Geology topics

Christina Amy Murphy

Publications and source records attributed to Christina Amy Murphy.

27 records · Page 2Linked to original sources

USGS2024

Unique diet and Philonema sp. infections in reservoir-rearing juvenile Chinook Salmon

Objective Dams and reservoirs can alter juvenile growth and survival of migratory salmonids through several physical and biological mechanisms. Juvenile Chinook Salmon Oncorhynchus tshawytscha that are produced upstream of large hydropower dams may have associated passage mortality, but the reservoirs created by these dams can support rapid growth. Characterizing the biotic drivers of growth and mortality in reservoirs may aid in understanding the cumulative effects of river impoundments on migratory salmonid populations. The purpose of this study was to understand how reservoirs facilitate rapid growth in juvenile Chinook Salmon. Methods We analyzed stomach contents to determine diet composition throughout the summer and fall. We also recorded prevalence of the parasitic nematode Philonema sp. in the coeloms of fish. Result We found that juvenile Chinook Salmon frequently consumed young-of-year centrarchids, which likely contributed to rapid growth. Piscivory was highest from July through October and decreased with surface temperature from November through December. Correspondingly, zooplankton and arthropod consumption increased in November and December. Prevalence of visible Philonema sp. infections in the coelom was high (34.6%), negatively associated with time, and nonlinearly associated with fork length. Conclusion These findings reveal unique diet patterns and suggest potential parasite-associated mortality in reservoir-rearing Chinook Salmon, but more detailed studies across a longer time scale are needed to robustly assess the population-level effects of this parasite.

Transaction of the American Fisheries Society↗

USGS2024

Global patterns of allochthony in stream–riparian meta-ecosystems

Ecosystems that are coupled by reciprocal flows of energy and nutrient subsidies can be viewed as a single “meta-ecosystem.” Despite these connections, the reciprocal flow of subsidies is greatly asymmetrical and seasonally pulsed. Here, we synthesize existing literature on stream–riparian meta-ecosystems to quantify global patterns of the amount of subsidy consumption by organisms, known as “allochthony.” These resource flows are important since they can comprise a large portion of consumer diets, but can be disrupted by human modification of streams and riparian zones. Despite asymmetrical subsidy flows, we found stream and riparian consumer allochthony to be equivalent. Although both fish and stream invertebrates rely on seasonally pulsed allochthonous resources, we find allochthony varies seasonally only for fish, being nearly three times greater during the summer and fall than during the winter and spring. We also find that consumer allochthony varies with feeding traits for aquatic invertebrates, fish, and terrestrial arthropods, but not for terrestrial vertebrates. Finally, we find that allochthony varies by climate for aquatic invertebrates, being nearly twice as great in arid climates than in tropical climates, but not for fish. These findings are critical to understanding the consequences of global change, as ecosystem connections are being increasingly disrupted.

Ecology Letters↗

USGS2024

Documenting historical anchorworm parasitism of introduced warmwater fishes in the Willamette River Basin, Oregon

Anchorworms ( Lernaea spp.) are freshwater parasitic copepods that use a wide range of hosts. Yet little is known about their prevalence, distribution, and which species are their primary fish hosts in the state of Oregon. Institutional fish collections serve as banks which allow investigators to look at historical fish specimens and ascertain their health status at the time of their collection. We examined 1,039 specimens collected between 1941 and 2016 from the Oregon State Ichthyology Collection to detect the presence of anchorworms on non-native warmwater fishes from the Willamette River Basin, Oregon. Adult female anchorworms were found on 11 of the 17 fish species that we examined. The most infected species included common carp ( Cyprinus carpio ), bluegill ( Lepomis macrochirus ), and smallmouth bass ( Micropterus dolomieu ). We suggest these introduced warmwater fishes can act not only as hosts, but also as potential reservoirs for these under-studied parasites posing a potential risk for Endangered Species Act (ESA)-listed native fishes. Our findings reveal unique insights that will serve as a baseline to detect future changes in parasite loads in the Willamette River Basin.

Oregon↗

USGS2023

Evidence for infection influencing survival of the freshwater copepod Salmincola californiensis, a parasite of Pacific salmon and trout

Objective We explore apparent infection of Salmincola californiensis arising during investigations involving this lernaeopodid copepod parasitic on Pacific salmon and trout Oncorhynchus spp. Methods We noted occasional unusual coloration of adult female copepods collected from the wild. These females were bright blue and pink in contrast to the cream white coloration characteristic of the copepod. We also observed that similar color patterns developed under laboratory settings when copepod eggs were held for hatching. In paired egg cases, we found consistent hatching failure of blue and pink eggs and patterns in apparent disease development that would be consistent with both vertical and horizontal transmission. Result Attempts to identify the cause of the apparent infection using genetic methods and transmission electron microscopy were inconclusive. Conclusion Iridovirus infection was initially suspected, but bacterial infection is also plausible. This apparent reduced hatching success of S. californiensis warrants further exploration as it could reduce local abundances. Given the potential importance of a disease impacting this copepod, a parasite that itself affects endangered and commercially important Pacific salmon and trout, future research would benefit from clarification of the apparent infection through additional sequencing, primer development, visualization, and exploration into specificity and transmission.

