Growth and recession of aquatic macrophytes on a shaded section of the River Lambourn, England, from 1971 to 1980

SUMMARY. The growth and recession of macrophytes on a shaded section of the R. Lambourn were documented by a mapping procedure. With the exception of Ranunculus spp., the changes in total cover did not indicate directly the pattern of growth and recession of the macrophyles. Analysis of gross changes, expressed as gains and losses on cover, indicated that colonization of gravel and silt by the dominant macrophyte, Berula erecta, did not vary seasonally. Colonization was at a constant rate of about 8% of the site each month throughout the year and this accounted for 50% of the total number of gains by Berula. Gains of Berula from Ranunculus showed an annual cycle with a maximum during the summer when Ranunculus was in recession. Gains of Berula from Callitriche spp. also varied annually but the maximum was during the autumn. Total losses of Berula were at a constant rate throughout the year but were to gravel and silt during the winter, to Ranunculus in spring and early summer and to Callitriche in late summer and autumn. Analysis of loss of Berula with time indicated that the position of the Berula carpet was constantly changing. The growth and recession of Berula could not be linked in a meaningful way to environmental variables. Callitriche and Ranunculus both showed an annual pattern of growth and recession. There was temporal separation of the two macrophytes with Ranunculus growing mainly in spring and early summer and Callitriche showing maximum growth in late summer and autumn, and some evidence of spatial separation. The observed differences between years in the growth of Callitriche could not be attributed to any of the environmental variables measured. Discharge was thought to be an important variable controlling the growth of Ranunculus since increase of Ranunculus in the spring was positively correlated with the mean discharge at that time. In years when discharge was low, the growth of Rununculus appeared to be restricted by shading from epiphytic algae which accumulated on the plant surfaces under these conditions.     

LATITUDINAL TRENDS IN THE GROWTH AND REPRODUCTIVE SEASONALITY OF DELESSERIA SANGUINEA,MEMBRANOPTERA ALATA,AND PHYCODRYS RUBENS (RHODOPHYTA)1

The seasonality of Delesseria sanguinea, Membranoptera alata, and Phycodrys rubens (Rhodophyta) was studied at Helgoland (North Sea, Germany) and Roscoff (Brittany, France). Plants were collected at bimonthly intervals, and growth and reproduction were monitored. Growth of blades was observed mainly in spring, although small blades were found on plants of M. alata and P. rubens all year round. In summer, plants started to degenerate and in autumn they became fertile. The reproductive season of D. sanguinea lasted from October to February/April at both locations, whereas reproductive plants of M. alata and P. rubens were found until April at Helgoland and until June and August, respectively, in Roscoff_: Lower winter temperatures at Helgoland than at Rascoff may have caused these differences in the duration of the reproductive season. Using published data, the seasonal patterns at Helgoland and Roscoff were compared to those found at other locations (e.g. Barents Sea; Maine, USA; Isle of Man, UK) and local temperature/daylength conditions. Blade growth was synchronized across all populations and occurred in spring, when temperatures were usually still suboptimal for growth. Maximum reproduction was generally found in the colder half of the year but started earlier in autumn in the Barents Sea. Adaptive strategies in the seasonal control of growth and reproduction are discussed. Adequate timing of the history events (e.g. appearance of juveniles in spring) appears more important than maximal growth and reproduction of adults during the season with the most favorable temperatures.     

Biomass and oxygen dynamics of the epiphyte community in a Danish lowland stream

SUMMARY. 1. We examined the abundance and oxygen metabolism of epiphytic organisms on the dominant macrophyte, Potamogeton pectinatus , in headwaters of the eutrophic River Suså. Microbenthic algae were abundant in the stream during spring and macrophytes during summer.
2. The low macrophyte biomass in spring supported a dense epiphyte cover whereas the high macrophyte biomass during summer had a thin epiphyte cover of 10–100-fold lower abundance per unit area of macrophyte surface. The epiphyte community was dominated by microalgae in spring and by heterotrophs, probably bacteria, during summer. This seasonal shift was shown by pronounced reductions of the chlorophyll a content (from 2–3% to 0.1–0.7% of organic DW), the gross photosynthetic rate (from 20–85 to 3–15 mg O₂, g-¹ organic DW h⁻¹) and the ratio of gross photosynthesis to dark respiration in the epiphyte community (from 5–18 to 1). The reduced contributions of epiphytic microalgae correlated with reduced light availability during summer.
3. Both the density and the photosynthetic activity of epiphytic algae were low on a stream area basis relative to those of microbenthic algae and macrophytes. Rapid variations in water velocity and extensive light attenuation in water and macrophyte stands probably constrained the development of epiphytic algae. The epiphyte community was more important in overall stream respiration, contributing c. 10% to total summer respiration and c. 20% to summer respiration within the predominantly heterotrophic microbial communities on sediments and macrophyte surfaces.     

