Effects of riparian canopy cover on salmonid diet and prey selectivity in low nutrient streams

This study focuses on stream sections within a relatively low nutrient catchment in south‐east Ireland in an attempt to characterize the probable effects of riparian canopy on salmonid diet and prey selectivity within two size classes of nursery stream. Sampling found that brown trout Salmo trutta diet changed significantly in response to riparian canopy regardless of stream size. The observation that S. trutta within unshaded stream sites did not feed on drifting terrestrial prey items to the same extent as those within shaded streams was not due to a lack of availability of this food source. There was no evidence to suggest that S. trutta selectively choose particular prey items.     

The growth history of anadromous white-spotted charr in northern Japan: a comparison between river and sea life

Anadromous white-spotted charr Salvelinus leucomaenis in a natural river in northern Japan migrated to the sea mainly at age 3+ years. Sea-run charr grew faster than parr, particularly as first time migrants. Sea-run charr repeated seaward migration up to three times; the observed maximum age was 5+ years old. The likelihood ratio test identified significant differences in asymptotic size and individual growth variability between parr and sea-run charr. Sea-run charr had an asymptotic size ( L ^∞) twice as large as parr, while the growth parameter ( K ) was similar between sea-run and parr. Growth variability was higher for parr than for sea-run charr.     

The response of benthic macroinvertebrate communities to climate change: evidence from subtropical mountain streams in Central China

Ecological effects of climate change on terrestrial and marine ecosystems are increasingly apparent but evidence from freshwater is scarce, particularly in Asia. Using data from two subtropical Central China streams, we predicted the changes of some benthic macroinvertebrate communities under various climatic scenarios. Our results show that the average annual air temperature, in the study watershed, increased significantly (P < 0.05) by 0.6 °C over the last 30 years (1978–2007), whereas the average annual water flow declined by 30.9 m³ s^–1. Based on the winter sampling of benthic macroinvertebrates at four stream locations over last six years, we observed that macroinvertebrate abundance and Margalef diversity dropped with increasing water temperatures or decreasing smoothed sea surface temperatures (SSST). The winter macroinvertebrate abundance and biodiversity declined by 11.1% and 6.8% for every 1 °C water temperature rise. In contrast, increases in future SSST by one unit would increase winter macroinvertebrate abundance and biodiversity by 38.2% and 16.0%, respectively. Although many dominant taxa were predicted to persist when water temperatures increase by 1 °C, several scarce taxa, e.g., Orthocladius clarkei and Hippeutis umbilicalis, could be at a level of potential local extinction. Our identification of these links, between climate change and stream macroinvertebrate communities, has wide implications for the conservation of mountain stream ecosystems in the upper Yangtze River under scenarios of climate change. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Environmental requirements of common riverine European salmonid fish species in fresh water with particular reference to physical and chemical aspects

This review attempts to assess, as quantitatively as possible, the habitat requirements in fresh water of three common and widespread European salmonid species. Namely: the trout (Salmo trutta L.), the salmon (S. salar L.) and the grayling (Thymallus thymallus L.). Requirements are considered for spawning, incubation and emergence, juveniles and smolts and for adults and spawning movements.     

Growth, production and bioenergetics of brown trout in upland streams with contrasting riparian vegetation

1. A series of laboratory-based equations on trout growth and bioenergetics developed by J.M. Elliott were applied to data collected for brown trout ( Salmo trutta L.) under field conditions in Co. Mayo, Western Ireland. Fish were collected by electrofishing eight upland streams with contrasting riparian vegetation; grassland, open canopy and closed canopy deciduous.
2. Stream temperatures, one of the main influencing factors on fish growth and energetics, did not differ significantly between riparian types.
3. Observed growth rates were lower than the predicted maximum growth rates and were not influenced by riparian vegetation type. Growth ranged between 0.66% day⁻¹ for 0 + trout to 0.08% day⁻¹ for 2 + trout.
4. Production estimates showed no clear difference between riparian vegetation types over the growing season.
5. Fish densities and biomass tended to be greater in closed canopy streams particularly in summer.
6. Actual ration sizes calculated for trout were similar to the ration required for maintenance metabolism and were only 45–63% of the maximum potential rations. Although there was an ontogenetic increase in ration size with increasing fish age, the proportion of ration available for growth (i.e. the difference between actual and maintenance rations) did not differ between age classes but was greatest in summer. 1+ and 2+ trout show greatest ration available for growth in grassland streams.
7. Trout growth did not differ between riparian vegetation types but did vary seasonally with greatest attainment in summer. Growth was limited in the present study possibly due to combined effects of reduced prey available to fish and low stream temperatures reducing metabolic requirements. In such food limited systems, terrestrial invertebrate energy subsidies could have significant benefits to brown trout growth, production and bioenergetics.     

