Productivity of a herbivorous pupfish population (Cyprinodon nevadensis) in a warm desert stream

Production and food intake by an herbivorous pupfish population ( Cyprinodon nevadensis amargosae ) living in the outflow of a thermal artesian well (Tecopa Bore) near Death Valley, California is described. Water issues from the ground at 47.5° C and cools 8.12° C before leaving the study area 300 m from the source. High stream temperatures restricted the pupfish population to some 41 % of the study area, with a resulting mean density of 89 individuals m⁻² (range = 13 to 196m⁻²). Biomass estimates ranged from 7 kcal m⁻² to 42 kcal m⁻². The mean annual standing crop of pupfishes (24 kcal m⁻²) turned over about five times annually. Growth rates were highest in juveniles (♂= 9.5% day⁻¹) and slowest in large adults (♀= 08% day⁻¹). Monthly production ranged from 22 kcal m⁻² in September to 3 kcal m⁻² in July and August. Pupfish in Tecopa Bore fed on algae and detritus, ingesting 1941 kcal m⁻² yr⁻¹ or 17.5% of the annual net primary production. 119 kcal m⁻² yr⁻¹ was deposited in growth. This latter value is approximately ten times greater than values previously reported for large carnivorous fishes but is comparable lo values reported for herbivorous fishes under pond culture.     

A limnological investigation of the tarn Syslaktjønn, W Norway

An investigation covering hydrography, chemistry, vascular and cryptogamic plants, nitrogen fixation, phytoplankton biomass and production, and zooplankton was carried out from April to November 1976 in tarn in W Norway, The volume of the tarn was 18000 m³ and the turnover time about 30 d. Temperature ranged between 3.6 and 23.4°C and pH between 4.8 and 5.5. Nuphar luteum and Carex rostrata were the two dominating vasculars-with biomasses of 117 and 97 g m⁻², respectively The biomass of the bryophytes ( Sphagnum spp.) was about 510 g m⁻² and the production of the order 0.2–2.1 μg (mg d.w.)⁻¹h⁻¹. Nitrogen fixation in association with Sphagnum spp. was estimated at 25 g yr⁻¹ for the whole tarn. Phytoplankton was dominated by diatoms, green algae and chrysophyceans. The chlorophyll a content ranged from 2 to 20 mg m⁻³ and the carbon assimilation rates from 0.03 to 20 mg C m⁻³h⁻¹ at 0–4 m depths. Production in the period was of the magnitude 22 g C m⁻². The copepod Eudiaptomus gracilis was the most common netzooplankter. Large numbers of rotationrians were found during summer.     

A light intensity threshold for schooling in the Atlantic mackerel, Scomber scombrus

The schooling behaviour of Atlantic mackerel was studied in a large tank at different light intensities in the range 12.6–1.8 × 10⁻¹⁰μEs⁻¹ m⁻². Variable light intensity was produced by accurately controlling the current to a green light-emitting diode (LED) 3 m above the experimental tank. Under high light levels (1.8 × 10⁻⁶μEs⁻¹ m⁻²) mackerel always formed a single school, whereas at lower levels (1.8 × 10⁻⁸μEs⁻¹ m⁻²) they swam as individuals. At light levels down to 1.0 × 10⁻⁶μEs⁻¹ m⁻² the mean nearest neighbour distance in a school remained relatively constant (0.3–0.9 body lengths), and individual mackerel swam along a path which deviated from the position of their nearest neighbours by less than 14°. As light dropped below 1.8 × 10⁻⁷μEs⁻¹ m⁻², both nearest neighbour distance and heading angle between nearest neighbours increased, with mean values of 1–1.8 body lengths and 23–92°, respectively, at 1.8 × 10⁻⁹μEs⁻¹ m⁻². The results are discussed in terms of ambient light conditions in the sea.     

Long-term study of the ecology of wild Atlantic salmon smolts in a small Norwegian river

Backcalculated lengths at the end of the first growth season in wild Atlantic salmon Salmo salar differed significantly between parr smolting at age 1, 2 and 3 years over a period of 11 years (i.e. 1983–1993). Mean body lengths of the respective age groups at the end of the first growth period were 11·1, 6·2 and 4·7 cm, respectively. The mean percentage distribution of fish smolting at age 1, 2 and 3 was 14, 78 and 7%, and the mean smolt age was 1·95 years. Mean lengths at smolting of age groups 1, 2 and 3 were 13·6, 15·8 and 17·5 cm, respectively. Females outnumbered males among the downstream migrating smolts with a mean sex ratio (females/ males) estimated at 1·61, with a significant female surplus in 7 of the 11 years sampled. Of the smolts sampled, 14% exhibited enlarged gonads indicative of parr maturation, and all were males (37% of the parr males sampled). Mean annual smolt density from 1975 to 1996 was 13·4 individuals 100 m⁻² ranging between 0·3–31 smolts 100 m⁻². Mean densities (100 m⁻²) of the smolts aged 1, 2 and 3 years were 1·5, 9·3 and 0·9 fish, respectively. Mean annual biomass for the 22-year period (1975–1996) was estimated at 437 g 100 m⁻², with a range of variation from 136 to 683 g 100 m⁻². Smolt age 2 made up 81% of the mean annual biomass (355 g 100 m⁻²) and smolt age 1 and 3, 8% (35 g 100 m⁻²) and 11% (47 g 100 m⁻²), respectively.     

Energetics of a population of the isopod Asellus aquaticus: Life history and production

SUMMARY. A population of Asellus aquaticus in Wistow Lake, England, was sampled at monthly intervals from September 1973 to September 1974. The mean population density was 586 m⁻² in autumn 1973 but it fell to 67 m⁻² by autumn 1974. Evidence suggests that the lower density in autumn 1974 was due to premature mortality of gravid females. The cause of this is not known.
Gravid females were present from February to June and July to September, giving rise to spring and autumn cohorts. The larger members of the spring cohort reproduced in the autumn, the remainder in the following spring. The autumn cohort reproduced mainly in the following spring but later than the spring cohort. The bimodal length-frequency curves were analysed to separate the two cohorts and to estimate growth and production of each cohort separately. The overwintering spring cohort had a faster relative growth rate than the smaller individuals of the autumn cohort. Thus the spring cohort showed a P/B ratio of 2.62 for the period September–April compared with a ratio of 1.81 for the autumn cohort. The highest ratio of 6.42 was shown by the spring cohort in the summer (May–September).
Annual population production (P) was 3004.9 mg dry wt m⁻² from a mean biomass (B) of 757.2 mg dry wt m⁻². The P/B ratio of 3.96 is double the value reported for A. aquaticus in Sweden.     

Denitrification in stream epilithon: Seasonal variation in Gelbæk and Rabis Bæk, Denmark

Abstract Seasonal variations of denitrification activity were determined and compared with various environmental parameters in undisrupted epilithon communities (biofilm) from two Danish lowland streams. In the nutrient-rich Gelbæk, denitrification activity followed extensive changes in biofilm thickness, dry weight and chlorophyll a content during the season. The absolute maximum of denitrification (1.4 mmol N m⁻² d⁻¹, dark incubation) was recorded when the biofilm was best developed in the spring (April and May). Activity decreased dramatically after most of the biofilm suddenly disintegrated and peeled off in early summer. Photosynthetic O₂ production was an important controlling factor of denitrification on a diurnal scale, since the activities were always 2–3 fold lower in the light (50 μE m⁻² s⁻¹) than in the dark. In the more nutrient-poor Rabis Bæk, the biofilm was much less developed and denitrification activities were relatively small (maximum of 0.2 mmol N m⁻² d⁻¹ under dark incubation). The results indicate that productivity of the micro-algae regulates both the seasonal and diurnal patterns of denitrification in the biofilms.     

An examination of the fish population in the River Trent, Nottinghamshire using angler catches

During this study, anglers caught over 580 kg of fish, comprising over 29 500 individuals of 14 species. Nine times as many gudgeon, Gobio gobio , as roach, Rutilus rutilus , were caught. Gudgeon represented 35.94% of the total catch weight compared with 44.64% for roach. The mean total catch per man-hour was 8.9 fish and the mean catch rate was 176 g per man-hour. Population estimates for fish longer than 12 cm for all species other than gudgeon and bleak, Alburnus alburnus , gave fish densities of 0.21 fish m⁻², the roach population was 0.15 m⁻², and that for dace Leuciscus leuciscus , 0.02 m⁻². The population density for all sizes of all species caught was estimated to be 2.25 fish m⁻².
The fish biomass available to the angler was 447 kg ha⁻². The rate of exploitation of the fishery over the period of sampling was high at 17%, representing an annual exploitation rate of 94%.     

