Diurnal stratification, photosynthesis and nitrogenfixation in a shallow, equatorial Lake (Lake George, Uganda)

From a series of experiments and measurements covering one 24-h period in Lake George the diurnal patterns of photosynthesis, nitrogen-fixation and stratification are described. The thermal cycle shows three distinct phases of isothermy, intense stratification and mixing. During stratification the surface water temperature reached 36°C, whereas the bottom temperature remained at 25°C. The phytoplankton are evenly distributed at dawn, sink out during the day and tend towards an even redistribution as thermal stratification breaks down. Depth-time profiles of oxygen concentration and pH values showed that intense photosynthetic and respiratory activity occurred. The shortness of the predominant limnological cycle is thought to be instrumental in restricting species fluctuations. Changes of total CO2 concentration in situ within the euphotic zone indicated that 2.25 g C/m².12 h were photosynthetically fixed during daytime. From changes of in situ oxygen concentration, gross photosynthesis was estimated to be 12 g O₂/m².12 h and net particulate production over 24 h as zero. Photosynthetic activity was also measured with the i^C and oxygen techniques by enclosing algal samples in light and dark bottles. The patterns of activity recorded by the two methods were similar, although quantitatively the oxygen method gave rather higher values than did the method. Daily gross photosynthesis was estimated as 15.56 g O₂/m².12 h and 4.5 gC/m².12 h. These figures are compatible with one another and with the production estimates calculated from Tailing's model of integral daily photosynthesis. The balance between respiration and photosynthesis is described as a function of the underwater light climate and the relative rate of respiration. Both the experimental and theoretical approaches suggest that the column 24-h net particulate production is an extremely small percentage of gross photosynthesis. Nitrogen-fixation was measured using both the ¹⁵N₂ and the acetylene reduction techniques. The day-long incubation of the ¹⁵N₂ experiment showed that 11 mg N/m².day were fixed. The series of shorter acetylene reduction experiments gave a value of 58 mg N/m².day. The acetylene technique showed relatively high nitro-genase activity at very low light intensities. The ¹⁵N₂ results indicated little N2-fixation at low light intensities. The differences between the two techniques are discussed. Gross photosynthesis estimates calculated from seven different methods run simultaneously are compared. The figures show reasonable agreement, but since the gaseous environment in the euphotic zone is particularly suitable for photo respiration the values are not considered reliable estimates of phytoplankton photosynthesis.     

Fungal diseases of fish in Nanak Sagar,Naini Tal,India

Forty nine patients with mycologically confirmedTinea cruris were investigated for the association of hypersensitivity to trichophytin and the isolation of dermatophytes from clinically normal sites with chronicity and recurrence of infection. At the end of six months following specific therapy, 24 patients returned for follow up and they were similarly studied. Dermatophytes were isolated from clinically asymptomatic sites in 46% patients before treatment and in 21% of the patients on follow up. Immediate weal reaction and increased concentration of IgE antibodies were seen in 73% and 80% of the patients respectively. However, the delayed hypersensitivity reaction was more associated with patients having lesions for more than 6 months (48%) in comparison with patients with a short history (17%). On follow up after 6 months, the different hypersensitivity reactions and IgE antibody concentration maintained more or less the same association. Therefore in persistent or recurrentTinea cruris infection, besides potential carriage in clinically normal sites, hypersensitivity to antigens of dermatophytes possibly plays an important role in pathogenicity.     

Photosynthetic potential of phytoplankton in the deep water of Lake Baikal,Russia

We examined the photosynthetic activity of the phytoplankton community collected from the surface to a depth of 1000m in the south basin of Lake Baikal. Experiments were conducted in June (mixing period) and August (stratified period). The carbon fixation rate was measured by the use of a ¹³C tracer after the incubation of samples under light conditions in the upper water column. Photosynthetic fixation of ¹³C was detected for samples collected from a depth of 500m, indicating the viability of phytoplankton in deep water. The community composition was dominated by Bacillariophyceae in deep water. The finding of lower activity at a depth of 200m than that at a depth of 500m in August suggests that the spring diatom bloom could be a significant source of viable populations at a depth of 500m. Photosynthetic activity was not detected in samples collected at a depth of 1000m.     

