Pebble Substrates Research Articles

Broadscale and fine‐scale variables predict the occurrence of a stream‐breading bufonid: Habitat use by the Arizona toad (Anaxyrus microscaphus)

AbstractArizona toad (Anaxyrus microscaphus) is a stream‐breeding bufonid of conservation concern in Arizona, New Mexico, Utah, and Nevada. We determined the occupancy and habitat use of the Arizona toad throughout its range. We surveyed 500‐m reaches along perennial and intermittent streams during the summers of 2021 and 2022 (n = 232) in Arizona. We recorded the presence of all toad life stages, focusing on larval stages. We related toad occupancy to broadscale environmental variables, including measures of bioclimate, habitat heterogeneity, solar radiation, and topography. We collected fine‐scale variables to summarize vegetation cover and substrate within plots (n = 53). We applied multiple occupancy models. Single‐species model results found low toad occupancy with high detection. Two principal component analyses (PCA) were run on broadscale and fine‐scale variables to reduce the number of variables included in the models. Toad occupancy was best predicted by top models with bioclimatic components; occupancy decreases with extremely hot temperatures and less precipitation. A logistic regression related toad presence to fine‐scale components with top models describing riparian complexity and algae. Arizona toads were selected for areas with foliar canopy cover, shallow water, algae cover, and pebble substrates. Arizona toad is an uncommon species and maintaining riparian forests of complex habitats with shallow and side‐channel flow will be important for toad conservation. Implications of less water cause riparian habitat to dry, which ultimately harms aquatic life.

Growth and behaviour of juvenile European eel (Anguilla anguilla) in sandy and stony bottom substrates

AbstractUnderstanding how the physical habitat influences growth and behaviour is essential for developing effective habitat restoration programmes of threatened and endangered fish species. In our study, we compared the growth and behaviour of juvenile European eel during 13 weeks in aquaria with either sand (0.8–2 mm) or pebbles (25–40 mm) as bottom substrate. In aquaria with the pebble substrate, eel grew significantly faster than in aquaria with sand (specific growth rate 0.15 vs. 0.11% day−1). Moreover, growth rates varied more for individuals inhabiting aquaria with sand than in those with pebbles (coefficient of variation 1.26 vs. 0.67). Habitat‐dependent growth rates may partly be explained by the observed differences in behavioural patterns. In aquaria with sand, eel left the substrate more often and moved close to the bottom or freely in water column. In aquaria with pebbles, eel remained hidden in the substrate to a high degree, also during feeding. These results may be important for prioritising connectivity‐ and habitat‐restoring measures and for optimization of restocking programmes.

Riverbed Substrate Requirements for Natural Reproduction of Gymnocypris przewalskii.

Simple SummaryRiverbed substrate plays a vital role in the growth, reproduction, predation of fish as an important aspect of a river ecosystem. This research represents the first systematic examination of the riverbed substrate requirements for the natural reproduction of Gymnocypris przewalskii through artificial simulation and spawning ground substrate transformation experiments. Results showed that pebble was an indispensable factor for the reproduction of Gymnocypris przewalskii and the increase of pebble had an obvious promoting effect on the reproduction. The findings of this study could provide guidance for the wild population recovery, artificial reproduction, and restoration of natural spawning grounds of this fish species.Gymnocypris przewalskii (i.e., Qinghai Lake naked carp) is a migratory fish species that lives in highland brackish water. It is important to understand the abiotic environment required by this fish to reproduce naturally so that its habitat can be protected and the wild population can be conserved. Here, artificial simulation and spawning ground substrate transformation experiments were conducted to examine the riverbed substrate requirements for G. przewalskii to naturally reproduce. Using various techniques (in vitro markers, videography, and Ethovision XT behavior tracking), this study systematically investigated the riverbed substrate preferences of G. przewalskii as well as the characteristics and effectiveness of natural reproduction induced by pebble riverbed substrate. The findings can be summarized as follows: (1) the habitat preferences of G. przewalskii differed significantly between various riverbed substrate, with pebble substrate being preferred during natural reproduction, and sand substrate being preferred pre- and post-spawning, and (2) the natural reproduction of G. przewalskii was heavily reliant on pebble riverbed substrate. Specifically, pebble substrate significantly improved spawn quantity and fertilization rate. These findings provide scientific evidence for the improvement and restoration of G. przewalskii spawning grounds, and insights regarding the artificial bionic reproduction of G. przewalskii.