Early effects of excess cadmium uptake in Phaseolus vulgaris

Abstract. Seedlings of Phaseolus vulgaris were exposed to solutions containing Cd²⁺ in the range 0 to 1 molm⁻³. Ethylene formation started following 3 h of exposure to 10⁻², 10⁻¹ and 1 mol m⁻³ Cd²⁺, peaked at 18 h and returned to a relatively low rate after 24 h. Cadmium-induced ethylene formation depended on the formation of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminoethoxyvinylglycine (AVG, 0.1 mol m⁻³) inhibited ACC accumulation and ethylene production during exposure to 0.2 mol m⁻³ Cd²⁺.
Activity of soluble and ionically-bound peroxidase increased after 18 h of exposure to Cd²⁺ concentrations above 10⁻³ mol m⁻³ due to an increase in activity of cathodic isoperoxidases. Stimulation of soluble and ionically-bound peroxidase by 0.2 mol m⁻³ Cd²⁺ was reduced in the presence of 0.1 mol m⁻³ AVG.
Accumulation of soluble and insoluble ('ligninlike') phenolics was found in plants exposed to Cd²⁺ (10⁻² mol m⁻³ or above) in the presence or absence of AVG. Deposition of insoluble (autofluorescing) material occurred in cell walls around vessels and was associated with reduced expansion and water content of leaves.     

Comparative primary productivity of algal epiphytes on three species of macrophyte in the littoral zone of Lake Ohrid, Yugoslavia

Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton , and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using ¹⁴C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non-miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.
Mean total surface area available for epiphytic colonization during the study period was 1.032 m² macrophyte surface per m² of littoral zone for Phragmites , 0.810 m² for Potamogeton , and 0.167 m² for Nuphar . Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light-compensation depth ranged from 84–1406 mg C m⁻² littoral zone d⁻¹; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m⁻² littoral zone d⁻¹, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m⁻² littoral zone d⁻¹. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m⁻² littoral zone yr⁻¹. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.     

Effect of ultraviolet radiation on accumulation and leakage of 86Rb+ in guard cells of Vicia faba

The effects of UV-C (254 nm), UV-A (365 nm) and broad-band UV (280–380 nm) on guard cells of Vicia faba L. cv. Long Pod were investigated in the presence of white light (450 μmol m⁻² s⁻¹). UV-C (7 μmol m⁻² s⁻¹) was found to cause leakage of ⁸⁶Rb⁺ from guard cells, while UV-A (0.3 μmol m⁻² s⁻¹) stimulated increased uptake in these cells. A relatively small stimulatory effect was observed by broad-band UV (3 μmol m⁻² s⁻¹) during the first 30 min of irradiation with an apparent equilibration of influx and efflux thereafter. Leakage of ⁸⁶Rb⁺ from guard cells continued despite the removal of UV-C and an increase in the amount of white light from 450 to 1500 μmol m⁻² s⁻¹, suggesting that membranes were irreversibly damaged. Irradiation of guard cells with UV-C for 30, 45 and 90 min indicated that these cells began to be affected already by 30 min UV-C irradiation.     

Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake

SUMMARY. 1. Regeneration of ammonium and phosphate by macro-zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×10⁴ and 3×10⁵ individuals m⁻².
2. Phosphate regeneration ranged from 0.2 to 1.3 μ mol PO₄ m⁻² b⁻¹at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO₄ m⁻² h ⁻¹ at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH₄ m⁻² h⁻¹. respectively.
3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.     

Light effects on in vitro adventitious root formation in axillary shoots of mature Prunus serotina

Light effects on in vitro adventitious root formation in axillary shoots of a 95-year-old black cherry ( Prunus serotina Ehrh.) were examined using microcuttings derived from cultured vegetative buds. Three studies were performed: 1) complete darkness and 4 levels of continuous white light irradiance were tested at 70, 278, 555 and 833 μmol m⁻² s⁻¹; 2) white, red, yellow and blue light were tested to assess the importance of spectral quality; and 3) the effect of blue light at intensities of 7,15, 22 and 30 μmol m⁻² s⁻¹ was also studied, Measurements included rooting percentage, total number of roots per shoot, and shoot and root dry weight. There was a strong negative effect of white light intensity upon root formation. Blue light between 15 and 22 μmol m⁻²: s⁻¹ significantly retarded root formation and completely inhibited it at 36 μmol m⁻² s⁻¹. Shoots treated with yellow light exhibited the highest rooting percentage, mean number of roots per shoot, and root dry weight.     