Ixodes trianguliceps (Parasitiformes, Ixodidae) in the southern Lake Baikal area

In the southern Lake Baikal area, in the region of the Khamar-Daban ridge, which borders the banks of Lake Baikal, there was found in abundant population the tick I. trianguliceps. Data on the ecology of the tick in this particular part of its distribution area and on its ecological links revealed by factor analysis of the tick's habitat of the first and second order by means of electronic computers are given.     

Diurnal variation in algal acetylene reduction (nitrogen fixation) in situ

Diurnal variation in algal nitrogen fixation was studied in Lake Mendota, Wisconsin, during the summers of 1971 to 1973. Approximately two-thirds of the daily acetylene reduction in the surface decimeter occurred before noon. The decline in acetylene reduction (nmoles/liter·hr) near midday was partially because the algae relocated themselves at greater depths. However, acetylene reducing activity (nmoles per A₆₆₃ unit chlorophyll a per hour) also decreased as midday approached. Occasionally algae would resurface near the end of the day. On average, acetylene reduction (nmoles per liter per hour) was maximum at about 0900 Central standard time in the top decimeter, and acetylene reduction between 0830 and 0930 Central standard time represented 13% of the total daily acetylene reduction. Furthermore, acetylene reduction in the top decimeter, on average, represented 3.6% of the total acetylene reduction in the column. Calculation of the contribution by nitrogen fixation to a lake's fixed nitrogen budget is discussed.     

Studies on the Primary Production of Phytoplankton in Suraha Lake (Ballia,India)

The paper describes the seasonal variation in the rate of phytoplankton primary production in Suraha Lake – a large shallow water body – in relation to certain physico-chemical parameters and the abundance and composition of the phytoplankton over a period of two years.     

Morphological variation of Keratella cochlearis (Gosse) in Lake Biwa,Japan

The length of the lorica (LL) of Keratella cochlearis cochlearis and of K. cochlearis tecta and the length of posterior spine (PSL) of the latter morphotype were measured in the strongly eutrophic basin and also in the mesotrophic basin of Lake Biwa, Japan, from September to December, 1980. In the population from the mesotrophic basin, the individuals with longer PSL prevail and the tecta forms are extremely rare. The LL values of both morphotypes from one sample do not differ. In December the LL increased to 95 µm in both morphotypes from 80 µm observed in September, while the PSL values decreased abrubtly in both basins in the middle of this period. It is suggested that the observed increase of LL could be related to the thermic factor, i.e. a steady decrease of water temperature, and the changes of PSL are correlated with the increase of nannoplankton and detritus aggregates noted in November. In this month an increase in fecundity and in the total numbers of rotifers took place as well (Hillbricht-Ilkowska, in press).     

A comparison of the abilities of three sympatric species of Petrotilapia (Cichlidae,Lake Malawi) to penetrate deep water

Synopsis The ability of three sympatric species ofPetrotolapia, from Monkey Bay, Lake Malawi, to penetrate deep water was tested using pressure chambers. The three species were found to differ in terms of the maximum pressure (= depth) to which each was able to equilibrate. Mean maximum equilibration pressures were for the form designated MOL 39.0 m, for MBB 35.5 m and for the form MOC 30.4 m. The rate of compensation to pressure changes was slower in MBB (2.59 m day^–1) than in other two forms (MOL = 3.97 m day^–1, MOC = 3.98 day^–1). Natural depth distribution of all three forms, in particular MBB and MOC, is not determined by limits imposed by swin bladder physiology.     