Environmental conditions modify density-dependent salmonid recruitment: Insights into the 2016 recruitment crash in Wales

1. Understanding the effects of density-dependent and density-independent factors on recruitment is often inhibited by difficulties quantifying their relative contributions in highly variable recruitment data. Use of data-driven statistical methods with data that include one or more extreme recruitment events could help overcome these difficulties.
2. Juvenile Atlantic salmon and trout abundances in Wales have declined over the last 2 decades, and 2016 was a notably poor recruitment year in rivers around southern Europe, including England and Wales. The 2016 recruitment crash coincided with extreme winter weather conditions, leading to speculation that unusually warm temperatures and high flows adversely affect salmonid recruitment and caused the 2016 crash, although this remains untested.
3. We developed data-driven statistical models to: (1) describe juvenile salmonid recruitment from density-dependent and density-independent factors; and (2) assess whether the density-independent factors probably contributed to the 2016 salmon recruitment crash. We compiled salmon and trout young-of-year juvenile abundances from electrofishing surveys, egg deposition estimates and river flow and air temperature data from 2001–2017 for seven Welsh rivers, broadly representative of rivers around Wales. We used river flow and air temperature data to derive ecologically and behaviourally meaningful density-independent explanatory variables.
4. Salmonid recruitment in Wales was best described using density-dependent and density-independent factors, especially for salmon: after accounting for a concave relationship with egg deposition, salmon juvenile abundance was reduced under (1) warmer spawning temperatures that might inhibit spawning, and (2) higher flood frequencies during pre-emergence and emergence that might washout eggs or alevins. Results were less clear for trout, perhaps because they are behaviourally more plastic.
5. Our findings provide empirical support for general and predictable effects of temperature and flow during spawning and emergence on salmonid—especially salmon—recruitment in Wales. Furthermore, we suggest that the 2016 salmon recruitment crash was caused—in part—by particularly inclement spawning and emergence conditions, which could be more common under future climate change. Our findings suggest that future salmonid stock assessment models could include the effects of density-independent variables on recruitment to improve their predictive power.

     

Intraspecific variability in the response of bloom-forming marine microalgae to changed climate conditions

Phytoplankton populations can display high levels of genetic diversity that, when reflected by phenotypic variability, may stabilize a species response to environmental changes. We studied the effects of increased temperature and CO(2) availability as predicted consequences of global change, on 16 genetically different isolates of the diatom Skeletonema marinoi from the Adriatic Sea and the Skagerrak (North Sea), and on eight strains of the PST (paralytic shellfish toxin)-producing dinoflagellate Alexandrium ostenfeldii from the Baltic Sea. Maximum growth rates were estimated in batch cultures of acclimated isolates grown for five to 10 generations in a factorial design at 20 and 24°C, and present day and next century applied atmospheric pCO(2), respectively. In both species, individual strains were affected in different ways by increased temperature and pCO(2). The strongest response variability, buffering overall effects, was detected among Adriatic S. marinoi strains. Skagerrak strains showed a more uniform response, particularly to increased temperature, with an overall positive effect on growth. Increased temperature also caused a general growth stimulation in A. ostenfeldii, despite notable variability in strain-specific response patterns. Our data revealed a significant relationship between strain-specific growth rates and the impact of pCO(2) on growth-slow growing cultures were generally positively affected, while fast growing cultures showed no or negative responses to increased pCO(2). Toxin composition of A. ostenfeldii was consistently altered by elevated temperature and increased CO(2) supply in the tested strains, resulting in overall promotion of saxitoxin production by both treatments. Our findings suggest that phenotypic variability within populations plays an important role in the adaptation of phytoplankton to changing environments, potentially attenuating short-term effects and forming the basis for selection. In particular, A. ostenfeldii blooms may expand and increase in toxicity under increased water temperature and atmospheric pCO(2) conditions, with potentially severe consequences for the coastal ecosystem.     