IMPORTÂNCIA DE MICROHABITATS NA OCORRÊNCIA DE GÊNEROS DE EPHEMEROPTERA E TRICHOPTERA EM UMA ILHA NO RIO XINGU

IMPORTANCE OF MICROHABITATS IN THE OCCURRENCE OF EPHEMEROPTERA AND TRICHOPTERA SPECIES IN AN ISLAND IN RIO XINGU. This work described the abundance, richness and composition of genera and the functional food groups (GFA) of Ephemeroptera and Trichoptera (ET), in different microhabitats of a fluvial island, in Volta Grande of the Xingu River, Brazilian Amazon. Aquatic insects were collected from 30 samples located in puddles situated in the interior of the island (rocks as substrate); and another 30 samples located in the coastal margin of the island (pebble as substrate). The different facets of diversity (abundance, richness and composition of genera and GFA) were compared between puddle samples with rock substrate and those from the coastal region with pebble substrate. In total, 56 individuals were collected, distributed in 15 genera ET. The greatest estimated genera richness and the largest number of individuals occurred in the rocks of the puddle environments. The composition of genera differed between the rocks in the puddle environments and the pebbles in the coastal environments, with the community of the latter being more homogeneous. There were more scraper organisms distributed predominantly in the rocks of the puddle environments and filtering organisms arranged predominantly in the pebbles of the coastal environments. The distribution of scrapers is related to the availability of food, since the island has little vegetation and the light on the rocks is favorable for colonization by biofilm, its main food resource. In the coastal region, the greater distribution of filters is related to the greater number of fine particles suspended in water, its main food resource. The results demonstrate that even in spatially close environments, such as on a small island, differences in the availability of food resources in different microhabitats can influence the distribution in multiple facets of diversity. Thus, even in dynamic environments such as large rivers, maintaining microhabitats is important for aquatic insect communities.

Estimates of Chinook Salmon Spawning Habitat in a Blocked Reach of the Columbia River Upstream of Grand Coulee Dam

Spawning habitat of Chinook salmon (Oncorhynchus tshawytscha) was estimated upstream of Grand Coulee Dam to support the feasibility evaluations of reintroducing anadromous salmon to this blocked reach of the Columbia River. A two-dimensional depth-averaged hydrodynamic model was developed for a 76-km reach between Kettle Falls, Washington, and the US-Canada international border and used to predict water velocities and depths at 10%, 50%, and 90% flow exceedance values. Hydrodynamic model outputs were combined with calculated bed slopes and empirical and modeled data on substrate availability to estimate salmon spawning habitat availability. A probabilistic spawning model was developed to estimate suitability for spawning salmon based on habitat characteristics at the exceedance flow levels and three substrate classifications. A majority of the highest probability salmon spawning habitat was located between Northport, Washington, and the international border. The model predicted 17.6 ha of spawning habitat at the 50% exceedance flow level for areas with pebble and cobble substrates; this equates to an approximate redd capacity of 2,893 to 4,091 non-overlapping redds, depending on mean redd size. Estimated capacity of spawning adults ranged from 5,786 (assuming two fish per redd and lowest number of redds) to 32,728 (assuming eight fish per redd at highest number of redds). We conclude that suitable Chinook salmon spawning habitat is available upstream of Grand Coulee Dam. The results of this study will be useful to fisheries managers considering salmon reintroduction and ecosystem function in various processes including the modernization of the Columbia River Treaty, the Northwest Power and Conservation Council's Fish and Wildlife Program, and tribal and other natural resource conservation initiatives.

