Ectomycorrhizal mycelial species composition in apatite amended and non-amended mesh bags buried in a phosphorus-poor spruce forest

We studied the effect of apatite amendment on ectomycorrhizal (EM) mycelial biomass production and species composition in a phosphorus-poor spruce forest using sand-filled mesh bags. Control and apatite-amended bags were buried in pairs in the lower part of the organic horizon for one growth season. DNA extraction, PCR of the ITS region, cloning and random sequencing were used to examine the fungal species composition in each bag. Sequences were identified by comparison with the UNITE database and GenBank. Our study confirmed previous results that the major fungal ingrowth in mesh bags was of EM origin. On average 13 species were detected in each bag. Tylospora fibrillosa, Amphinema sp., Tomentellopsis submollis, and Xerocomus badius made up almost 80 % of the EM sequences. High biomass was related to increased dominance of specific species. There were no statistically significant differences in biomass production estimated from PLFA 18:2ω6, 9, or between fungal communities of apatite-amended and control bags estimated from DNA after one growth season. The potential of the mesh bag method in studies of functional diversity of EM mycelia in the field is discussed.     

Planktonic food chains of a highly humic lake

The development and metabolism of the plankton of a highly humic lake were followed over the vernal primary production maximum. The study was made in a mesocosm in which large filter feeders, typical of this lake in summer, were absent. During the rising phase of phytoplankton, the community was predominantly autotrophic. The most important constituents in the algal biomass were a dinoflagellate, Gymnodinium sp. (40–50%), and a prasinophycean, Scourfieldia cordiformis (7%). The biomasses of Chlamydomonas spp. and Chrysococcus spp. reached their maxima a few days later and Cryptomonas sp. became most abundant at the end of the experiment. After the phytoplankton maximum, about one week from the beginning ofthe experiment, grazing of algae by phagotrophic protozoans and phosphate depletion led to a rapid decrease of algal biomass and the community became predominantly heterotrophic. In spite of a large variation in algal biomass and primary production, the biomass of bacteria remained of the same order of magnitude as in algae both before and after the algal maximum. Bacteria were mostly responsible for the plankton respiration, which also showed no dependence on primary production. Since exudation by phytoplankton was also low, the nutrition of bacterioplankton was probably mainly based on allochthonous dissolved organic matter rather than or primary production. Thus the production of bacteria was an additional food source for higher trophic levels along with phytoplankton. Because filter feeding zooplankton was absent in the experiment, protozoans were the only grazers utilizing algae and bacteria. Essentially all growth of bacteria was used by bacterivores.     

Trophic cascades in a temperate seagrass community

We assessed the relative importance of bottom–up and top–down processes in structuring an eelgrass community in Sweden, a system impacted both by eutrophication and overfishing. Using artificial seagrass as substrate, we manipulated nutrient levels and predator abundance in a full‐factorial cage‐experiment. The results revealed a seagrass community dominated by strong top–down processes controlling the aggregate biomass of mesograzers and macroalgae. In the absence of predators the large amphipod Gammarus locusta became very abundant resulting in a leaf community with low biomass of algae and smaller mobile fauna. One enclosed gobid fish predator reduced the abundance of adult G. locusta by >90%, causing a three to six times increase in the biomass of algae, smaller mesograzers and meiofauna. Numerous small predators in uncaged habitats reduced the biomass of G. locusta and other mesograzers by >95% in comparison to the fish treatment, further increasing the biomass of epiphytic algae and meiofauna. Although water column nutrient enrichment caused a temporal bloom of the filamentous macroalgae Ulva spp., no significant nutrient‐effects were found on the algal community at the end of the experiment. The only lasting nutrient‐effect was a significant increase in the biomass of G. locusta, but only in the absence of ambient predators. These results demonstrate that mesograzers can respond to enhanced food supply, increase their biomass and control the algal growth when predation rates are low. However, in the assessed system, high predation rates appear to make mesograzers functionally extinct, causing a community‐wide trophic cascade that promotes the growth of ephemeral algae. This top–down effect could penetrate down, despite a complex food‐web because the interaction strength in the community was strongly skewed towards two functionally dominant algal and grazer species that were vulnerable to consumption. These results indicate that overexploitation of gadoid fish may be linked to increased macroalgal blooms and loss of eelgrass in the area through a trophic cascade affecting the abundance of mesograzers.     

