bluuebunny/crossref_metadata_2025_split huggingface dataset:
Primary production and phytoplankton composition in relation to DOC input and bacterioplankton production in humic Lake Örträsket
Authors: Drakare Stina , Blomqvist Peter , Bergström Ann‐Kristin , Jansson Mats 
Published: March 2003

1. The biomass and production of picophytoplankton, large phytoplankton and heterotrophic bacterioplankton were measured in humic Lake Örträsket, northern Sweden during four consecutive summers.2. High flow episodes, carrying fresh dissolved organic carbon (DOC) into the lake, always stimulated heterotrophic bacterial production at the expense of primary production. Primary production never exceeded bacterial production for approximately 20 days after such an episode had replenished epilimnial DOC. We suggest that allochthonous DOC is an energy source that stimulates bacterioplankton that, because of their efficient uptake of inorganic nutrients, are then able to outcompete phytoplankton. After the exhaustion of readily available DOC, phytoplankton were able to dominate epilimnion production in Lake Örträsket.3. Biomass production was higher when dominated by phytoplankton than by bacterioplankton, despite a similar utilization of nutrients in the epilimnion throughout the summer. We propose that different C : N : P ratios of bacterioplankton and phytoplankton permit the latter to produce more carbon (C) biomass per unit of available inorganic nutrients than bacterioplankton.
Effects of substratum stability on diversity of stream invertebrates during baseflow at two spatial scales
Authors: Miyake Yo , Nakano Shigeru 
Published: March 2003

1. The effects of substratum stability on the diversity of stream invertebrates were assessed at two spatial scales in a Japanese stream during baseflow, from May to June 1998. Deposition and erosion were examined separately as distinct elements of substratum stability by a newly developed method using small steel pins. Stream invertebrates were sampled after 28 days of measurement of substratum stability. We also measured physical environmental variables, current velocity and depth, and food resource parameters including periphyton and particulate organic matter (POM) standing crops.2. At the scale of the habitat patch, the effects of substratum stability on invertebrates were overwhelmed by those of POM standing crop. Moreover, higher taxon richness at high abundance may simply result from a higher likelihood of more taxa being included in samples. Therefore, this small scale revealed no role for substratum stability in explaining spatial pattern of community diversity.3. At the reach scale (n=10), taxon richness and evenness peaked at an intermediate level of deposition, whereas invertebrate abundance did not show any significant relationship. This result, and the pattern of relative abundance of common taxa, implies that the diversity of stream invertebrates was determined by subtle substratum movements and by the habitat preference of each taxon.4. The difference in the determinant of community parameters between the habitat patch and the reach affirm the importance of a cross‐scale analysis to choose an appropriate spatial scale for investigating the community structure of stream invertebrates. Prominent effects of substratum stability, particularly the deposition of substratum particles, during baseflow suggest that subtle and constant movement of small substratum particles can contribute to determine the diversity of stream invertebrates.
Effects of freshwater shrimp assemblages on benthic communities along an altitudinal gradient of a tropical island stream
Authors: MARCH JAMES G. , PRINGLE CATHERINE M. , TOWNSEND MATT J. , WILSON AMANDA I. 
Published: March 2003