Terrestrial locomotion in elongate fishes: exploring the roles of morphology and substrate in facilitating locomotion

AbstractHighly elongate body plans have evolved multiple times in the Actinopterygii, and members of many of these groups are known to use lateral undulation on land. Here, we quantified components of the axial skeleton for four phylogenetically disparate actinopterygian fishes and one sarcopterygian to determine whether axial morphology may affect their locomotor kinematics. We tested species in water and on two terrestrial substrates: loose wet pebbles and wet sand. Differences in axial morphology translated to differences in wavelengths, amplitudes, and frequencies at the center of the body and tail while swimming, but overall, we consistently observed a similar shift in kinematic patterns when fish were moving on the two terrestrial treatments. Generally, our kinematic data support our hypothesis that elongate fishes increased their wave frequency and shorten their wavelengths on terrestrial substrates but we also observed lower wave amplitudes contrary to our prediction. As anticipated, animals exhibited a higher distance ratio (DR), our metric of locomotor efficiency, at the head, center of the body, and tail in aquatic trials. DRs were between 25% and 50% higher in water compared to terrestrial treatments. Locomotion was less effective on wet sand substrate compared to loose wet pebble substrate as exhibited by the discrepancy in DRs and wave patterns along the fish. These data suggest that loose wet pebble substrates do indeed provide vertical points for lateral force transmission and that highly elongate fish have an advantage when moving along this substrate. Our species varied greatly in their total vertebral numbers, 93–129, and in their proportion of precaudal (42–102) and caudal vertebral numbers (10–64). Therefore, despite major differences in vertebral proportions, we find that fishes with anguilliform body plans share similar suites of kinematic patterns within aquatic versus terrestrial treatments and that a pebble substrate can better facilitate axial movements.

Terrestrial Locomotion in American Eels (Anguilla rostrata): How Substrate and Incline Affect Movement Patterns

Fishes overcome a variety of challenges in order to invade the terrestrial environment. Terrestrial invasions by fish occur over a variety of environmental contexts. In order to advance their bodies on land, fishes capable of terrestrial excursions tend to use one of three different types of locomotor modes: axial-based, appendage-based, or axial-appendage-based. Elongate species with reduced appendages, such as the American eel, Anguilla rostrata, rely on axial based locomotion in water and on land. When eels move from water to land as part of their complex life cycle, they inevitably encounter a variety of substrates and must traverse variable degrees of incline. The aim of this study was to determine the effect of substrate and incline on the terrestrial locomotion of the American eel. In order to do this, eels were filmed from a dorsal view on three substrates and four inclines: sand, loose pebbles, and fixed (glued) pebbles at 0°, 5°, 10°, and 15°. We digitized 20 evenly spaced points along the body to examine the following characteristics of locomotion: velocity, distance ratio, and wave parameters such as wave amplitude, frequency and length, and assessed whether substrate, incline, or body position affected these parameters. Distance ratio, our metric of movement efficiency, was highest on the flat sand condition and lowest on 15° pebble conditions. Efficiency also varied across the body. Velocity followed a similar pattern being highest on sand at 0° and lowest at the steepest inclines. Wave amplitude generally increased towards the tail but was similar across substrates and inclines. Wave frequency was relatively consistent across the body on both pebble substrates, but on sand, frequency was higher towards the head and decreased towards the tail. Wavelengths on sand were the longest at 0° near the head and shorter wavelengths were observed on steeper inclines. Both pebble substrates elicited lower wavelengths that were more similar across the body. Overall, A. rostrata were more effective in navigating compliant substrates but struggled at steeper inclines. Our findings provide insight into locomotor challenges that American eels may encounter as they move from and between bodies of water.

Microhabitat use of landlocked juvenile Atlantic salmon (Salmo salar)

Large-scale reintroduction programs for landlocked Atlantic salmon Salmo salar are ongoing in Lakes Ontario and Champlain. Commonly, these programs involve stocking hatchery reared juveniles into streams and thus, quantifying the in situ habitat use of stocked fish can help support these efforts. To examine habitat use, we stocked young-of-the-year (YOY) Atlantic salmon into 14 reaches of the Boquet River in the Lake Champlain Basin. The habitat used by YOY Atlantic salmon, measured from microhabitats that were used versus not used, differed between early and late summer for water depth. In early summer, YOY Atlantic salmon used a more narrow range of habitats compared to late summer. However, in both early and late summer, YOY most often used intermediate values in habitat variables except for water velocity in early summer. In early summer, YOY Atlantic salmon had the highest probability of using a water depth of 26 cm, a water velocity of 1 cm/sec, and a pebble substrate. In late summer, the probability of use was highest at a water depth of 61 cm, a water velocity of 11 cm/sec, and a pebble substrate. Our results show that stocked landlocked YOY Atlantic salmon use similar habitats to anadromous populations and may help managers when determining stocking locations or habitat alterations.