First survey of fungi in hypersaline soil and water of Mono Lake area (California)

Mono Lake is a closed lake located in central California, east of the Sierra Nevada mountains. It contains dissolved carbonates, sulfates and chlorides at high concentrations. Due to its high salinity, Mono Lake was sometimes compared to the Dead Sea. However, it appears that Mono Lake water and vicinity abound with life. In this work, the fungal flora living in this extreme ecosystem was studied for the first time. Soil, tufa, water and sediment samples were also analyzed for their mineral and salt composition. Results showed that water was particularly rich in sodium, potassium, phosphorus and boron. Soil and sediments contained very high levels of calcium and magnesium, but also barium, boron and strontium. Sodium, phosphorus and iron levels varied in a large extent from one to another sample. Neutral to very alkaline pH were recorded. Water samples were found sterile in the conditions chosen for fungi isolation, while sediment, soil and tufa samples led to the isolation of a total of 67 fungal species (from 23 samples), belonging to various taxonomic groups. From our results no clear effects of the chemical parameters of the samples were observed on fungal life apart from the pH. The methods chosen did not allow the isolation of extremely halotolerant species. We isolated in this work a series of ubiquitous species, suggesting that a selection of resistant and/or adaptable strains of some common species could have occurred. Depending on the medium and the temperature of isolation, it can be hypothesized that some species were present as dormant structures, while some others, isolated at pH 8 on a medium enriched in Na and Ca, could be in a growing form adapted to alkaline and saline conditions. This work contributes to a better knowledge of the mycobiota present in the Mono Lake's ecosystem.     

Morpho-Functional Groups and phytoplankton development in two deep lakes (Lake Garda,Italy and Lake Stechlin,Germany)

Phylogenetic classifications of plants often do not reflect their ecological functions. In fact, the functional mechanisms of biological communities may be better understood if species are pooled into groups having similar characteristics. The objective of this work is to evaluate, with the use of multivariate methods, classifications based on the morphological and functional characteristics (size and form, mobility, potential mixotrophy, nutrient requirements, presence of gelatinous envelopes) of cyanobacteria and eukaryotic algae to explain the seasonal dynamic of the phytoplankton community. The analyses involve data from two deep lakes: Lake Garda, southern Alps, z _max = 350 m; biennium 2002–2003) and Lake Stechlin (north-east Germany, z _max = 67 m; 1995, 1998 and 2001). In both lakes, the temporal evolution of the phytoplankton communities within individual years followed a regular annual cycle, with the exception of Lake Stechlin in 1998, when an irregular phytoplankton pattern was caused by a sudden mass appearance of Planktothrix rubescens in the spring and summer months, resulting in a collapse of the whole community in autumn. Overall, the temporal developments of the phytoplankton communities obtained on the basis of patterns of the morpho-functional groups appeared highly comparable with those obtained, in the single years, on the basis of the original phytoplankton species matrices. The comparison of the morpho-functional groups of the lakes Garda and Stechlin showed important differences in the abundance and seasonality of the dominant phytoplankton types. The results obtained in this study underline that the use of classifications based on the adaptive strategies of the single species may represent a useful tool to investigate the community evolution and to compare phytoplankton assemblages of different lakes, overcoming problems related to possible differences of taxonomic accuracy and identification.     

Morphological variation in the deep ocean-dwelling coccolithophore Florisphaera profunda (Haptophyta)

Detailed analysis of the morphology of Florisphaera profunda from plankton samples collected at three sites in the Atlantic and Pacific Oceans reveals wide variation in this deep ocean-dwelling coccolithophore. In addition to the two varieties described previously, we found a third distinctive form, Florisphaera profunda var. rhinocera var. nov. All three varieties occur at each of the sampling sites. The analysis of monthly samples from different levels in the lower photic zone (LPZ) (100–200?m) at the Hawaii Ocean Time series station suggests that the varieties have similar distributions, which are correlated to primary productivity and the availability of light. The analysis of coccolith and coccosphere size in F. profunda reveals the existence of several size modes in Florisphaera profunda var. profunda and F. profunda var. elongata. The biological significance of these modes, or morphotypes is not known. However, their co-occurrence in single samples from different oceanic areas suggests that they are not ecophenotypes. In the light of recent molecular genetic analyses of intraspecific groups within commonly occurring coccolithophores, the varieties and size morphotypes of F. profunda are of significant interest for the study of marine phytoplankton biodiversity. Coccolithophores inhabiting the LPZ may be adapted to the low light, high nutrient conditions of this layer and hold great potential as a means to reconstruct past oceanographic conditions such as the position of the nutricline. However, coccolithophore biodiversity in the LPZ is poorly documented and the number of species may be much higher than previously thought.     

Seasonal variation in the plankton of Porto Novo Waters (India)

Summary The seasonal variations of marine (collected at the ten fathom line-Station A) and estuarine (collected at the Mouth of the Vellar estuary-Station I) plankton of Porto Novo (India) are described, covering the period 1960–63. The biological, temporal and numerical variations of phytoplankton and zooplankton are described for the two stations. The succession of species was more or less similar at both stations, but certain forms like colonial Radiolaria, Scyphomedusae, Anthozoa, trochophore of Sipunculids, Stomatopod larvae and Protochordate larvae were relatively more confined to Station A, and crustacean larvae other than Stomatopods Actinotrocha larva, fish eggs and larvae were relatively more confined to Station I.The Diatom main peak was about June–July at Station A and about May–July at Station I. The Diatom peak was generally heralded with the appearance of Coscinodiscus. Noticluca usually showed three spurts- mainly two distict ones about May–June and August. The third development was only during certain years and not so intensive. Copepods showed two peaks generally during June–July after few days of the Diatom bloom, and during October–November following the first monsoon rains.The peaks of Diatoms, Peridinians, Noctiluca, Molluscan larvae and Tunicate larvae were more marked at Station A than at Station I. A rich and varied zooplankton was observed about February at Station A. The appearance of salps at Station A seems in a way to be related to salinity, when the salinity values were between 28.89–34.55, the salps appearing more with a fall in salinity. Similarly at Station I, Creseis acicula, Prawn larvae and fish larvae seem to be associated with a sudden fall in temperature and salinity when the monsoon rains start, at Station I.The numerical relationship of plankton at Station A was generally inverse between phyto- and zooplankton and this was generally parallel at Station I.

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Sumario La variación estacional del plancton marino (collectado en la ten fathom lineestacción A) y estuarino (Mouth of the Vellar estuary) és descrita para el período 1960–63. Las variaciones biológicas, temporales y numéricas del fitoplancton y del zooplancton son descritas para las dos estacciones. La succesión de especies fué más o menos comparable en las dos estacciones; algunas formas como colonial radiolaria, scyphomedusae, anthozoa, trochophore y sipunculids, stomatopod larvae, y protochordate larvae fuéron confinadas a la estacción A, y otras como crustacean larvae, Actinotrocha larva, peces eggs y larvae confinades a la estacción I.El maximum para las diatomeas ocurrió en Junio–Julio en la estacción A,y Mayo–Junio en la estación I. Las diatomeas están representadas principalmente por el génere Coscinodiscus antes del maximum. El maximum para Noctiluca fue observado en Mayo–Junio y en Agosto. Los copepodes presentaran dos períodos de maximum Junio–Julio despues del maximum de las diatomeas y en Octubre–Noviembre. El maximum de las diatomeas, peridianians, Noctiluca, molluscan larvae y tunicate larvae en la estacción A fué mas distincto que en la estacción en el estuario. El zooplancton se mostró rico y variado en Febrero en la estacción A.La presencia de salpas en la estacción A parace ser relacionada en ciertos aspectos con la diminuición de la salinidad cuando esta fué 28.89–34.55. Por la misma forma la presencia de Creseis acicula, prawn larvae, peces eggs y larvae parace ser relacionada con diminuición de salinidad y temperatura del agua durante Octobre–Noviembre–Deciembre en la estacción I. Las relaciones numéricas del plancton indican que en la estacción A fueran contrarias y en la estacción I paralelas.