1. In tropical island stream ecosystems freshwater shrimps are often the dominant macroconsumers and can play an important role in determining benthic community composition. However, most studies of the ecological role of shrimps are limited to high‐altitude shrimp‐dominated sites where other biota (fishes and snails) are absent or significantly less abundant than at lower altitudes.2. We examined how effects of different shrimp assemblages on benthic communities changed along an altitudinal gradient in a tropical island stream in Puerto Rico. We used electroshocking and observations to quantify abundance and taxonomic composition of shrimp assemblages at three sites (300, 90 and 10 m a. s. l) along the Río Espíritu Santo. We also experimentally manipulated access of shrimps to the benthic environment simultaneously at each site using electric fences over a 35‐day period.3. At the high‐altitude site, exclusion of shrimps (predominantlyAtyaspp. andXiphocariselongata) resulted in significantly greater accrual of organic and inorganic material, chlorophyllaand algal biovolume. In the absence of shrimps, the algal community was dominated by filamentous green algae (Chlorophyta:OedogoniumandRhizoclonium). Excluding shrimps did not affect total insect biomass but significantly increased sessile chironomids (Diptera: Chironomidae). We observed similar treatment effects at the mid‐altitude site where shrimps (primarilyMacrobrachiumspp. andX. elongata) occurred at lower densities. In contrast, at the low‐altitude site there were no treatment differences in organic and inorganic material, chlorophylla, algal biovolume, algal assemblage composition and insects.4. The lack of treatment differences at the low‐altitude site was probably because of very high densities of grazing snails (ThiaragraniferaandNeritinaspp.) which reduced organic and inorganic resources and obscured potential shrimp effects.5. This study demonstrates that freshwater shrimps can play an important role in determining benthic community composition; however, their effects vary and appear to depend on the presence of other biota. This study suggests that loss of shrimps as a result of anthropogenic disturbances will have different effects on the stream community depending upon location along the altitude gradient.
The drift distances and time spent in the drift by freshwater shrimps, Gammarus pulex, in a small stony stream, and their implications for the interpretation of downstream dispersal
Authors: ELLIOTT J. M. 
Published: March 2003

1. The objectives were (i) to determine experimentally and to model the relationship between mean water velocity and both the mean distance travelled, and the mean time spent, in the drift by freshwater shrimps, Gammarus pulex; (ii) to develop a drift distance–water velocity model from the experimental study, and validate it with field data; (iii) to examine the relationship between drift rate, water velocity and benthic density with the latter expressed as a mean value for the whole stream and a mean value corrected for the distance travelled in the drift.2. In field experiments at 10 water velocities (0.032–0.962 m s−1), the significant relationship between the mean drift distance and mean water velocity was described both by a power function (power, 0.96) and a linear relationship. The mean drift time was fairly constant at 8.3 s (95% CL ± 0.4). A simple model estimated the drift distance and time spent in the drift by different percentages of the drifting invertebrates. This model predicted correctly the positive relationship between drift rate and water velocity for field data over a year.3. The relationship between drift rate per hour and the independent variables, water velocity and benthic density, was well described by a multiple‐regression model. Adding temperature and date did not improve model fit. Variations in water velocity and benthic density explained 96% of the variation in nocturnal drift rate (65% to velocity, 31% to benthic density), but only 40% of the variation in diurnal drift rate (29% to velocity, 11% to benthic density). Correcting benthic density for the drift distances did not improve model fit.4. The significance of this study is that it developed models to predict drift distances and time, values being similar to those obtained in another, larger stream. It also illustrated the importance of spatial scale in the interpretation of drift by showing that when drift distances were taken into account, the impact of drift on the population was higher (4–10% lost day−1) than when drift distances were ignored (usually < 3% lost day−1), especially at a local level.
Temporal patterns of diatom ingestion by larval net‐winged midges (Diptera: Blephariceridae: Blepharicera)
Authors: Alverson Andrew J. , Courtney Gregory W. 
Published: March 2003

SUMMARY 1. Monthly patterns of diatom ingestion by Blepharicera magna and B. similans (Diptera: Blephariceridae) larvae were examined to determine whether dietary attributes fluctuate within the final‐instar stadium. The two species are isolated temporally: B. magna diets were examined from October to December, and B. similans diets were examined from June to August. Each month, the diatom assemblage of larval diets was assessed and compared with that of the forage base. In addition, total diatom ingestion was estimated.2. Larval gut samples were ordinated on the basis of relative abundance of common diatom taxa, and month–month comparisons of larval diets were made, which revealed that (i) B. magna dietary assemblages did not vary significantly from October to December; (ii) diatom species composition of B. magna diets generally resembled that of the forage base; and (iii) B. similans dietary assemblages varied significantly from June to August, with few changes attributable to seasonality of ambient diatom flora.3. Total diatom ingestion by B. magna was relatively stable from October to December. For B. similans, total diatom ingestion was greatest in July, when larvae were midstage of instar IV. The latter result was accompanied by increased ingestion of grazer‐resistant diatom taxa (e.g. Achnanthes deflexa var. alpestris, Achnanthidium minutissimum, and Cocconeis placentula var. lineata), which can be more digestible than grazer‐susceptible taxa (e.g. chain‐forming Fragilaria and rosette‐forming Synedra species). This result suggests demand for a large quantity of nutritionally rich food at midstage of instar IV, which could represent a period of critical growth for B. similans.
Fish induced macrophyte loss in shallow lakes: top–down and bottom–up processes in mesocosm experiments
Authors: Williams Adrian E. , Moss Brian , Eaton John 
Published: March 2003

