Search

We study the dynamics of bloom-forming cyanobacteria and determined the major driving forces in subtropical lake of the Kumaun Himalayas, India. Water and plankton samples from different sites and depths of the lake were analyzed. Multivariate analyses were used to evaluate the factors controlling the distribution pattern of cyanobacteria.

Understanding the ecological mechanisms driving the dynamics of field rotifer populations remains a challenge in ecology. Brachionus angularis (Rotifera) is preferred in such studies because of their planktonic behavior, high fecundity, and absence of cryptic species. In this study, one-year zooplankton samples were collected twice a month from a subtropical lake and the roles of abiotic and biotic factors regulating the population dynamics of B. angularis were analyzed. The sampled B. angularis were composed of two discontinuous populations: ‘summer and autumn’ and ‘spring and winter’, segmented by high mixis rates. The ‘summer and autumn’ population had high egg ratios, but low egg volumes. Water temperature was the main factor driving temporal dynamics in density, thereby counteracting the negative effect of top-down force. Based on the synchronous dynamics of two fractions of chlorophyll-a, the densities of B. angularis, its potential competitors and predators, together with the reverse correlations between the egg ratio and population density, and Secchi-disk depth, we found that bottom-up and top-down forces were plausible factors regulating variations in population density in spring (March and April). However, the density peak of B. angularis in winter might be primarily ascribed to recruitment from the sediment. We further addressed the necessity for diverse evidence from the speciation of cryptic species, abundance, reproduction, and morphology, in understanding the population dynamics of a field rotifer population.

Summary 1. We use morphology-based functional groups (MBFGs) of phytoplankton to predict ecological performance of groups with a mechanistic model. We evaluate MBFGs’ performance in relation to hypothetical examples of succession and compare it with empirical data for a shallow subtropical hypertrophic lake (Lake Rodo, Uruguay). 2. Our model predicts a trade-off between maximum growth rate (μmax) and competitive ability (Tilman’s R*) for most MBFGs. The model predicts that phytoplankton succession will proceed from groups with high surface/volume, high μmax and without specialised structures (opportunists) towards the dominance of large colonial or filamentous algae with lower μmax and specialised traits (gleaners). These predictions are generally congruent with empirical data for Lake Rodo. 3. The MBFG classification explained ecological performance of phytoplankton community dynamics while reducing system dimensionality. Despite species aggregation, MBFGs can resolve the occurrence of potentially noxious groups and thus is a promising tool for understanding and managing ponds and lakes.

1. Lake Chicamba, Mozambique (19°08′S; 33°08′E) is a large (116 km2) impoundment in the headwaters of the Buzi River system, which was invaded by Oreochromis niloticus in 1996 from a small (

During two controlled enclosure experiments using water from a subtropical lake, the plankton food web displayed a highly variable response to combined addition of nitrogen and phosphorus. In July, the nutrients stimulated growth ofCylindrospermopsis raciborskii, and the biomass of macrozooplankton and microbial food web components did not increase. In October, the same addition of nutrients stimulated growth of small edibleLyngbyaspp., and there were coincident increases in biomass of macrozooplankton and components of the microbial web. Past generalizations that cyanobacteria blooms inhibit growth of other food web components may not always hold true.

