Long-term effects of local disturbance history on mobile stream invertebrates

The patchy distribution of benthic invertebrates in streams and rivers is an important and widely researched phenomenon. Previous studies on reasons for this patchiness have neglected the potential role of local disturbance history, probably because most lotic invertebrates are mobile and any effect of disturbance history was thought to be short-lived. Here we demonstrate for a New Zealand gravel-bed stream that local disturbance history can have long-term effects on the distribution of highly mobile stream invertebrates. Buried scour chains (100 at each of three 20-m sites within a 350-m reach) indicated that a spate with a return period of 5 months caused a mosaic of bed patches with different stabilities. More than 2 months after the spate, we took random, quantitative samples at each site from five patches that had experienced 4 cm or more of scour during the spate, from five patches with 4 cm or more of fill, and from five stable patches. Density of the dominant invertebrate taxon, the highly mobile mayfly Deleatidium spp., and densities of another three of the seven most common taxa differed significantly between patch stability categories. Larvae of Deleatidium, the black fly Austrosimulium spp. and the dipteran Eriopterini were most abundant in fill patches, whereas Isopoda were most abundant in scour patches. Total invertebrate densities and densities of six common taxa also differed between sites, although these were only 95–120 m apart. These results show that local disturbance history can have long-term effects on lotic invertebrates and be an important cause of invertebrate patchiness. The observed effects might have been even stronger had we sampled sooner after the spate or after a large flood. Disturbance history may influence invertebrates both directly (through dislodgement or mortality) and indirectly, through effects on the spatial distribution of their resources. Our results suggest that the role of disturbance in structuring animal communities dominated by mobile species may be more important than previously thought. Received: 25 January 2000 / Accepted: 14 April 2000     

Dams and Flow in the Cotter River, Australia: Effects on Instream Trophic Structure and Benthic Metabolism

This study assessed benthic macroinvertebrates and periphyton and its responses to managed river-flows, in riffles downstream of three dams on the Cotter River, Australian Capital Territory. Benthic macroinvertebrates and periphyton were also assessed in adjacent tributaries of the river, as well as in a nearby unregulated river and its tributaries. Food sources of four macroinvertebrate taxa (Leptophlebiidae, Elmidae, Glossosomatidae and Orthocladiinae) were determined by stable isotope analysis of the invertebrates and their potential food, in conjunction with examination of the gut contents of individual invertebrates. Components of benthic periphyton were the main food source for the selected taxa. Orthocladiinae consumed primarily amorphous detritus, while Elmidae, Glossosomatidae and Leptophlebiidae consumed diatoms. Enclosed benthic chambers were used to measure the response of benthic metabolism to monthly flow spikes released from one of the dams. The balance of benthic metabolism as measured by the Production/Respiration ratio (P/R) showed a shift towards production after the release of flow spikes. At sites downstream of the dams, there was more periphyton chlorophyll-a in the form of filamentous green algae than at sites in the unregulated river and the tributaries, and macroinvertebrate taxa using periphyton as a food resource were missing or reduced in abundance relative to sites without dams. However, the site downstream of the dam with environmental flow releases had more macroinvertebrate taxa and less periphyton cholorophyll-a content than sites downstream of dams without managed environmental flows, suggesting that a more suitable food supply resulting from environmental flow releases shifted macroinvertebrate communities towards those of unregulated streams.     

Coral reef invertebrate microbiomes correlate with the presence of photosymbionts

