Upstream-downstream movements of aquatic invertebrates in a Rocky Mountain stream

Simultaneous collections of drift and organisms moving either upstream or downstream in association with the substrate were made using a specially designed sampler. Samples were taken in a diel series along a transect across the study riffle of a Colorado foothills stream on six dates over an annual cycle. In addition to longitudinal movements, taxonomic composition and diel periodicity were evaluated. The insect-dominated fauna showed a net downstream displacement. Only the caddisflies Helicopsyche borealis and Hesperophylax occidentalis exhibited net upstream movement, primarily a result of low drift frequencies. The taxonomic composition of moving invertebrates differed from that of the benthos. Drift resembled downstream moving substrate-associated invertebrates in composition, but differed from that of the upstream directed fauna. Taxa collectively exhibited four types of diel patterns: 1) similar downstream (drift and substrate-associated movements) patterns, which generally differed from the upstream pattern; 2) similar benthic (upstream and downstream) patterns, which differed from that of drift; 3) aperiodic patterns; and 4) independent patterns for each type of directional movement. Analysis of size classes based on head capsule width for the mayfly Baetis tricaudatus showed significantly smaller size in stationary individuals compared with moving individuals in the population and revealed that nymphs moving during the day were smaller than those moving at night.     

Effects of electroshocking on macroinvertebrate drift in three cold water streams

The effect of electroshocking and walking on the substrate on macroinvertebrate drift was evaluated in three streams located in southwestern Oregon, USA. A randomized block experimental design was used to determine treatment (electroshocking and walking, electroshocking-only, walking-only) and drift distance effects on the number, biomass, and length of macroinvertebrates drifting up to 30 m downstream. In all streams, electroshocking caused significantly (p < 0.05) greater number of macroinvertebrates to drift compared to merely walking on the substrate. The differences among treatments decreased the farther downstream the macroinvertebrates drifted. No significant difference (p > 0.05) was observed in mean biomass between electroshocking and walking on the substrate among the drift distances. The longest macroinvertebrates were collected from the electroshocking treatment at the shortest drift distance (2.5 m) in all of the streams. The length of macroinvertebrates collected between electroshocking and walking on the substrate were similar at drift distances of 10 m and greater and represented predominately the smaller, poor swimming taxa.     

Tool use by aquatic animals

Tool-use research has focused primarily on land-based animals, with less consideration given to aquatic animals and the environmental challenges and conditions they face. Here, we review aquatic tool use and examine the contributing ecological, physiological, cognitive and social factors. Tool use among aquatic animals is rare but taxonomically diverse, occurring in fish, cephalopods, mammals, crabs, urchins and possibly gastropods. While additional research is required, the scarcity of tool use can likely be attributable to the characteristics of aquatic habitats, which are generally not conducive to tool use. Nonetheless, studying tool use by aquatic animals provides insights into the conditions that promote and inhibit tool-use behaviour across biomes. Like land-based tool users, aquatic animals tend to find tools on the substrate and use tools during foraging. However, unlike on land, tool users in water often use other animals (and their products) and water itself as a tool. Among sea otters and dolphins, the two aquatic tool users studied in greatest detail, some individuals specialize in tool use, which is vertically socially transmitted possibly because of their long dependency periods. In all, the contrasts between aquatic- and land-based tool users enlighten our understanding of the adaptive value of tool-use behaviour.     