Spatial and temporal occurrence of invertebrates in a chalk stream,Berkshire, England

The invertebrate assemblages of the River Lambourn and its tributary, the Winterbourne stream, were investigated as part of a broad ecological study prior to water resource development in the catchment. The longitudinal distribution of the invertebrate fauna within the Winterbourne stream was examined in detail and supporting data for the R. Lambourn revealed that the upstream intermittent section of each water course had an invertebrate assemblage which was distinct from the fauna downstream where flow was permanent. Within the perennial zone taxon richness tended to increase downstream.A one-year programme of monthly quantitative sampling on five distinct biotopes (Ranunculus, Berula, Callitriche, gravel and silt) at two contrasted sites (shaded and unshaded) was undertaken in the lower perennial of the R. Lambourn below the confluence with the Winterbourne. On each study site, the taxon richness, numerical abundance and biomass of invertebrates were significantly higher on the three macrophytes than on gravel and silt. There were also statistically significant seasonal changes in the biomass of invertebrates on each site. Estimates of total biomass of invertebrates per site revealed a late spring peak (May/June) and a late autumn (November/December) peak, neither of which coincided with the summer peak biomass of macrophytes. This suggested that, in the lower perennial, the level of food resources (epiphytic algae in late spring and fallen tree leaves plus decaying macrophytes in autumn) rather than available habitat, were a major influence on population levels for most of the year.Quantitative sampling of each biotope on each site continued in June and December only for a period of 8 years (1971–78), during which time the river experienced a minor drought (1973) and a severe drought (1976). The Chironomidae showed a strong positive response to conditions of low flow in June of 1973 and 1976, when exceptionally high densities of larvae were recorded. Although further between-year differences were recorded in several other major components of the invertebrate fauna, which may have been related to conditions of low discharge, they did not have long-term consequences for the fauna in the lower perennial of the R. Lambourn.In contrast, in the upper perennial, the prolonged drought of 1976 resulted in the loss of wetted perimeter and macrophytes, coupled with deposition of silt, all of which had deleterious effects on the invertebrate assemblages. The following year, despite a normal discharge regime and the removal of silt, some submerged macrophytes were slow to return to their pre-drought condition. In the intermittent section, the drought of 1976 resulted in the total loss of flow for a 16 month period instead of a more typical four month period of water loss.Thus, chalk streams encompass within a single system both stable and extreme hydrological regimes which offer unique opportunities for investigating the processes of community formation and maintenance.     

Ecology of the whiskered sole in the Sado Estuary, Portugal

The abundance of the wiskered sole Monochirus hispidus in the Sado Estuary showed a marked seasonal pattern, the highest densities occurred in spring and summer. The density of this species was mainly related, non‐linearly, to depth, water transparency and percentage of gravel, fine sand and mud in the sediment. Monochirus hispidus fed mainly on crustaceans and polychaets. Significant differences were found between the proportions of prey items eaten and total length class; larger fish consumed more decapods and polychaets. The von Bertalanffy growth equation coefficients differed between sexes. The asymptotic length L _∞ obtained for females was higher compared to males, while the growth coefficient ( K ) was higher for males. Individuals with mature gonads were found between March and September, but the main spawning period of M. hispidus in the Sado Estuary was from March to June.     

Seasonal patterns of feeding of juvenile major carp, Labeo rohita (Ham.) in a Bangladesh pond

The results of the studies on the seasonal patterns of feeding of 203 Labeo rohita (Ham.) taken by cast and seine net for one year from a Bangladesh pond are presented. Studies were based on the frequency of occurrence and the points method. A change in the volume of food with change of seasons was noted. The amounts of food eaten were greater for the warmer than for other months and very low during winter indicating an upturn in late spring with a higher level continuing during the summer.
Organic detritus formed the bulk of the gut contents throughout the study period. On a seasonal basis, phytoplankton and aquatic macrophytes were the group of organisms frequently ingested but the former was more important. Animal food was scarce but appreciable quantities of sand and mud were found.     