Coral reefs provide habitat for an array of marine invertebrates that host symbiotic microbiomes. Photosynthetic symbionts including Symbiodinium dinoflagellates and diatoms potentially influence the diversity of their host-associated microbiomes by releasing carbon-containing photosynthates and other organic compounds that fuel microbial metabolism. Here we used 16S ribosomal RNA (rRNA) gene amplicon pyrosequencing to characterise the microbiomes of 11 common Great Barrier Reef marine invertebrate species that host photosynthetic symbionts and five taxa in which they are absent. The presence of photosynthetic symbionts influenced the composition but not the species richness, evenness and phylogenetic diversity of invertebrate-associated microbiomes. Invertebrates without photosynthetic symbionts were dominated by Alphaproteobacteria, whereas those hosting photosynthetic symbionts were dominated by Gammaproteobacteria. Interestingly, many microbial species from photosymbiont-bearing invertebrates, including Oceanospirillales spp., Alteromonas spp., Pseudomonas spp., Halomonas spp., are implicated in the metabolism of dimethylsulfoniopropionate (DMSP). DMSP is produced in high concentrations by photosynthetic dinoflagellates and is involved in climate regulation by facilitating cloud formation. Microbiomes correlated with host taxa and replicate individuals from most sampled species grouped in distance-based redundancy analysis of retrieved 16S rRNA gene sequences. This study highlights the complex nature of invertebrate holobionts and confirms the importance of photosynthetic symbionts in structuring marine invertebrate bacterial communities.     

Mayfly production in a New Zealand glacial stream and the potential effect of climate change

In contrast to the northern hemisphere where species of Chironomidae are usually the dominant benthic invertebrates in the coldest upper reaches of glacial streams, mayflies (Deleatidium spp.: Leptophlebiidae) predominate in equivalent conditions in New Zealand. We examined the life histories and annual production of Deleatidium spp. at two sites on the Matukituki River (South Island, New Zealand) and at three sites in its glacier-fed tributary, Rob Roy Stream. Mean annual water temperature at the five sites ranged from 2.1 to 7.0°C. Monthly sampling showed that mayfly populations were poorly synchronised at all sites but were probably univoltine. The large Deleatidium cornutum was the dominant mayfly species found at the upper sites (Sites 1 and 2) on Rob Roy Stream, whereas above the confluence with Matukituki River (Site 3) it co-existed with a complex of smaller species we refer to as D. “angustum”. Deleatidium “angustum” also dominated at the Matukituki sites. Deleatidium production calculated for the five sites, assuming an 11-month nymphal life, ranged from 0.48 g dry weight/m²/year (Site 1) to 3.07 g dry weight/m²/year (Site 3). The values for D. cornutum at Sites 2 and 3 are high for a species of Deleatidium and reflect its large size. This species appears to be strongly adapted for growth at low temperatures. Climate change scenarios for New Zealand predict the gradual and ultimate loss of small South Island glaciers and a consequent warming of streams as runoff from rainfall and snow melt becomes more dominant in spring. As a result, suitable habitats will be lost for cold-water specialists such as D. cornutum, and they are likely to suffer reductions in their distributional range and local extinction. In contrast, species such as those in the D. “angustum” complex may extend their ranges into streams formerly dominated by glacial meltwater. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: S. Stendera     

Invertebrate community dynamics and insect emergence in response to pool drying in a temporary river

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The impact of physical disturbance on stream communities: lessons from road culverts

This study examined the impact of physical disturbance from long-established road culverts on stream macroinvertebrate communities. Three streams within a 6 km section of highway on the Avalon Peninsula, Newfoundland, Canada, were sampled. Streams had the entire upstream watershed and at least 100 m downstream of the road with natural boreal forest/barren vegetation and all had, within the sampled reaches, similar physical streambed characteristics. The fauna on stones from riffles was sampled at two upstream and three downstream sites, i.e., from 50 m above to about 100 m below the road in each stream. A total of 33 taxa were identified among the streams, with differences limited to a few rare taxa. The sample site communities did not significantly differ from each other with respect to the taxa present. Total macroinvertebrate abundance by site, for combined data of all streams, indicated the site at the exit of culvert plunge pool (site 3) had significantly elevated abundances. Analysis of individual taxa showed this was primarily due to very high numbers of Simulium spp. The other most notable changes were a decrease in numbers of Hydropsyche spp. and Elmidae below the road. The abundances of the remaining taxa were more variable among all sites. The study indicated that long-standing point source physical disturbance primarily impacted taxa abundance rather than community present/absent data, which will recolonize the disturbed zone by downstream drift. The differences in abundance are probably the result of the cleaning of substrate by abrasion, movement of substrate and reduction of detritus during each spate. Handling editor: D. Dudgeon     

