Differences In Thermal Regimes Research Articles

Oceanic differences in coral-bleaching responses to marine heatwaves

Anomalously high ocean temperatures have increased in frequency, intensity, and duration over the last several decades because of greenhouse gas emissions that cause global warming and marine heatwaves. Reef-building corals are sensitive to such temperature anomalies that commonly lead to coral bleaching, mortality, and changes in community structure. Yet, despite these overarching effects, there are geographical differences in thermal regimes, evolutionary histories, and past disturbances that may lead to different bleaching responses of corals within and among oceans. Here we examined the overall bleaching responses of corals in the Atlantic, Indian, and Pacific Oceans, using both a spatially explicit Bayesian mixed-effects model and a deep-learning neural-network model. We used a 40-year global dataset encompassing 23,288 coral-reef surveys at 11,058 sites in 88 countries, from 1980 to 2020. Focusing on ocean-wide differences we assessed the relationships between the percentage of bleached corals and different temperature-related metrics alongside a suite of environmental variables. We found that while high sea-surface temperatures were consistently, and strongly, related to coral bleaching within all oceans, there were clear geographical differences in the relationships between coral bleaching and most environmental variables. For instance, there was an increase in coral bleaching with depth in the Atlantic Ocean whereas the opposite was observed in the Indian Ocean, and no clear trend could be seen in the Pacific Ocean. The standard deviation of thermal-stress anomalies was negatively related to coral bleaching in the Atlantic and Pacific Oceans, but not in the Indian Ocean. Globally, coral bleaching has progressively occurred at higher temperatures over the last four decades within the Atlantic, Indian, and Pacific Oceans, although, again, there were differences among the three oceans. Together, such patterns highlight that historical circumstances and geographical differences in oceanographic conditions play a central role in contemporary coral-bleaching responses.

Linkages between temperature, macroinvertebrates, and young-of-year Coho Salmon growth in surface-water and groundwater streams

Ecological resources for fishes in stream food webs shift over space and time, providing a complex template of available resources that can be used for growth. We tracked water temperature in conjunction with young-of-year Coho Salmon size, growth, and diet in 2 streams with contrasting thermal regimes: a groundwater stream with colder temperatures and lower thermal variability all year and a surface-water stream with greater thermal variability and warmer summer temperatures more conducive to young-of-year salmon growth. We hypothesized that fry emergence would occur when rearing conditions are optimal for growth and that, all else being equal, summer fish growth will be greater in the surface-water stream. Previous work on Coho Salmon phenology in these streams showed that peak fry emergence occurred at the same time in early summer in both streams. We measured salmon fry emergence in relation to thermal variability and macroinvertebrate prey availability with subsequent tracking of somatic growth, diet, and body size during the 1st year of life in both streams. Macroinvertebrate prey availability was highest overall in the colder and thermally-stable groundwater stream than the surface-water stream. Prey availability was particularly high in the thalweg drift during peak fry emergence in the groundwater stream. There was no difference in Coho Salmon diet composition between streams, which included invertebrates from benthic, drift, and riparian habitats. We found no differences in young-of-year Coho Salmon body size, growth, or consumption between streams. Overall, our results suggest that large differences in thermal regimes do not necessarily translate to large differences in young-of-year Coho Salmon size, growth, or diet. Many variables can influence fish growth, and there is not always a direct connection between spatial and temporal dimensions of environmental variability and their cascading effects on young-of-year Coho Salmon growth during the 1st summer of life.

Relics of a Paleoproterozoic orogen: New petrological, phase equilibria and geochronological studies on high-pressure pelitic granulites from the Pingdu-Laiyang areas, southwest of the Jiaobei terrane, North China Craton