SUMMARY 1. Macrophyte loss from Sites of Special Scientific Interest in England has become widespread over the last 20 years. One reason for this may be changing trends in angling, a multimillion pound industry that has an enormous impact on aquatic ecosystems. Stocking with cyprinid fish is a common angling management practice but the particular fish species and distribution of their biomass may be crucial to the ecosystem.2. Carp (Cyprinus carpio), roach (Rutilus rutilus), bream (Abramis brama) and tench (Tinca tinca) at biomasses ranging from 0 to 800 kg ha−1 and at various sizes were placed into experimental mesocosms in Little Mere, a shallow, fertile lake in Cheshire, U.K. The effects these treatments had on the aquatic ecosystem were studied over two summers. Specifically the effects of the treatments on macrophyte growth, benthic and macrophytic macro‐invertebrate populations, water chemistry, epiphyton production and plankton survival were investigated.3. Carp had a greater detrimental effect on the macrophytes than bream, tench and in particular roach. A biomass of fish > 200 kg ha−1 adversely affected the extent of macrophyte growth.4. The decline in macrophyte growth was most likely as a result of increased epiphyton growth that probably reduced the amount of light and carbon dioxide available to the plant. There were no observed direct fish impacts on macrophytes.5. The chemical data suggested that inorganic nitrogen levels were low and it is possible that release of nitrogen, from fish excreta, followed by immediate uptake, could have been a major factor stimulating epiphyton growth and subsequently macrophyte loss. Phosphorus concentrations increased even in the controls and substantial amounts were available. Phosphorus stimulation can therefore be discounted. Macrophyte‐associated macro‐invertebrates were positively correlated with epiphyton load but had no impact on the extent of epiphytic growth. Shading from disturbed sediment or phytoplankton was also unimportant.
Effects of a filter‐feeding fish [silver carp, Hypophthalmichthys molitrix (Val.)] on phyto‐ and zooplankton in a mesotrophic reservoir: results from an enclosure experiment
Authors: Radke Robert J. , Kahl Uwe 
Published: March 2003

SUMMARY 1. Silver carp, Hypophthalmichthys molitrix (Val.), feeds on both phyto‐ and zooplankton and has been used in lake biomanipulation studies to suppress algal biomass. Because reports on the effects of silver carp on lake food webs have been contradictory, we conducted an enclosure experiment to test how a moderate biomass of the fish (10 g wet weight m−3) affects phytoplankton and crustacean zooplankton in a mesotrophic temperate reservoir.2. Phytoplankton biomass <30 μm and particulate organic carbon (POC) <30 μm were significantly higher in enclosures with silver carp than in enclosures without fish, whereas Secchi depth was lower. Total copepod biomass declined strongly in both treatments during the experiment, but it was significantly higher in fish‐free enclosures. Daphnid biomass was also consistently higher in enclosures without fish, although this effect was not significant. However, the presence of fish led to a fast and significant decrease in the size at maturity of Daphnia galeata Sars. Thus, the moderate biomass of silver carp had a stronger negative effect on cladoceran zooplankton than on phytoplankton.3. Based on these results and those of previous studies, we conclude that silver carp should be used for biomanipulation only if the primary aim is to reduce nuisance blooms of large phytoplankton species (e.g. cyanobacteria) that cannot be effectively controlled by large herbivorous zooplankton. Therefore, stocking of silver carp appears to be most appropriate in tropical lakes that are highly productive and naturally lack large cladoceran zooplankton.
Differences in composition of macroinvertebrate communities with invasive and native Gammarus spp. (Crustacea: Amphipoda)
Authors: Kelly D. W. , Dick J. T. A. , Montgomery W. I. , Macneil C. 
Published: March 2003