Seasonal fluctuations in androgen levels in females of the hermaphroditic gag, Mycteroperca microlepis, with an emphasis on juvenile animals

Androgens are known to play many roles in the reproductive physiology of teleosts, but less information exists on the role that they play in the development of larval and juvenile fish. This study examines an observed seasonal cycle of 11-ketotestosterone (11KT) in females of the hermaphroditic gag grouper (Mycteroperca microlepis). Otoliths, gonads, and plasma samples from gag were collected quarterly (spring, summer, fall, and winter), with complete data (age, sex, and androgen levels) obtained from a total of 225 individuals. Ages ranged from zero to 11 years, and all individuals were female. Testosterone (T) peaked in the spring, coincident with spawning, and was low throughout the remainder of the year. The androgen 11KT peaked in summer and declined through the following spring. 11KT levels were negatively correlated with fish size in both the summer and winter, while T was negatively correlated in the summer and positively correlated in the winter. T levels showed little seasonal variation in juveniles (0-1 and 2-3 age groups), but showed a seasonal increase from fall through spring in older fish (4-5 and 6+ age groups). Age 0-1 fish had significantly higher levels of 11KT than the age 4-5 group during the summer and both the 4-5 and 6+ age groups in the winter. The gag is a protogynous hermaphrodite that goes through several ontogenetic shifts during its life, and this seasonal fluctuation in plasma levels of 11KT may play a role in the growth and development, behavior, or control of sex change of gag.     

Feeding patterns and population structure of an invasive cyprinid,the rudd <Emphasis Type="Italic">Scardinius erythrophthalmu</Emphasis>s (Cypriniformes,Cyprinidae), in Buffalo Harbor (Lake Erie) and the upper Niagara River

Feeding patterns and population structure of the non-native rudd Scardinius erythrophthalmus (Linnaeus) were examined to understand their ecology in Buffalo Harbor and the Niagara River. We hypothesized that (1) the diet of rudds would be omnivorous, but contain greater proportions of macrophytes in summer months, (2) feeding intensity would increase with water temperature, and (3) condition and growth would be similar to other populations. We collected rudds with a variety of gears in 2009 to test these hypotheses, and used data from 2007 to 2010 seining surveys to determine if the relative abundance of young-of-the-year rudd differed among sites with different flow conditions. Rudds were mostly herbivorous; they consumed aquatic macrophytes in summer and supplemented their diet with algae and fish in spring and fall. Feeding intensity was positively correlated with water temperature, but significantly reduced during spawning. Rudd condition and growth were greater than estimates from other populations, suggesting increases in abundance and range expansion are possible. Furthermore, reproduction was successful at lotic sites but very poor at sites without measureable flow, contrary to the paradigm of optimal rudd habitat. Research is needed to understand how herbivory by abundant rudd populations affects native aquatic communities.     

Seasonal phytoplankton variations in the shallow Pahlavi Mordab,Iran

Pelagic phytoplankton variations in the shallow, western basin of the Pahlavi Mordab, Iran were monitored by the chlorophyll a, gross oxygen productivity and cell enumeration techniques. Annual maxima were 29.4 mg/m³, 0.98 mg O₂/l/hr and 32, 639, 467 cells/liter respectively and were recorded from late summer until early autumn. During the spring and summer, dense growths of Ceratophyllum, Hydrilla and Myriophyllum flourished. Competition between the phytoplankton and submerged aquatic macrophytes was minimal following late summer, when water depths increased following heavy seasonal precipitation and the die-back of submerged aquatic macrophytes occurred.     

Diet composition of chub,Squalius cephalus (Teleostei: Cyprinidae), in Lake Tödürge,Sivas, Turkey

Digestive tract contents of 241 specimens captured between March 1998 and November 1999 were analysed using both qualitative and quantitative methods to determine diet composition and feeding habits of Squalius cephalus (L., 1758) inhabiting Lake Tödürge, Turkey. Ages ranged from I to VI years; 60.6% of the fish were females, 39.4% males. The chub population appeared to consume a wide range of food items such as phytoplankton, zooplankton, nematodes, insects, fish, macrophytes, plant and animal detritus, whereby zooplankton (69.2%) predominated. Although individuals in the age I group preferred plankton (phytoplankton frequently; zooplankton infrequently), the older specimens (age groups IV, V and VI) behaved mostly as carnivores but also consumed some macrophytes. While there were no significant differences between diet compositions of males and females, seasonal changes were observed in frequency of occurrence, quality and quantity of consumption, and feeding activity. The chub specimens fed most heavily during spring (the pre‐spawning period: March, April and May). Highest food volume (13.0 cm³) consumed was in May and the lowest in September (2.0 cm³) while also being correlated with temperature. All of the food items were found in the digestive tract (82.1% of the specimens examined over all seasons). Highest fullness (84.9%) was reached in autumn and the lowest during summer (79.8%).     