Macroinvertebrate colonization of acrylic plates in a large river

From April 1977 through June 1978, scuba divers used a double-cup bar-clamp sampler to monitor colonization rates and standing crops of macroinvertebrates on acrylic plates near the rocky bottom of the Susquehanna River in northeastern Pennsylvania. Monthly, bimonthly, and cumulative plates were exposed for about 30, 60, and 124–362 days, respectively.The upper surface of monthly plates was colonized from June through September at rates ranging from 125 organisms/m²/day in June 1978 to 3,200 org/m²/day in August ({xx\-x} = 1,300 org/m²/day). Chironomids (Rheotanytarsus spp.) and hydropsychids (Hydropsyche phalerata and Cheumatopsyche spp.) composed 97% of the total. The lower surface of monthly plates was colonized from May through September at rates ranging from 110 org/m²/day in June 1977 to 760 org/m²/day in May 1977 ({xx\-x} = 260 org/m²/day). Naidids (Nais spp. and Chaetogaster spp.) and chironomids (Nanocladius spp.) composed 89% of the total.Macroinvertebrates remained on cumulative plates after colonization of monthly plates ceased. The upper surface of cumulative plates was inhabited from June through October at densities ranging from 5,800 org/m² in June 1977 to 78,000 org/m² in August ({xx\-x} = 40,000 org/m²). The lower surface of cumulative plates was inhabited year-round, at densities ranging from t,000 org/m² in December to 15,000 org/m² in June 1977 ({xx\-x} = 6,100 org/m²).This study was supported by Pennsylvania Power and Light CompanyThis study was supported by Pennsylvania Power and Light Company     

Colonization,variability, and the use of substratum-filled trays for biomonitoring benthic communities

Sampling variability and colonization rate of introduced substrates (plastic trays filled with pebble and cobble) in two southwestern Virginia streams are described. Substrates were rapidly colonized by aquatic macroinvertebrates, but colonization rates differed between years, possibly due to annual variability in macroinvertebrate abundance. To examine the applicability of using these substrates for biomonitoring benthic communities, trays were placed at several locations in a river receiving power plant discharges. Only six samples were necessary to detect a 15%reduction in macroinvertebrate density and a 12% reduction in number of taxa at effluent sites. Benthic communities established on rock-filled trays and multiplate samplers collected from the same stations during the same period were compared. Although multiplate samplers were more variable than rock trays and were selective for different taxa, both substrate types showed significant differences in community parameters among locations. Rock trays at all sites were dominated by Cheumatopsyche sp., whereas chironomids were more abundant on multiplate samplers. The relative abundance of mayflies was reduced at the effluent site on both substrate types.     

Determinants of habitat use in large roach

In this study gillnet catches of large roach Rutilus rutilus and their potential predators, large perch Perca fluviatilis , pikeperch Sander lucioperca and pike Esox lucius , in combination with data on food resources and abiotic variables were used to reveal the variables influencing the habitat use of large roach in Lake Großer Vätersee. The occurrence of large roach was negatively coupled with the occurrence of potential predators. Although almost all roach studied were larger than those actually fed on by the predators, high roach catches never coincided with high predator catches. Since the overall habitat-specific distribution of roach and its predators was nevertheless highly similar, this indicated that large roach obviously avoided the immediate vicinity of the predators without being forced to a full habitat shift. The behavioural response to predators of roach in Lake Großer Vätersee was clearly length dependent, since the patterns of diel habitat use differed between large and small roach. For lake-wide estimates of trophic interactions, size groups of prey should be separated, since size-dependent trait changes may impact habitat-specific resources in a contrasting way.     

Aquatic macrophytes, macroinvertebrate associations and water levels in a lowland Tasmanian river

Aquatic macrophytes are a common habitat for macroinvertebrates and may occupy depth zones in the littoral region of lowland rivers. Studies have indicated that different species of macrophyte typically support different assemblages, abundances and numbers of species of macroinvertebrates. This has often been attributed to differences in the dissectedness of stems and leaves of the macrophytes, resulting in differences in the surface area and/or the number of microhabitats available to invertebrates. I set out to measure the abundance and taxonomic richness and to describe the macroinvertebrate assemblages associated with three species of aquatic macrophyte in a pool in the Macquarie River, Tasmania and to examine responses of these variables to changes in water levels over summer. The macrophyte species sampled wereMyriophyllum simulans/variifolium, Triglochin procera} and Eleocharis sphacelata, each one differing in the dissectedness of its stems and leaves and its location in the littoral zone. Whereas the greatest abundance of macroinvertebrates was found associated in all months (i.e. at all water levels) with the structurally complex and shallowest macrophyte species, Myriophyllum, the number of taxa associated with this species was in several cases lower than for the structurally simpler and deeper water Triglochin and Eleocharis. While water depth and total plant biomass of samples were often correlated with invertebrate abundance and richness, these relationships were different for each macrophyte species. Of the nine most common invertebrate taxa collected from all samples, the abundances of more than half showed consistent differences among macrophyte species across months, two showed differences among macrophytes, but with an interaction with month and two showed no differences among macrophytes. There were major differences in the invertebrate assemblages associated with each macrophyte species in any one month, however, there was also a large turnover of taxa associated with the species of macrophytes from one month to the next. Changes in water level and concomitant changes in environmental variables are suggested as factors influencing the invertebrate fauna in the littoral zone of the pool of the Macquarie River. It is thus important for river managers to be aware that species of macroinvertebrates are not evenly distributed across species of macrophyte and that water levels and their influence on macrophytes as invertebrate habitat may play an integral part in determining the abundance, richness and assemblage of invertebrates in rivers.     