Top-down and bottom-up processes in grassland and forested streams

The influence of predatory fish on the structure of stream food webs may be altered by the presence of forest canopy cover, and consequent differences in allochthonous inputs and primary production. Eight sites containing introduced brown trout (Salmo trutta) and eight sites that did not were sampled in the Cass region, South Island, New Zealand. For each predator category, half the sites were located in southern beech (Nothofagus) forest patches (range of canopy cover, 65–90%) and the other half were in tussock grassland. Food resources used by two dominant herbivores-detritivores were assessed using stable isotopes. ¹³C/¹²C ratios were obtained for coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), algal dominated biofilm from rocks, and larvae of Deleatidium (Ephemeroptera) and Olinga (Trichoptera). Total abundance and biomass of macroinvertebrates did not differ between streams with and without trout, but were significantly higher at grassland sites than forested sites. However, taxon richness and species composition differed substantially between trout and no-trout sites, irrespective of whether streams were located in forest or not. Trout streams typically contained more taxa, had low biomass of predatory invertebrates and large shredders, but a high proportion of consumers with cases or shells. The standing stock of CPOM was higher at forested sites, but there was less FPOM and more algae at sites with trout, regardless of the presence or absence of forest cover. The stable carbon isotope range for biofilm on rocks was broad and encompassed the narrow CPOM and FPOM ranges. At trout sites, carbon isotope ratios of Deleatidium, the most abundant invertebrate primary consumer, were closely related to biofilm values, but no relationship was found at no-trout sites where algal biomass was much lower. These results support a role for both bottom-up and top-down processes in controlling the structure of the stream communities studied, but indicate that predatory fish and forest cover had largely independent effects.     

The macroinvertebrate fauna of a New Zealand forest stream

Abstract

The distribution, abundance, and life histories of benthic invertebrates were investigated in a small, Nothofagus forest stream in North Canterbury, South Island, New Zealand. The fauna was dominated by Trichoptera and Plecoptera; Mollusca and fish were absent. Large particle detritivores and scrapers were the predominant functional groups found. Larval Philopotamidae (Trichoptera) were the only abundant filter feeders. Nymphs of the stonefly Spaniocerca zelandica and of mayflies, Deleatidium spp., were the most abundant animals on plant detritus; Deleatidium spp. were abundant on stones also. The distribution of invertebrates in riffles, loose stones, pools, and plunge pools was examined using mesh colonisation trays lifted in September, November, February, and May after respectively 88, 69, 98, and 94 days in situ. Most species were widely distributed, and sample densities of the more abundant insect species showed weak positive correlations with the biomass of detritus present in trays in most months. The turbellarian Neppia montana was overrepresented in trays compared with stream samples, but the relative abundance of most other species appeared to be similar to that on the stream bed. A large amount of silt accumulated in trays during a heavy flood, and was colonised mainly by the oligochaete Eiseniella tetraedra. Information on the life histories of 15 species of Plecoptera, Trichoptera, Ephemeroptera, and Coleoptera was obtained from a 1-year monthly sampling programme, in which 36 taxa were distinguished, and from collections of adult insects made over a 3–4-year period. Most species had poorly synchronised life histories, in that a wide size range was apparent among individuals in most months. Eight species emerged in at least 4 months; S. zelandica and the philopotamid Hydrobiosella stenocerca were taken in 8 and 9 months respectively.     