Journal of Aquatic Animal Health↗

USGS2023

Contemporary distribution of non-native Chinook salmon (Oncorhynchus tshawytscha) in South America

Chinook salmon represent one of the most successful salmonid introductions in South America, and today multiple naturalized populations exist across Patagonia. Here, we present an updated regional distribution of Chinook salmon that includes new records of occurrences collected between 2006 and 2022. We found a significant range expansion in terms of occurrences for adult (18 new basins; 2,854,108 km 2 ) and adult spawners or juvenile (12 new basins; 53,262 km 2 ) salmon extending both to the north and south of the previously known colonized range in South America. This range expansion (38% of the area considering only occurrences indicating reproduction via adult spawners or juvenile salmon) included major basins draining to both the Pacific Ocean and Atlantic Ocean coasts of the continent. Adult Chinook salmon are currently reported from 48 large basins (33.62°–54.97° S) covering a total drainage area of 3,047,197 km 2 . The observed expansion we document here has been likely driven by the dispersal of straying adults from historically naturalized populations. Our findings provide evidence that the invasion of Chinook salmon in South America is ongoing and updated information relevant to the management of this invasive and socio-ecologically important fish.

Biological Invasions↗

USGS2023

Linked foraging and bioenergetics modeling may inform fish parasite infection dynamics

The parasitic copepod Salmincola californiensis infects Pacific salmon and trout ( Oncorhynchus spp.) and often reaches high prevalence and intensity in reservoirs compared to stream systems. Recent research indicates that temperature plays a fundamental role in copepod development and fish susceptibility. Here, we expand a linked foraging and bioenergetics model to simulate infection risk. Based on juvenile salmon vertical migration patterns, we add estimates of copepod generations produced and thermal strata metrics that appear associated with copepodid aggregations and increased infection. Severe damage on hosts may be caused by the infectious copepodid, a life-stage not readily visible and thus not detectable using traditional fish screenings. We discuss model limitations, opportunities for future research, and the potential for inclusion of copepod expansion equations to existing linked bioenergetics models or observed behaviors of salmonids in other lentic systems. We demonstrate that using a temperature sensitive model framework that includes copepod infection dynamics is useful in interpreting other lines of evidence, such as fish mortality estimates. Collectively, our work provides a testable framework for future comparisons of infection potential and demonstrates how bioenergetics models may be useful in understanding host–parasite interactions.

Environmental Biology of Fishes↗

USGS2023

HABs and HAB nots: Dynamics of phytoplankton blooms across similar oligotrophic reservoirs

Increasing frequency and intensity of cyanobacterial Harmful Algal Blooms (HABs) threaten human and aquatic ecosystem health. Improving our understanding of HABs across a range of systems will be critical to understanding and potentially minimizing risk, especially where HABs are occurring in less productive and less studied waterbodies. Here, the characteristics and annual dynamics of phytoplankton communities were examined, focusing on the timing, magnitude, and predictability of cyanobacterial blooms in five multi-purpose flood-control reservoirs from the Willamette Basin, Oregon, USA. A high similarity in phytoplankton composition and consistency in the timing of cyanobacterial dominance was hypothesized to occur across these oligotrophic reservoirs. However, periods of dominance by potentially HABs producing genera were inconsistent both in their timing and abundances among reservoirs and across years within each reservoir. The lack of regional predictability indicates the importance of local drivers in the formation, intensity, and composition of phytoplankton blooms. These findings have important implications for reservoir management and safeguarding freshwater drinking sources, as not all reservoirs appear to experience cyanobacterial blooms at the same time, demonstrating non-concurrent risks of HABs.

Limnologica - Ecology and Management of Inland Wat↗

USGS2023

Caddisfly dives for oviposition: Record-shattering depths and poor life choices in a dammed river system

Oviposition is a critical step in the life cycles of aquatic insects. Adult caddisflies exhibit a variety of oviposition methods. In some species, females enter freshwaters to oviposit on submerged substrates. Here, we compile information on North American caddisflies that are known to dive and swim to oviposit and have sexually dimorphic leg characteristics that may be adaptations for swimming, diving, or both. We also report unexpected underwater captures of adult females of 3 caddisfly species in Willamette Basin reservoirs in Oregon, USA, including the deepest dive depths ever recorded for adult female caddisflies. From these captures, we note sexually dimorphic leg widening in the species Hydropsyche centra Ross, 1938 for the first time, confirm widened mesothoracic leg segments of Hydropsyche occidentalis Banks, 1900 adult females, and note fringes of long hairs on meso- and metathoracic tibiae and basal tarsal segments of Hydroptila argosa Ross, 1938 females. We also note fringes of long hairs on the meso- and metathoracic legs of Hydroptila ajax Ross, 1938 females from the banks of the Willamette River. The presumed oviposition attempts of caddisflies underwater in large, deep reservoirs suggest that these caddisflies may misinterpret oviposition cues in altered habitats and waste reproductive efforts. Greater understanding of caddisfly oviposition methods and abilities may be important for long-term conservation and restoration efforts supporting biodiversity in freshwater habitats.

Oregon↗

USGS2022

Minimal diel vertical migration and consistent zooplankton capturability in low productivity reservoirs, Oregon

Diel migrations of zooplanktons occur in marine and freshwater systems and can complicate inferences from studies. If populations perform vertical or horizontal diel migrations, daytime-only sampling can mischaracterize distributions and abundances. Zooplanktons also often display reduced capture avoidance at night and occupy areas easier to sample near the surface and away from littoral structure and the benthos. We examined zooplankton abundance, water column position and taxonomic composition during daytime and nighttime new moon periods using discrete depth sampling in oligo-mesotrophic reservoirs in Oregon, USA. These reservoirs have limited littoral structures, but support populations of zooplanktivorous fishes that we expected to drive diel vertical migrations. Contrary to our expectations, at night, most zooplankton taxa were within 2 m of their daytime distributional peak and did not display differences in abundance from day to night sampling. We consider factors that may help predict whether diel vertical migration occurs in a system. Where daytime sampling is sufficient to characterize zooplankton densities and distributions, costs and risks specific to nighttime sampling may be avoided. Improving our knowledge of zooplankton dynamics, particularly in ecosystems with limited diurnal variability, is an important part of understanding lake and reservoir food webs and can optimize the efforts of future studies.

Oregon↗