Comparison of several techniques for sampling macroinvertebrates in different habitats of a North Iberian pond

Several habitats of a Mediterranean pond were sampled for macroinvertebrates using different techniques: quantitative methods, semiquantitative hand-net sweep sampling and a qualitative protocol based on hand-net sweeps with fixed counts of individuals. The taxonomic composition was analyzed by DCA and several indices based on taxon composition or percentage of individuals were calculated. The aim of the study was to compare the results provided by these techniques and, in particular, to check if the qualitative approach could be an appropriate low-cost methodology for use in biomonitoring. The results provided by the three sampling methods in relation to submerged macrophytes were very similar. In soft sediment, certain differences were found between the quantitative and semiquantitative techniques. The qualitative protocol applied to single habitats collected fewer taxa than the corresponding quantitative or semiquantitative techniques. However, the overall protocol, consisting of samples from three habitats, provided higher richness values than all the quantitative and semiquantitative methods together, with 59 taxa out of the 70 collected during the study. It is concluded that this qualitative methodology performed reasonably well since it offers a reliable view of the community and it misses few taxa. Moreover, it is not so time consuming as other techniques and can be applied in a variety of habitats. It, therefore, seems to be an efficient method for bioassessment of the macroinvertebrate communities of ponds or the littoral zone of lakes.     

Spatial and temporal variability of aquatic habitat use by amphibians in a hydrologically modified landscape

1. Habitat loss is a major driver of biodiversity decline worldwide. Temporary waterbodies are especially vulnerable because they are sensitive both to human impact and to climatic variations. Pond‐breeding amphibians are often dependent on temporary waterbodies for their reproduction, and hence are sensitive to loss of temporary ponds. 2. Here we present the results of a 5‐year study regarding the use of temporary aquatic habitats by amphibians in a hydrologically modified area of Eastern Europe (Romania). The annual number of aquatic habitats varied between 30 and ～120. Each aquatic habitat was characterised by a number of variables such as: ‘type’ (pond, drainage ditch and archaeological ditch), ‘hydroperiod’ (number of weeks the ponds were filled in a given year), ‘depth’ (cm), ‘area’ (m²) and the density of predatory insects (‘predation’). The turnover rate for each amphibian species for each wetland was calculated based on the pond occupancy. 3. Eight amphibian species were recorded from the aquatic habitats. Hydroperiod was the most important variable, positively influencing wetland use by amphibians and their reproductive success. Most species preferred drainage ditches for reproduction, and the reproductive success was highest in this habitat type every year. For most of the species, the local extinction rate was higher than the colonisation rate in the first 4 years, but the situation reversed in the last year of the study when wetland use by amphibians sharply increased because of high rainfall. 4. This study confirms the importance for amphibians of maintaining and managing aquatic habitat diversity at small spatial scales. Man‐made aquatic habitats such as drainage ditches may be important habitats for amphibians, and this should be considered in restoration activities.     