Plasma steroid concentrations in relation to the reproductive cycle of cultured male Rhamdia quelen

Seepage water through a lake bottom and the layering of tight and high-permeable layers in the aquifer produce groundwater under greater pressure than the water column of the lake. This results in under-water springs and seepages. When spawning substrata were available, there was a spatial correlation between the degree of groundwater influx and the redd density of brown trout Salmo trutta . In high density spawning areas with > 100 observed redds ha⁻¹, the mean seepage water influx during spring was c . 1200 ml m⁻² min⁻¹ compared to a mean flux of 113 ml m⁻² min⁻¹ in low density spawning areas with 5–10 redds ha⁻¹.     

Influence of UV-B radiation on developmental changes, ethylene, CO2 flux and polyamines in cv. Doyenne d'Hiver pear shoots grown in vitro

In vitro shoots of cv. Doyenne ďHiver pear ( Pyrus communis L.) were irradiated under controlled environments for 6 h per day at 5 different levels of biologically effective UV-B radiation (UV-B_BE). UV-B exposure caused a progressive increase in apical necrosis above background levels and stimulated leaf abscission. Shoots grown for 2 weeks at 7. 8 mol m⁻² day ⁻¹ of photosynthetic photon flux (PPF) and treated with 8. 4 or 12. 0 kJ m⁻² day ⁻¹ UV-B_BE produced up to 4 times more ethylene than those given 2. 2 or 5. 1 kJ m⁻² day⁻¹ UV-B_BE or untreated controls. Exposure of shoots to 12 kJ m⁻² day ⁻¹ of UV-B_BE caused an increase in free putreseine content after 4 to 14 days of irradiation. Shoots showed a decrease in CO₂ uptake after 3 days of UV-B: thereafter, they appeared to recover their photosynthetic capacity. Under typical PPF conditions used in micropropagation (90 μmol m⁻² S⁻¹). 8. 4 kJ m⁻² day ⁻¹ of UV-B radiation was injurious to realatively tender tissues of in vitro pear shoots: increasing the level of UV-B_BE to 12 kJ m⁻² day⁻¹ produced even more adverse effects.     

The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds

Yolk-sac pike fry were stocked at densities of 0.74 – 81.4 m⁻² in two ponds, each divided into eight sectors (mean area 155.8 m²). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size-range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density-independent but switched by late June/July to density-dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May-July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm⁻² and in Pond 2 was 3.49gm⁻².
Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m⁻².
Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m⁻² is advised if large, density-dependent mortalities are to be avoided.     

Development of leaf thickness for Plectranthus parviflorus – Influence of photosynthetically active radiation

Photosynthetically active radiation (PhAR) is apparently the environmental factor having the greatest influence on leaf thickness for Plectranthus parviflorus Henckel (Labiatae). A four-fold increase in leaf thickness from 280 to 1170 μm occurred as the PhAR was raised from 1.3 to 32.5 mol m⁻² day⁻¹. Compared to a constant PhAR of 2.5 mol m⁻² day⁻¹, a PhAR of 32.5 mol m⁻² day⁻¹ for one week during the first week (with return to 2.5 mol m⁻² day⁻¹ during the second and third weeks) led to an increase in final leaf thickness by 323 μm (to 802 μm). When increased PhAR was applied during the second week the increase in final thickness over the control was 217 μm, and when increased PhAR was applied during the third week it was 99 μm. However, leaf thickness was not simply responding to total daily PhAR, since a leaf 450 μm thick could occur at a low instantaneous PhAR for a long daytime (total daily PhAR of 1.5 mol m⁻² day⁻¹) and at a high PhAR for a short daytime (4.5 mol m⁻² day⁻¹). Total daily CO₂ uptake (net photosynthesis) was approximately the same in the two cases, suggesting that this is an important factor underlying the differences in leaf thickness. Leaf thickness is physiologically important, since thicker leaves tend to have greater mesophyll surface area per unit leaf area ( A ^mes/ A ) and hence higher photosynthetic rates.     