STATUS, DISTRIBUTION AND HABITAT SPECIFICITY OF BENTHIC MACRO-INVERTEBRATES: A CASE STUDY IN FIVE TRIBUTARIES OF BUDDHIGANGA RIVER IN WESTERN NEPAL

Benthic macro-invertebrates are organisms that inhabit the bottom of substrates such as sediments, debris, logs, macrophytes and filamentous algae of streams, rivers and lakes for some span of their lifecycle. They are important part of food chain since they are source of food for different species of fishes and process organic matters. These organisms are considered vital tools to assess any environmental change caused by anthropogenic interference in the river ecosystems. In this study, we sampled macro-invertebrates from 5 different rivers across altitudinal ranges of 600- 800 m and 1500-1700 m above sea level. We observed that the macro-invertebrate diversity varied substantially across altitudinal ranges. The diversity of macro-invertebrates was higher in lower altitudinal range, where 11 families were found, more than the higher altitudinal range. Some rare and dominant families were also identified in our study. We also examined the substrate specificity of macro-invertebrates. Results revealed that Ephemeroptera,Tricoptera, Coleoptera, Diptera and Odonata were found in all seven substrates namely bedrock, boulder, cobble, stone, pebble, gravel and sand. The richness and abundance of macro-invertebrates were documented in cobble, stone and pebble substrates. Similarly we also investigated the ecological river quality class of rivers using Ganga River System Biotic Score-Average Score per Taxon (GRS-BioS/ASPT) system which indicated good status. The outcomes of this study serve as a baseline data since no prior research has been done in these rivers.

Low tolerance of salt water in a marine fish: new and historical evidence for surprising local adaption in the well-studied commercially exploited capelin

Intraspecific biodiversity among populations is ecologically and evolutionarily notable. Substantial adaptations in well-studied commercial species should be obvious and ought to have been uncovered. The tenet of marine stability posits relatively little local adaptation in the sea, except for temperature responses to latitude for widespread species. However, aquatic reproduction is tightly constrained by water chemistry, which may lead to abstruse adaptations. Capelin (Mallotus villosus) reproduction has been studied for over a century, occurring within pebble substrate on beaches or the seafloor of continental shelves. Offshore spawners (Iceland/Barents Sea) have embryos with tolerance of high salinity. I provide new and historical data on beach spawners from several areas indicating that their embryos perform well from ∼2 to 28 psu, but at higher salinities indicative of coastal seawater, there is poor hatch success, larvae take longer to hatch, hatch at a smaller size, and starve more quickly. The body of evidence supports the hypothesis that beach spawning evolved from anadromy, with offshore spawning a derived state, enabled by increased salinity tolerance. The results have recovery implications for depleted Newfoundland stocks, which have been spawning seasonally late under relatively high salinity for over 25 years.

Seabed Habitat Determines Fish and Macroinvertebrate Community Associations in a Subarctic Marine Coastal Nursery

AbstractFish exhibit habitat‐specific distributions in heterogeneous landscapes. Many sampling techniques are limited to specific seabed types and have limited utility in comparisons of fish abundance among multiple habitats. We measured the relative abundance and the composition of fish communities in four naturally occurring coastal marine seabed types (sand–pebble, cobble, bedrock, and eelgrass) and one anthropogenic habitat type (wharf) in Newman Sound, Newfoundland, Canada, by using baited video cameras. Fish and macroinvertebrate communities were significantly different among habitat types. Winter Flounder Pseudopleuronectes americanus, Atlantic Cod Gadus morhua, and Shorthorn Sculpin Myoxocephalus scorpius were significantly more abundant over sand–pebble substrate compared with bedrock and wharf sites. Cunners Tautogolabrus adspersus and Greenland Cod Gadus macrocephalus ogac were most abundant at wharf sites. Atlantic rock crabs Cancer irroratus and American lobsters Homarus americanus avoided sand–pebble seabeds, and American lobsters were almost exclusive to bedrock sites. Cunners, Winter Flounder, and Atlantic Cod were more abundant in summer, whereas Greenland Cod and Atlantic rock crabs were more abundant during autumn months. In paired comparisons of eelgrass habitats, the community sampled by two methods was different. Relative abundance estimates from baited video cameras matched beach seine estimates for abundant predatory species (e.g., Cunner, Greenland Cod, and Atlantic rock crab), but other species, including age‐0 Greenland Cod, Shorthorn Sculpin, and White Hake Urophycis tenuis, were better represented in beach seine samples. We demonstrated substrate preferences by common coastal marine fish and crab species, which have proven difficult to enumerate via active sampling techniques in the past. Our findings will facilitate comparative studies for these species among habitat components. For species that are well sampled by using baited video cameras, this technique will advance our ability to plan for their management in the nearshore.

Mechanisms for invasion success by Didemnum vexillum (Chordata: Ascidiacea): observations versus manipulations

The widespread success of the invasive colonial ascidian Didemnum vexillum has led to descriptions of the species as fast-growing and competitively dominant, with few predators in its introduced range. However, recent experiments assessing the competitive strength and predation resistance of D. vexillum suggest that this ascidian is not a stronger competitor compared to other non-native colonial ascidians (e.g., Botrylloides violaceus, Botryllus schlosseri). To examine this apparent contradiction, juvenile D. vexillum colonies of varying size and age from an invasive population were exposed to competitive interactions with other epifaunal invertebrates and predation by mobile benthic invertebrates. Results indicate that both competition and predation had a significant negative effect on D. vexillum growth as well as on the composition of and percent cover of D. vexillum in 6- to 8-week-old experimental communities. In smaller colonies, predation also had a significant negative effect on D. vexillum survival. The discrepancy between field observations describing D. vexillum as a superlative competitive dominant and recent manipulative experiments indicating the opposite may be a function of the intrinsic life history characteristics of D. vexillum: (a) frequent colony fusion in non-native regions, (b) transport of larvae over relatively long distances via tendril detachment, (c) unique formation of colony mats on pebble substrates, and (d) calcified structures embedded in the tunic. The combined effects of these characteristics could make non-native populations of D. vexillum appear to be competitively dominant species with few predators, even though manipulative experiments on individual colonies suggest otherwise.

Unionid mussel composition and ditch environments in floodplain and alluvial fan geomorphic types: a case study of a Lake Biwa river basin

To determine the differences in the ditch environments and mussel composition between floodplains and alluvial fans, two geomorphic types in a Lake Biwa river basin were surveyed. An intrinsic Gaussian conditional autoregressive (CAR) model was applied to assess the relationship between the density of Nodularia douglasiae biwae, the dominant species in the floodplain area, and ditch environment. Relative to the alluvial fan area, ditches in the floodplain area had higher percentages of muddy and sandy substrates, a lower percentage of pebble substrates, greater sediment softness, faster flow velocity, and deeper water depth. N. d. biwae and Pronodularia japanensis were collected in both the floodplain and alluvial fan areas. Lanceolaria grayana and Sinanodonta japonica were captured only in the floodplain area, and Sinanodonta lauta was found only in the alluvial fan area. The differences in the ditch environments between the two geomorphic types and the drought tolerance of the mussel species may explain why the mussel composition differs between the two geomorphic types. The CAR model indicated that N. d. biwae was more abundant in ditches with sandy and soft sediment and with deeper water. It also points to the importance of microhabitat-scale sampling to determine the relationship between unionid density and ditch environment.

