Elevated stream temperatures represent an important stressor affecting Pacific salmon (Oncorhynchus spp.). In thermally impaired streams, upwellings of shallow subsurface (i.e., hyporheic) water have the potential to create patches of cool-water refuge that allow salmon to persist in otherwise unsuitable water temperatures. Since patterns of hyporheic upwelling are influenced by variations in streambed topography, habitat restoration actions such as engineered logjam construction may be used to preserve or promote upwellings. This strategy requires that hyporheic flows remain cooler in summer, relative to the overlying surface stream, but this might not always be the case. Here we characterize the relationship between hyporheic and overlying surface temperatures during a summer low-flow season in a restored reach of the South Fork Nooksack River. Among six sampling sites, we found that one had hyporheic temperatures that were consistently colder than the overlying surface stream, two had hyporheic temperatures that were variable but more moderate than those of the overlying surface stream, and three had hyporheic temperatures that were not cooler or more stable than those of the overlying surface stream. Habitat mapping suggests that thermally stable hyporheic flow paths may be associated with specific combinations of channel geomorphic units, which influence flow path length, depth, and discharge. These findings may be used to identify potential areas of cool-water refuge and guide the design and placement of habitat restoration actions to promote climate adaptation for salmon populations in thermally impaired streams.
In this study we examined a small, fringing eelgrass (Zostera marina) bed in Rosario Bay, WA to determine the factors limiting its growth and persistence. The bed is less than 1 ha and entirely subtidal, with around 2 m depth difference between the shallow and deep margins of the bed. Substrate within and seaward of the bed is silty sand, while shoreward and to the north are gravel and rocks. The bay is periodically exposed to heavy wave action which causes disturbance down to eelgrass depth, and light attenuation and large tidal changes limit light levels. Nevertheless, light usually reaches saturation levels for a limited time in all seasons. Sediment nutrient and organic content seem adequate for eelgrass growth within the beds, but not in the gravels on the shoreward side. We determined that the most likely limiting factors are lack of adequate light along the deeper edge of the bed, sediment disturbance by waves along the shoreward margin, and incompatible substrate plus competition with macroalgae along the northern margin. The shallowest depth imposed by wave turbulence appears to be close to the deepest depth imposed by light limitation, so maintenance of low light attenuation in the water column appears to be one of the most important factors contributing to the persistence of this bed. In addition, a previously unreported amensal interaction with anchored but motile bull kelp (Nereocystis luetkeana) may create patches of damage throughout the bed during storms.
Spring-run Chinook salmon in the Pacific Northwest can be vulnerable to prespawn mortality because they exhibit a premature migration life history, often holding in warm, degraded natal tributaries for months prior to spawning. Premature migration may result in high prespawn mortality if adequate holding conditions are not present in the terminal reaches of natal streams. This study investigated the fine-scale movement patterns and survival of prespawn, hatchery-origin spring Chinook salmon in the terminal reaches of the Upper Grande Ronde River, Oregon. We tracked fish implanted with radio transmitters and constructed a one-dimensional Hidden Markov Model using the river kilometer of fish detections and two behavioral states, move and hold, to quantify the influence of environmental factors on prespawn movement patterns. Higher temperatures were generally associated with increased movement behavior, though some fish continued holding or switched from moving to holding at peak water temperatures. Larger fish were associated with an increased frequency of transitioning between behavioral states. Our results suggest three tactics for behavioral thermoregulation: (1) rapid movement to cold terminal reaches prior to thermal stress exposure in lower reaches; (2) sprinting, whereby fish initiate movement during thermal stress; and (3) stalling, whereby fish exhibit prolonged holding below spawning grounds during thermal stress. Stalling behavior in the warmest, most downstream reaches was associated with the highest prespawn mortality. Our findings suggest that some migration strategies within spring Chinook salmon populations may be more susceptible to prespawn mortality as climatic conditions continue to warm.
