nutrient addition were detected on vascular plants. The biomass of larger filamentous algae (mainly Cladophora spp.) was significantly increased by nutrient enrichment in cold streams but reduced by nutrients in warm streams. Thalloid cyanobacteria (Nostoc spp.) were not affected by nutrients in cold streams but decreased with nutrient addition in warm streams. Epilithic algal chlorophyll a was increased by nutrients in all streams and to a greater extent in 2007 than in 2006. Nutrient addition did not affect the epilithic chlorophyll a differently in streams of different temperatures. 4. There were small differential effects of nutrients, influenced by pH and conductivity, on different epilithic algal groups. 5. As global temperatures increase, animal husbandry and perhaps crop agriculture are likely to increase in Iceland. Temperature will directly influence the stream communities, but its secondary effects, manifested through agricultural eutrophication, are likely to be much greater.     

Factors affecting the distribution of stream macroinvertebrates in geothermal areas: Taupo Volcanic Zone,New Zealand

The distribution of macroinvertebrates was investigated among sites within five geothermally influenced and two non- or minimally-influenced streams in the Taupo Volcanic Zone, New Zealand, to examine the responses of communities to broad environmental gradients within and among habitats. To date, examination of geothermal stream macroinvertebrates has typically been from single habitats, and has not been examined over a regional scale. Sites within and among streams represented a range of sizes, depths, water velocities and substrate types. Sites with little or no geothermal influence typically had temperatures less than 15°C and pH between 5 and 8. Four of the geothermally influenced streams had temperatures greater than 25°C, and ranged from alkaline (pH 9.1) to highly acidic (pH 3.0). Most taxa recorded were typical inhabitants of non-geothermal streams that are tolerant to elevated temperatures, extreme pH conditions and/or high toxicant levels. Diptera, Coleoptera and Mollusca dominated geothermal sites, and Ephemeroptera, Plecoptera and Trichoptera were absent. In addition, an obligate dweller of geothermal habitats, Ephydrella thermarum, and a nonindigenous tropical gastropod, Melanoides tuberculata, were recorded. Canonical correspondence analysis implicated multiple factors in determining the distribution of invertebrates over the region. Overall, distribution was most strongly associated with temperature gradients, particularly longitudinally within streams. This distribution was likely directly related to species temperature tolerances, but also temperature effects on algal abundance and composition, its differential effects on species’ potential competitors and predators, and its effects on toxicant availability. Differences in invertebrate composition among streams were associated with major differences in pH and substrate. Increased acidity was associated with a significant decrease in invertebrate taxa richness, with acidic sites having a limited fauna dominated by dipterans (e.g., Naonella sp., Polypedilum sp.). Stability of flow and environmental conditions may enhance competitive interactions among taxa, enhancing the importance of substrate type in these systems. The presence of non-indigenous species (e.g., M. tuberculata, Poecilia reticulata), currently limited in distribution, also affected species composition. Overall, communities become less speciose, although more unusual in composition, with increased geothermal influence. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens