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At least 181 records · Page 10Linked to original sources
USGS2026

Spatial and temporal drivers of variability in abundance of two stream fishes

An understanding of how and why animal populations vary in space and time informs effective conservation and management. We used spatial and temporal flow metrics to explore flow-ecology relationships for two fish species, Mountain Sucker Pantosteus platyrhynchus (Cope, 1874) and Mottled Sculpin Cottus bairdii Girard, 1850, across 64 sites and 8 years in Wyoming, U.S.A. We found variation in Mottled Sculpin and Mountain Sucker abundance was driven to a greater extent by spatial flow metrics (e.g., drainage area, median summer flow) with differing direction of response between species. The opposing responses to spatial variation in median summer flow could reflect the ability of Mountain Sucker to persist in non-perennial habitats, likely due to their relatively high mobility and recolonization capacity. Responses to temporal flow metrics (e.g., previous year spring flow, previous year autumn flow) were weaker but consistent across species likely due to similar reproductive strategies and timing. The lack of stronger flow effects on population variability in both species likely corresponds to high variability in local habitat characteristics that are mediating population response. These findings underscore how considering spatial context informs conservation planning and suggest that flow-ecology relationships may be mediated by species-specific traits and local habitat conditions.

Wyoming↗
USGS2026

Effects of prey and tissue type on δ13C and δ15N discrimination and turnover rates of rainbow trout

Stable isotope analysis is used often in ecological studies to examine dietary patterns of consumers and food web structure, yet we still know little regarding some underlying assumptions, including for well-studied species like rainbow trout Oncorhynchus mykiss . We assessed δ 13 C and δ 15 N discrimination (∆) and turnover rates in blood, liver and white muscle of rainbow trout fed natural prey items (sculpin and chironomids). Liver had the fastest turnover rates for both δ 15 N and δ 13 C (4–6 months), followed by blood (4–7 months) and white muscle (7–9 months). Metabolism accounted for more isotopic turnover (82–93%) than growth, with the exception of δ13C in the blood of rainbow trout fed chironomids (33% of isotopic turnover was metabolic). Discrimination factors differed by tissue and diet, with ∆δ 15 N showing highest enrichment in white muscle (3.8‰; 95% CI 3.3–4.3), followed by blood (2.9‰; 95% CI 2.4–3.4) and liver (2.5‰; 95% CI 1.9–3.1) compared to the hatchery diet. The ∆δ 13 C of liver showed higher enrichment (1.9‰; 95% CI 1.7–2.1) than white muscle (1.7‰; 95% CI 1.4–2.0) and blood (1.5‰; 95% CI 1.3–1.7). It is crucial that future models incorporate species-specific tissue turnover and discrimination factors to enable drawing strong inferences and improve accuracy of model predictions.

Hydrobiologia↗
USGS2026

Invasion potential of nonnative fishes through a large western dam into an iconic and vulnerable ecosystem

Native fishes face imperilment due to habitat loss and fragmentation, megadrought, invasive species, and synergies amongst threats. These threats coalesce at Glen Canyon Dam (GCD), which impounds the Colorado River to create Lake Powell, a reservoir inhabited by a suite of nonnative fishes. Water level in Lake Powell has declined precipitously due to water overallocation and megadrought, increasing the risk of nonnative fish entrainment through the dam, as the penstocks draw water from the epilimnion. Our goal was to characterize the distribution and abundance of nonnative fishes in the vicinity of GCD and identify environmental conditions that may increase entrainment. We used active and passive sampling, hydroacoustics, and acoustic telemetry to assess the distribution and abundance of fishes. When the reservoir was stratified fish remained in the epilimnion, were present near the GCD penstocks, and thus at high risk of entrainment. When the reservoir was mixed, fish generally occupied shallower, warmer areas further from GCD, but this varied among species. The distribution of nonnative fish and accompanying risk of entrainment varied by season and epilimnion depth. Retaining more water in Lake Powell to draw water from below the thermocline would reduce the risk of nonnative fish entrainment into Grand Canyon.

Arizona, Utah↗
USGS2026

Understanding co-invading species’ ecological strategies and interactions with causal inference and simple dynamic models: Bighead (Hypophthalmichthys nobilis) and Silver carp (H. molitrix) in the Illinois River, USA

Species interactions among multiple invasive species can present hidden challenges for management and eradication efforts. Bighead and Silver carp ( Hypophthalmichthys nobilis and H. molitrix , respectively) are closely related species that have co-invaded the Mississippi River and many of its tributaries, including the Illinois River. We used a combination of causal inference and dynamic models to test for interspecific interactions in a 10-year data set of hydroacoustic density data from the Illinois River. The results suggest that Bighead and Silver carp are exploiting different ecological strategies; where Bighead carp shows fast initial growth but low equilibrium density and Silver carp had a lower low-density growth rate but larger equilibrium population density. Further, we found evidence for a positive interspecific effect of Silver carp on Bighead carp. The mechanism leading to the observed positive interactions is unknown, but could be an effect of ecological facilitation, differential responses to harvest of both species, or hybridization and introgression. Finally, while these results provide valuable information in the ecological strategies and relationships between these species, simulations of the resulting models suggest that the magnitude of the positive interaction is likely too small to be exploited for innovative multispecies management interventions.

Illinois↗
USGS2026

Long-term predictive modeling of stream condition suggests wide-spread changes within the Chesapeake Bay Watershed, USA

Stream ecosystems worldwide face ongoing degradation, underscoring the urgent need for conservation and restoration. Regional analyses of stream condition have been limited by sparse spatial and temporal data, particularly at long time scales. To address this gap, we used observed data to predict annual biological condition for 360,893 small, nontidal stream reaches in the Chesapeake Bay watershed from 1985 to 2023 (39 years). Predictions were generated using random forest models trained on extensive benthic macroinvertebrate data sets and predictors including natural landscape features, land cover, and climate variables. Four biological metrics were assessed: percent Ephemeroptera, Plecoptera, and Trichoptera excluding Hydropsychidae (EPT-H), percent Ephemeroptera, percent clinger functional group, and the Index of Biological Integrity (IBI). Results revealed degraded biological conditions near Washington, D.C. and Baltimore, Maryland, with declining trends across all metrics in these urbanized areas. Spatial heterogeneity was evident: IBI and clinger percentages increased in many southern streams but declined in northern streams, whereas EPT-H and Ephemeroptera decreased watershed wide except in the Southeastern Plains bioregion. By 2021, watershed wide IBI improvements were predicted for 0.9–1.1% of stream length, falling short of management goals. This study demonstrates the utility of long-term data and machine learning for predicting stream condition, identifying key stressors, and guiding restoration and conservation site selection.

Delaware, Maryland, New York, Pennsylvania, Virgin↗
USGS1997

Effects of zebra mussels on food webs: Interactions with juvenile bluegill and water residence time

We evaluated how water residence time mediated the impact of zebramussels Dreissena polymorpha and bluegill sunfish Lepomis macrochirus on experimental food webs established in1100-l outdoor mesocosms. Water residence time was manipulated asa surrogate for seston resupply – a critical variable affectinggrowth and survival of suspension-feeding invertebrates. We used a2×2×2 factorial experimental design witheight treatment combinations (3 replicates/treatment) including thepresence or absence of Dreissena (2000 per m 2 ), juvenilebluegill (40 per mesocosm), and short (1100 l per d) or long (220 lper d) water residence time. Measures of seston concentration(chlorophyll a, turbidity and suspended solids) were greaterin the short- compared to long water-residence mesocosms, butintermediate in short water-residence mesocosms containing Dreissena. Abundance of rotifers (Keratella and Polyarthra) was reduced in Dreissena mesocosms and elevatedin short residence time mesocosms. Cladocera abundance, in general,was unaffected by the presence of Dreissena; densities werehigher in short-residence time mesocosms, and reduced in thepresence of Lepomis. The growth of juvenile Lepomiswere unaffected by Dreissena because of abundant benthicfood. The final total mass of Dreissena was significantlygreater in short- than long-residence mesocosms. Impacts of Dreissena on planktonic food webs may not only depend on thedensity of zebra mussels but also on the residence time of thesurrounding water and the resupply of seston.

Hydrobiologia↗
USGS1997

Population genetic structure of a California endemic Branchiopod, Branchinecta sandiegonensis

Branchinecta sandiegonensis (Crustacea: Anostraca) is a narrow range endemic fairy shrimp discontinuously distributed in ephemeral pools on coastal mesas in San Diego County, USA. Ten populations across the range of the species were subjected to allozyme analysis for eleven loci. The species exhibits low variability (P 95 =9.1–45.5) and one third of the loci tested did not conform to Hardy-Weinberg equilibrium expectations. The species also exhibited a high degree of genetic differentiation between populations. F ST values (fixation index) for most pairs of populations were above 0.25 (0.036–0.889).Low genetic variability and high genetic structure may result from low gene flow and founder effects due to habitat fragmentation and the lack of potential vectors for cyst dispersal. The unpredictable rainfall of the region also creates potential for variable population sizes which could affect structure and variability.

Hydrobiologia↗
USGS1999

The effects of chlorpyrifos on cholinesterase activity and foraging behavior in the dragonfly, Anax junius (Odonata)

We examined head capsule cholinesterase (ChE) and foraging behavior in nymphs of the dragonfly, Anax junius, exposed for 24 h to 0.2, 0.6 and 1.0 ??g l-1 of the organophosphorus (OP) insecticide, chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate]. The invertebrate community is an important component of the structure and function of wetland ecosystems, yet the potential effects of insecticides on wetland ecosystems are largely unknown. Our objectives were to determine if exposure to environmentally realistic concentrations of chlorpyrifos affected foraging behavior and ChE activity in head capsules of dragonfly nymphs. Nymphs were exposed to different concentrations of chlorpyrifos and different prey densities in a factorial design. ChE activities and foraging behaviors of treated nymphs were not statistically different (p ??? 0.05) from control groups. Prey density effects exerted a greater effect on dragonfly foraging than toxicant exposures. Nymphs offered higher prey densities exhibited more foraging behaviors but also missed their prey more often. High variability in ChE activities within the control group and across treated groups precluded determination of relationships between ChE and foraging behaviors. It appears that A. junius is relatively tolerant of chlorpyrifos, although the concentrations we tested have been shown in other work to adversely affect the prey base; therefore the introduction of this insecticide may have indirect adverse affects on top invertebrate predators such as Odonata.

Hydrobiologia↗
USGS1999

Variability in bacterial community structure during upwelling in the coastal ocean

Over the last 30 years, investigations at the community level of marine bacteria and phytoplankton populations suggest they are tightly coupled. However, traditional oceanographic approaches cannot assess whether associations between specific bacteria and phytoplankton exist. Recently, molecular based approaches have been implemented to characterize specific members of different marine bacterial communities. Yet, few molecular-based studies have examined coastal upwelling situations. This is important since upwelling systems provide a unique opportunity for analyzing the association between specific bacteria and specific phytoplankton in the ocean. It is widely believed that upwelling can lead to changes in phytoplankton populations (blooms). Thus, if specific associations exist, we would expect to observe changes in the bacterial population triggered by the bloom. In this paper, we present preliminary data from coastal waters off New Jersey that confirm a shift in bacterial communities during a 1995 upwelling event recorded at a long-term earth observatory (LEO-15) in the Mid-Atlantic Bight. Using PCR amplification and cloning, specific bacterial 16S ribosomal RNA sequences were found which were present in upwelling samples during a phytoplankton bloom, but were not detected in non-bloom samples (surface seawater, offshore sites or sediment samples) collected at the same time or in the same area. These findings are consistent with the notion of specific associations between bacteria and phytoplankton in the ocean. However, further examination of episodic events, such as coastal upwelling, are needed to confirm the existence of specific associations. Additionally, experiments need to be performed to elucidate the mechanisms leading to the specific linkages between a group of bacteria and a group of phytoplankton.

Hydrobiologia↗
USGS1999

Zebra mussel filter feeding and food-limited production of Daphnia: Recent changes in lower trophic level dynamics of Oneida Lake, New York, U.S.A.

Exotic zebra mussels can alter lower trophic level dynamics in lakes that they colonize by consuming large quantities of phytoplankton. We simulated the indirect effects of zebra mussel grazing on Daphnia by artificially reducing phytoplankton concentration for in situ Daphnia reproduction experiments. The response of Daphnia reproduction to reduced phytoplankton was evaluated for both the in situ experiments and field observations in Oneida Lake, New York, U.S.A. Oneida Lake has had an abundant population of zebra mussels since 1992. Our experiments revealed that fecundity of individuals from two species of Daphnia was positively related to phytoplankton concentration during the spring clearwater phase, although there was no discernible effect of food concentration on fecundity in summer cyanobacteria-dominated assemblages. The experimental results suggest that Daphnia fecundity responds to chlorophyll a concentrations < 2 ??g l-1. The years since zebra mussels became abundant in Oneida Lake have been characterized by high water clarity, low chlorophyll concentrations, long clearwater phases, and low Daphnia biomass compared with the previous 17 years. The food web effects of zebra mussel grazing are complex and it will take more years for impacts at higher trophic levels to develop and be identified.

Hydrobiologia↗
USGS2000

Acidophilic and acid-tolerant fungi and yeasts

Fungi have not been systematically studied from mines and mine drainage waters, even though they are often encountered there. This paper provides a key from literature sources and lists morphological characteristics and habitat information for the 81 fungal species that have been collected or identified in pH <4 environments.

Hydrobiologia↗
USGS2000

Ecogeochemistry of the subsurface food web at pH 0–2.5 in Iron Mountain, California, U.S.A.

Pyrite oxidation in the underground mining environment of Iron Mountain, California, has created the most acidic pH values ever reported in aquatic systems. Sulfate values as high as 120 000 mg l −1 and iron as high as 27 600 mg l −1 have been measured in the mine water, which also carries abundant other dissolved metals including Al, Zn, Cu, Cd, Mn, Sb and Pb. Extreme acidity and high metal concentrations apparently do not preclude the presence of an underground acidophilic food web, which has developed with bacterial biomass at the base and heliozoans as top predators. Slimes, oil-like films, flexible and inflexible stalactites, sediments, water and precipitates were found to have distinctive communities. A variety of filamentous and non-filamentous bacteria grew in slimes in water having pH values <1.0. Fungal hyphae colonize stalactites dripping pH 1.0 water; they may help to form these drip structures. Motile hypotrichous ciliates and bdelloid rotifers are particularly abundant in slimes having a pH of 1.5. Holdfasts of the iron bacterium Leptothrix discophora attach to biofilms covering pools of standing water having a pH of 2.5 in the mine. The mine is not a closed environment – people, forced air flow and massive flushing during high intensity rainfall provide intermittent contact between the surface and underground habitats, so the mine ecosystem probably is not a restricted one.

California↗
USGS2000

Bacteria and Archaea in acidic environments and a key to morphological identification

Natural and anthropogenic acidic environments are dominated by bacteria and Archaea. As many as 86 genera or species have been identified or isolated from pH <4.5 environments. This paper reviews the worldwide literature and provide tables of morphological characteristics, habitat information and a key for light microscope identification for the non-microbiologist.

Hydrobiologia↗
USGS2000

The impact of extremely low frequency electromagnetic fields on stream periphyton: An eleven-year study

Potential effects of extremely low frequency (ELF) electromagnetic fields on periphyton were studied from 1983 to 1993 using a Before, After, Control and Impact design. The study was conducted at two sites on the Ford River, a fourth-order brown water trout stream in Dickinson County, Michigan. The Reference site received 4.9-6.5 times less exposure to ground electric fields and from 300 to 334 times less exposure to magnetic flux from 1989 to 1993 when the antenna was operational at 76 Hz than did the Antenna site. The objective of the study was to determine if ELF electromagnetic fields had caused changes in structure and/or function of algal communities in the Ford River. Significant differences in chlorophyll a standing crop and daily accumulation rate (a surrogate for primary productivity), and organic matter standing crop and daily accumulation rate were observed between the Reference and Antenna site after the antenna became operational. These four related community function variables all increased at the Antenna site with largest and most consistent increases occurring for chlorophyll measures. Compared to pre-operational data, the increase in chlorophyll at the Antenna site also occurred during a period of low amperage testing in 1986-1988, and did not increase further when the antenna became fully operational in 1989, indicating a low threshold for response. There was no significant differences between the Antenna and Reference sites in community structure variables such as diversity, evenness and the relative abundance of dominant diatoms. Thus, 76 Hz ELF electromagnetic radiation apparently did not change the basic makeup of the diatom community but did increase accumulation rates and standing crops of chlorophyll a and organic matter.

Hydrobiologia↗
USGS2001

Inter-annual changes in the benthic community structure of riffles and pools in reaches of contrasting gradient

The inter-annual variation in the structure of the benthic community of riffles and pools was evaluated in contrasting geomorphic settings. The community structure of riffles and pools was a function of habitat, reach gradient, and discharge and was taxon specific. In years of below average peak discharge, riffles had higher taxon richness than pools (66 versus 47) but richness was similar between habitats during a year of average discharge (56 versus 54). The percentage composition of oligochaetes and elmid beetles was more variable inter-annually in pools and low gradient reaches than in high gradient reaches. Differences in the percentage of collector-gatherers and scrapers in riffles and pools appeared related to inter-annual differences in discharge regimes. Two components of the annual discharge regime appear to differentially affect the composition of the benthic community in the snowmelt dominated stream studied: the magnitude of the annual peak discharge and the duration and timing of the period of extended high flow.

Hydrobiologia↗
USGS2001

How are climate and marine biological outbreaks functionally linked?