Alaska has 33,904 miles of coastline and most coastal infrastructure in the state is armored for erosion protection, yet little is known about colonization or recolonization rates post-disturbance in high northern latitudes. This study quantifies the recruitment and colonization of new armor rock at the Kodiak Airport and documents algal and sessile invertebrate species abundance and assemblage (percent cover) at the airport study sites compared to reference sites with similar substrates, salinity, wave exposure, and depth. Over four years of annual intertidal and subtidal monitoring, average percent cover by algae and invertebrates at study sites ranged from 13% to 100%. Study sites showed extensive cover by early colonizing algae and invertebrates in both the intertidal and subtidal substrates at 15 months post-construction silt curtain removal (Year 1). Prominent biobands of monospecies (e.g., bay mussels [Mytilus trossulus]) observed in Year 1 largely changed to barnacles (Balanus sp.) and algal species by Year 4. Both algal cover and number of species increased over time at airport study sites; total cover and number of species at these study sites were similar to reference sites by Year 4. The colonization rate of armor rock and the successional timeframe to develop full ecological functions are important because of the potential effects of armor rock on aquatic habitats at both local and landscape scales. This study illustrates that colonization of new armor rock in southcentral Alaska can be rapid (average 80.8% cover of intertidal and subtidal substrates after one year) and that interannual variability of species abundance may occur throughout the successional cycle.
Smallmouth Bass (Micropterus dolomieu) has been widely introduced beyond its native distribution where interactions with other organisms are largely unknown. We examined the food habits of Smallmouth Bass in Coeur d'Alene Lake, Idaho. Smallmouth Bass were sampled monthly from March 2012 to May 2013 using short duration (1-2 hr sets) gill netting and electrofishing. In total, food habits were evaluated from 904 Smallmouth Bass varying in total length from 39 to 492 mm using gastric lavage. Diet composition varied by season and age. Smallmouth Bass less than 100 mm had diets dominated by invertebrates, particularly Ephemeroptera, Odonata, and Diptera. Fishes were increasingly important in the diet of Smallmouth Bass longer than 100 mm. Interestingly, crayfish (Decapoda) were virtually absent in Smallmouth Bass stomachs; only eight Smallmouth Bass had crayfish in their diet. Native vertebrates were also rare in Smallmouth Bass diets. Rather, kokanee (Oncorhynchus nerka), a nonnative species, was generally the most commonly consumed fish prey item (present in 5-15% of Smallmouth Bass across seasons). Kokanee contributed the highest percentage of total energy (approximately 45% of all energy) of any prey item. Results of this study suggest that native fishes of conservation concern are a minor component of Smallmouth Bass diets and that kokanee is important in meeting the energy demands of nonnative Smallmouth Bass. Further research on the distribution and abundance of crayfish in the system and on the population-level effects of Smallmouth Bass predation on kokanee would be insightful and help guide management actions in Coeur d'Alene Lake and similar systems in western North America.
Variability in plant functional traits is key to population resilience in the face of changing environments. This intraspecific trait variation is especially important at the vulnerable seedling stage, but the sources of trait variation among seedlings are not fully understood. In this study, we tested the hypothesis that population-level trait variation can be partly attributed to variation in developmental timing. We recorded the date of germination of individual showy milkweed (Asclepias speciosa) seedlings, then tracked their functional traits during the first growing season. Showy milkweed is native to the western United States and is a major host plant for monarch butterflies (Danaus plexippus) in the Pacific Northwest. We found that germination timing occurred over a 26-day range even in a common environment. This variation in developmental timing was a significant predictor of later intraspecific trait variation among milkweed seedlings. Variation in height and aboveground leaf area ratio were particularly influenced by developmental timing. These findings suggest that developmental timing variability may be an important yet under-studied source of intraspecific trait variation, with implications for ecological interactions and resilience.
