Spatial variability of marine bacterial and archaeal communities along the particulate matter continuum

Biotic and abiotic particles shape the microspatial architecture that defines the microbial aquatic habitat, being particles highly variable in size and quality along oceanic horizontal and vertical gradients. We analysed the prokaryotic (bacterial and archaeal) diversity and community composition present in six distinct particle size classes ranging from the pico‐ to the microscale (0.2 to 200 μm). Further, we studied their variations along oceanographic horizontal (from the coast to open oceanic waters) and vertical (from the ocean surface into the meso‐ and bathypelagic ocean) gradients. In general, prokaryotic community composition was more variable with depth than in the transition from the coast to the open ocean. Comparing the six size‐fractions, distinct prokaryotic communities were detected in each size‐fraction, and whereas bacteria were more diverse in the larger size‐fractions, archaea were more diverse in the smaller size‐fractions. Comparison of prokaryotic community composition among particle size‐fractions showed that most, but not all, taxonomic groups have a preference for a certain size‐fraction sustained with depth. Species sorting, or the presence of diverse ecotypes with distinct size‐fraction preferences, may explain why this trend is not conserved in all taxa.     

Food selection of Tanytarsus gracilentus larvae (Diptera: Chironomidae): An analysis of instars and cohorts

Gut contents of the detritivorous Tanytarsus gracilentus larvae were studied at one site in Lake Myvatn, Iceland. Samples were collected with a sediment corer. Sediment samples were taken from the surface of the intact core before the larvae were collected. Gut contents were compared between different larval instars and cohorts, and to the surface sediment. The composition of the gut contents of all instars was different from that of the sediment surface. The first instar selected small diatoms of the genus Fragilaria, as single and paired cells, and the fourth instar selected detritus items of more variable size and origin. Apart from the third instar larvae, there were similar trends in food selectivity between the same instar of different cohorts. No major changes occurred in the composition of the surface sediment during the time of this study.     

Seston capture by Hydropsyche siltalai and the accuracy of capture efficiency estimates

1. Suspension feeding by caseless caddisfly larvae (Trichoptera) constitutes a major pathway for energy flow, and strongly influences productivity, in streams and rivers. 2. Consideration of the impact of these animals on lotic ecosystems has been strongly influenced by a single study investigating the efficiency of particle capture of nets built by one species of hydropsychid caddisfly. 3. Using water sampling techniques at appropriate spatial scales, and taking greater consideration of local hydrodynamics than previously, we examined the size‐frequency distribution of particles captured by the nets of Hydropsyche siltalai. Our results confirm that capture nets are selective in terms of particle size, and in addition suggest that this selectivity is for particles likely to provide the most energy. 4. By incorporating estimates of flow diversion around the nets of caseless caddisfly larvae, we show that capture efficiency (CE) is considerably higher than previously estimated, and conclude that more consideration of local hydrodynamics is needed to evaluate the efficiency of particle capture. 5. We use our results to postulate a mechanistic explanation for a recent example of interspecific facilitation, whereby a reduction of near‐bed velocities seen in single species monocultures leads to increased capture rates and local depletion of seston within the region of reduced velocity.     

The effect of tubificids and chironomids on particle redistribution of lake sediment

The effects of chironomid larvae,Chironomus plumosus, and tubificid worms,Limnodrilus spp., on particle redistribution in lake sediment were investigated experimentally using pots containing sediments obtained from Lake Suwa, Japan. The chironomids and tubificids increased the water content of surface sediment. The chironomid larvae had no effect on particle size distribution, while tubificids continuously accumulated small particles on the surface sediment through their selective feeding activity. Particles larger than 0.125 mm were buried at a sediment depth of 6 cm. In Lake Suwa, long diatom frustules, large plant debris and blue-green algal flocs were found to accumulate in the deeper layer of the lake sediment inhabited by tubificids at high density.     