Summary Excess loading of phosphorus (P) and nitrogen (N) triggers a shift in the trophic structure of shallow lakes from a clear-water, macrophyte-dominated state to an algal-dominated turbid state. However, the role of N in the shift is debated, and experimental evidence is, with a few exceptions, based on short-term studies (days to a few months). We studied the effect of N loading on macrophytes (dominated by Potamogeton lucens and Cabomba caroliniana), periphyton, filamentous algae and phytoplankton in mesocosms over 10 months (starting in October) in subtropical China (Wuhan). There were three N treatments: controls (CN) without nitrogen addition (mean TN = 1.9 mg L−1), low nitrogen (LN) addition (mean TN = 3.5 mg L−1) and high nitrogen (HN) addition (mean TN = 5.5 mg L−1). Total phosphorus (TP) concentration in the water column remained moderate (0.05–0.07 mg L−1) during the experiment in all treatments. Macrophyte abundance declined in the LN and HN treatments in the first 6 months, but not in controls, followed by a partial recovery in the LN treatments. They disappeared completely in the HN treatments the following summer. Periphyton (biofilm on plastic) and phytoplankton biomass remained unaffected during the first 6 months but increased over the summer by two or three times, compared with controls, in low and high nitrogen treatments, respectively. By contrast, the abundance of filamentous algae increased over winter but declined during the summer with no obvious relationship to the N treatments. There was no difference in the TN or nitrate concentrations or soluble protein, soluble sugar and Chl-a content of P. lucens leaves and stems with increasing N load. Macrophyte populations are partially resilient to abrupt increases in N loading at moderate TP concentrations, but, after prolonged exposure, a complete collapse occurs. Our results further indicate that macrophyte loss is exacerbated by shading by filamentous algae during the winter, and by phytoplankton and periphyton in the summer, while there was no indication of direct N toxicity.

Between January 1998 and January 1999 a quantitative investigation was done on the fish populations of Lake Tzaneen, Northern Province, South Africa. Two graded series of multi-filament gillnets were set overnight every six weeks capturing 14 species of fish. Of the 2 692 fish caught, Schilbe intermedius was most abundant both in number and weight. Significantly more fish were caught where the two major rivers, the Great Letaba and the Ramadiepa, enter the lake. The smaller gillnet sizes (30–70mm) caught the highest number of S. intermedius, while the 90mm gillnet caught the highest number of Oreochromis mossambicus. Female S. intermedius greatly outnumbered males. Significant differences were found between the monthly catch per unit of effort and the sampling site catch per unit of effort. Keywords: fisheries potential; population structure; freshwater fish; length-frequency distribution; catch per unit effort; Lake Tzaneen; South Africa (Afr J Aqua Sci: 2002 27(2): 151-157)

Growth rates of indigenous Oreochromis mortimeri and alien Oreochromis niloticus from Lake Kariba were estimated from samples collected in 1997–2000, 2003–2005 and 2010–2011. Growth zones on scales and otoliths of O. niloticus and on the otoliths and opercula of O. mortimeri were deposited annually. Age estimates obtained from otoliths, scales and opercula were similar for both species. Length at age was described by the von Bertalanffy equations L(t) = 32.4(1 − exp(−0.25(t + 2.3))) and L(t) = 30.2(1 − exp(−0.23(t + 3.73))) for O. niloticus and O. mortimeri, respectively, in 1997–2000, and by L(t) = 44.6(1 − exp(−0.29(t − 0.05))) and L(t) = 36.8(1 − exp(−0.64(t − 0.73))), respectively, in 2003–2005. There were more older (≥10 years) age classes and lower L ∞ in the 1997–2000 dataset for both species than in the later sampling periods. Mean length at age of O. niloticus was higher than that of O. mortimeri for the 1997–2000 dataset, but similar for the 2003–2005 dataset. This study supports the hypothesis that, in Lake Kariba, the alien O. niloticus has a higher growth rate than O. mortimeri , and infers its competitive advantage over the indigenous species.Keywords: ageing, comparison, invasive, Nile tilapia, non-nativeAfrican Journal of Aquatic Science 2014, 39(2): 167–176