Effects of acidic pH and phytoplankton on survival and condition of Bosmina longirostris and Daphnia pulex

The effects of pH, algal composition and algal biomass on abundance, size, reproduction and condition of Daphnia pulex and Bosmina longirostris were tested in a field experiment using water and natural phytoplankton assemblages from a circumneutral (pH 6.43) and a moderately acidic (pH 5.75) lake in south-central Ontario. Both species were affected by pH and phytoplankton composition, with decreased egg production, lipid reserves, body size or abundance in treatments containing algae and/or water from the more acidic lake compared to treatments containing water and phytoplankton from the circumneutral lake. This result was unexpected for Bosmina, which often increases in relative and/or absolute abundance in acidified lakes. The negative effect of acidic conditions on Bosmina suggests that the population increase observed in most acidified lakes is not due to a positive response to low pH or ambient phytoplankton, but to altered biotic interactions possibly involving reduced competition.     

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.     

Leaf Decomposition in a Mountain Stream in the Sultanate of Oman

Decomposition of Juglans regia leaves was studied in fine and coarse mesh bags in a permanent mountain stream in Oman. A rapid initial mass loss, attributed to leaching, was followed by a more gradual decline. Daily exponential decay rates (k) calculated over 32 days were 0.011 (fine mesh litter bags) and 0.014 (coarse mesh litter bags). The difference between bag types was not significant, suggesting limited impact of leaf‐shredding invertebrates. Ergosterol levels on leaves from fine mesh bags peaked at 0.3 mg g^–1 AFDM after 16 days of stream exposure. During the experimental period, which followed the annual leaf fall, the concentration of aquatic hyphomycete conidia in the stream varied between 82 and 1362 l^–1. Based on the morphology of conidia found in the water column or released from leaves, we identified 14 species of aquatic hyphomycetes. Tetracladium apiense was the most common taxon (62.2% of conidia in water column during the field experiment). Three other Tetracladium species contributed another 8%. Plating out leaf particles yielded common epiphytic taxa such as Alternaria sp., Aureobasidium pullulans and Phoma sp. The measured metrics of leaf decay in this desert stream fall within the range of values observed in temperate and tropical streams, with clear evidence for an early leaching phase, and no evidence of a strong impact of leaf shredders. The community of aquatic hyphomycetes appears impoverished. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of water-stress on the fungal growth and quality of vegetable amaranth in storage

Amaranthus crucentus are usually short lived annual crops which probably originated in the Andcan region of South America. An experiment was conducted to determine the effects of water stress on the microbial growth and quality of vegetable Amaranth. Analysis of variance showed that microbial growth was significant at 17.63% as well as moisture stress at 128.1%. However nitrogen composition and water content was not significant at the 5% probability level. A polyethylene bag recorded the highest microbial growth 38.33% in comparison with a paper bag 14.67%, when those exposed had the lowest microbial growth 7.33%. Amaranthus crucentus packaged with polythene bags recorded the highest microbial growth, followed by those packaged with paper bags while those exposed had the lowest. The microbes observed were mainly Aspergillus species. The result of the investigation showed that on the first day, vegetable Amaranth packaged with paper bag had the highest weight loss of 17.02 g in comparison with the exposed sample of 14.08 g, while those packaged with polyethylene bags had the lowest weight loss of 0.33. Similar trends were observed on the third and sixth days respectively. Investigation showed that the exposed samples recorded the highest nitrogen composition of 0.06% followed by paper bag 0.030%, while polythene had the lowest 0.028%. However, vegetables packaged with polythene bags had the highest water content, followed by paper bag 62.25%, while the exposed recorded the lowest water content of 43.96%.     

Grazing effects of a gammaridean Amphipoda,Ampithoe sp., on the seagrass,Syringodium isoetifolium,and epiphytes in a tropical seagrass bed of Fiji