Effects of water velocity on photosynthesis and dark respiration in submerged stream macrophytes

The effects of flow velocities on dark respiration and net photosynthesis of eight submerged stream macrophytes were examined in a laboratory oxygen chamber. The shoots/leaves were exposed to saturating free-CO₂ concentrations and were attached basally so that they could move in the flowing water. Net photosynthesis declined by 34–61% as flow velocity increased from 1 to 8.6cm s^?1, while dark respiration increased 2.4-fold over the same range. The increase in dark respiration could only account for between 19 and 67% of the decrease in net photosynthesis. The relationship between flow velocity (U) and net photosynthesis (P) was described by: P=b×U^a. The exponent, a, varied from -0.20 to –0.48 and showed a negative correlation to the surface: volume (SA: V) ratio of the plants, i.e. species with high SA: V ratio were more sensitive to flow. In contrast, net photosynthesis of plants firmly attached to a supporting frame was not significantly affected by increasing flow velocity. This result indicates that the physical stress imposed on the plants by agitation or stretching in the flowing water is a key factor for the observed response.     

Decomposition dynamics of aquatic macrophytes in the lower Atchafalaya, a large floodplain river

Decomposition of aquatic macrophytes can considerably influence carbon cycling and energy flow in shallow freshwater aquatic ecosystems. The Atchafalaya River Basin (ARB) is a large floodplain river in southern Louisiana that experiences a seasonal floodpulse and is spatially composed of a mosaic of turbid riverine and stagnant backwater areas. During two seasons, winter and fall of 1995, we examined decomposition of four common aquatic macrophytes in the ARB: water hyacinth (Eichhornia crassipes), arrowhead (Sagittaria platyphylla), coontail (Ceratophyllum demersum) and hydrilla (Hydrilla verticillata). To determine decay rates, we used litter bags of two mesh sizes (5 mm and 0.25 mm) and analyzed data with a single exponential decay model. Analysis of decay rates established several trends for aquatic macrophyte decomposition in the ARB. First, macrophytes decayed faster in fall than winter due to the effect of increased temperature. Second, macroinvertebrates were the primary decomposers of macrophytes in riverine sites and microbes were the primary decomposers in backwater areas. These trends may have been related to decomposer-habitat interactions, with well-oxygenated riverine sites more hospitable to invertebrates and backwater areas more favorable to microbes because of high organic inputs and reduced flow. Decay rates for macrophytes, ranked from slowest to fastest, were E. crassipes<S. platyphylla<C. demersum<H. verticillata. Slower decomposition of E. crassipes was probably a result of microbial inhibition by the waxy-cutin outer layer and low nutritional value. The accelerated decomposition of C. demersum and H. verticillata was most likely a function of the large surface area of the highly dissected leaves. Macroinvertebrate numbers were twice as high in riverine sites compared to backwater sites. In the winter, amphipods Gammarus spp. and Hyallela azteca composed a large percentage of the total density on detritus. In the fall, Caenis sp. was prevalent in the backwater habitat and dipterans were abundant in the riverine site. We investigated the microbial component involved in the decomposition of E. crassipes and S. platyphylla and found that the highest microbial respiration rates occurred early in the winter at the backwater site. Bacterial density in the winter on E. crassipes and S. platyphylla averaged 1.4×10⁶ cm^-2 after two days and decreased to 2.0×10⁵ cm^-2 after 28 d. Our results emphasized the importance of the microbial community in the decomposition of macrophytes in the ARB, especially in backwater habitats and in the early stages of decay.     

Colony persistence in waterbirds is constrained by pond quality and land use

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Niche partitioning and the effect of interspecific competition on microhabitat use by two sympatric galaxiid stream fishes