High-pressure (HP) pelitic granulites have been used as important targets in evaluating ancient geodynamic processes similar to subduction, collision and exhumation operating in modern plate tectonics. In this contribution, relic HP pelitic granulites were identified from the Pingdu-Laiyang areas of the Jiaobei terrane that are dominated by low- to medium-pressure (LMP) pelitic granulites, suggesting their linear distribution and that at least some of LMP types should be retrograde products of the HP pelitic granulites. Their metamorphic P-T-t paths were traced by integrated methods of petrographic observation, mineral chemistry, P-T-X pseudosection modeling, Zr-in-rutile thermometry, and zircon and monazite geochronology. These HP pelitic granulites record consistent clockwise P-T-t paths that are manifested by similar peak metamorphism of high-pressure granulite-facies, with P-T conditions of P > 13 kbar, T > 850 °C possibly during 1950–1900 Ma, followed by near isothermal decompression (ITD) to mid-crustal level at 1900–1850 Ma and subsequent near isobaric cooling (IBC) to low temperature during 1850–1800 Ma. The consistent clockwise P-T-t paths and linear distribution of HP pelitic granulites explicitly indicate a sequence of geodynamic processes similar to modern-style plate tectonics must have operated during formation of the Paleoproterozoic Jiao-Liao-Ji belt (JLJB). These include a process similar to subduction that brought sedimentary precursors of HP pelitic granulites down, which was followed by continental orogeny during 1950–1900 Ma, leading to crustal thickening (40–50 km) and high-pressure granulite-facies metamorphism, and a post-orogenic collapse during 1900–1800 Ma that resulted in exhumation and cooling of HP granulites along ITD and IBC paths. Therefore, it is argued that ancient HP pelitic granulites can be regarded as relics of orogen and ascertain tectonic interpretation of the dominated LMP pelitic granulites in the same Precambrian metamorphic terranes. Notably, the apparent thermal gradients estimated from peak metamorphism are 15–20 °C/km, much higher than those of typical products in Phanerozoic plate tectonics, and the HP pelitic granulites that contain well-preserved kyanite probably require relatively high exhumation rates during ITD to middle crustal level. These seem to mark the differences in thermal regimes and tectonic mechanisms between Paleoproterozoic and Phanerozoic collisional orogenic systems.

Phenology of hatching, emergence, and end-of-season body size in young-of-year coho salmon in thermally contrasting streams draining the Copper River Delta, Alaska

Phenology can be linked to individual fitness, particularly in strongly seasonal environments where the timing of events has important consequences for growth, condition, and survival. We studied the phenology of coho salmon (Oncorhynchus kisutch) hatching and emergence in streams with contrasting thermal variability but in close geographic proximity. Following emergence, we tracked body sizes of cohorts of young-of-year fish until the end of the growing season. Hatch and emergence occurred at the same time among streams with marked variability in thermal regimes. We demonstrate that this can be explained in part by the thermal units accumulated during embryo development. At the end of the first growing season, there were some differences in body size, but overall fish size was similar among streams despite strong differences in thermal regimes. Collectively, these results provide novel insights into the interactions between environmental variability and the early life-history stages of coho salmon, furthering our understanding of the consequences of phenology on growth and survival for individuals within the critical first summer of life.

Vertical electrical sounding of soils and permafrost of marine terraces of Gronfjord (Svalbard archipelago)

Vertical electrical resistivity sounding (VERS) of soil-permafrost strata has been performed during the field work within the sea terraces of Gronfjord (Svalbard archipelago, West Spitsbergen island). Vertical electrical resistivity sounding of soil-permafrost strata was performed by portable device LandMapper. Then these data have been analyzed via ZondIP software (1d model). Apparent electrical resistivity values on the soil-permafrost strata usually change rapidly. It was established that studied soils with different origin and morphological properties are referred to 2 trunks, 2 orders, 4 types and 7 subtypes. Histic Gleysols, Cryosols, Gleysols and their subtypes have been investigated within the key plots (Grendasselva, Aldegonda rivers and catena on the sea terrace in surroundings of Barentsburg aerodrome). Several trends in profile distribution of electrical resistivity values have been distinguished. The main is connected with monotonous increasing of electrical resistivity values with a depth. Values of apparent electrical resistivity increase rapidly on the border of active layer-permafrost layer. The contrasts in profile distribution of electrical resistivity values are caused mainly by differences in water content, texture class and degree of strata heterogeneity (due to cryogenic processes). The depths of active layer-permafrost boundary have been distinguished using ZondIP software. Regional differences in this indicator may be explained not only by local differences in thermal regime of soil and permafrost layers, but also by different character of anthropogenic influence on key plots. Vertical electrical resistivity sounding method provides significant information for understanding soil electrical properties without any mechanical disturbances of soil cover. The data obtained is clearly coincided with field work data on soil morphology.

Response of Development and Body Mass to Daily Temperature Fluctuations: a Study on Tribolium castaneum.

Differences in thermal regimes are of paramount importance in insect development. However, experiments that examine trait development under constant temperature conditions may yield less evolutionarily relevant results than those that take naturally occurring temperature fluctuations into account. We investigated the effect of different temperature regimes (constant 30 °C, constant 35 °C, fluctuating with a daily mean of 30 °C, or fluctuating with a daily mean of 35 °C) on sex-specific development time and body mass in Tribolium castaneum. Using a half-sib breeding design, we also examined whether there is any evidence for genotype-by-environment interactions (GEI) for the studied traits. In response to fluctuating temperature regimes, beetles demonstrated reaction norm patterns in which thermal fluctuations influenced traits negatively above the species’ thermal optimum but had little to no effect close to the thermal optimum. Estimated heritabilities of development time were in general low and non-significant. In case of body mass of pupae and adults, despite significant genetic variance, we did not find any GEI due to crossing of reaction norms, both between temperatures and between variability treatments. We have observed a weak tendency towards higher heritabilities of adult and pupa body mass in optimal fluctuating thermal conditions. Thus, we have not found any biasing effect of stable thermal conditions as compared to fluctuating temperatures on the breeding values of heritable body-size traits. Contrary to this we have observed a strong population-wide effect of thermal fluctuations, indicated by the significant temperature-fluctuations interaction in both adult and pupa mass.Electronic supplementary materialThe online version of this article (doi:10.1007/s11692-016-9375-6) contains supplementary material, which is available to authorized users.

Temperature regimes and turbulent heat fluxes across a heterogeneous canopy in an Alaskan boreal forest

AbstractWe evaluate local differences in thermal regimes and turbulent heat fluxes across the heterogeneous canopy of a black spruce boreal forest on discontinuous permafrost in interior Alaska. The data were taken during an intensive observing period in the summer of 2013 from two micrometeorological towers 600 m apart in a central section of boreal forest, one in a denser canopy (DC) and the other in a sparser canopy, but under approximately similar atmospheric boundary layer (ABL) flow conditions. Results suggest that on average 34% of the half‐hourly periods in a day are nonstationary, primarily during night and during ABL transitions. Also, thermal regimes differ between the two towers; specifically between midnight and 0500 Alaska Standard Time (AKST) it is about 3°C warmer at DC. On average, the sensible heat flux at DC was greater. For midday periods, the difference between those fluxes exceeded 30% of the measured flux and over 30 W m−2 in magnitude more than 60% of the time. These differences are due to higher mechanical mixing as a result of the increased density of roughness elements at DC. Finally, the vertical distribution of turbulent heat fluxes verifies a maximum atop the canopy crown (2.6 h) when compared with the subcanopy (0.6 h) and above canopy (5.1 h), where h is the mean canopy height. We argue that these spatial and vertical variations of sensible heat fluxes result from the complex scale aggregation of energy fluxes over a heterogeneous canopy.

Influence of natural inshore and offshore thermal regimes on egg development and time of hatch in American lobsters, Homarus americanus.

Some egg-bearing (ovigerous) American lobsters (Homarus americanus) make seasonal inshore-to-offshore movements, subjecting their eggs to different thermal regimes than those of eggs carried by lobsters that do not make these movements. Our goal was to determine if differences in thermal regimes influence the rate of egg development and the subsequent time of hatch. We subjected ovigerous lobsters to typical inshore or offshore water temperatures from September to August in the laboratory (n=8 inshore and 8 offshore, each year) and in the field (n=8 each, inshore and offshore), over 2 successive years. Although the rate of egg development did not differ significantly between treatments in the fall (P∼0.570), eggs exposed to inshore thermal regimes developed faster in the spring (P<0.001). "Inshore" eggs hatched about 30 days earlier (mean=26 June) than "offshore" eggs (mean=27 July), and their time of development from the onset of eyespot to hatch was significantly shorter (inshore=287±11 days vs. offshore: 311.5±7.5 days, P=0.034). Associated growing degree-days (GDD) did not differ significantly between inshore and offshore thermal treatments (P=0.061). However, eggs retained by lobsters exposed to offshore thermal regimes accumulated more GDD in the winter than did eggs carried by inshore lobsters, while eggs exposed to inshore temperatures acquired them more rapidly in the spring. Results suggest that seasonal movements of ovigerous lobsters influence the time and location of hatching, and thus the transport and recruitment of larvae to coastal and offshore locations.

Thermal sensitivity does not determine acclimation capacity for a tropical reef fish

1. Short-term measures of metabolic responses to warmer environments are expected to indicate the sensitivity of species to regional warming. However, given time, species may be able to acclimate to increasing temperature. Thus, it is useful to determine if short-term responses provide a good predictor for long-term acclimation ability. 2. The tropical reef fish Acanthochromis polyacanthus was used to test whether the ability for developmental thermal acclimation of two populations was indicated by their short-term metabolic response to temperature. 3. While both populations exhibited similar short-term responses of resting metabolic rate (RMR) to temperature, fish from the higher-latitude population were able to fully acclimate RMR, while the lower-latitude population could only partially compensate RMR at the warmest temperature. These differences in acclimation ability are most likely due to genetic differences between the populations rather than differences in thermal regimes. 4. This research indicates that acclimation ability may vary greatly between populations and that understanding such variation will be critical for predicting the impacts of warming environmental temperatures. Moreover, the thermal metabolic reaction norm does not appear to be a good predictor of long-term acclimation ability.

Variation in Reproductive Life History Traits between Two Populations of Blackbanded Darters (Percina nigrofasciata)

We examined the life history of Blackbanded Darters (Percina nigrofasciata) from two streams in the Choctawhatchee River drainage, Florida, over a three-year study period. Blackbanded Darters from Turkey Creek were longer than fish from Ten Mile Creek; however, size-adjusted clutch and egg sizes were similar between populations. Larger females produced larger clutches, whereas egg size did not vary with female body size. Seasonally, clutch sizes were greater in May than in August. When contrasted with previous studies of Blackbanded Darters in Alabama and Louisiana, the reproductive season of Blackbanded Darters in Florida was unusually long, ceasing for only a few months in late fall. The reproductive season was longer in Turkey Creek than in Ten Mile Creek. Differences in thermal regime among streams may explain differences in life history traits among local and distant populations of Blackbanded Darters. This research, alone and in combination with previous studies of this species, emphasizes two main points. First, it reaffirms that life history studies based on a single locality or conducted at a single point in time may fail to capture the full range of variation in life history traits. Second, it highlights the extensive phenotypic variation found in species with broad geographic ranges. Such species lend themselves to comparative and experimental research on patterns and causes of life history variation. general aim of life history studies is to identify spatial and temporal patterns of variation in life history traits and to understand the underlying causes of variation among populations and species. Life histories represent adaptations to environmental conditions experienced by populations over time (Roff, 1992; Stearns, 1992). Measuring and characterizing variation in life history traits, therefore, enhances our understanding of the selective pressures faced by different populations as well as constraints on their ability to respond adaptively to these pressures. North American darters (Perciformes: Percidae) commonly exhibit spatial and temporal variation in reproductive traits. Body size, duration of spawning season, clutch size, and egg size vary within and among populations for many

INFLUENCE OF SCALE ON THERMAL CHARACTERISTICS IN A LARGE MONTANE RIVER BASIN

ABSTRACTThis study monitored stream temperatures over two hydrological years at various nested scales within the large, unregulated river Dee catchment (North East Scotland). These scales were (i) the whole catchment (11 sites along main stem Dee); (ii) the tributary (single sites in main tributaries); (iii) the Girnock (five sites in one subcatchment); and (iv) the reach (26 points across single reach). The aim was to characterize the thermal regime of all locations and compare the magnitude of variation between each scale. The controls on this variation were assessed via a multiple linear regression model using Geographic Information System‐derived catchment data. Temperatures were collected at 15‐min resolution and for further analysis and discussion combined to daily means. At the catchment and subcatchment scales, a west to east gradient in mean and minimum temperatures was observed, largely paralleling changes in altitude. Temperature differences between subcatchments were generally greater than between the sites along the main stem of the Dee. Differences between tributaries reflected differences in their morphology and land use. However, some tributaries had similar thermal regimes, despite different catchment and riparian characteristics. Subcatchment differences in thermal regimes of one of the tributaries corresponded to riparian vegetation reduced diurnal variability in sections dominated by broadleaf woodland. Compared with the larger scales, reach differences in thermal regime were small (e.g. mean temperatures of riffle, pool and margin habitats were within 0.3°C). The most noticeable difference was in relation to the point samples within the backwater area, which has a more constant thermal regime, most probably reflecting its groundwater source. The regression analysis indicated that monthly mean temperatures can be predicted well using elevation and catchment area. Forest cover was a significant explanatory variable during the summer months. However, some of the empirical temperature data from the Dee indicate that similar thermal regimes can result from different physical controls and processes that have important implications for the extrapolation of such predictive models. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Plasticity in population biology of Cherax cainii (Decapoda: Parastacidae) inhabiting lentic and lotic environments in south-western Australia: Implications for the sustainable management of the recreational fishery

The Smooth Marron Cherax cainii is endemic to south-western Australia and supports an iconic recreational fishery that exploits stocks in both lentic and lotic systems. This study is the first to determine and compare the population biology of a parastacid from both lentic and lotic systems and aimed to gather the information necessary for more effective management of the fishery. Modal progression demonstrated growth rates of juvenile C. cainii were greater in the lentic (Wellington Dam) compared to the lotic (Warren River) system, however, mark-recapture suggested the growth rate of the adult component of the lentic population was stunted whereas in the lotic population 60–90 mm OCL individuals were common and had a faster growth rate. The Wellington Dam stock appeared to be over-exploited and had very low productivity whereas the Warren River stock had relatively low fishing exploitation and a high productivity resulting from higher growth rates coupled with higher population densities (with the trappable population sizes estimated using the open POPAN formulation in the MARK software program). Comparisons of these biological parameters were made with populations elsewhere and there existed a considerable plasticity that is probably due to differences in thermal regimes, degree of habitat complexity, food resource availability and fisher accessibility. The findings demonstrate the need to determine the level of intraspecific biological plasticity in freshwater crayfish in order to sustainably manage their fisheries.

Metabolic cold adaptation and developmental plasticity in metabolic rates among species in the Fundulus notatus species complex

Summary 1. In ectotherms, temperature and body size are the most influential and well studied variables affecting metabolic rate. Understanding mechanisms driving the evolution of metabolic rates is crucial to broader ecological theory. The metabolic cold adaptation hypothesis (MCA) makes predictions about the evolution of ectotherm metabolic rates and temperature‐metabolic rate reaction norms. 2. We examined intra and interspecific patterns in metabolic rate among populations in the Fundulus notatus species group (F. notatus, F. olivaceus and F. euryzonus). We ask if patterns of intra and interspecific variability in metabolic rate are consistent with the MCA and if metabolic rates in general are developmentally plastic. 3. Support for the MCA was mixed among intra and interspecific tests. The northern population of F. olivaceus had increased metabolic rate and no difference in temperature sensitivity (slope of temperature‐metabolic rate reaction norm). Northern populations of F. notatus had lower temperature sensitivity and no difference in overall metabolic rate. The southern coastal drainage endemic (F. euryzonus) had intermediate metabolic rates compared to southern populations of the other two more broadly distributed species. Metabolic rates were also developmentally plastic. Adults reared at warmer temperatures had lower metabolic rates after accounting for body size and temperature. 4. Differences in thermal regimes explain some variability in metabolic rates among populations consistent with MCA. However, interspecific comparisons are not consistent with MCA and are likely influenced by species differences in ecology and life history strategies.