Substratum as Determining Factor for the Distribution of Benthic Macroinvertebrate Fauna in a River Ecosystem

Present study was focused on the Ken river for determination of the distribution of benthic macroinvertebrate fauna with respect to substrate variation. The invertebrate samples were collected during December 2003 to March 2004 at four different stations by lifting of stones and sieving of clay–silt substratum from 0.09 m2 area. The collected samples were preserved in 5 % formalin and identified at family level. The count data was used to determine the density and composition of benthic macroinvertebrate fauna. Total mean density decreased from station S1 to S3 but increased at S4 and differed significantly among the stations. The maximum density was found in the stony substratum (boulder and cobble) as compared to small particle size (pebble, gravel and sand). The fauna was predominated by insects at stations S1 (84 %), S2 (90 %) and S3 (93 %), while reduced at S4 (48 %). Neoephemeridae and Caenidae were abundant taxa in boulder–cobble and cobble–pebble substrate, respectively. Leptophlebiidae, Baetidae and Hydropsychidae were abundant at pebble–gravel substrate and Thiaridae–Chironomidae–Nephthydae were abundant in silt–clay substrate. Principal component analysis also indicated the above observation. Canonical correspondence analysis at each station indicated that substratum (abiotic and biotic) was responsible for the distribution of benthic macroinvertebrate fauna in the Ken. Functionally, the collector insects dominate the fauna, at all the four stations because of substratum as well as the continuous source of particulate organic matter in the river.

Activity, substrate selection, and effect of a simulated Amazon flood regime on the behaviour of the apple snail, Pomacea bridgesii

This study investigated the behaviour of Pomacea bridgesii, describing the daily activity, substrate selection and the influence of the flood regime in the Amazon, the species’ native habitat. The present study described the daily activity and substrate selection, and evaluated the activity adaptations of the gastropods in a simulated flood-pulse regime. Gastropods were collected in Amazonas, Brazil, in June 2013. Assessments of the daily behaviour, substrate selection, and flood-pulse simulation were made in experimental water tanks. The snails were observed hourly for 48h, and their behaviour recorded on an ethogram. The snails were more active during the night, when up to 80% of them moved about. In general, during both day and night, the gastropods used the pebble substrate most often. Comparing the day periods, a significant proportion of the individuals that were using the pebbles moved to other substrates (t=5; d.f.=2; P=0.03). The interaction of the behaviour of P. bridgesii with the simulated flood-pulse regime showed a statistical difference between the dry period and the period of maximum water level. The water regime of the Amazon floodplain directly influenced the activity of P. bridgesii, with responses including self-burying and activity interruption, with the operculum closed to minimise water loss.

Habitat utilization, movement and use of groundwater seepages by larval and juvenile Black Redhorse, Moxostoma duquesnei

Black Redhorse (Moxostoma duquesnei) larval and juvenile habitat was characterized in the Grand River, Ontario from June to September 2007–2012. Similar to adult Black Redhorse and their congeners, larval Black Redhorse were most likely to be located in clean, clear, stable runs with low to moderate flow, over pebble, gravel and cobble substrate, mixed with sand. Areas (n = 22) where 0+ Black Redhorse were observed and collected were 1.4 ± 0.2 m from shore, with a mean water temperature of 22.0 ± 0.5 °C, mean depth of 0.20 ± 0.02 m and mean water velocity of 0.12 ± 0.05 m/s. Larval and juvenile Black Redhorse occupied riffles, runs, pools and backwater areas; however, there was a strong preference for runs. Juvenile Black Redhorse moved upstream in the early evening and at night to overwintering areas in the Grand River in November when water temperature approached 5 °C. The persistence of Black Redhorse populations in the Grand River may be related to the presence of groundwater, which provides refuge from extreme temperature and poor water quality during the summer.