337 Lake Donghu is a 32-km 2 shallow, subtropical lake near the Yangtze River (P.R. China) that has experienced dramatic changes in the past five decades. These changes include: (1) a trophic state change from mesotrophy to hypertrophy; (2) dense blooms of cyanobacteria during every summer from the 1970s to 1984; (3) a cessation of blooms starting in 1985, with no recurrence; and (4) an increase, coincident with bloom declines, in the production of silver and bighead carp (filter-feeders) by more than tenfold. There are several possible explanations for the disappearance of blooms, including changes in nutrient concentrations, increased zooplankton grazing, and increased grazing on algae by fish. The long-term data suggest that changes in nutrients or in zooplankton were not important, but that the remarkably increased fish densities might have played the key role. To test this hypothesis, in situ enclosure experiments were conducted in three years. The main conclusions are as follows: (1) an increased stocking of the lake with carp played a decisive role in the elimination of cyanobacteria blooms; (2) both silver and bighead carp can eliminate cyanobacteria blooms directly by grazing; (3) zooplankton cannot suppress the blooms; and (4) the lake still is vulnerable to the outbreak of blooms, should fish grazing decline. The critical biomass of carp is approximately 50 g m 3 . The results suggest the applicability of a new food-web manipulation (increased stocking with filter-feeding fish) for controlling cyanobacteria blooms in hypereutrophic lakes. The approach differs from traditional biomanipulation in Europe and North America, where piscivores are added to control planktivores, and this in turn increases zooplankton and decreases algae. The new biomanipulation method is being used or being tested to counteract cyanobacteria blooms in many Chinese lakes such as Lake Dianchi?Xie and Liu: Biomanipulation to Control Cyanobacteria TheScientificWorld (2001) 1, 337-356 in Yunnan Province, Lake Chaohu in Anhui Province, and Lake Taihu in Jiangsu Province. The method has great potential as an important component of an integrated approach to counteract cyanobacteria blooms, especially in lakes where nutrient inputs cannot be reduced sufficiently, and where zooplankton cannot effectively control phytoplankton production.

A method for identification of correlation zones was applied to test the spatial relationship of Peridinium cell density, chlorophyll concentration and cellular chlorophyll content, using data of sampling surveys carried out on the subtropical Lake Kinneret, Israel. Zones of correlation and correlation disturbance were observed. A method is suggested for determining the significance of the correlation zones, taking into account the values of the variables at sampling points where the correlation was actually measured. The method used was expedient for the description of spatial lake homogeneity/heterogeneity with regard to the examined variables. Heterogeneities, their spatial extent and intensity are defined by the method of identifying correlation zones and determining the significance of the zones while pinpointing the areas of interest in the lake.

This study of age and growth, reproduction and juvenile recruitment of Tilapia rendalli and Oreochromis mossambicus was undertaken in Lake Chicamba, a large, clear subtropical lake in central Mozambique. Sectioned otoliths were used to estimate age. Marginal zone analysis showed that annulus formation occurred during winter, in July and August. Maximum age estimates for T. rendalli and O. mossambicus were 16 and 10 years, respectively. Growth was described by the 3 parameter von Bertalanffy model as Lt = 238.74 (1-e-0,636(1 + 00905)) mm TL for T. rendalli and Lt = 266.06 (1-e-0 70904(1 + 0269)) mm TL for O. mossambicus. The length-at-50% maturity (Lm50) of male T. rendalli was 218 mm total lenglh (TL) and 205 mm TL in females. In O. mossambicus the L50 for males was 251 mm TL and for females 223 mm TL. Both species spawned throughout summer. Lake level was found to have no effect on spawning periodicity although recruitment was flood dependent.

Algal bioassays were conducted to determine whether phosphorus available for algal growth was released during sediment resuspension in Lake Okeechobee. The bioassays included evaluations of resuspension of sediments at different times of the year. Treatments consisted of floc and surface sediment layers mixed with surface lake water, then filtered to remove all but soluble phosphorus. The presence of phosphorus available for algal growth was manifested as the growth responses of unialgal cultures of phosphorus-starved cyanobacteria isolated from Lake Okeechobee. Floc and sediment treatments caused different algal growth responses depending on the sampling dates. In two summer experiments, there was enhanced growth response of the algae in the surface water previously mixed with sediments and floc. This result contrasted with the winter experiments when algal yields were lower in surface water samples mixed with sediment or floc. The results support recent hypotheses that sediment resuspension in ...