Downed Wood Microclimates and Their Potential Impact on Plethodontid Salamander Habitat in the Oregon Coast Range

Downed wood provides important faunal microhabitat in forests for numerous invertebrate taxa, small mammals and amphibians. Habitat suitability of downed wood as refugia is an increasing concern in managed Pacific Northwest forests, where overstory reduction may result in both reduced downed wood recruitment and increased temperatures within logs. We examined temperature profiles in western Oregon to assess differences in thermal regimes of logs and soil relative to summer air temperature extremes and their implications with respect to habitat suitability for plethodontid salamanders. Temperature profiles of small- (0.3–0.45 m) and large- (0.7–1.0 m) diameter logs, as well as ambient soil and air temperatures, were measured in a 60-year-old forest stand at two different positions (0–5 m and 35–40 m from stream edge) in three case studies: 1) along a headwater stream with a narrow riparian buffer (∼6 m) and moderate upslope thinning; 2) along a headwater stream with a wider riparian buffer (∼15 m) and moderate upslope thinning; and 3) along a headwater stream with an unthinned upslope. Streamside and upslope maximum air temperatures measured during July 2006 along all three streams were near or exceeded 30°C, the critical thermal tolerance threshold for western plethodontid salamanders. Streamside and upslope temperatures inside small logs, large logs and soils stayed below critical temperatures. Our results suggest that logs of a wide size range, as well as soils, may provide sufficient protection against thermal extremes in uncut forests and thinned stands with limited overstory.

DECOMPOSITION OF DIVERSE LITTER MIXTURES IN STREAMS

In view of growing interest in understanding how biodiversity affects ecosystem functioning, we investigated effects of riparian plant diversity on litter decomposition in forest streams. Leaf litter from 10 deciduous tree species was collected during natural leaf fall at two locations (Massif Central in France and Carpathians in Romania) and exposed in the field in litter bags. There were 35 species combinations, with species richness ranging 1-10. Nonadditive effects on the decomposition of mixed-species litter were minor, although a small synergistic effect was observed in the Massif Central stream where observed litter mass remaining was significantly lower overall than expected from data on single-species litter. In addition, variability in litter mass remaining decreased with litter diversity at both locations. Mean nitrogen concentration of single- and mixed-species litters (0.68-4.47% of litter ash-free dry mass) accounted for a large part of the variation in litter mass loss across species combinations. For a given species or mixture, litter mass loss was also consistently faster in the Massif Central than in the Carpathians, and the similarity in general stream characteristics, other than temperature, suggests that this effect was largely due to differences in thermal regimes. These results support the notion that decomposition of litter mixtures is primarily driven by litter quality and environmental factors, rather than by species richness per se. However, the observed consistent decrease in variability of decomposition rate with increasing plant species richness indicates that conservation of riparian tree diversity is important even when decomposition rates are not greatly influenced by litter mixing.

RELATIONSHIPS OF STREAM INVERTEBRATE COMMUNITIES TO DEFORESTATION IN EASTERN MADAGASCAR

Madagascar has been recently identified as a global hotspot for freshwater biodiversity. Loss of most of its eastern rain forest, combined with a high incidence of micro‐endemism and specialization to forest stream habitats, has likely led to extinction of many of the island's stream insect species. We compared habitat and macroinvertebrate community structure in three streams draining protected rain forest within Ranomafana National Park in eastern Madagascar and three agriculture streams draining the park's largely deforested peripheral zone. Multivariate analyses showed that macroinvertebrate communities differed between stream types. Forest streams were characterized by species‐rich, diverse communities composed primarily of collector–gatherers and collector–filterers belonging to the orders Trichoptera, Ephemeroptera, Plecoptera, and Diptera. In contrast, relatively depauperate agriculture stream communities were dominated by generalist collector–gatherer taxa mostly belonging to the order Ephemeroptera. Agriculture streams had 0–14% canopy cover, significantly higher mean and maximum water temperatures, and significantly lower benthic organic matter storage than forest streams (71–83% canopy cover). We found no evidence for higher sedimentation rates or nutrient concentrations in agriculture streams. Differences in thermal regime may be important in the declines of certain taxa in agriculture streams (e.g., Plecoptera). However, our data support the hypothesis that differences in stream communities are caused mainly by differences among taxa in ability to track shifts in basal resources (i.e., terrestrial detritus vs. in situ algal production) caused by deforestation. Community simplification and loss of endemic specialist taxa will continue if projections of future deforestation are proved correct. We recommend that stream biodiversity be considered in future conservation planning and propose the creation and maintenance of multiuse riparian forests that could serve both ecological and economic functions. Given that more than 5 × 105 km of stream and river channel are affected by tropical deforestation annually, our results have potential applications in other tropical regions.