The effects of potential larval supply, settlement and post-settlement processes on the distribution of two species of filter-feeding caddisflies

1. Hydropsychid caddisfly larvae are often abundant in fast flow habitats and on highly textured substrata. Such patterns are usually inferred to result from habitat preference, but the roles of larval supply to the benthos and post‐settlement events are rarely examined for stream populations. We describe a manipulative field experiment that examined larval supply, habitat preference and post‐settlement events simultaneously for two co‐occurring species of hydropsychids. 2. Ten artificial channels were constructed in a natural riffle to create fast and slow flow habitats and within each channel we placed six artificial substrata whose surfaces had been modified to create three different texture treatments. We measured discharge through channels and monitored hydropsychid colonisation of substrata every 3–4 days. Half of the substrata had all hydropsychids and nets removed every 3–4 days (short‐term colonisation) whereas the remaining half were counted but nets and hydropsychids left attached (long‐term colonisation). Short‐term counts of nets and individuals were summed to allow comparison with long‐term colonisation substrata. 3. Smicrophylax sp. AV2 larvae were more abundant in fast flow channels than slow flow channels, but these differences were proportional to discharge through each of the channels, suggesting that supply of settlers can explain this pattern. Smicrophylax larvae were least abundant on smooth substrata, which suggests that this species selects habitats based on surface texture. Alternatively, Asmicridea sp. AV1 larvae were only found in fast flow channels and this most likely reflects an active habitat choice by this species, but there was no significant difference between different texture treatments. 4. There were no differences between summed, short‐ and long‐term counts of recruits for either species, but there were more nets than larvae, especially in slow flow channels, by the end of the experiment, suggesting that larval mortality or re‐dispersal after settlement could be considerable. 5. Our results indicate that supply, habitat selection at settlement and post‐settlement processes all contributed variously to the distribution of hydropsychid caddisfly larvae, but that each species was affected differentially by these factors. Larval supply and post‐settlement processes are rarely examined by stream researchers and our results demonstrate these factors deserve much more consideration. Calculating accurate larval supply rates to sites is challenging, but we suggest that such detailed information is necessary if we are to sort out what sets limits to distributions and the underlying population structure of stream invertebrate populations.     

Larval growth and development in the caddisfly Cheumatopsyche brevilineata under natural thermal regimes

Cheumatopsyche brevilineata (Iwata) is a filter‐feeding caddisfly without distinct or distinguishable cohorts. In a semi‐natural channel, we reared fourth and fifth instar larvae of C. brevilineata in individual cages with hourly recording of water temperature. We calculated the individual growth rate from the wet‐weight gain of each larva, and the development rate from the ratio of larvae that progressed to the next instar or pupal stage during each rearing experiment. We analyzed the linear regressions of growth (increase in size) and development (physiological and morphological progression toward maturity) rates against the statistical parameters of water temperatures during each rearing period, i.e. mean and given percentiles of water temperatures. We presumed that the most appropriate parameter of water temperature to explain larval growth and development would show a peak value of the determination coefficients (r²) in the linear regressions. There were highly significant regressions in the growth rates for fourth and fifth instar larvae and in development rates for fourth instar larvae against every statistical parameter of water temperature, but not in the development rates for fifth instar larvae. For the growth of fourth and fifth instar larvae, we could not specify the most appropriate parameters of water temperatures, because we observed no clear peaks in the determination coefficients. For the development of fourth instar larvae, this parameter could be the 65th percentile value, where the development zero temperature and effective degree‐days were 11.1°C and 56 degree‐days, respectively.     

Host preference and sex allocation of three hymenopteran parasitoid species (Ichneumonidae and Braconidae) of a longicorn pest, Oemona hirta (Fabr.) (Col., Cerambycidae)

The host preference and sex allocation of two ichneumond parasitoids, Xanthocryptus novozealandicus (Dalla Torre) and Campoplex sp., and one braconid parasitoid, Apsicolpus hudsoni Turner of the longicorn borer, Oemona hirta , were studied in New Zealand. The size of the borer larvae attacked by the parasitoids can be determined by measuring the gallery width of the borers. These parasitoids are idiobionts and their secondary sex ratio is female-biased. Females of these species are significantly larger than males, and the females allocate the sex of offspring depending on the size of host larvae, by laying female-producing eggs on significantly larger host larvae. Xanthocryptus novozealandicus is larger in body size and shorter in ovipositor length than Campoplex sp. and A. hudsoni , and consumes late instar larvae or prepupae in shallow galleries whereas the latter two utilize early to middle instar larvae in deep galleries. Campoplex sp. and A. hudsoni preferred host larvae in significantly larger tree twigs than X. novozealandicus .     