     

Diurnal variation in thermal and metabolic parameters of the golden hamster (Mesocricetus auratus)

The purpose of this study is to examine diurnal variation in several thermal and metabolic parameters of the golden hamster, Mesocricetus auratus. Metabolic rate, core temperature, and evaporative water loss were measured during night and day at several ambient temperatures. Wet minimal thermal conductance, dry minimal thermal conductance, basal metabolic rate, minimal net heat production and the lower critical temperature difference were estimated from these measurements. Wet and dry minimal thermal conductance, evaporative water loss, core temperature, basal metabolic rate, and lower critical temperature difference were greater during the active phase than during the resting phase. The diurnal variation in wet minimal thermal conductance was much smaller than that predicted from published allometric equations. The diurnal variation in wet minimal thermal conductance was 9% of the 24-h mean. The diurnal variation in dry minimal thermal conductance was 26% of the 24-h mean. The higher active-phase core temperature and basal metabolic rate may function to enhance peak metabolic performance during the active phase. The lower resting phase metabolism and core temperature may reduce energetic costs. The greater active-phase lower critical temperature difference may be a result of the greater active-phase basal metabolic rate. Diurnal variation in minimal thermal conductance may be caused by changes in peripheral circulation.Abbreviations BMR basal metabolic rate - T difference between core and ambient temperatures - T _1c lower critical temperature difference - EWL evaporative water loss - MTC minimal thermal conductance - MR metabolic rate - Q _ev evaporative heat loss - RQ respiratory quotient - T _a ambient temperature - T _c core temperature - T _1c lower critical temperature     

Ecological studies on Chaoborus (Diptera, Chaoboridae) in Lake George, Uganda

(1) Chaoborus anomalus and Chaoborus ceratopogones were found together throughout the year in Lake George, Uganda, the larvae forming 65-85% by number of the macro-benthos of the central lake area. (2) First and second instar larvae were wholly planktonic and third and fourth instar larvae mainly benthic during the day, migrating into the water column at night. A proportion of the third and fourth instar larvae were found in the water column during the day in the centre of the lake where light attenuation was greatest. C. anomalus showed a greater tendency to be benthic than C. ceratopogones. (3) Planktonic larvae were distributed in dense patches thought to be cohorts resulting from oviposition by swarms of adult females. The maximum density of planktonic larvae recorded was 31.7 × 10²/m² column. Third and fourth instar larvae were more evenly distributed in the benthos of the central lake area, the maximum density recorded was 79.9×10²/m². (4) First and second instar larvae occurred mainly in the inshore regions, very few were found in the centre of the lake. Oviposition is likely to take place inshore. The patches of planktonic larvae were not stationary. Dispersal of larvae away from the shore may be active or may result from complex oscillations of the water mass produced by storms. In C. ceratopogones the floating egg batches could he carried away from the north shore by currents produced by inflows and prevailing winds. (5) Adults of C. ceratopogones were more numerous during the rainy seasons than during the dry seasons. A similar, though less marked seasonality was found in the occurrence of C. anomalus adults. The biomass of benthic larvae of C. ceratopo-gones was estimated at 387.0 mg C/m² in the dry season, June 1970, and 130 0 mg C/m² in the rainy season, October 1970. That of C. anomalus was constant at 241.7 and 254.3 mg C/m² in June and October, 1970 respectively. (6) No difference was found in the horizontal distribution of the larvae, or in the size and weight attained by the various stages. (7) Interspecific differences were found in the mean number of eggs per adult female (309, C. anomalus and 224, C. ceratopogones); in the nature ofthe egg batches; n i the morphology of the larval mouthparts and pharyngeal sphincters, as well as i n the vertical distribution of the larvae and seasonal occurrence of the adults. On the basis of these differences the co-existing species are thought not to be competing for the same resources.     