The response of perennial and temporary headwater stream invertebrate communities to hydrological extremes

The headwaters of karst rivers experience considerable hydrological variability, including spates and streambed drying. Extreme summer flooding on the River Lathkill (Derbyshire, UK) provided the opportunity to examine the invertebrate community response to unseasonal spate flows, flow recession and, at temporary sites, streambed drying. Invertebrates were sampled at sites with differing flow permanence regimes during and after the spates. Following streambed drying at temporary sites, dewatered surface sediments were investigated as a refugium for aquatic invertebrates. Experimental rehydration of these dewatered sediments was conducted to promote development of desiccation-tolerant life stages. At perennial sites, spate flows reduced invertebrate abundance and diversity, whilst at temporary sites, flow reactivation facilitated rapid colonisation of the surface channel by a limited number of invertebrate taxa. Following streambed drying, 38 taxa were recorded from the dewatered and rehydrated sediments, with Oligochaeta being the most abundant taxon and Chironomidae (Diptera) the most diverse. Experimental rehydration of dewatered sediments revealed the presence of additional taxa, including Stenophylax sp. (Trichoptera: Limnephilidae) and Nemoura sp. (Plecoptera: Nemouridae). The influence of flow permanence on invertebrate community composition was apparent despite the aseasonal high-magnitude flood events. Flow permanence was also critical in determining the community response to the spate flows. Following streambed drying at temporary sites, the surficial sediments overlying the karstic bedrock functioned as an effective refugium for several taxa. The development of aquatic insects following experimental rehydration indicated that these taxa survived in dewatered sediments as desiccation-resistant eggs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: Sonja Stendera     

Winter diet of brown trout Salmo trutta in groundwater‐dominated streams: influence of environmental factors on spatial and temporal variation

Winter diet composition of brown trout Salmo trutta was quantified from November to March in 35 temperate groundwater‐dominated streams in south‐eastern Minnesota, U.S.A., in relation to stream physical characteristics including drainage area, channel slope and influence of groundwater on stream thermal regime. Aquatic invertebrates made up the majority of S. trutta diet in all streams and sampling periods and individual S. trutta typically had consumed 30 or more prey items at each sampling event. Differences in diet composition were greater among streams than between sampling periods within a stream, with Gammarus spp., Brachycentrus spp., Glossosoma spp., Chironomidae and Physella spp. the most common taxa. Landscape‐scale stream characteristics were not significantly associated with S. trutta consumption or diet composition. Winter was period of significant activity in groundwater‐dominated streams, as S. trutta fed on a variety of aquatic prey taxa highlighting the importance of winter base‐flow in moderating S. trutta populations in seasonally cold catchments.     

Changes in mechanisms of summer detritus processing between wooded and agricultural sites in a Michigan headwater stream

The mechanisms of leaf decay, leaf-associated macroinvertebrate community structure, leaf-associated microbial activity and physicochemical stream characteristics were investigated on a mid-Michigan headwater stream in summer. An undisturbed wooded site was compared with two agriculturally perturbed sites. Discharge, total suspended particulates, and nutrients were all higher and more variable throughout the season within the agricultural reaches. Leaf decay rates were higher at the agricultural sites and results suggest discharge abrasion was the major leaf processing mechanism at these sites while microbial decay and macroinvertebrate shredding appear to be the primary mediators of leaf weight loss at the wooded site. Total macroinvertebrate densities on leaf packs at the agricultural sites were 1.9 times the densities at the wooded site. It is suggested that experimentally introduced leaf packs acted as a lure for net-spinning invertebrates limited by stable substratum at the agricultural sites. Species shifts were observed from wooded reaches where Pychnopsyche spp., Gammarus, Ephemeroptera, Bezzia, and Nigronia serricornis were important, to downstream agricultural reaches which were dominated by Cheumatopsyche, Chironomidae, Elmidae, Hydracarina, Hemerodromia, and Caecidotea.     