2000—2016年云南地区植被覆盖时空变化及其对水热因子的响应

基于2000-2016年MODIS-NDVI数据,利用趋势分析法以及线性相关分析等方法对云南地区植被月变化趋势、年际变化趋势进行详细分析;探讨植被覆盖变化与主要气候水热因子的关系。结果表明：研究区大部分地区植被覆盖良好,年NDVI的平均值为0.55,其中NDVI较高值（> 0.8）区域主要分布于南部,而西北部和中部城市地区NDVI值较低;自2000年开始,研究区NDVI总体呈显著（P < 0.05）增加趋势,年NDVI的变化斜率为0.0036,植被覆盖呈增加趋势的区域占研究区总面积79.80%;不同季节（春、夏、秋、冬）和生长季的植被状况均呈良性发展趋势;湿润指数和水热综合因子在滇西北与NDVI多呈负相关,在滇中地区以正相关为主;春、夏、秋3个季节NDVI受降水影响较大,而冬季NDVI则受气温影响较大;受降水影响较大的区域主要分布在中部和南部,受气温影响较大区域主要分布在滇西北、滇东北地区;NDVI在不同月份对气候因子的滞后时间存在差异,NDVI与当月气温的相关性强于与当月降水的相关性,植被生长对气温的响应无明显滞后效应,对降水存在3个月的滞后期。     

Correlations between chironomid pupal skin collections and habitats recorded from a chalk river

Chironomid pupal skins were collected during one year from three sites along a chalk stream in southern England. The sites had similar chemistry and discharge but differed in their current and temperature regimes. Substrate composition upstream of each collection point was surveyed during spring, summer and autumn. Proportions of macrophytes and sediments were compared with proportions of chironomid species and trophic groups. Seasonal changes in substrate and pupal skin collections were correlated by classification and direct ordination techniques. The distribution of chironomid species were indicated as being significantly related to the recorded substrate data.     

Leaf traits and relationships differ with season as well as among species groupings in a managed Southeastern China forest landscape

The relationships among leaf traits often reflect plant adaptation for coping with nutrient resources. However, the seasonal variations in leaf traits and their relationship with soil nutrients are not well understood. We sampled seven major functional traits of thirty trees and nine shrubs (sorted into different plant functional groups, PFGs, based on their growth form, leaf lifespan, and leaf shape) at different seasons in a managed forest plantation of Southeastern China. Both green leaf nitrogen and phosphorus concentrations (N_green and P_green) decreased significantly from spring and summer to autumn, and varied significantly with PFGs (P?<?0.05) at different times of the year. Across all plants, specific leaf area correlated positively with N_green and P_green in spring, summer, and winter, but not in autumn; N resorption proficiency generally correlated positively with N_green in each season, while P resorption efficiency correlated positively with P_green in spring and summer, but not in autumn and winter. Soil nitrogen availability correlated negatively with leaf nutrient traits in some seasons. In conclusion, leaf trait relationships varied among the seasons and among PFGs. Seasonal dynamics of leaf traits as well as soil nutrients?? relations must be considered when exploring plant feedback to soil nutrients.     

Effects of waterfowl, large fish and periphyton on the spring growth of Potamogeton pectinatus L. in Lake Mogan, Turkey