Studies were carried out on the phytoplankton of a subtropical polluted lake (Lake Maryut, Egypt) over a 1 year sampling period. The elemental composition of two major algal constituents-Spirulina platensis (Cyanophyta) and Cyclotella meneghiniana (Bacillariophyceae)—was determined from mixed plankton samples using electron-probe X-ray microanalysis. X-ray emission spectra obtained from S. platensis revealed a wide range of detectable elements. Clear positive (e.g. K-P, Na-Cl) and negative (e.g. Na-S, P-Cl) statistical correlations were interpreted in terms of elemental associations and compartmentation within the cell. C. meneghiniana had a broadly similar range of elements, but differed in the additional presence of Al and frequent peaks of Fe and Cu. The high concentration of Si reduced the detectability of other elements, causing a general reduction in mass fraction levels. Comparison of correlation coefficients derived from four sets of data revealed a clear pattern of elemental occurrence in the cel...

To understand the dynamics of planktonic prokaryotes in a subtropical lake and its relationship with carbon, we conducted water sampling through four 48 h periods in Peri Lake for one year. Planktonic prokaryotes were characterized by the abundance and biomass of heterotrophic bacteria and of cyanobacteria (coccoid and filamentous cells). During all experiments, we measured wind speed, water temperature (WT), pH, dissolved oxygen (DO), precipitation, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and carbon dioxide (CO2). DOC was higher in the summer experiment (average = 465 μM - WT = 27°C) and lower in the winter experiment (average = 235 μM – WT = 17°C), with no significant variability throughout the daily cycles. CO2 concentrations presented a different pattern, with a minimum in the warm waters of the summer period (8.31 μM) and a maximum in the spring (37.13 μM). Daily trends were observed for pH, DO, WT, and CO2. At an annual scale, both biological and physical-chemical controls were important regulators of CO2. Heterotrophic bacteria abundance and biomass were higher in the winter experiment (5.60 x 109 cells L-1 and 20.83 μmol C L-1) and lower in the summer (1.87 x 109 cells L-1 and 3.95 μmol C L-1). Filamentous cyanobacteria (0.23 x 108 – 0.68 x 108 filaments L-1) produced up to 167.16 μmol C L-1 as biomass (during the warmer period), whereas coccoid cyanobacteria contributed only 0.38 μmol C L-1. Precipitation, temperature, and the biomass of heterotrophic bacteria were the main regulators of CO2 concentrations. Temperature had a negative effect on the concentration of CO2, which may be indirectly attributed to high heterotroph activity in the autumn and winter periods. DOC was positively correlated with the abundance of total cyanobacteria and negatively with heterotrophic bacteria. Thus, planktonic prokaryotes have played an important role in the dynamics of both dissolved inorganic and organic carbon in the lake.

Occurrence of limnic molluscs and crustaceous on clusters of the golden mussel Limnoperna fortunei (Dunker, 1857), formed on “sarandi” at Guaíba Lake (RS, Brazil). In order to verify the occurrence of invetebrates associated with macro clusters of Limnoperna fortunei (Dunker, 1857) formed on branches of “sarandi” (Chephalanthus glabratus (Spreng.) K. Schum), quantitative samplings (N=28) were conducted for two years (2002 to 2004) at Veludo Beach on Guaíba Lake (municipality of Porto Alegre, RS, Brazil). From the results, the gastropod Heleobia piscium (Orbigny, 1835) was identifi ed as a constant (78.57%) species,while Potamolithus jacuhyensis Pilsbry 1899 (35.71%) and the crustaceous Hyalella curvispina Shoemaker 1942 (26%) were indicated as accessory species. The other taxa were accidental (

Presentation de donnees sur les preferences alimentaires de Coleps hirtus et contribution aux recherches sur le role ecologique des cilies dans la chaine alimentaire du Lac Kinneret