Secondary production,longevity and resource consumption rates of freshwater shrimps in two tropical streams with contrasting geomorphology and food web structure

1. Freshwater shrimps often dominate the biomass of tropical island streams and are known to have strong effects on stream ecosystem structure and function, but little effort has been dedicated toward quantifying basic energetic and life history attributes such as growth, production and longevity. Such information is critical for understanding both the role of shrimps in ecosystem dynamics and the gravity of threats to shrimp populations posed by human activities such as shrimp harvesting, dam construction and water withdrawal. 2. We quantified growth rates and secondary production of dominant freshwater shrimps for 3 years in two Puerto Rican headwater streams that differ in food web structure because of the presence or absence of predatory fishes that are excluded from reaches above waterfalls. Using growth data, we constructed a minimum longevity model to explore the likely minimum life spans of the two dominant taxa (Atya spp. and Xiphocaris elongata). Finally, we used a bioenergetics model to quantify annual consumption rates of major basal resources by the two taxa. 3. Daily growth rates ranged from ?0.001 to 0.011 day^?1, were inversely related to body size, and were higher for small individuals of X. elongata than Atya spp. Mean annual shrimp biomass and secondary production were an order of magnitude higher in the stream that lacked predatory fishes (biomass: 4.34 g AFDM m^?2; production: 0.89 g AFDM m^?2 year^?1) than in the stream with predatory fishes (biomass: 0.12 g AFDM m^?2; production: 0.02 g AFDM m^?2 year^?1). Production : biomass ratios ranged from 0.01 to 0.38. 4. Our longevity model predicted a minimum life span of 8 years for Atya spp. and 5 years for X. elongata in the stream lacking predatory fishes. In contrast, due to a larger average size of X. elongata in the stream with predatory fishes, our model predicted a minimum life span of 11 years. Actual life spans of these taxa are likely to be much longer based on long‐term observations of marked individuals. 5. Estimated consumption rates from the bioenergetics model indicated that Atya spp. and X. elongata are important processors of organic matter resources in streams where they occur at high densities. Atya spp. and X. elongata appeared capable of consuming a large proportion of algal and insect production and the proportion of direct leaf litter inputs consumed was also appreciable (c. 40–60%). However, the consumption of suspended fine particulate organic matter (SFPOM) by Atya spp. is probably only a minor proportion of total SFPOM flux in these streams. 6. Our study suggests that geomorphic features such as waterfalls may play an important role in controlling the distribution and production of freshwater shrimps through their effects on predatory fish movement. Spatial differences in shrimp densities result in landscape‐scale variation in the significance to ecosystem processes of these long‐lived organisms, particularly as processors of major organic matter resources.     

Short-term responses of winter soil respiration to snow removal in a Picea asperata forest of western Sichuan

Aims Seasonal snow cover is one of the most important factors that control winter soil respiration in the cold biomes. The warming-induced decreases in snowpack could affect winter soil respiration of subalpine forests. The aim of this study was to explore the effects of snow removal on winter soil respiration in a Picea asperata forest.Methods A snow removal experiment was conducted in a P. asperata forest stand in western Sichuan during the winter of 2015/2016. The snow removal treatment was implemented using wooden roof method. Soil temperatures, snow depth and soil respiration rate were simultaneously measured in plots of snow removal and controls during the experimental period.Important findings Compared to the control, snow removal increased the fluctuations of soil temperatures. The average daily temperature of the soil surface and that at 5 cm depth were 1.12 °C and 0.34 °C lower, respectively, and the numbers of freeze-thaw cycles of the soil surface and that at 5 cm depth were increased by 39 and 12, respectively, in plots of snow removal than in the controls. The average rate of winter soil respiration and CO₂ efflux were 0.52 μmol·m^-2·s^-1 and 88.44 g·m^-2, respectively. On average, snow removal reduced soil respiration rate by 21.02% and CO₂ efflux by 25.99%, respectively. More importantly, the snow effect mainly occurred in the early winter. The winter soil respiration rate had a significant exponential relationship with soil temperature. However, snow removal significantly reduced temperature sensitivity of the winter soil respiration. Our results suggest that seasonal snow reduction associated with climate change could inhibit winter soil respiration in the subalpine forests of western Sichuan, with significant implications for the carbon dynamics of the subalpine forests.     