Diurnal variation in temperature, mental and physical performance, and tasks specifically related to football (soccer)

Football (soccer) training and matches are scheduled at different times throughout the day. Association football involves a variety of fitness components as well as psychomotor and game-related cognitive skills. The purpose of the present research, consisting of two separate studies, was to determine whether game-related skills varied with time of day in phase with global markers of both performance and the body clock. In the first study, eight diurnally active male association football players (19.1+/-1.9 yrs of age; mean+/-SD) with 10.8+/-2.1 yrs playing experience participated. Measurements were made on different days at 08:00, 12:00, 16:00, and 20:00 h in a counterbalanced manner. Time-of-day changes in intra-aural temperature (used as a marker of the body clock), grip strength, reaction times, flexibility (markers of aspects of performance), juggling and dribbling tasks, and wall-volley test (football-specific skills) were compared. Significant (repeated measures analysis of variance, ANOVA) diurnal variations were found for body temperature (p<0.0005), choice reaction time (p<0.05), self-rated alertness (p<0.0005), fatigue (p<0.05), forward (sit-and-reach) flexibility (p<0.02), and right-hand grip strength (p<0.02), but not left-hand grip strength (p=0.40) nor whole-body (stand-and-reach) flexibility (p=0.07). Alertness was highest and fatigue lowest at 20:00 h. Football-specific skills of juggling performance showed significant diurnal variation (p<0.05, peak at 16:00 h), whereas performance on the wall-volley test tended to peak at 20:00 h and dribbling showed no time-of-day effect (p=0.55). In a second study, eight diurnally active subjects (23.0+/-0.7 yrs of age) completed five test sessions, at the same times as in the first study but with a second session at 08:00 h. Test-re-test comparisons at 08:00 h for all components indicated good reliability. Intra-aural temperature showed a significant time-of-day effect (p<0.001) with mean temperature at 16:00 h (36.4 degrees C) higher than at 08:00 h (35.4 degrees C). There was no significant effect of chronotype on the temperature acrophase (peak time) (p>0.05). Diurnal variation was found for performance tests, including sit-and-reach flexibility (p<0.01) and spinal hyper-extension (p<0.05). Peaks occurred between 16:00 and 20:00 h and the daytime changes paralleled the temperature rhythm. Diurnal variation was also found for football-specific tests, including dribbling time (p<0.001, peak at 20:00 h) and chip test performance (p<0.01), being more accurate at 16:00 h (mean error=0.75 m) than at 08:00 h (mean error=1.01 m). Results indicate football players perform at an optimum between 16:00 and 20:00 h when not only football-specific skills but also measures of physical performance are at their peak. Body temperature peaked at a similar time, but positive mood states seemed to peak slightly earlier. While causal links cannot be established in these experiments, the results indicate that the diurnal variation of some aspects of football performance is affected by factor(s) other than body temperature alone.     

Seasonal variation in pigmentation of the dinoflagellate Peridinium gatunense (Dinophyceae) in Lake Kinneret, Israel

1. Pigment composition was measured in natural phytoplankton samples from Lake Kinneret, Israel. From March through June 1998, the dinoflagellate Peridinium gatunense Nygaard mostly contributed more than 95% of the algal biomass. Peak densities were found in April, close to the water surface, with >10⁹ cells m^?3, chlorophyll (Chl) a concentration of 380 mg m^?3 and areal Chl‐a density of >1300 mg m^?2. 2. Cellular concentrations of Chl‐a changed between 201 and 282 pg cell^?1, but did not show a defined temporal fluctuation. 3. The mass ratio of Chl‐c to Chl‐a changed from March to June between 0.16 and 0.22, and the peridinin to Chl‐a ratio changed from 0.25 to 0.41. Neither ratio showed a clear pattern of seasonal change. Conversely, there was a progressive increase in diadinoxanthin and β‐carotene ratios to Chl‐a through the season, parallel to the increase in photon flux impinging upon the lake surface. The diadinoxanthin to Chl‐a ratio changed from 0.11 to 0.28 and the β‐carotene to Chl‐a ratio varied from 0.03 to 0.08 from March through June. 4. Diatoxanthin was not detected in natural samples. However, it was present in experiments with P. gatunense cultures, when concentration of diatoxanthin increased rapidly, concurrent with a decrease in diadinoxanthin and β‐carotene concentrations, while Chl‐c and peridinin ratios to Chl‐a were almost stable with photon flux increase. 5. The seasonal variation in cellular pigmentation of P. gatunense in Lake Kinneret suggests that accumulation of photoprotective pigments is essential for optimisation of photosynthetic activity of this large dinoflagellate.