Onshore–offshore variations of copepod community in northern South China Sea

Previous studies which have tested the feeding preferences of shredders for fungal species and the food quality of fungi used detritus uniformly colonized by a fungus, which is not the case for decaying leaves in streams. It is not known whether shredders in different development stages exhibit variations in feeding preference and larval performance. This study examined the feeding preferences and the growth of the third and the fifth instars of Pycnopsyche gentilis larvae using fungal-colonized patches and whole leaves, respectively, having different fungal species compositions (Alatospora acuminata, Anguillospora filiformis, Articulospora tetracladia, Tetrachaetum elegans, and all species combined). The aquatic hyphomycetes used were co-dominant on leaves in the stream inhabited by the caddisfly. During 14 d of feeding, the larvae of both instars did not show significant differences in feeding preferences for the patches growing on oak leaves, although the third instar larvae were slightly more selective than the fifth instar larvae. When fed with maple leaves for 18 d, larval growth rates, gross growth efficiencies, and survivorship were not significantly different among the fungal treatments. However, the larval growth of both instars fed with fungal-colonized leaves was always significantly greater than the growth of larvae fed with diets of uncolonized leaves. The third instar larvae grew faster than the fifth instar larvae, but the growth efficiencies of the two instars were similar. These results suggest that P. gentilis larvae exhibit less selectivity in their feeding than other caddisfly shredders that have been examined and that the dominant fungi colonizing leaves in their habitat are similar in palatability and food quality for this shredder. Handling editor: B. Oertli     

Effect of habitat complexity on the predation of Buenoa fuscipennis (Heteroptera: Notonectidae) on mosquito immature stages and alternative prey

Notonectids are well‐known predators in aquatic habitats, where mosquito larvae, chironomids, and cladocerans constitute their main diet. Our purpose was to assess the effect of structural complexity on the predatory ability of Buenoa fuscipennis, a common predator in aquatic habitats of Buenos Aires city (Argentina). Buenoa fuscipennis showed type 2 functional responses in both the presence and absence of prey refuge and no differences in attack rate or handling time between refuge treatments. Regarding mosquito size classes, B. fuscipennis exhibited a significantly higher preference for 2^nd instar larvae and no predation on pupae. In the presence of mosquito larvae and alternative prey, B. fuscipennis preferred mosquitoes over chironomid larvae and adult cladocerans over mosquito larvae. No switching behavior was detected in our experiments. Habitat structure only slightly affected the predator´s consumption rates on mosquito larvae. Overall, preference for prey did not vary with the presence of refuge, except for the preference for mosquitoes over chironomid larvae, which was significantly decreased in the presence of refuge as a consequence of reduced predation on mosquito larvae. The results suggest that B. fuscipennis could efficiently control mosquitoes in structurally simple habitats where chironomids are the most abundant alternative prey but not in temporary pools where cladocerans are abundant.     

Preparation and In Vitro Aerosol Performance of Spray-Dried Shuang-Huang-Lian Corrugated Particles in Carrier-Based Dry Powder Inhalers

The development of dry powder inhalation (DPI) products of traditional Chinese medicine (TCM) remains to be a challenge due to chemical complexity and batch-to-batch variations in constituent composition. This study was to investigate the feasibility of using spray-dried corrugated particles to improve the aerodynamic performance of a TCM, Shuang-Huang-Lian (SHL), in carrier-based DPI. Particles with different surface roughness were spray-dried by the addition of leucine and concomitant manipulation of spray-drying parameters. The surface roughness was determined by atomic force microscopy, whilst the aerodynamic performance of drug particle–mannitol/lactose blends was evaluated using a next-generation pharmaceutical impactor through a Cyclohaler. Although the emission efficiency for corrugated particle-based DPI was ∼10% lower than that for smooth SHL, the fine particle fractions (FPF_<4.4 μm) of 32.4–36.8% for the former were significantly higher than those of 14.7–16.2% for the latter. In particular, the FPF and fraction of drug detached from the carrier appeared not to be significantly affected by the variation in constituent composition of SHL. This study demonstrates that the use of corrugated particles in carrier-based DPI improved aerosol performance by facilitating drug detachment from the carrier, independent of variation in constituent composition, and such particles were potentially applicable to the development of SHL DPI products.KEY WORDS: dry powder inhaler, Shuang-Huang-Lian, spray-drying, surface roughness, traditional Chinese medicine     