It has been argued that waterfowl and fish may threaten growth of submerged macrophytes, especially in spring during the early growth phase when plant biomass is low. A small reduction of biomass at that time might delay growth or decrease subsequent productivity. We investigated the impact of waterfowl and large fish on the spring growth of fennel pondweed (Potamogeton pectinatusL.) by employing an exclosure experiment in the macrophyte-dominated clear-water Lake Mogan, Turkey. Birds and large fish were excluded from eight plots and both in situvegetation and macrophytes kept in pots were compared to eight open plots. Also, to investigate the effect of periphyton on plant growth it was removed from half of the pot plants. Exclusion of waterfowl and fish may decrease predation on macroinvertebrates, which in turn may affect periphyton, and macrophyte growth, why macroinvertebrates also were sampled. Waterfowl density was high (15–70 ind. of coot, Fulica atraL. ha^–1), abundance of submerged plants was also high with a surface coverage of 70–80%, and benthivorous fish were present, mainly tench, (Tinca tincaL.) and carp, (Cyprinus carpioL.). Exclusion of waterfowl and large fish did not significantly affect the spring growth of pondweed; neither plants growing in situnor kept in pots. Removal of periphyton from the plants in the pots did not favour growth. The density of macroinvertebrates was not affected by the exclusion of waterfowl and large fish, but it was positively related to aboveground biomass of fennel pondweed. We suggest that even if waterfowl and large fish are in high densities, their effect on fennel pondweed spring growth in lakes with abundant submerged vegetation, such as Lake Mogan, is low.     

Growth of opossums (Trichosurus vulpecula) in the Orongorongo Valley,Wellington, New Zealand, 1953–61

The growth of pouch young and juvenile Trichosurus vulpecula to maturity is described, based on animals gin‐trapped in 800 ha of indigenous forest in the Orongorongo Valley, near Wellington. Commencing in March 1953 opossums were trapped continuously for 1 year, and then intermittently until 1961. Four ageing criteria were considered: ossification of limb epiphyses and development of cranial ridges were unreliable; tooth wear and closure of the spheno‐occipital skull sutures were more satisfactory, and were adopted. For the first 180 days the mean growth followed a rectilinear regression when size, expressed as cube root of weight, was plotted against age. Thereafter growth accelerated greatly, but steadied towards the end of the first year; its rate increased after several months, and ceased at 2 to 21/2 years. Though adult males (2.65 kg) and females (2.41 kg) differed significantly in weight, there was no detectable difference during the growth phase. Births occurred throughout the year, but were markedly seasonal, 86% occurring between mid March and the end of May. A secondary birth peak in spring, recorded in other areas, was barely apparent. Most young consequently grew fastest in their first spring and summer. The growth pattern appeared to be mainly dependent on age rather than season_^ since all young reared in captivity conformed, irrespective of the season of birth.     

Marine post-smolt growth and age at maturity of Atlantic salmon

The annual variation in sea-age of maturation for a hatchery dependent stock of Atlantic salmon was compared to variation in post-smolt growth as evidenced by circuli spacing patterns. The proportion of returns of 1-seawinter (1 SW) and 2 SW salmon and the fraction of the smolt year class or cohort that maturated as 1 SW fish, were compared to seasonal growth indices determined from circuli spacing on the scales of smolt class survivors returning as 1 SW and 2 SW spawners. Using image processing techniques, we extracted inter-circuli distances from scales from 2244 recaptured fish. Spacing data for the first year at sea were collected and then expressed as seasonal growth indices for the spring period, when post-smolts first enter the ocean; the summer, when growth appears maximal; and winter, when growth appears to be at a minimum. In general, circuli spacings were wider for 1 SW than for the 2 SW returns of the same smolt cohort. The 1 SW fraction was significantly and positively correlated with late summer growth, suggesting that growth during this season is pivotal in determining the proportion of a smolt class that matures early.     

Application of a bioenergetics model for analysis of growth and food consumption of subarctic whitefish Coregonus lavaretus (L.) in Lake Kilpisjärvi, Finnish Lapland

A bioenergetics model was used to estimate daily food consumption and growth of benthic whitefish Coregonus lavaretus (L.) of age groups 1+ to 10+, in oligotrophic Lake Kilpisjärvi, northern Finnish Lapland. Fish and zooplankton samples and water temperature data were collected twice per month from February to December 1993. Simulation results indicated wide seasonal variations in consumption and growth rates. Growth was in general slow; especially in age-group 6 the net increase in weight was slight. The fit of the model to the weight data was good, and the model was able to follow even rapid seasonal variations in the weight. There were clear changes in the diet during the year. In March, when the food intake was reduced, copepods, mainly adult calanoids, formed the bulk of the food consumed. The most intensive consumption period lasted from June to late September. Chironomid pupae and planktonic cladocerans were the major summer food items. The largest individuals fed mainly on molluscs during summer. Zooplankton survey and consumption estimates did not show directly that the population density of copepodids and adults of Eudiaptomus graciloides were affected by whitefish predation although their population density decreased in spring. Nauplii, showing the maximum population density in April, were not consumed. The role of copepod consumption in the timing of Diphyllobothrium ditremum plerocercoid transmission to whitefish was also discussed. The increased copepod consumption rate during winter results in high energy intake but also an increased risk of food transmitted parasite infection.     