Natural otolith microstructure patterns reveal precise homing to natal incubation sites by sockeye salmon (Oncorhynchus nerka)

Experimental results suggest that anadromous salmon and trout learn (imprint) the odors of their natal site just prior to or during seaward migration. In contrast, information on the life histories of several species and the genetic structure of populations indicate that they must imprint earlier in life, probably during incubation in the gravel or when they emerge as free-swimming fry. To test the hypothesis that sockeye salmon (Oncorhynchus nerka) home to their incubation-emergence sites (rather than just to the lake where they reared before migrating to sea), we took advantage of the natural variation in otolith microstructure caused by differences in thermal regimes during incubation. We collected otoliths from adult sockeye salmon that returned to discrete spawning areas in Iliamna Lake, Alaska, and Lake Washington, Washington, and, in blind trials, these were classified based on comparison with otoliths from juveniles from the same sites and using information on site-specific thermal regimes. Our analysis showed that the salmon were much more likely to return to their natal incubation site than would have occurred by chance. Estimated straying rates were about 0.1% from the Woody Island population to the Pedro Pond population in Iliamna Lake and about 1% from the Cedar River population to the Pleasure Point population in Lake Washington. The results were consistent with genetic evidence for fine-scale structure of salmon populations and with conservation based on spatial scales appropriate for the early life history of the fish.

Comparison of leaf processing rates under different temperature regimes in three headwater streams

1. We studied the effects of different temperature regimes on leaf litter processing in three forested Appalachian headwater streams of different pH (mean pH = 4.2, 6.5, 7.5).2. We compared leaf breakdown rates, microbial biomass and macroinvertebrate shredder density and biomass between two 12‐week processing periods (October–January and November–February) in each stream. Leaf processing rates were calculated both as k (day–1) and kd (degree day–1).3. There were no significant differences in processing rates (k day–1) between the two study periods for any leaf species in any stream. The average difference in temperature between the two study periods was 175 degree days. Shredder density was significantly higher during the earlier study period on 40% of the sample dates, but shredder biomass was not significantly different between the two study periods. ATP concentration was significantly higher during the early study period for 60% of the sample dates.4. More significant differences in these variables (shredder density and biomass, ATP concentration) were seen among the three study streams than between the two study periods. This indicates that in this study other factors, particularly stream pH, contributed more to processing rate variation than did differences in thermal regime.

Spatial and Temporal Variation in the Growth and Production of Ephoron leukon (Ephemeroptera:Polymitarcyidae)

Variation in growth rates, maximum nymphal sizes, densities, and production estimates of Ephoron leukon (Ephemeroptera:Polymitarcyidae) were investigated at two sites over a 3-yr period on the South River, Virginia. Ephoron leukon is univoltine with development confined to a short (3-4 mo) period during the summer followed by a long (8-9 mo) egg diapause. The short growing season combined with a high degree of developmental syncrony makes this species ideal for comparative field studies. Relative growth rates ranged from 0.014 to 0.028 mg/mg/day and significant differences were observed between sites and years. Spatial differences in growth rates were explained by between-site differences in thermal regime but between-year differences were not. Differences in average densities between years may have been important in explaining annual differences in growth rates. Maximum nymphal weights averaged between 3.22 and 4.78 mg (AFDM) and were significantly higher at the downstream site for all three years. Diffe...

Metabolic organization in swimming muscle of anadromous coregonines from James and Hudson bays

The metabolic organization of swimming muscles from anadromous cisco (Coregonus artedii) and lake whitefish (Coregonus clupeaformis) sampled in two rivers presenting different regimes of migratory difficulty and temperature was compared. Cisco muscle showed an increased aerobic capacity in the river where the fishes' migration is longer, as shown by the activities of several enzymes and by the proportion of red muscle in their swimming muscle. Lake whitefish, generally larger than cisco, did not show any compensation for the difficulty of migration. For both species, latitudinal differences in thermal regime were not correlated with differences in aerobic capacity. As estimated from published allometric equations, scaling effects can account for only a small proportion of the interstation variation in the aerobic enzyme activities of cisco. Our results suggest that because cisco are smaller than lake whitefish in these rivers, and thus are more affected by the degree of difficulty of the prereproductive migration at a given temperature, cisco have compensated by increasing the aerobic capacity of their swimming musculature in populations facing greater swimming requirements.