Biochar can be used as a soil amendment to restore degraded soils, sequester carbon, and increase soil water holding capacity and plant available water following harvest operations in a forest. On-site production and utilization of biochar is being explored as a forest management tactic. One benefit of the practice is the sequestration of carbon by using unmerchantable forest biomass to produce biochar. Forest insects may be exposed to biochar when the material is applied to surface organic horizons and downed trees. How biochar affects insects' ability to locate and utilize downed woody material in the forest is undetermined. Two field experiments with freshly downed sections (bolts) of ponderosa pine (Pinus ponderosa Lawson & C. Lawson) were conducted to determine the potential impact of applied biochar on insect communities utilizing the bolts. In the first experiment, bolts were baited with a pheromone lure and biochar was applied at a rate equivalent to 2,914 kgha-1 (1.30 tonsacre-1). The biochar treatment did not interfere with attack or emergence of the pine engraver Ips pini (Say) (Coleoptera: Curculionidae: Scolytinae) compared to untreated control bolts. In the second experiment, biochar applied at a rate equivalent to 5,604 kgha-1 (2.50 tonsacre-1) lowered insect species richness compared to non-treated bolts. In addition, one species, red turpentine beetle Dendroctonous valens (LeConte) (Coleoptera: Curculionidae: Scolytinae), was more abundant in non-treated bolts compared with biochar-treated bolts. Utilization of bolts by other insect taxa such as longhorn beetles (Coleoptera: Cerambycidae) was similar in non-treated and biochar-treated bolts.
Cacti are iconic members of arid ecosystems. Pediocactus nigrispinus is a species of cactus endemic to the Pacific Northwest and has been listed as a sensitive species due to its vulnerability to habitat loss. Best conservation methods for this species are poorly understood, due in part to a limited understanding of its demography and habitat associations that may help define its occurrence. A demographic study from four plots in Washington State was implemented in 2016 to provide a baseline of the population dynamics for P. nigrispinus and to enhance conservation efforts for this sensitive species. Five years of size, fecundity, and survival information for the cactus were recorded. A stochastic analysis was performed to assess survival and fecundity rates in relation to different climatic variables. To better understand the cacti's limited habitat, biotic and abiotic associations were assessed in an additional 16 plots throughout Washington and Oregon by spatial analysis of soil and climatic variables and in situ assessment of vegetation and ground cover associations. These variables were then compared with population density, overall size of the individuals, and number of fruits to assess how changes in associations may correlate with changes in these traits. The demographic study found no juvenile recruitment and a declining population over the four years of analysis regardless of variation in annual precipitation. The association analysis found no correlation between population density or fecundity and biotic or abiotic associations but indicated higher fruit production in Oregon than in Washington. With the declining population and narrow endemism of the species observed, further monitoring and study for conservation efforts are recommended.
Joint Base Lewis-McChord, Washington, has the largest population of ponderosa pine (Pinus ponderosa) west of the Cascade Range in the Pacific Northwest. Field mapping showed a modern geographic range of approximately 13,270 ha. The ages and locations of the largest, oldest pines indicated that at the time of Euro-American settlement in the mid-1800s, most pines grew in a single area of approximately 1,730 ha within a landscape of woodland, savanna, and grassland maintained by Native American fire. After settlement ended burning, conifer forest replaced much of the original vegetation and the range of pine expanded. I repeatedly measured permanent plots over an 11-year period (2007-2018) within the two forest types with pine: Closed Forest (mean canopy cover >= 60%) dominated by Douglas-fir (Pseudotsuga menziesii), and Woodland/Savanna (mean cover 5-59%) often mixed with Douglas-fir and Oregon white oak (Quercus garryana). Pine basal area and density were similar between forest types. Overstory pines in Woodland/Savanna had a larger diameter growth and crown ratio, lower height and height:diameter ratio, and averaged 40 years younger than those in Closed Forest. Pine regeneration was scarce or absent in Closed Forest, except for a pulse in 2018. The only notable temporal trend was log accumulation in Woodland/Savanna following a wildfire. Pine diameter and age distributions showed an increasing deficit of young pines over time. Major impediments to pine regeneration are competition from Douglas-fir in Closed Forest, competition from a non-native shrub Scotch broom (Cytisus scoparius) in Woodland/Savanna, and fires that burn hotter than historic fires. Active management will be necessary to perpetuate this pine population long-term in Woodland/Savanna; it may not be possible to do so in Closed Forest.