On the ecology of the filter-feeding Neureclipsis bimaculata (Trichoptera, Polycentropodidae) in an acid and iron rich post-mining stream

Open-pit mining of lignite in East Germany has created landscapes with extreme environmental conditions. Post-mining aquatic habitats are characterized by low biodiversity and simple food webs due to the impact of acid mine drainage. In this study, the ecology of the filter-feeding caddisfly Neureclipsis bimaculata (L.) was examined, which is abundant in the acidic Floßgraben stream (pH 2.5–3.6) in Lower Lusatia, Germany. From benthic samples, we measured larval size and biomass and estimated population dynamics. The seston drift was sampled and retention efficiency of the larvae’s nets was assessed in a field tracer experiment to evaluate diet availability. Mean annual abundance was 1,380 ind m^?2 with a biomass of 1,010 mg m^?2. Annual secondary production of N. bimaculata was 8,450 mg m^?2. The larval microdistribution reflected the preference for in-stream wood and a limitation by low flow velocity. Morphometric factors of the larvae in the acidic stream were in the range of morphometric factors found in circumneutral streams that covered a range of trophic levels. Although coverage by iron particles reduced flow, the nets account for 63% of the mean particle retention. It is suggested that the retention efficiency and the availability of drifting organisms allowed the larvae to feed on 8.4 mg m^?2 per day, which revealed a ratio of biomass production to ingested food of 60%.     

Burrowing,feeding, and spatial distribution of the school prawn Metapenaeus macleayi (Haswell) in the Hunter river region,Australia

The influence of the food content and the particle size of the substratum on the distribution and relative abundance of Metapenaeus macleayi (Haswell) has been investigated by periodic trawl sampling for prawns and laboratory studies of their food, feeding, and burrowing behaviour.M. macleayi are opportunistic omnivores; they pick up material from the bottom with their chelipeds and convey it to the mouthparts where edible matter is sorted and ingested. They burrow into the sediment with their pereopods and pleopods, and are usually totally buried beneath the surface. A respiratory water current enters a tube formed by the antennal scales and the antennules, flows over the gills and then out of the carapace; this current is regularly reversed with increased strength, presumably to carry away de-oxygenated water. The results of experiments on substratum preference with adequately nourished juveniles suggest that the particle size of the sediment is more important than the food in the substratum in determining the distribution; the apparent preference of juveniles for a fine sandy substratum both in the laboratory and in the natural habitat may be attributed to the minimum threshold velocity of the sand particles.Adults are most abundant in turbid coastal waters arising from estuarine discharge and here the size of the sediment particles appears to be less important than the food content of the substratum in determining the distribution. The mangrove and reed swamps in the Hunter region play an important rôle in the food requirements of juvenile and adult prawns.     

The nature of a shield lake sediment

The nature of the sediment of Drinking Lake in the Churchill River Basin in Canada was studied with special reference to its chemical and colloidal composition. Crystalline minerals present in the colloidal fractions of the sediment are quartz, cristobalite, feldspars, micas, amphiboles, vermiculite, chlorite and kaolinite. Sesquioxidic components and the extractable Ca and Mg are present not only in the colloidal fractions but also in the non-colloidal fractions of the sediment. Over 99% of the nitrogen in the sediment is organic and about 60% of the sediment phosphorus is inorganic. The importance of the crystalline and non-crystalline mineral components of the sediment studied in the exchange of nutrients between the sediment and its overlying water is discussed. In view of the important roles of these mineral components in affecting the transfer of nutrients, possible significant modifications of the quality of the lake water after impoundment, if a dam were constructed in the basin for a hydro-electric development, deserve close attention.     

Size selection of latex beads by blackfly larvae (Diptera: Simuliidae) in the laboratory

In laboratory experiments, blackfly larvae collected from a lake outlet, a woodland and a meadow stream were tested for size selection of latex beads of < Ito > 100 μm diameters. 3 suspensions of varying proportions for each size category were supplied to these blackfly larvae in common experiments. Comparisons between the size frequency distributions of particles supplied and the particle compositions in the larval guts showed intra- and interspecific differences and were quantified by calculating Jacobs' electivity index. In all species selection of larger particles increased with the larger larval instars. Although there was a positive selectivity of small particles in some cases, the ingested proportion of large particles increases volumes and biomasses of gut content and may be more important for larval growth than small particles.     