Meiofauna constitute a considerable portion of invertebrate drift among moss-rich patches within a karst hydrosystem

Aiming to establish the most frequent invertebrate taxa in drift at the small spatial scale within a moss-rich karst tufa-precipitating hydrosystem, we sampled drift among microhabitats differing in substratum type and flow conditions along a tufa barrier-cascading lotic reach. Additionally, we addressed the question of the contribution and the potential significance of meiofauna within the overall invertebrate drift at the small spatial scale. During the study period, a total of 60 invertebrate taxa were recorded in the drift. Six of these taxa belonged to the annelid/arthropod meiofauna and they represented 35% of total drift density. Macroinvertebrates found in drift were represented mainly by larval insects. The composition of the most abundant taxa in total drift was as follows: Alona spp. (Cladocera 26.7%), Riolus spp. (Coleoptera: Elmidae 13.2%), Simulium spp. (Diptera: Simuliidae 12.2%), Enchytraeidae (Oligochaeta 10.4%), Hydrachnidia (6.3%), Orthocladinae (Diptera: Chironomidae 3.9%) and Naididae (Oligochaeta 3.6%). Faunal drift densities and amounts of transported particulate matter (PM) were highest at the fast-flowing sites located at the barriers and lowest at the slow-flowing sites within pools. Similarly to the seasonal amounts of transported PM, faunal drift was lowest in winter, and peaked in autumn and in late spring/early summer. Correlation between flow velocity and PM-faunal drift densities suggested a significant effect of the dislodged PM, though a minor influence of discharge and flow velocity on faunal drift. We suggest that the small-scale habitat heterogeneity and the respective feeding and refugial strategies of the fauna, as well as faunal passive dislodgement initiated by the shear forces of the flow were the most important drivers of observed drift patterns.     

Differences Found in the Macroinvertebrate Community Composition in the Presence or Absence of the Invasive Alien Crayfish,Orconectes hylas

Introductions of alien species into aquatic ecosystems have been well documented, including invasions of crayfish species; however, little is known about the effects of these introductions on macroinvertebrate communities. The woodland crayfish (Orconectes hylas (Faxon)) has been introduced into the St. Francis River watershed in southeast Missouri and has displaced populations of native crayfish. The effects of O. hylas on macroinvertebrate community composition were investigated in a fourth-order Ozark stream at two locations, one with the presence of O. hylas and one without. Significant differences between sites and across four sampling periods and two habitats were found in five categories of benthic macroinvertebrate metrics: species richness, percent/composition, dominance/diversity, functional feeding groups, and biotic indices. In most seasons and habitat combinations, the invaded site had significantly higher relative abundance of riffle beetles (Coleoptera: Elmidae), and significantly lower Missouri biotic index values, total taxa richness, and both richness and relative abundance of midges (Diptera: Chironomidae). Overall study results indicate that some macroinvertebrate community differences due to the O. hylas invasion were not consistent between seasons and habitats, suggesting that further research on spatial and temporal habitat use and feeding ecology of Ozark crayfish species is needed to improve our understanding of the effects of these invasions on aquatic communities.     

Effects of desiccation duration on the community structure and nutrient retention of short and long-hydroperiod Everglades periphyton mats

Responses of periphyton communities to different relevant durations of dry down were assessed. Long-hydroperiod sites within Everglades National Park remain wet for greater than 8 months of the year while short-hydroperiod mats are wet for fewer than 4 months of the year. Dry down duration of long and short-hydroperiod Everglades periphyton was manipulated from 0 to 1, 3, or 8 months after which periphyton was rewetted 1 month and examined for algal species composition. The effects of desiccation and rewetting on periphyton nutrient retention were also assessed. Relative abundance of diatoms declined from an average of 47% in the long-hydroperiod community at the start of the experiment to 24% after 1 month of desiccation and only 12% after 8 months of desiccation. Short-hydroperiod periphyton contained a lower proportion of diatoms at the outset (3%), which declined to less than 1% after the 8-month desiccation treatment. A significant increase in the filamentous cyanobacteria Schizothrix calcicola occurred in long-hydroperiod periphyton mats during this same period, but not in short-hydroperiod mats. Long-hydroperiod periphyton communities had a greater response to desiccation overall, but short-hydroperiod community structure responded to desiccation more rapidly. Because short-hydroperiod communities dry frequently, they appear to cope better to desiccating conditions than long-hydroperiod periphyton communities. This is indicated by the dominance of desiccation resistant algal taxa such as the cyanobacterial filaments S. calcicola and Scytonema hofmanni. Long-hydroperiod periphyton mat communities converge compositionally to short-hydroperiod periphyton communities after prolonged desiccation. Desiccation and rewetting caused long-hydroperiod periphyton to flux greater concentrations of nutrients than short-hydroperiod periphyton. Significant increases in efflux occurred from 1 to 8 months for total phosphorus (TP) and from 1 to 3 and 8 months for total nitrogen (TN) and total organic carbon (TOC). Thus, changes in periphyton mat community structure and function with altered hydroperiod may have long-term ecosystem effects.     