Seasonal changes in characteristics of cattle dung as a resource for an insect in southwestern Australia

The value of cattle dung as a food resource for the bush fly Musca vetustissima (Walker) in the winter rainfall agricultural region of southwestern Australia was assessed by bioassay in the laboratory. The size (headwidth) of adult females was measured from flies reared on different samples of dung. Variation in size correlated with seasonal patterns of pasture growth, larger flies being produced during the growing season from autumn to spring. Size declined with senescence of annual pastures in late spring and early summer, occurring later in southern areas where the growing season was longer. After pasture senescence, dung from shorter growing season areas usually produced larger flies, apparently a result of the inverse relationship between digestibility of feed and length of growing season. Dung from irrigated perennial pastures never produced flies as large as that from annual pastures but generally high values were sustained during summer. Grazing of cereal stubble and feeding of hay in annual pasture areas during summer usually caused some increase in fly size. A spontaneous resurgence in the size of flies often occurred several weeks after pasture senescence and was attributed to more thorough digestion as a result of reduced intake of less palatable dry pasture.     

Enhanced monsoon precipitation and nitrogen deposition affect leaf traits and photosynthesis differently in spring and summer in the desert shrub Larrea tridentata

Leaf-level CO2 assimilation (A(area)) can largely be predicted from stomatal conductance (g(s)), leaf morphology (SLA) and nitrogen (N) content (N(area)) in species across biomes and functional groups. The effects of simulated global change scenarios, increased summer monsoon rain (+H2O), N deposition (+N) and the combination (+H2O +N), were hypothesized to affect leaf trait-photosynthesis relationships differently in the short- and long-term for the desert shrub Larrea tridentata. During the spring, +H2O and +H2O +N plants had lower A(area) and g(s), but similar shoot water potential (Psi(shoot)) compared with control and +N plants; differences in A(area) were attributed to lower leaf N(area) and g(s). During the summer, +H2O and +H2O +N plants displayed higher A(area) than control and +N plants, which was attributed to higher Psi(shoot), g(s) and SLA. Throughout the year, A(area) was strongly correlated with g(s) but weakly correlated with leaf N(area) and SLA. We concluded that increased summer monsoon had a stronger effect on the performance of Larrea than increased N deposition. In the short term, the +H2O and +H2O +N treatments were associated with increasing A(area) in summer, but also with low leaf N(area) and lower A(area) in the long term the following spring.     

Habitat and resource use by larval and juvenile fishes in an arid-land river (Rio Grande, New Mexico)

1. Studies of mesic temperate and tropical rivers suggest an important role for floodplain habitats as nursery areas for larval and juvenile fishes. In arid‐land rivers the extent and duration of flooding is diminished and habitats and resources used by larval fishes are poorly known. Our study documented habitat and resource use of larval fishes in the Rio Grande, New Mexico, an arid‐land river. 2. Spatial and temporal distribution of larval and juvenile fishes and their inferred microhabitat preferences were studied during spring, summer and autumn, 2003. Stable carbon (¹³C : ¹²C) and nitrogen (¹⁵N : ¹⁴N) isotope ratios were measured to identify nutrient sources and characterise trophic positions of young‐of‐year fishes in this system. 3. Some fishes recruited during high flows (in spring), whereas others recruited during low‐flow periods in late summer. Regardless of the timing of reproduction, microhabitats with lower current velocity and higher temperature appeared to serve as vital nursery grounds for Rio Grande fishes. Ephemeral backwaters and disconnected side channels held the highest abundance and diversity of larvae and juveniles. 4. Stable isotope analyses revealed that fish larvae obtained carbon predominately from algal production in early summer, but used organic carbon derived from emergent macrophytes as river discharge decreased in mid‐summer. This shift may have been facilitated by microinvertebrate prey that grazed down edible algae and then switched to macrophytes in mid‐summer. Nitrogen isotope ratios did not differ among species or early life stages, suggesting that larval and juvenile fishes use similar food resources, especially when restricted to isolated pools in summer.