Localization of Fe-containing superoxide dismutase in cyanobacteria from the Baltic Sea: depth and light dependency

The abundance and cellular location of Fe-containing superoxide dismutase (Fe-SOD) in trichomes of Nodularia , Aphanizomenon and Anabaena collected from various depths in the Baltic Sea, and in trichomes of a cultured Nodularia strain, BC Nod-9427, isolated from the Baltic Sea, was examined by immunogold labelling. For trichomes collected from natural populations the areal concentration of Fe-SOD labelling decreased with depth: trichomes collected from surface accumulations had between 8 and 11 gold particles μm⁻² whereas trichomes collected from a depth of 18 m were unlabelled. When trichomes collected from a depth of 10 m (mean areal labelling density 0·5 gold particles μm⁻²) were exposed to the higher irradiances present at 1 m, the areal concentration of Fe-SOD increased to 3·5–4 gold particles μm⁻² within 4 h. When cultures of Nodularia strain BC Nod-9427, adapted to low light (10 μmol m⁻² s⁻¹), were transferred to an incident irradiance of 1350 μmol m⁻² s⁻¹, a doubling of the areal concentration of Fe-SOD gold label was observed within 1 h. Addition of 3-(3,4-dichlorophenyl)-1,1'-dimethylurea (DCMU) to cultures immediately before their transfer to increased illumination resulted in a decrease in areal Fe-SOD concentrations whereas addition of CdCl₂ caused an increase over and above that induced by the elevated irradiance. These results suggest that Baltic Sea cyanobacteria are able to modulate their Fe-SOD content but that this might be in response to oxidative stress rather than to light per se .     

The distribution and production of Gammarus pseudolimnaeus (Crustacea: Amphipoda) along a reach of the Credit River, Ontario

SUMMARY. The population density of the univoltine amphipod Gammarus pseudolimnaeus was estimated monthly from April 1977 to June 1978 along a 600-m reach using a form of removal sampling at 0.5, 1.5 and 2.5 m from the bank. The probability of catching an amphipod with three sweeps over an area of 0.15 m² was 0.95. Drift and upstream migration were measured for 24 h, also monthly. Population density varied from 1600 m⁻² (newly-hatched young in July) to 26 m⁻² (adults) within 3 m of the bank with 95% confidence limits of 40–60% of the mean; density was highest < 1 m from the bank and beyond 3 m it declined to insignificant levels. No significant difference could be shown between the total catches in the drift and upstream nets over a year and there appeared to be no net migration of amphipods. Mean drift was 2 amphipods day⁻¹.
Growth was estimated from the length composition of monthly samples. Annual production ( P ) was 29.4 kg ha⁻¹ for one generation of the amphipod with a P/B ratio of 4.65. Egg production accounted for only 2% of this estimate. Recruitment was calculated from regressions relating female length to clutch size and egg development time to temperature in the laboratory; mean temperature was measured in the field.
Mortality was greatest in July at the beginning of the generation. It was high again in September and during winter; at these later times it was suggested that starvation occurred in addition to predation. Annual consumption ( C ) of organic matter for the generation calculated from published data on feeding rate was 1547 kg ha⁻¹ which results in a P/C ratio of 1.9%.     

Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid-May to mid-June. Tiny nymphs occurred from June to late August.
2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day⁻¹), very low from November to February (0.8% wet wt day⁻¹) and high until emergence (2.3% wet wt day⁻¹); short day length seemed to be the major factor reducing growth rate during winter.
3. Mortality was close to zero during winter and 1.4—1.7% day⁻¹during other seasons. Total mortality from egg to adult was 99.6%.
4. The annual production was about 9g wet wt m⁻² year⁻¹ and the annual P/ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m⁻² day⁻¹) and zero in February.     

Effect of temporary changes in light intensity on carbon transport, partitioning and respiratory loss in young tomato seedlings raised under different light intensities

Tomato plants were grown under light intensities of 36 or 90 W m⁻² [photosynthetically active radiation (PAR)], and then the light intensity was changed to 36, 90 or 180 W m⁻² for 8 h to investigate the effect of temporary changes in light intensity on the carbon budget of photoassimilates from the third leaf using a ¹⁴CO₂ steady-state feeding method. In the plants that were raised under 90 W m⁻², the photosynthetic rate increased when the light intensity was increased to 180 W m⁻², whereas no increase occurred in the plants that were raised under 36 W m⁻². Although the total amount of carbon fixed during the 8-h light period showed a large difference between plants grown at the two initial light intensities, the proportion of carbon exported during the light period did not differ apparently, irrespective of the change in light intensity. However, the amount of carbon exported during the time course was higher in plants that were raised under 90 W m⁻² than those raised under 36 W m⁻², irrespective of the change in light intensity. The partitioning pattern of ¹⁴C-photoassimilates was not changed by the change in light intensity, irrespective of whether the light intensity was increased or not. However, the amount of ¹⁴C-photoassimilates accumulated in each part differed according to the two initial light intensities. The carbon transport from a source leaf was also investigated through a quantitative analysis of carbon balance.