Influence of small scale conditions on the diversity of wood decay fungi in a temperate,mixed deciduous forest canopy

Studies on fungal richness and ecology have been largely disregarded since the first intensive efforts to investigate organismal diversity in forest canopies. We used the Leipzig Canopy Crane research facility to sample wood-decaying fungi in a mixed deciduous forest canopy 10-30 m in height. The structural complexity of the canopy was analysed using different methods, including meteorological measurements. With respect to temperature and relative humidity, marked differences existed between forest floor and upper canopy layers that persisted on smaller scales. Of the 118 taxa found in 128 sample units, pyrenomycetes and corticioid fungi outnumbered other macrofungal groups. Fungal communities showed distinct variations both in species richness and composition with respect to substrate (tree species), height in the canopy, stage of decay, and branch diameter. Pyrenomycetes and their anamorphs dominated the mycobiota on thin, exposed twigs at great heights, indicating their ability to overcome extended periods of drought and high levels of solar irradiance. Other taxa of Tremellales (Exidia spp.), Orbiliales (Hyalorbilia inflatula, Orbilia spp.) or Agaricales (Episphaeria fraxinicola, Cyphellopsis anomala, Lachnella spp.) also exhibited features that enabled them to develop in lesser protected habitats within tree crowns.     

Benthic and hyporheic invertebrate assemblages along a flow intermittence gradient: effects of duration of dry events

1. A large proportion of the total river length on Earth comprises rivers that are temporary in nature. However, the effects of periodical dry events have received far less attention from ecologists than those of floods and low flows. 2. This study concomitantly examined the effects of flow intermittence on invertebrates from the streambed surface and from a depth of 30 cm in the hyporheic zone. Invertebrates were collected during 3 years in the Albarine River, France, before and after summer dry events from 18 sites (seven were perennial) distributed along a longitudinal flow intermittence gradient. 3. I predicted benthic and hyporheic density and taxonomic richness to decrease, and assemblage composition to shift from desiccation‐sensitive to desiccation‐resistant taxa with increased dry event duration. Second, I predicted benthic and hyporheic assemblages from sites that dried for longer periods to be nested subsets of assemblages from sites that dried for shorter periods. Last, I predicted a convergence in benthic and hyporheic assemblage composition with increasing duration of dry events, resulting from increased vertical migration of benthic taxa into the hyporheic sediments to cope with dry events. 4. Increased dry event duration in the Albarine River led to a decrease in both benthic and hyporheic density and taxonomic richness. Invertebrate assemblage composition shifted along the gradient of increasing flow intermittence, but broad taxonomic overlap between perennial and temporary reaches and nestedness patterns indicated that these shifts were because of the loss of taxa susceptible to drying rather than selection for desiccation‐resistant specialists. 5. Assemblage composition between benthic and hyporheic invertebrates diverged with increasing dry event duration, suggesting that the hyporheic zone did not act as a refuge during dry events in this river. 6. Quantitative studies on the relationships between ecology and intermittence are still rare but are needed to predict the consequences of future changes in flow intermittence. The relationships found in this study should be tested across a wide range of temporary rivers to better evaluate the generality of these findings.     