In the pure stand of tropical seagrass,Syringodium isoetifolium, in a small oceanic island, Fiji, grazing effects of the seagrass-associated gammarid,Ampithoe sp., on seagrass and epiphytes were assessed in October 1989, November 1991, November 1992. Density of the gammarid was estimated with two methods, mesh bag method and tuft method. During the three years surveyed the density of the gammarid increased remarkably from 1989 to 1991, with heavy epiphytism. Gut contents of the gammarid were examined. Grazing rates on seagrass leaf with and without epiphytic blue-green algae were measured in a bottle experiment. Litter bag experiments were conducted using different mesh sizes each containing seagrass only and seagrass and gammarids. The seagrass leaf biomass in the litter bag reduced abruptly in both bags. After one week, 78–86% of seagrass biomass disappeared from the bags. Enhancement of decomposition of seagrass leaf by the gammarid grazing was observed. Oxygen consumption and ammonium excretion rates were measured simultaneously in bottle experiments. Carbon budget in the seagrass bed was estimated as follows: 0.9 gC m⁻² day⁻¹ in seagrass growth, gammarid grazing was about a half of it and further assimilated a half of it, about 0.1 gC m⁻² day⁻¹, and more than half of it become CO₂ by respiration. Grazing effects on epiphyte and seagrass growth and production were discussed through the carbon budget and indirect interactions between seagrass, epiphytes and associated gammarids to explain the temporal change of seagrass and epiphyte dynamics.     

Aggregate formation in a freshwater bacterial strain induced by growth state and conspecific chemical cues

We investigated the induction of aggregate formation in the freshwater bacterium Sphingobium sp. strain Z007 by growth state and protistan grazing. Dialysis bag batch culture experiments were conducted in which these bacteria were grown spatially separated from bacteria or from co‐cultures of bacteria and predators. In pure cultures of Sphingobium sp. strain Z007, the concentrations of single cells and aggregates inside and outside the dialysis membranes developed in a similar manner over 3 days of incubation, and the proportions of aggregates were highest during the exponential growth phase. Cell production of Sphingobium sp. strain Z007 was enhanced in the presence of another isolate, Limnohabitans planktonicus, from an abundant freshwater lineage (R‐BT065) outside the bags, and even more so if that strain was additionally grazed upon by the bacterivorous flagellate Poterioochromonas sp. However, the ratios of single cells to aggregates of Sphingobium sp. strain Z007 were not affected in either case. By contrast, the feeding of flagellates on Sphingobium sp. strain Z007 outside the dialysis bags led to significantly higher proportions of aggregates inside the bags. This was not paralleled by an increase in growth rates, and all cultures were in a comparable growth state at the end of the experiment. We conclude that two mechanisms, growth state and the possible release of infochemicals by the predator, may induce aggregate formation of Sphingobium sp. strain Z007. Moreover, these infochemicals only appeared to be generated by predation on cells from the same species.     

The invasive green alga Avrainvillea sp. transforms native epifauna and algal communities on a tropical hard substrate reef

Some introduced species compete directly with native species for resources and their spread can alter communities, while others do not proliferate and remain benign. This study compares community structure and diversity in adjacent areas dominated by the introduced alga Avrainvillea sp. or native algal species on a hard substrate reef. The biomass and species composition of 15 paired plots (30 in total, plot type based on dominance of Avrainvillea sp. or native species) were quantified. Plots dominated by Avrainvillea sp. had a significantly different assemblage of species characterized by lower algal diversity, mostly Dictyota spp. and Laurencia sp., and a higher abundance and diversity of invertebrates, such as small arthropods, polychaetes, and brittlestars. These results suggest that as Avrainvillea sp. becomes more abundant on hard substrate reefs, it will engineer a different community composed of algal epiphytes and an invertebrate assemblage more typically associated with algae in soft sediments.     

Microcrustacean community structure and biomass in marsh and lake habitats of the Okefenokee Swamp: seasonal dynamics and responses to resource manipulations