1. Numerous interacting abiotic and biotic factors influence niche use and assemblage structure of freshwater fishes, but the strength of each factor changes with spatial scale. Few studies have examined the role of interspecific competition in structuring stream fish assemblages across spatial scales. We used field and laboratory approaches to examine microhabitat partitioning and the effect of interspecific competition on microhabitat use in two sympatric stream fishes (Galaxias‘southern’ and Galaxias gollumoides) at large (among streams and among sites within streams) and small (within artificial stream channels) spatial scales. 2. Diurnal microhabitat partitioning and interspecific competition at large spatial scales were analysed among three sympatry streams (streams with allotopic and syntopic sites; three separate catchments) and four allopatry streams (streams with only allotopic sites; two separate catchments). Electro‐fishing was used to sample habitat use of fishes at 30 random points within each site by quantifying four variables for each individual: water velocity, depth, distance to nearest cover and substratum size. Habitat availability was then quantified for each site by measuring those variables at each of 50 random points. Diet and stable isotope partitioning was analysed from syntopic sites only. Diel cycles of microhabitat use and interspecific competition at small spatial scales were examined by monitoring water velocity use over 48 h in artificial stream channels for three treatments: (i) allopatric G. ‘southern’ (10 G. ‘southern’); (ii) allopatric G. gollumoides (10 G. gollumoides) and (iii) sympatry (five individuals of each species). 3. One hundred and ninety‐four G. ‘southern’ and 239 G. gollumoides were sampled across all seven streams, and habitat availability between the two species was similar among all sites. Galaxias‘southern’ utilised faster water velocities than G. gollumoides in both the field and in channel experiments. Both species utilised faster water velocities in channels at night than during the day. Diet differences were observed and were supported by isotopic differences (two of three sites). No interspecific differences were observed for the other three microhabitat variables in the field, and multivariate habitat selection did not differ between species. Interspecific competition had no effect on microhabitat use of either species against any variable either in the field (large scale) or in channels (small scale). 4. The results suggest that niche partitioning occurs along a subset of microhabitat variables (water velocity use and diet). Interspecific competition does not appear to be a major biotic factor controlling microhabitat use by these sympatric taxa at any spatial scale. The results further suggest that stream fish assemblages are not primarily structured by biotic factors, reinforcing other studies de‐emphasising interspecific competition.     

Wetland use by brood‐rearing female ducks in a boreal forest landscape: the importance of food and habitat

Habitat use by birds may be related to single or interacting effects of habitat characteristics, food resources and predators, but little is known about factors affecting habitat use by wetland species in boreal ecosystems. We surveyed brood‐rearing females and ducklings of four common boreal duck species to assess the effects of habitat structure and food resources on the use of wetlands by brood‐rearing ducks. Although wetland use by duck broods was related to habitat structure and food abundance, their relative importance varied among duck species. For the Common Goldeneye Bucephala clangula, a diving duck, aquatic invertebrates and large emerging insects were the most important factors associated with wetland use. Common Teal Anas crecca broods were observed more often on wetlands with greater Dipteran emergence, whereas in Mallard Anas platyrhynchos both habitat structure and large emerging insects were important. The occurrence of Eurasian Wigeon Anas penelope broods was related to emerging Diptera and habitat structure but the associations were not strong. The varying habitat and food requirements of common duck species could influence the success of wetland management programmes, and consideration of these factors may be particularly important for initiatives aimed at harvested species or species of conservation concern.     

Adaptations of an Emergence Trap for Use in Tropical Streams

An emergence trap based on the MPI Schlitz model was designed for use in the tropics and it was tested over one year in Palawan, the Philippines. Instructions for construction and use are given here. Only commonly available materials were used, except for the collection assembly made of UV‐light permeable acrylic glass. Heavy and bulky assemblies were avoided to enable easy transportation in the field. A special modification allows a fast and easy replacement of the screen when damaged by flooding, as is often required when traps are used downstream of headwaters. This type of trap also allows sampling of a wide littoral strip. Problems concerning the use of emergence traps in the humid tropics are discussed based on experience at different longitudinal stream sections in Palawan. The results presented here suggest that this trap should be used especially for qualitative or semi‐quantitative approaches. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Land use changes biomass and temporal patterns of insect cross-ecosystem flows