SUMMARY 1. Assessing the effects on communities of invasive species is often confounded by environmental factors. In Irish rivers, the introduced amphipod Gammarus pulex replaces the native G. duebeni celticus in lowland stretches. The two amphipods are associated with different macroinvertebrate communities, which may in part be the result of natural longitudinal physicochemical change. However, this hinders assessment of any direct community impacts of the invasive as compared with the native species. Here, we report on a fortuitous circumstance that allowed us to uncouple the community effects of Gammarus species from environmental differences.2. The lowland stretch of the River Lissan is dissected by a weir, which has slowed the upstream invasion by G. pulex. We took physicochemical measurements and macroinvertebrate samples from three contiguous 150 m reaches of this stretch with G. pulex only, mixed Gammarus and G. d. celticus only communities.3. We found no biologically significant differences in physicochemistry among the three reaches. Overall invertebrate densities did not differ among reaches. However, G. pulex numerically dominated its reach, whilst G. d. celticus abundance was relatively low in its reach. The G. pulex reach had significantly higher overall biomass because of high invader abundance. In addition, both diversity and species richness of macroinvertebrate communities were lower in the G. pulex than the G. d. celticus reach, with the mixed Gammarus reach intermediate.4. Ordination indicated distinctly different associations of invertebrate community samples and taxa that were best explained by the distributions of the Gammarus species. Again, the mixed Gammarus species samples were intermediate.5. This study indicates that the invasive G. pulex has a greater impact on macroinvertebrate community composition than the native G. d. celticus, probably through biotic interactions such as predation.
Stream macroinvertebrate response to catchment urbanisation (Georgia, U.S.A.)
Authors: Roy A. H. , Rosemond A. D. , Paul M. J. , Leigh D. S. , Wallace J. B. 
Published: March 2003

SUMMARY 1. The effects of catchment urbanisation on water quality were examined for 30 streams (stratified into 15, 50 and 100 km2 ± 25% catchments) in the Etowah River basin, Georgia, U.S.A. We examined relationships between land cover (implying cover and use) in these catchments (e.g. urban, forest and agriculture) and macroinvertebrate assemblage attributes using several previously published indices to summarise macroinvertebrate response. Based on a priori predictions as to mechanisms of biotic impairment under changing land cover, additional measurements were made to assess geomorphology, hydrology and chemistry in each stream.2. We found strong relationships between catchment land cover and stream biota. Taxon richness and other biotic indices that reflected good water quality were negatively related to urban land cover and positively related to forest land cover. Urban land cover alone explained 29–38% of the variation in some macroinvertebrate indices. Reduced water quality was detectable at c. >15% urban land cover.3. Urban land cover correlated with a number of geomorphic variables such as stream bed sediment size (–) and total suspended solids (+) as well as a number of water chemistry variables including nitrogen and phosphorus concentrations (+), specific conductance (+) and turbidity (+). Biotic indices were better predicted by these reach scale variables than single, catchment scale land cover variables. Multiple regression models explained 69% of variation in total taxon richness and 78% of the variation in the Invertebrate Community Index (ICI) using phi variability, specific conductance and depth, and riffle phi, specific conductance and phi variability, respectively.4. Indirect ordination analysis was used to describe assemblage and functional group changes among sites and corroborate which environmental variables were most important in driving differences in macroinvertebrate assemblages. The first axis in a non‐metric multidimensional scaling ordination was highly related to environmental variables (slope, specific conductance, phi variability; adj. R2=0.83) that were also important in our multiple regression models.5. Catchment urbanisation resulted in less diverse and more tolerant stream macroinvertebrate assemblages via increased sediment transport, reduced stream bed sediment size and increased solutes. The biotic indices that were most sensitive to environmental variation were taxon richness, EPT richness and the ICI. Our results were largely consistent over the range in basin size we tested.
Herbivory on a chemically defended plant as a predation deterrent in Hyalella azteca
Authors: Rowell Kirsten , Blinn Dean W. 
Published: March 2003