Microcrustacean community and biomass dynamics were studied for two years in a Nymphaea-Eriocaulon macrophyte marsh and a nearby shallow lake which lacked macrophytes in the Okefenokee Swamp. In this blackwater, acidic wetland, microcrustacean diversity and biomass were similar to other circumneutral lakes and littoral areas, contributing to a productive fish assemblage. In the lake, the annual biomass pattern (15–1627 μg 1⁻¹) was unimodal and was dominated by the crustaceans Diaptomus sinuatus and Eubosmina tubicen. Rotifers were occasionally important, constituting up to 55% of total biomass. Over the long term, mean annual biomass in this post-drought study are higher than in pre-drought years. In the marsh, biomass (11–777 μg 1⁻¹) fluctuated biomodally with late winter depressions corresponding to low temperatures and midsummer declines indicative of increasing fish predation. Summer dominance shifted between years from Macrothricidae in 1982 to Sididae in 1983. Variation in biomass correlated most strongly with algal chlorophyll in the marsh and with bacterial density in the lake. In field enclosure experiments in which primary production was reduced by shading, microcrustacean responses varied between lake and marsh habitats and with season. Lake zooplankton were consistently suppressed by reduced algal resources in winter, spring and summer experiments, with greatest responses to shading in the summer. Marsh microcrustacea were most affected in the winter experiment and became less sensitive to manipulated resource levels in spring and summer. Decoupling of these consumers from autotrophic resources in the marsh, but not in the lake, coincides with times of high macrophyte turnover and warming temperatures which promote the conversion of detritus into heterotrophic resources such as bacteria. The conflict between interactions implied by the experimental approach vs statistical criteria emphasizes a need to interpret resource dependence from seasonal dynamics of field populations with caution.     

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.     

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.

     

How do grazers affect periphyton heterogeneity in streams?

The effects of grazing by stream invertebrates on algal biomass and spatial heterogeneity were tested experimentally in flow-through microcosms with natural substrates (rocks). One experiment tested the effects of fixed densities of three species of grazers (the caddisfly Allomyia sp. and two mayflies, Epeorus deceptivus and Baetis bicaudatus) on periphyton. Baetis was tested with and without chemical cues from fish predators, which reduced grazer foraging activity to levels similar to the less mobile mayfly (Epeorus). Mean algal biomass (chlorophyll a; chl a) was reduced in grazer treatments compared to ungrazed controls, but there were no differences among grazer treatments. Algal heterogeneity (Morisita index) increased with grazer mobility, with the highest heterogeneity occurring in the Baetis-no fish treatment (most mobile grazer) and the lowest in the caddisfly treatment (most sedentary grazer). A second experiment used a three factorial design, and tested whether initial resource distribution (homogeneous vs. heterogeneous), Baetis density (high vs. low) and fish odor (present vs. absent) affected grazer impact on algal resources. Abundances of Baetis and chl a on individual rocks were recorded to explore the mechanisms responsible for the observed distributions of algae. Initial resource heterogeneity was maintained despite being subjected to grazing. Mean chl a was highest in controls, as in experiment I, and effects of Baetis on algal biomass increased with grazer density. There were no fish effects on algal biomass and no effects of grazer density or fish on algal heterogeneity. At the scale of individual rocks Baetis was unselective when food was homogeneously distributed, but chose high-food rocks when it was heterogeneously distributed. Results of these mechanistic experiments showed that Baetis can track resources at the scale of single rocks; and at moderate densities mobile grazers could potentially maintain periphyton distributions observed in natural streams.     

Effects of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community of a deep,tropical reservoir: an enclosure experiment

1. An in situ enclosure experiment was conducted in a deep reservoir of southern China to examine (i) the effects of a low biomass (4 g wet weight m^?3) of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community and (ii) the response of Daphnia to eutrophication. 2. In the absence of fish, Daphnia galeata dominated the zooplankton community, whereas calanoids were dominant in the fish treatments, followed by D. galeata. Silver carp stocking significantly reduced total zooplankton biomass, and that of D. galeata and Leptodorarichardi, but markedly increased the biomass of smaller cladocerans, copepod nauplii and rotifers. In contrast, nutrient enrichment had no significant effect on the plankton community except for cyclopoids. 3. Chlorophyta, Cryptophyta and Bacillariophyta were dominant phytoplankton groups during the experiment. Chlorophyta with high growth rates (mainly Chlorella vulgaris in the fish enclosures and Ankyra sp. in the fishless enclosures) eventually dominated the phytoplankton community. Total phytoplankton biomass and the biomass of edible phytoplankton [greatest axial linear dimension (GALD) < 30 μm], Chlorophyta, Cryptophyta, Bacillariophyta and Cyanobacteria showed positive responses to fish stocking, while inedible phytoplankton (GALD ≥ 30 μm) was significantly reduced in the fish enclosures. However, there was no significant effect on the plankton community from the interaction of fish and nutrients. 4. Overall, the impact of fish on the plankton community was much greater than that of nutrients. High total phosphorus concentrations in the control treatment and relatively low temperatures may reduce the importance of nutrient enrichment. These results suggest it is not appropriate to use a low biomass of silver carp to control phytoplankton biomass in warmer, eutrophic fresh waters containing large herbivorous cladocerans.     