Species composition, biomass and diversity of the phytoplankton in a subtropical lake (27°29'S; 58°45'W) were studied from February 1995 to March 1996. One or two samples were taken monthly in the limnetic and the littoral area. Cell counts were done by the Utermöhl method (1958). Phytoplankton biomass varied among 2.38 and 45.59 mm³.m-2 with a mean value of 12.11 (±10.52) mm³.m-2. The population density oscillated among 0.3x10(6) and 4.7x10(6) ind.cm-2. Cyanophyta was the dominant group all the year contributing among 25% and 83% of the total biomass. Cylindrospermopsis raciborskii, Aphanizomenon sp. and Microcystis aeruginosa were the dominant species. The Chlorophyta, second group in importance, contributed among 8% and 50% being Botryococcus braunii the dominant species. Bacillariophyceae, Xanthophyceae, Euglenophyceae and Cryptophyceae they did not surpass 20% of total biomass. Chrysophyceae and Dinophyceae they did not surpass 5% of total biomass. Chlorophyll a content ranged between 0.7 and 8 µg.L-1 reflecting the annual variation of phytoplankton biomass. Phytoplankton density diversity varied among 0.34 and 3.69 bits.ind-1. Biomass diversity varied among 1.04 and 2.92 bits.µm³, with a similar variation in the depths of the lake. The lowest biomass and the highest diversity were always found in the littoral zone. CStrategists, with a high SA/V ratios prevailed in density (Monoraphidium contortum, M. tortile, Chlorella vulgaris and other small flagellates of Chlorophyta) while SStrategists (with a low SA/V ratios) such as Microcystis aeruginosa and Botryococcus braunii prevailed during the greater part of the year. Cylindrospermopsis raciborskii and Aphanizomenon sp. were dominant in density and biomass when the temperatures were superior to 20°C and the solar radiation surpassed 20 MJ.m-2. The RStrategists (Aulacoseira italica and Gymnodinium sp.) prevailed during great unstability of water column. Phytoplankton biomass was positively correlated with rain falls 10 days before each sampling (r = 0.772; p < 0.01; g.1. = 30). During the period that prevailed the filamentous Cyanophyceae an increase in the heterocysts frequency was observed in coincidence with a period of notorous drought.

SUMMARY. The horizontal distribution of nauplii, CI-CIII, CIV-Cv and adult stages of the copepod Pseudodiaptomus hessei within the main basin of Lake Sibaya (27° 20′ S, 32° 37′ E) is described on the basis of semi-synoptic cruises on 6 August 1971, 28 January 1972 and 11 February 1972. The distribution observed is considered in relation to variations in food availability and water temperature over this homothermal lake. It is concluded that these factors are not primarily responsible for observed patterns of distribution. Rather, wind-induced currents appear to be of major significance in determining horizontal distribution. Stage-related differences in the nature and extent of horizontal redistribution following severe wind are described. A consideration of the vertical distribution of groups of life-history stages over a diel cycle in relation to the direction and relative strength of currents encountered by the copepods within their respective depth ranges provides an explanation for the differences in horizontal redistribution observed.

SUMMARY. This paper describes a day/night feeding rhythm in the copepod Pseudodiaptomus hessei in subtropical Lake Sibaya (27°20′ S, 32°40′ E) and examines the origin of this rhythmicity on the basis of field and laboratory observations. Under natural conditions, adult and late copepodite stages (CIV-CV) of this copepod were predominantly benthic during daylight and migrated at dusk into pelagic waters in which they remained until dawn. Pronounced changes in feeding activity (based on the proportion of animals which contained food in the gut) were associated with this transition from a benthic to pelagic distribution; feeding activity was low by day and high at night. The younger copepodite stages (CI-CIII) were less strongly benthic during daylight and showed correspondingly less pronounced diel changes in feeding activity. Laboratory experiments involving concurrent light/dark and continuous dark regimes showed that batches of adult and CIV—CV stages fed throughout 24 h, although faecal pellet production increased with time under both light regimes. The laboratory observations are interpreted as negating the possibility that diel differences observed in the field arose through an endogenous feeding rhythm. The possibility that food resources in near-bottom waters was inadequate to support reasonable feeding activity is rejected on several counts. It is concluded that the feeding rhythm in P. hessei arises from an inferred infaunal distribution during daylight which would preclude filter-feeding activity. The circumstantial evidence supporting this suggestion is given and the suggestion is evaluated.