Emergent aquatic insects constitute an important food source for higher trophic levels, linking aquatic to terrestrial ecosystems. Little is known about how land use affects the biomass or composition of insect emergence. Previous studies are limited to individual time points or seasons, hampering understanding of annual biomass export patterns and detection of phenological changes. Over 1 year's primary emergence period, we continuously determined the biomass, abundance, and identity of >45,000 aquatic insects and recorded land-use-related environmental variables in 20 stream sites using a paired design with upstream forested sites and downstream agricultural sites. Total insect biomass and abundance were 2–7 mg day⁻¹ m⁻² and 7–36 ind day⁻¹ m⁻² higher in agricultural than forested sites. However, we found turnover of families between forested and agricultural sites, with more insects with shorter generation time in agriculture, indicating lower sensitivity to land-use-related stress because of higher recovery potential. Except for stoneflies, biomass and abundance of major orders were higher in agriculture, but their phenology differed. For different orders, emergence peaked 30 days earlier to 51 days later in agriculture than forest, whereas total abundance and biomass both peaked earlier in agriculture: 3–5 and 3–19 days, respectively. The most important land-use-related drivers were pesticide toxicity and electrical conductivity, which were differentially associated with different aquatic insect order abundances and biomass. Overall, we found that land use was related to changes in composition and phenology of aquatic insect emergence, which is likely to affect food-web dynamics in a cross-ecosystem context.     

Partitioning beta‐diversity through different pond hydroperiod lengths reveals predominance of nestedness in assemblages of immature odonates

Patterns of freshwater invertebrate assemblage structure in the transition from permanent to non‐permanent lentic habitats are well described in the literature. However, the effects of small changes in the hydroperiod of non‐permanent ponds on invertebrate assemblage structure remain less studied, especially on β‐diversity. Thus, we tested the effects of different pond hydroperiod lengths on the assemblage structure of immature odonates, in terms of both α‐ and β‐diversity. Small high‐altitude ponds with different hydroperiod lengths (assigned to ‘short’, ‘medium’ and ‘long’ hydroperiods) were sampled in southern Brazil between 2013 and 2014. Based on the hypothesis that shorter hydroperiods filter constituents of lentic fauna, i.e. that long‐living species cannot inhabit shorter‐hydroperiod ponds, we expected to find higher α‐ and β‐diversity in longer hydroperiods, as well as predominance of the nestedness component in β‐diversity. Restricted occurrence of some genera and higher α‐diversity of immature odonate assemblages was detected in long‐hydroperiod ponds. Within‐hydroperiod β‐diversity values did not vary among hydroperiods, because the occasional occurrence of some genera with high dispersal ability of adults in short‐hydroperiod ponds yielded similar values of the β‐diversity among hydroperiods. Partitioning of β‐diversity among hydroperiods revealed a significant higher contribution of the nestedness component rather than turnover. This pattern is explained by the occurrence of some generalist genera across the whole gradient of hydroperiod, as a subset of fauna in longer‐hydroperiod ponds. Thus, our results suggest that reduction in hydroperiod length, if occurring in the future climate change, would favor habitat‐generalist taxa in lentic ecosystems.     

Interdependence of CO2 and inorganic nitrogen on crassulacean acid metabolism and efficiency of nitrogen use by Littorella uniflora (L.) Aschers

The hypothesis is tested that crassulacean acid metabolism (CAM) in isoetids is a mechanism which not only conserves inorganic carbon but also plays a role in nitrogen economy of the plants. This hypothesis was tested in an outdoor experiment, where Littorella uniflora (L.) Aschers. were grown at two CO₂ and five inorganic nitrogen concentrations in a crossed factorial design. The growth of Littorella responded positively to enhanced nitrogen availability at high but not at low CO₂ indicating that growth was limited by nitrogen at high CO₂ only. For the nitrogen-limited plants, the capacity for CAM (CAM_cap) increased with the degree of nitrogen limitation of growth and an inverse coupling between CAM and tissue-N was found. Although this might indicate a role of CAM in economizing on nitrogen in Littorella , the hypothesis was rejected for the following reasons: (1) although CAM_cap was related to tissue-N no relationship between tissue-N and ambient CAM activity (CAM_ambient) was found whereas a close relationship would be expected if CAM was regulated by nitrogen availability; (2) the photosynthetic nitrogen use efficiency for high CO₂-grown plants declined with increased CAM_ambient and with CAM_cap; and (3) growth per unit tissue-N per unit time declined with increased CAM_ambient and CAM_cap.