Some Bag Experiments on Tibbs Run Lake,W.V., A Eutrophic Acidified Lake

Tibbs Run Lake was sampled from December 1979 to December 1980, monthly during the winter and biweekly during the spring, summer, and autumn. Primary production was measured from March 1980 to February 1981, either monthly or biweekly, as indicated above. The mean annual hydrogen ion concentration was equivalent to pH 4.33. This pH was 46% lower (based on H⁺ concentrations) than the 1977–1978 mean. The low pH of the lake is due to inputs of acid precipitation and the low buffering capacity of the watershed. Predictions of further reductions in the lake pH, based on mean annual hydrogen ion concentrations and hydrogen ion retention coefficients (RH) from Shellito (1979) and this study, indicate that the lake pH should reach an equilibrium with the precipitation pH between 1982 and 1985, assuming the precipitation pH continues to average 4.10. The stratified period mean chlorophyll a and total phosphorus concentrations were 22.1 mg/m³ and 19.3 μg/1, respectively. Total phosphorus loading to the lake was 0.233 gP/m²/yr. To examine the effects of neutralization and fertilization with phosphorus an in situ bag enclosure experiment, lasting 16 days, was performed during the summer of 1980. In the bags, phosphorus (20 μg/1 on days 0,4,8,12 as KH₂PO₄) was added alone and in combination with a base addition (IN KOH). The base additions raised the pH to approximately 7.8. Other treatments included base addition alone and a control. The maximum chlorophyll a concentration was found in the phosphorus treatment (∼30 mg/m³) on day 6. The phosphorus plus base treatment exhibited a 10 day lag before reaching a maximum chlorophyll a concentration (∼27 mg/m³) on day 16. The highest production rate was found in the phosphorus plus base treatment on day 12 (∼27 mgC/m³/hr.). A similar bag experiment, lasting 46 days, was performed during the late summer and early autumn of 1980. The treatments were the same as in the first experiment, however, the nitrate-nitrogen depletion in the lake and treatments necessitated the addition of nitrogen (2 mg/1 as NaNO₃) to one of each replicate treatment on day 5. On day 34, the maximum chlorophyll a concentrations were found in the phosphorus plus base nitrogen treatment (∼120 mg/m³) and the phosphorus plus nitrogen treatment (∼38.8 mg/m³). The control plus nitrogen treatment was submerged and possibly contaminated on day 5. All treatments not receiving nitrogen, except for the phosphorus plus base treatment, decreased in the chlorophyll a concentration throughout the experiment. The phosphorus plus base treatment peaked in the chlorophyll a concentration on day 45 (∼28 mg/m³) despite non-detectable levels of nitrate-nitrogen. The maximum primary production rate was found in the phosphorus plus base plus nitrogen treatment (∼32 mgC/m³/hr.) on day 11.     

Re-establishment of epibiotic communities in reforested mangroves of Gazi Bay, Kenya

Recolonization of epibiotic flora and fauna in two fringing Sonneratia alba reforestation plots was investigated and compared to a natural mangrove stand and a denuded site in Gazi Bay, Kenya. The reforested sites differed with respect to land history and planting density. Habitat availability in the form of pneumatophore surface differed among forested sites (P<0.001), and between landward and seaward zones (P<0.05). Eighteen algal species were found in the natural area compared to 23 and 10 in replanted sites. Only one species was encountered in the denuded area. SIMPER analysis distinguished Enteromorpha ramulosa, Polysiphonia sp., Hypnea sp. and Caloglossa leprieuri as the main algal species responsible for differences between sites. Algal biomass was positively correlated to pneumatophores area (P<0.001). Total algal biomass differed markedly between forested sites: 1.4 (matrix replantation), 28.6 (natural stand) and 44.3 g m⁻² (integrated replantation) in the seaward zones. The matrix replantation showed strong differences in algal community assemblages compared to the other forested sites, and this site also had significantly lower biomass of sessile benthic fauna (P<0.001). Statistical differences in algal (P<0.01) and sponge (P<0.05) community composition between landward and seaward zones were observed in all sites and trunk fouling fauna was distinctly different between sites. Reasons for the above patterns are discussed and it is suggested that zonation patterns affecting pneumatophore surface and inundation time, in combination with proximity of sites to natural seeding areas, are the most likely explanations for observed patterns of epibiotic community distribution in this study.     