Flow cytometric characteristics of subchloroplast particles prepared by the action of various detergents

Agranal thylakoid membranes from leaves of Phaseolus vulgaris L. were fragmented using seven distinct detergents: digitonin, Triton X-100, cetylpyridinium chloride, sodium dodecylsulfate, and Zwittergents 3-12, 3-14, and 3-16, differing in chemical composition and/or electric charges. Subchloroplast particles separated on a Percoll gradient were examined by flow cytometry to determine their size and shape. Vesicle size was also determined by a haematological analyzer, which produced comparable results. Individual green bands consisted of vesicles of fairly wide size distribution. Simple direct proportionality between the particle density and their size was not observed in any case, nevertheless, bigger particles were more abundant in fractions of higher density. Some vesicles had even a larger size than the original thylakoids. This might reflect a specific action of the detergents in low concentrations on agranal membranes, with incorporation of detergent molecules into vesicles. Inner structures of particles of the same size and density were not necessarily identical, but represented several populations, as was apparent from the side scatter analysis. Flow cytometric analysis can thus be used for the investigation of mechanisms of membrane fragmentation by detergents.     

Influence of Starting Material Particle Size on Pellet Surface Roughness

The purpose of this study was to investigate the effect of pelletization aids, i.e., microcrystalline cellulose (MCC) and cross-linked polyvinyl pyrrolidone (XPVP), and filler, i.e., lactose, particle size on the surface roughness of pellets. Pellets were prepared from powder blends containing pelletization aid/lactose in 1:3 ratio by extrusion–spheronization. Surface roughness of pellets was assessed quantitatively and qualitatively using optical interferometry and scanning electron microscopy, respectively. Both quantitative and qualitative surface studies showed that surface roughness of pellets depended on the particle size of XPVP and lactose used in the formulation. Increase in XPVP or lactose particle size resulted in rougher pellets. Formulations containing MCC produced pellets with smoother surfaces than those containing XPVP. Furthermore, surface roughness of the resultant pellets did not appear to depend on MCC particle size. Starting material particle size was found to be a critical factor for determining the surface roughness of pellets produced by extrusion–spheronization. Smaller particles can pack well with lower peaks and valleys, resulting in pellets with smoother surfaces. Similar surface roughness of pellets containing different MCC grades could be due to the deaggregation of MCC particles into smaller subunits with more or less similar sizes during wet processing. Hence, for starting materials that deaggregate during the wet processing, pellet surface roughness is influenced by the particle size of the material upon deaggregation.     

Natural Mineral Particles Are Cytotoxic to Rainbow Trout Gill Epithelial Cells In Vitro

Worldwide increases in fluvial fine sediment are a threat to aquatic animal health. Fluvial fine sediment is always a mixture of particles whose mineralogical composition differs depending on the sediment source and catchment area geology. Nonetheless, whether particle impact in aquatic organisms differs between mineral species remains to be investigated. This study applied an in vitro approach to evaluate cytotoxicity and uptake of four common fluvial mineral particles (quartz, feldspar, mica, and kaolin; concentrations: 10, 50, 250 mg L⁻¹) in the rainbow trout epithelial gill cell line RTgill-W1. Cells were exposed for 24, 48, 72, and 96 h. Cytotoxicity assays for cell membrane integrity (propidium iodide assay), oxidative stress (H₂DCF-DA assay), and metabolic activity (MTT assay) were applied. These assays were complemented with cell counts and transmission electron microscopy. Regardless of mineral species, particles ≤2 µm in diameter were taken up by the cells, suggesting that particles of all mineral species came into contact and interacted with the cells. Not all particles, however, caused strong cytotoxicity: Among all assays the tectosilicates quartz and feldspar caused sporadic maximum changes of 0.8–1.2-fold compared to controls. In contrast, cytotoxicity of the clay particles was distinctly stronger and even differed between the two particle types: mica induced concentration-dependent increases in free radicals, with consistent 1.6–1.8-fold-changes at the 250 mg L⁻¹ concentration, and a dilated endoplasmic reticulum. Kaolin caused concentration-dependent increases in cell membrane damage, with consistent 1.3–1.6-fold increases at the 250 mg L⁻¹ concentration. All effects occurred in the presence or absence of 10% fetal bovine serum. Cell numbers per se were marginally affected. Results indicate that (i.) natural mineral particles can be cytotoxic to gill epithelial cells, (ii.) their cytotoxic potential differs between mineral species, with clay particles being more cytotoxic, and (iii.) some clays might induce effects comparable to engineered nanoparticles.     