Evolutionary history and climate conditions constrain the flower colours of woody plants in China

进化历史和气候条件共同影响中国木本植物花色的分布 本研究以中国木本植物为研究对象,主要探讨两个问题：(1)不同生活型物种花色组成的差异;(2)生物地理区、进化年龄和气候条件对不同花色地理分布格局的影响。研究使用7673种木本植物的物种分布数据和花色信息(分为白色、红色、黄色、黄绿色、绿色和蓝紫色),并结合属级系统进化树来比较不同生活型(包括灌木、乔木和藤本)物种花色组成的差异,分析不同生物地理区、进化年龄和现代气候对花色地理格局的影响。研究结果表明,与乔木和藤本植物相比,灌木具有更高比例 的由花青素着色的红色花和蓝紫色花物种。中国木本植物的花色地理格局受到区域效应和现代气候(尤其是降水和UVB辐射)的共同影响。倾向于蜂媒传粉的黄色花和蓝紫色花物种和由花青素着色、耐环境胁迫的红色花和蓝紫色花物种比例在中国西北部地区更高。绿色花物种的进化起源更早,但进化时间对花色地理格局的解释力很弱。这些结果说明中国木本植物花色的地理格局受到进化历史和现代环境的共同影响。     

Thermal evolution of pre-adult life history traits in Drosophila melanogaster

Replicated lines of Drosophila melanogaster were allowed to evolve in population cage culture at 16.5° C or 25° C for five years. Their larval and pupal development times, larval growth rates, larval critical weights for pupariation and pre-adult survival rates were then measured at both temperatures. Pre-adult survival showed evidence of adaptation of the lines to their thermal selection regimes, with each set of lines showing superior survival when tested at the temperature at which they had been evolving. Pupal periods were similar for all lines when growing at 16.5° C but, at 25° C, the low temperature lines had the longer pupal periods. Irrespective of experimental temperature, low temperature lines grew faster and had shorter larval development periods than the high temperature lines. Larval critical weights for pupariation were higher in the low temperature lines at the low experimental temperature, and higher in the high temperature lines at the higher experimental temperature. The correlations between these traits induced by thermal evolution were in general different from or opposite to the genetic correlations found within a single temperature.     

The role of environmental sodium chloride relative to calcium in gill morphology of freshwater salmonid fish

Summary Ultrastructure, distribution and abundance of cell types were examined in the gills of two freshwater salmonid species, Salmo fario and Salmo gairdneri, in media of selected ion content. In plain hard water (PW) with high concentrations of Ca²⁺, Na⁺, and Cl^-, gill chloride cells (CC) were confined to trailing edges and interlamellar regions of filaments whereas in mountain soft water (MW) with low concentrations of Ca²⁺, Na⁺, and Cl^-, CC were more numerous on filaments and covered lamellae, particularly along trailing edges. CC also appeared on lamellae of PW trout acclimated to soft water in a pond. This proliferation was not alleviated when ambient Ca²⁺ levels were raised (MW + Ca²⁺) but regressed in elevated NaCl media (MW + NaCl). The regression process involved an initial covering of CC by pavement cells followed by cytolysis and then eventual disappearance of CC. In MW, mucous cells were distributed mainly on trailing edges and, to a lesser extent, leading edges of filaments; they were absent from lamellae regardless of external ion levels.The results of this study shed some light on the functional significance of CC in freshwater fish. It is suggested that proliferation of CC is an adaptive response to dilute freshwater (i.e. [NaCl]<0.1 mequiv·1^-1).     