Production stability and biomass quality in microalgal cultivation – Contribution of community dynamics

The prospect of using constructed communities of microalgae in algal cultivation was confirmed in this study. Three different algal communities, constructed of diatoms (Diatom), green algae (Green), and cyanobacteria (Cyano), each mixed with a natural community of microalgae were cultivated in batch and semi‐continuous mode and fed CO₂ or cement flue gas (12–15% CO₂). Diatom had the highest growth rate but Green had the highest yield. Changes in the community composition occurred throughout the experiment. Green algae were the most competitive group, while filamentous cyanobacteria were outcompeted. Euglenoids, recruited from scarce species in the natural community became a large part of the biomass in semi‐steady state in all communities. High temporal and yield stability were demonstrated in all communities during semi‐steady state. Valuable products (lipids, proteins, and carbohydrates) comprised 61.5 ± 5% of ash‐free biomass and were similar for the three communities with lipids ranging 14–26% of dry mass (DM), proteins (15–28% DM) and carbohydrates (9–23% DM). Our results indicate that culture functions (stability, biomass quality) were maintained while dynamic changes occurred in community composition. We propose that a multispecies community approach can aid sustainability in microalgal cultivation, through complementary use of resources and higher culture stability.     

Two coexisting tank bromeliads host distinct algal communities on a tropical inselberg

The tank bromeliads Aechmea aquilega (Salisb.) and Catopsis berteroniana (Schultes f.) coexist on a sun‐exposed Neotropical inselberg in French Guiana, where they permit conspicuous freshwater pools to form that differ in size, complexity and detritus content. We sampled the algal communities (both eukaryotic and cyanobacterial taxa, including colourless forms) inhabiting either A. aquilega (n = 31) or C. berteroniana (n = 30) and examined differences in community composition and biomass patterns in relation to several biotic and abiotic variables. Chlorella sp. and Bumilleriopsis sp. were the most common taxa and dominated the algal biomass in A. aquilega and C. berteroniana, respectively. Using a redundancy analysis, we found that water volume, habitat complexity and the density of phagotrophic protozoa and collector‐gatherer invertebrates were the main factors explaining the distribution of the algal taxa among the samples. Hierarchical clustering procedures based on abundance and presence/absence data clearly segregated the samples according to bromeliad species, revealing that the algal communities in the smaller bromeliad species were not a subset of the communities found in the larger bromeliad species. We conclude that, even though two coexisting tank bromeliad populations create adjacent aquatic habitats, each population hosts a distinct algal community. Hence, bromeliad diversity is thought to promote the local diversity of freshwater algae in the Neotropics.     

Effects of organic matter and season on leaf litter colonisation and breakdown in cave streams

1. Low organic matter availability is thought to be a primary factor influencing evolutionary and ecological processes in cave ecosystems. We examined links among organic matter abundance, macroinvertebrate community structure and breakdown rates of red maple (Acer rubrum) and corn litter (Zea mays) in coarse‐ (10 × 8 mm) and fine‐mesh (500‐μm) litter bags over two seasonal periods in four cave streams in the south‐eastern U.S.A. 2. Organic matter abundance differed among cave streams, averaging from near zero to 850 g ash‐free dry mass m^?2. Each cave system harboured a different macroinvertebrate community. However, trophic structure was similar among caves, with low shredder biomass (2–17% of total biomass). 3. Corn litter breakdown rates (mean k = 0.005 day^?1) were faster than red maple (mean k = 0.003 day^?1). Breakdown rates in coarse‐mesh bags (k = 0.001–0.012 day^?1) were up to three times faster than in fine‐mesh bags (k = 0.001–0.004 day^?1). Neither invertebrate biomass in litter bags nor breakdown rates were correlated with the ambient abundance of organic matter. Litter breakdown rates showed no significant temporal variation. Epigean (surface‐adapted) invertebrates dominated biomass in litter bags, suggesting that their effects on cave ecosystem processes may be greater than hypogean (cave‐adapted) taxa, the traditional focus of cave studies. 4. The functional diversity of our cave communities and litter breakdown rates are comparable to those found in previous litter breakdown studies in cave streams, suggesting that the factors that control organic matter processing (e.g. trophic structure of communities) may be broadly similar across geographically diverse areas.