An unexpected source of invertebrate community recovery in intermittent streams from a humid continental climate

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Environmental factors and host genetic variation shape the fungal endophyte communities within needles of Scots pine (Pinus sylvestris)

To determine the role of environmental and host genetic factors in shaping fungal endophyte communities we used culturing and metabarcoding techniques to quantify fungal taxa within healthy Scots pine (Pinus sylvestris) needles in a 7-y old provenance-progeny trial replicated at three sites. Both methods revealed a community of ascomycete and basidiomycete taxa dominated by the needle pathogen Lophodermium seditiosum. Differences in fungal endophyte taxon composition and diversity indices were highly significant among trial sites. Within two sites, fungal endophyte communities varied significantly among provenances. Furthermore, the communities differed significantly among maternal families within provenances in 11/15 and 7/15 comparisons involving culture and metabarcoding data respectively. We conclude that both environmental and host genetic variation shape the fungal endophyte community of P. sylvestris needles.     

Elevated temperature prolongs long‐term effects of a pesticide on Daphnia spp. due to altered competition in zooplankton communities

Considerable research efforts have been made to predict the influences of climate change on species composition in biological communities. However, little is known about how changing environmental conditions and anthropogenic pollution can affect aquatic communities in combination. We investigated the influence of short warming periods on the response of a zooplankton community to the insecticide esfenvalerate at a range of environmentally realistic concentrations (0.03, 0.3 and 3 μg L^?1) in 55 outdoor pond microcosms. Warming periods increased the cumulative water temperature, but did not exceed the maximum temperature measured under ambient conditions. Under warming conditions alone the abundance of some zooplankton taxa increased selectively compared to ambient conditions. This resulted in a shift in the community composition that had not recovered by the end of the experiment, 8 weeks after the last warming period. Regarding the pesticide exposure, short‐term effects of esfenvalerate on the community structure and the sensitive taxa Daphnia spp. did not differ between the two temperature regimes. In contrast, long‐term effects of esfenvalerate on Daphnia spp., a taxon that did not benefit from elevated temperatures, were observed twice as long under warming than under ambient conditions. This resulted in long‐term effects on Daphnia spp. until 4 months after contamination at 3 μg L^?1 esfenvalerate. Under both temperature regimes, we identified strength of interspecific competition as the mechanism determining the time until recovery. However, enhanced interspecific competition under warming conditions was prolonged and explained the delayed recovery of Daphnia spp. from esfenvalerate. These results show that, for realistic prediction of the combined effects of changing environmental factors and toxicants on sensitive taxa, the impacts of stressors on the biotic interactions within the community need to be considered.     

Quantitative Microbial Community Analysis of Three Different Sulfidic Mine Tailing Dumps Generating Acid Mine Drainage

The microbial communities of three different sulfidic and acidic mine waste tailing dumps located in Botswana, Germany, and Sweden were quantitatively analyzed using quantitative real-time PCR (Q-PCR), fluorescence in situ hybridization (FISH), catalyzed reporter deposition-FISH (CARD-FISH), Sybr green II direct counting, and the most probable number (MPN) cultivation technique. Depth profiles of cell numbers showed that the compositions of the microbial communities are greatly different at the three sites and also strongly varied between zones of oxidized and unoxidized tailings. Maximum cell numbers of up to 10⁹ cells g⁻¹ dry weight were determined in the pyrite or pyrrhotite oxidation zones, whereas cell numbers in unoxidized tailings were significantly lower. Bacteria dominated over Archaea and Eukarya at all tailing sites. The acidophilic Fe(II)- and/or sulfur-oxidizing Acidithiobacillus spp. dominated over the acidophilic Fe(II)-oxidizing Leptospirillum spp. among the Bacteria at two sites. The two genera were equally abundant at the third site. The acidophilic Fe(II)- and sulfur-oxidizing Sulfobacillus spp. were generally less abundant. The acidophilic Fe(III)-reducing Acidiphilium spp. could be found at only one site. The neutrophilic Fe(III)-reducing Geobacteraceae as well as the dsrA gene of sulfate reducers were quantifiable at all three sites. FISH analysis provided reliable data only for tailing zones with high microbial activity, whereas CARD-FISH, Q-PCR, Sybr green II staining, and MPN were suitable methods for a quantitative microbial community analysis of tailings in general.