Productivity of outdoor algal cultures in unstable weather conditions

In the outdoor cyclic fed batch cultures of Chlorella pyrenoidosa, some typical growth kinetics patterns in unstable weather conditions were observed. On cloudy days, the biomass output rate (R) was low, but the bioenergetic growth yield (Y) was generally high. In the cloudy morning-sunny afternoon condition, the values of Y were low, especially in the afternoon. In the sunny morning-cloudy afternoon condition, both R and Y were high. A few very high short-term Y values were measured during the cloudy the cloudy afternoon. (c) 1993 Wiley & Sons, Inc.     

Threats and opportunities for freshwater conservation under future land use change scenarios in the United States

Freshwater ecosystems provide vital resources for humans and support high levels of biodiversity, yet are severely threatened throughout the world. The expansion of human land uses, such as urban and crop cover, typically degrades water quality and reduces freshwater biodiversity, thereby jeopardizing both biodiversity and ecosystem services. Identifying and mitigating future threats to freshwater ecosystems requires forecasting where land use changes are most likely. Our goal was to evaluate the potential consequences of future land use on freshwater ecosystems in the coterminous United States by comparing alternative scenarios of land use change (2001–2051) with current patterns of freshwater biodiversity and water quality risk. Using an econometric model, each of our land use scenarios projected greater changes in watersheds of the eastern half of the country, where freshwater ecosystems already experience higher stress from human activities. Future urban expansion emerged as a major threat in regions with high freshwater biodiversity (e.g., the Southeast) or severe water quality problems (e.g., the Midwest). Our scenarios reflecting environmentally oriented policies had some positive effects. Subsidizing afforestation for carbon sequestration reduced crop cover and increased natural vegetation in areas that are currently stressed by low water quality, while discouraging urban sprawl diminished urban expansion in areas of high biodiversity. On the other hand, we found that increases in crop commodity prices could lead to increased agricultural threats in areas of high freshwater biodiversity. Our analyses illustrate the potential for policy changes and market factors to influence future land use trends in certain regions of the country, with important consequences for freshwater ecosystems. Successful conservation of aquatic biodiversity and ecosystem services in the United States into the future will require attending to the potential threats and opportunities arising from policies and market changes affecting land use.     

Comparative phylogenetic analysis of the evolution of semelparity and life history in salmonid fishes

The selective pressures involved in the evolution of semelparity and its associated life-history traits are largely unknown. We used species-level analyses, independent contrasts, and reconstruction of ancestral states to study the evolution of body length, fecundity, egg weight, gonadosomatic index, and parity (semelparity vs. degree of iteroparity) in females of 12 species of salmonid fishes. According to both species-level analysis and independent contrasts analysis, body length was positively correlated with fecundity, egg weight, and gonadosomatic index, and semelparous species exhibited a significantly steeper slope for the regression of egg weight on body length than did iteroparous species. Percent repeat breeding (degree of iteroparity) was negatively correlated with gonadosomatic index using independent contrasts analysis. Semelparous species had significantly larger eggs by species-level analysis, and the egg weight contrast for the branch on which semelparity was inferred to have originated was significantly larger than the other egg weight contrasts, corresponding to a remarkable increase in egg weight. Reconstruction of ancestral states showed that egg weight and body length apparently increased with the origin of semelparity, but fecundity and gonadosomatic index remained more or less constant or decreased. Thus, the strong evolutionary linkages between body size, fecundity, and gonadosomatic index were broken during the transition from iteroparity to semelparity. These findings suggest that long-distance migrations, which increase adult mortality between breeding episodes, may have been necessary for the origin of semelparity in Pacific salmon, but that increased egg weight, leading to increased juvenile survivorship, was crucial in driving the transition. Our analyses support the life-history hypotheses that a lower degree of repeat breeding is linked to higher reproductive investment per breeding episode, and that semelparity evolves under a combination of relatively high juvenile survivorship and relatively low adult survivorship.     