Snowy plover nest site selection, spatial patterning, and temperatures in the Southern High Plains of Texas

AbstractSnowy plover (Charadrius nivosus) populations have declined throughout their range, in part because of habitat degradation and poor nest success, making information regarding regionally specific nest site selection and spatial patterns important when considering habitat conservation and management guidelines. We determined nest site selection characteristics (n = 180) and examined spatial patterns (n = 215) of snowy plover nests in saline lakes in the Southern High Plains (SHP) of Texas. At 104 nests, we examined the influence of substrate type on nest temperatures and heat mitigation. Snowy plover nests were more likely to be found near an object, on pebble substrate, and with fewer plants than random sites. High use areas were generally located in areas with pebble substrate and on human‐made or natural islands, berms, and peninsulas. Overall, nests placed on pebble substrate had lower temperatures during the day than nests placed on sand substrates. Nest placement on pebble substrate may be valuable to nesting snowy plovers, providing thermal advantages to incubating adults and depressing potentially high nest predation rates. Management guidelines for this region should emphasize the importance of addressing key elements of snowy plover nesting habitat including the presence of pebble substrate and reducing vegetation encroachment. © 2012 The Wildlife Society.

Alteration of leaf decomposition in copper‐contaminated freshwater mesocosms

The influence of copper on leaf litter decomposition was examined in experimental streams. Controls and three levels of contamination (5, 25, and 75 microg/L) were tested in triplicate in 20-m-long mesocosms. Equal quantities of alder, maple, and oak leaves were enclosed in mesh bags and placed in the upper and lower mesocosm sections that exhibited different habitat characteristics (shallow with pebble substrate or deep with fine substrate and macrophytes, respectively). Decomposition rate in the upper section of the 75 micro.g/L mesocosms was significantly reduced to 28% of control values. No significant reductions in the decomposition rate were seen in the lower section. No differences in the leaf-associated mycelial biomass and sporulation rates were observed between treatments, but they were consistently higher in the upper sections. The aquatic hyphomycete community was not affected by the contamination. The abundances of total leaf-associated macroinvertebrates and the dominant shredder (Gammarus pulex) were considerably reduced in the upper sections at 75 microg/L. Therefore, the reduced leaf decomposition probably resulted from a reduction in the abundance of macroinvertebrate detritivores. In addition, local variations in physical and biological characteristics of the habitat along the mesocosms significantly influenced the effects of copper on leaf-associated decomposers.

Selection of Spawning Sites by Coho Salmon in a Northern California Stream

AbstractWe assessed the relative importance of various factors contributing to spawning site use by a population of threatened coho salmon Oncorhynchus kisutch in Freshwater Creek, California, and created a predictive model of spawning habitat selection based on logistic regression analysis. We excluded sampling sites that previous studies had established as unsuitable on the basis of depth and substrate criteria and asked why fish chose particular locations and not others in seemingly suitable habitat. We evaluated surface water velocity, depth, substrate size composition, gravel inflow rates, vertical hydraulic gradient, geomorphic channel units, hyporheic water physicochemistry, cover, and proximity to other redds not in sampling sites during the 2004–2005 spawning season. In univariate comparisons with unused sites, coho salmon selected sites with a smaller median particle diameter, a larger percentage of gravel–pebble substrate, and higher gravel inflow rates. Based on multivariate logistic regression, the probability of a site's being used for spawning was best modeled as a positive function of the gravel–pebble fraction of the substrate, location at a pool or run tail, and the presence of existing redds in close proximity to the site. This model explained 38% of the variation in the data and was a better predictor of spawning habitat use than a more traditional model based on depth, velocity, and substrate. Our results highlight the potential importance of social behavior in contributing to habitat selection by spawning salmonids.

Microhabitat Use by Smallmouth Bass in an Ozark Stream

ABSTRACT Microhabitat use by smallmouth bass (Micropterus dolomieu) versus availability was evaluated in Baron Fork Creek, Oklahoma, an Ozark stream, using resource selection function analysis. Use of water depth and velocity, substrate size, and cover was measured at fish locations marked during underwater observation, and habitat availability was measured along transects. Resource selection functions discriminated use versus availability at an intermediate level for individuals <100 mm (receiver operating characteristic; c = 0.774) and a high level for those ≥100 mm (c = 0.866). Smallmouth bass <100 mm selected gravel and pebble substrates, intermediate water depths, and areas near large woody debris and rootwads (P < 0.15). Smallmouth bass ≥100 mm selected water depths that were related to water velocities, and they selected areas near large woody debris and overhanging vegetation (P < 0.15). Smallmouth bass selection of microhabitats in Baron Fork Creek differed to some degree from selection reported by other studies.