Since the mid-1970s, large-scale episodic events such as disease epidemics, mass mortalities, harmful algal blooms and other population explosions have been occurring in marine environments at an historically unprecedented rate. The variety of organisms involved (host, pathogens and other opportunists) and the absolute number of episodes have also increased during this period. Are these changes coincidental? Between 1972 and 1976, a global climate regime shift took place, and it is manifest most clearly by a change in strength of the North Pacific and North Atlantic pressure systems. Consequences of this regime shift are: (1) prolonged drought conditions in the Sahel region of Africa; (2) increased dust supply to the global atmosphere, by a factor of approximately four; (3) increased easterly trade winds across the Atlantic; (4) increased eolian transport of dust to the Atlantic and Caribbean basins; and (5) increased deposition of iron-rich eolian dust to typically iron-poor marine regions. On the basis of well-documented climate and dust observations and the widely accepted increase in marine outbreak rates, this paper proposes that the increased iron supply has altered the micronutrient factors limiting growth of opportunistic organisms and virulence of pathogenic microbes, particularly in macronutrient-rich coastal systems.

Hydrobiologia↗
USGS2001

Avian communities in baylands and artificial salt evaporation ponds of the San Francisco Bay estuary

San Francisco Bay wetlands, seasonal and tidal marshes between the historic low and high tide lines, are now highly fragmented because of development during the past 150 years. Artificial salt pond systems in the Bay are hypersaline and typically support simple assemblages of algae and invertebrates. In order to establish the value of salt ponds for migratory waterbirds, we used datasets to conduct a meta-analysis of avian communities in the baylands and salt ponds of San Pablo Bay. Fifty-three species of waterbirds in the salt ponds represented six foraging guilds: surface feeders, shallow probers, deep probers, dabblers, diving benthivores and piscivores. The total number of species and the Shannon-Weiner diversity index was higher in baylands than in salt ponds during all four seasons. However, overall bird density (number/ha) was higher in salt ponds compared with baylands in the winter and spring, primarily because of large concentrations of benthivores. Cessation of salt production in 1993 and subsequent reduction in water depth resulted in a decline of some diving duck populations that used the salt ponds.

Hydrobiologia↗
USGS2002

Possible importance of algal toxins in the Salton Sea, California

In response to wildlife mortality including unexplained eared grebe ( Podiceps nigricollis ) die-off events in 1992 and 1994 and other mortality events including large fish kills, a survey was conducted for the presence of algal toxins in the Salton Sea. Goals of this survey were to determine if and when algal toxins are present in the Salton Sea and to describe the phytoplankton composition during those times. A total of 29 samples was collected for toxicity analysis from both nearshore and midlake sites visited biweekly from January to December 1999. Dinoflagellates and diatoms dominated most samples, but some were dominated by a prymnesiophyte ( Pleurochrysis pseudoroscoffensis ) or a raphidophyte ( Chattonella marina ). Several types of blooms were observed and sampled. The dinoflagellate Gyrodinium uncatenum formed an extensive, dense (up to 310 000 cells ml −1 ) and long-lasting bloom during the winter in 1999. A coccolithophorid, Pleurochrysis pseudoroscoffensis , occurred at high densities in surface films and nearshore areas during the spring and summer of 1999. These surface films also contained high densities of one or two other species (an unidentified scrippsielloid, Heterocapsa niei , Chattonella marina ). Localized blooms were also observed in the Salton Sea. An unknown small dinoflagellate reached high densities (110 000 cells ml −1 ) inside Varner Harbor, and an unidentified species of Gymnodinium formed a dense (270 000 cells ml −1 ) band along part of the southern shoreline during the summer. Three species known to produce toxins in other systems were found. Protoceratium reticulatum (= Gonyaulax grindleyi ) and Chattonella marina were found in several samples taken during summer months, and Prorocentrum minimum was found in low densities in several samples. Extracts of most samples, including those containing known toxic species, showed a low level (<10% mortality across all concentrations) of activity in the brine shrimp lethality assay and were not considered toxic. All sample extracts tested in the mouse bioassay showed no activity. One sample extract taken from the bloom of the small dinoflagellate was highly active (100% mortality across all concentrations) in the brine shrimp lethality assay, but the active material could not be isolated. While dense algal blooms are common at the Salton Sea, no evidence gathered in this study suggests that algal toxins are present within phytoplankton cells; however, toxins actively excreted by cells may have been missed. Blooms of phytoplankton likely contribute to wildlife mortality at the Salton Sea. Possible mechanisms including intoxication due to ingestion of feathers in grebes and waterlogging caused by changes in surface tension are discussed.

California↗