Fluctuating recruitment and variable life history of migratory brown trout, Salmo trutta L., in a small, unstable stream

The recruitment dynamics and life history of migratory brown trout, Sulmo trutta L., were investigated in a small Baltic coast stream subject to recurring drought. Spawning males consisted of both mature male parr (101–206 mm t.l. ) and migrant males (205–780 mm t.l. ). Spawning females were all migrants which delayed maturity until reaching a significantly greater size on average (424–805 mm t.l. ) than migrant males. Male: female ratios were very high in spawning aggregations (9–12 males: 1 female) with males representing up to five year-classes or more. Gametes from several generations of males per spawning event may be important for maintaining the genetic viability of this population with few female spawners per year. The amount of spawning was dependent on precipitation just prior to and during the spawning period since migrants could not enter the stream under drought conditions. Migrants did not overwinter in the stream.
Drought also caused variable fry mortality following emergence in early summer. Recruitment of 0+ parr in autumn varied from c . 175 to 3000 during 3 years. Smolts were relatively young (ages 1–2) and small (≥8 cm), and were significantly longer on average than sibling parr. Yet emigration of 1-year-olds was not related to 0+ parr size the previous autumn because of overlapping growth rates.
Persistence of the migratory brown trout in this unstable environment may be the consequence of (i) life history adaptation (e.g. short freshwater residence of both juveniles and spawners), and (ii) a complementary set of individual life histories where variation in age of migrant spawners and the occurrence of mature male parr result in a stable spawner population despite inconsistent recruitment of migrants to the sea.     

Measurements of salmonid population performance in relation to habitat in eastern Newfoundland streams

The density, biomass and estimated production of brook trout Salvelinus fontinalis and Atlantic salmon Salmo salar were related to habitat factors in streams of Terra Nova National Park, Newfoundland, Canada. Fish communities at 29 sites (18 brooks; 15 watersheds) were sampled in the summer of 2002, 2003 and 2005. Salmonid density, biomass per unit area and production (derived from biomass and fish size using allometric P:B relationships) were compared with site habitat characteristics (wetted width, lactustrine habitat, per cent riffle habitat, canopy coverage and stream gradient), using an interactive stepwise multiple linear regression. Salmonid biomass (mean: 2·87 g m^?2; range: 0·33–10·88 g m^?2) and estimated production (mean: 3·05 g m^?2 year^?1; range: 0·32–10·98 g m^?2 year^?1) within the study area varied by an order of magnitude, however, habitat variables accounted for much of this variation. Specifically, wetted width and lacustrine area of the tributary played important roles in explaining density, biomass and production. Wetted width was important for all measurements of brook trout and total salmonids while lacustrine area was important for all measurements of Atlantic salmon and played a lesser role in total salmonid biomass. Other factors such as the percentage of riffle habitat, site gradient and canopy coverage provided modest improvements to the fit of some relationships. When models using the same environmental factors were compared, those using production estimates derived from allometric P:B equations in the literature provided improved predictive capability than did those from direct density and biomass estimates. It is proposed that allometric P:B relationships have utility in improving comparisons of stream fish communities, particularly in studies with insufficient resources to measure production directly.     

Untangling climate and water chemistry to predict changes in freshwater macrophyte distributions

Forecasting changes in the distributions of macrophytes is essential to understanding how aquatic ecosystems will respond to climate and environmental changes. Previous work in aquatic ecosystems has used climate data at large scales and chemistry data at small scales; the consequence of using these different data types has not been evaluated. This study combines a survey of macrophyte diversity and water chemistry measurements at a large regional scale to demonstrate the feasibility and necessity of including ecological measurements, in addition to climate data, in species distribution models of aquatic macrophytes. A survey of 740 water bodies stratified across 327,000 square kilometers was conducted to document Characeae (green macroalgae) species occurrence and water chemistry data. Chemistry variables and climate data were used separately and in concert to develop species distribution models for ten species across the study area. The impacts of future environmental changes on species distributions were modeled using a range of global climate models (GCMs), representative concentration pathways (RCPs), and pollution scenarios. Models developed with chemistry variables generally gave the most accurate predictions of species distributions when compared with those using climate variables. Calcium and conductivity had the highest total relative contribution to models across all species. Habitat changes were most pronounced in scenarios with increased road salt and deicer influences, with two species predicted to increase in range by >50% and four species predicted to decrease in range by >50%. Species of Characeae have distinct habitat ranges that closely follow spatial patterns of water chemistry. Species distribution models built with climate data alone were insufficient to predict changes in distributions in the study area. The development and implementation of standardized, large‐scale water chemistry databases will aid predictions of habitat changes for aquatic ecosystems.