SUMMARY 1. We investigated whether a population of the freshwater amphipod, Hyalella azteca, which consumed plants with defensive secondary compounds, reduced predation as reported for terrestrial and marine systems.2. Field observations in Montezuma Well, U.S.A., indicated a strong association between the emergent macrophyte, Berula erecta and H. azteca. We hypothesised that this geographically isolated population of sedentary amphipods was able to consume roots of the chemically defended B. erecta as a deterrent against predation. Berula erecta is in the family Apiaceae, which commonly produce coumarins that deter herbivory in terrestrial systems.3. Hyalella azteca consumed roots of B. erecta at a significantly greater rate than alternative macrophyte substrata in Montezuma Well. Additionally, H. azteca moulted at a significantly higher rate when consuming B. erecta compared with a diet of periphyton.4. Two insect predators (Telebasis salva and Belostoma bakeri) with different feeding strategies were used to assess the effects of a B. erecta diet on predation rates in the laboratory and in Montezuma Well. Hyalella azteca was preyed on at a significantly lower rate by both predators when given a strict diet of B. erecta roots compared with a diet of periphyton.5. This is the first experimental evidence that predation on a freshwater herbivore, H. azteca, was reduced when it consumed a chemically defended plant.
All creatures great and small: patterns in the stream benthos across a wide range of metazoan body size
Authors: Stead Tracey K. , Schmid‐Araya Jenny M. , Hildrew Alan G. 
Published: March 2003

SUMMARY1. The whole metazoan community (i.e. including the meiofauna) of an acidic, fishless stream in south‐east England was surveyed over 14 months between March 1999 and April 2000. Invertebrate density, biomass and taxonomic richness were assessed on each sampling occasion in relation to physico‐chemical variables.2. The meiofauna were more numerous and diverse than the macrofauna, while their total biomass occasionally equalled that of the macrofauna.3. The meiofaunal and macrofaunal assemblages appeared to respond to different environmental factors. The meiofauna showed genuine species turnover through the year, while the macrofauna varied less in taxonomic composition though there were substantial variations in density.4. These data suggest that the meiofauna and macrofauna exist at different temporal and spatial scales and perceive their environment with a different ‘grain’.
Photosynthesis of the cyanobacterial soil‐crust lichen Collema tenax from arid lands in southern Utah, USA: role of water content on light and temperature responses of CO2 exchange
Authors: Lange O. L. , Belnap J. , Reichenberger H. 
Published: March 2003

1. The gelatinous cyanobacterial Collema tenax is a dominant lichen of biotic soil crusts in the western United States. In laboratory experiments, we studied CO2 exchange of this species as dependent on water content (WC), light and temperature. Results are compared with performance of green‐algal lichens of the same site investigated earlier. 2. As compared with published data, photosynthetic capacity of C. tenax is higher than that of other cyanobacterial and green‐algal soil‐crust species studied. At all temperatures and photon flux densities of ecological relevance, net photosynthesis (NP) shows a strong depression at high degrees of hydration; maximal apparent quantum‐use efficiency of CO2 fixation is also reduced. Water requirements (moisture compensation point, WC for maximal NP) are higher than that of the green‐algal lichens. Collema tenax exhibits extreme ‘sun plant’ features and is adapted to high thallus temperatures. 3. Erratic rain showers are the main source of moisture for soil crusts on the Colorado Plateau, quickly saturating the lichens with liquid water. High water‐holding capacity of C. tenax ensures extended phases of favourable hydration at conditions of high light and temperature after the rain for substantial photosynthetic production. Under such conditions the cyanobacterial lichen appears superior over its green‐algal competitors, which seem better adapted to habitats with high air humidity, dew or fog as prevailing source of moisture.