Flow cytometric characteristics of subchloroplast particles prepared by the action of various detergents

Agranal thylakoid membranes from leaves of Phaseolus vulgaris L. were fragmented using seven distinct detergents: digitonin, Triton X-100, cetylpyridinium chloride, sodium dodecylsulfate, and Zwittergents 3-12, 3-14, and 3-16, differing in chemical composition and/or electric charges. Subchloroplast particles separated on a Percoll gradient were examined by flow cytometry to determine their size and shape. Vesicle size was also determined by a haematological analyzer, which produced comparable results. Individual green bands consisted of vesicles of fairly wide size distribution. Simple direct proportionality between the particle density and their size was not observed in any case, nevertheless, bigger particles were more abundant in fractions of higher density. Some vesicles had even a larger size than the original thylakoids. This might reflect a specific action of the detergents in low concentrations on agranal membranes, with incorporation of detergent molecules into vesicles. Inner structures of particles of the same size and density were not necessarily identical, but represented several populations, as was apparent from the side scatter analysis. Flow cytometric analysis can thus be used for the investigation of mechanisms of membrane fragmentation by detergents.     

Non-selective surface deposit feeding by the Zoophycos producers

The feeding mechanism of Zoophycos producers demonstrates non-selection by particle size or quality. The characteristic morphology and mode of Occurrence of Zoophycos and the presence of pellets with pyroclastic grains imply that the Zoophycos producers were surface deposit-feeders. They dwelt in a burrow within the sediment and ingested the grains with nutrient detritus on the sea floor around the burrow opening. Fecal pellets containing pyroclastic grains were compared with the overlying volcanic ash layers through the analyses of grain size and mineral composition based on samples from two horizons in the Upper Pliocene of Boso Peninsula, central Japan. Judging from the comparative analyses, no significant differences were found between the ash layer and the fecal pellets. This fact strongly suggests that the Zoophycos producers appear to indiscriminately ingest particles on the sediment surface. Environments of low nutrition input such as the deep sea, non-particle size and quality selection in Zoophycos producers may be the feeding strategy for the detritus-feeding burrow-dwellers. □ Zoophycos, surface deposit-feeding, Pliocene Shiramazu Formation, Boso peninsula, Japan.     

The influence of larval case design on vulnerability of Limnephilus frijole (Trichoptera) to predation

• 1 We examined the potential selective pressures exerted by different types of predators on morphological prey defences using the case-building larvae of the limnephilid caddisfly, Limnephilus frijole. The predators were a predaceous minnow, Gila pandora, and an aeschnid dragonfly naiad, Oplonaeschna armata.
• 2 The influence of larval case design on vulnerability to predators was evaluated in a series of laboratory experiments. Larval L. frijole were collected from a stream without fish or dragonflies. In the laboratory, larvae still occupying their field-built cases were exposed to the two predators, with which L. frijole co-occurs in other streams. Following 24 h exposure of caddisfly larvae to a specific predator, the pre-trial case length, case strength, case width, and case composition of victims and survivors were compared.
• 3 Principal components analysis (PCA) indicated substantial independent variation for all four case parameters in the study population. The cases of larvae surviving exposure to either dragonfly naiads or fish were significantly stronger and wider than cases of victims of predation. Cases of survivors were also longer and had a greater mineral fraction than those of victims, but differences were either marginally significant or not significant.
• 4 These results demonstrate that specific aspects of case design affect the vulnerability of caddisfly larvae. In addition, predaceous fish and predaceous invertebrates, using different predation techniques, may exert similar selective pressures on these defenses. Case aspects influencing vulnerability in these experiments are broadly consistent with natural variation in case design associated with predator-rich and predator-free habitats for related caddisfly species.