Algal Volume Research Articles

Do wave exposure and drifting algae drive the functional diversity of fishes in tropical ocean-exposed sandy beaches?

Tropical ocean-exposed sandy beaches have an essential ecological function for marine fish species, which use these turbulent areas as nurseries. These habitats are characterized as homogeneous environments, but previous studies report the influence of drifting algae in providing physical structure, which increases habitat complexity and heterogeneity. This additional habitat complexity is expected to have a crucial impact on fish assemblages. Here, we analyzed the influences of wave exposure and drifting algae volume on abundance and functional diversity on two beach types: wave-dominated and tide-modified. Beach seine samplings were carried out in the rainy and dry seasons to collect the fish at each beach. Four volume categories of drifting algae were selected: bare sand, low, mid and high. A total of 97 fish species were captured. The community attributes of fishes (abundance, richness and biomass), as well as algal volume, were higher in tide-modified beaches. For abundance, three distinct patterns emerged: 1) there was a trend of decreasing herrings and anchovies compared to other species, from the bare to high-volume drifting algae in tide-modified beaches, with the opposite trend for the wave-dominated beaches; 2) L. breviceps, M. littoralis, S. naso, S. rastrifer and S. stellifer increased in abundance from the bare to high drifting algae in wave-dominated beaches; 3) P. virginicus was abundant in both beach types. These trends were accompanied by functional diversity, principally by responses in the two types of traits: diet and habitat use. The differences in habitat characteristics (wave exposure and drifting algae) among beaches affected the composition and functional diversity and consequently supported distinct fish assemblages. The presence of drifting algae in this habitat favors the attractiveness for fishes, such as larvae and juveniles, and seems to drive habitat use by tropical fishes.

The removal of Microcystis ichthyoblabe cells and its hepatotoxin microcystin–LR during electrooxidation process using Pt/Ti electrodes

Electrooxidation is widely used to remove harmful organic and inorganic substances as well as pathogenic microorganisms. This study investigates the removal of Microcystis ichthyoblabe cells and their hepatotoxin microcystin–LR by the electrooxidation process using Pt/Ti electrodes. Additionally, the morphology changes and cell sizes were determined by scanning electron microscopy and a particle size analyzer, respectively. The algal cells were severely damaged by the electrooxidation process. During the initial treatment, intracellular microcystin–LR was released from the cells, increasing the extracellular microcystin–LR concentration. The electrooxidation charge required to remove cells and MC–LR was 3 × 104 C and 6 × 104 C, respectively. The removal efficiencies of M. ichthyoblabe cells and microcystin–LR were insensitive to initial cell density, initial microcystin–LR concentration and solution conductivity, but were heavily reduced at large algal suspension volume. Therefore, to achieve simultaneous removal of Microcystis cells and their MC, it is necessary to control the volume of algal suspension.

Variation of bioaccumulation ability of 2,2′,4,4′-tetrabromodiphenyl ether by marine diatom Skeletonema costatum under different N:P ratios

The growth, biochemical content and bioaccumulation quantity of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) in Skeletonema costatum were studied under different N:P ratios (1, 4, 16, 64 and 128). All cellular biochemical contents of S. costatum presented decreasing trend over cultivation time. At early stage of cultivation, the cellular protein, carbohydrate and lipid in S. costatum presented higher values in treatments of N:P=4 and 16. However, they were lower in these treatments at the late stage, but higher in treatments N:P=1 and 128. Similarly, BDE-47 levels per cell of S. costatum were higher in treatments of N:P=4 and 16 at early stage of cultivation, which were 3.8 and 3.7 ng (106 cells)−1, respectively. At the middle stage of cultivation, the BDE-47 level per S. costatum cell lowered; and it further reduced in the treatments of N:P=4 and 16 at the late stage with the values 0.6 and 0.5 ng (106 cells)−1, respectively. However, it rose in N:P=128, reaching up to 2.3 ng (106 cells)−1. Compared with BDE-47 per cell, BDE-47 per algal volume under different N:P ratios did not present obvious difference. The quantity BDE-47 accumulated per cell of S. costatum was positively correlated with protein, carbohydrate and lipid per cell; meanwhile, the BDE-47 per volume had a positive correlation with biochemical content per volume. The variation of bioaccumulation ability of BDE-47 in S. costatum can be explained by biochemical changes due to N:P ratios.

Patterns in the invertebrate assemblage associated with Corallina officinalis in tide pools

Ecological studies of diversity at different spatial scales are important for our understanding of community processes. Here the patterns in the invertebrate fauna associated with the turf-forming red alga, Corallina officinalis, with increasing tide pool depth and in pools of different surface area and at different tidal heights are presented for two similar shores in north Wales. Corallina turf supports a diverse assemblage of invertebrates achieving high densities of individuals which makes an important contribution to local biodiversity. Overall 123 different taxa were identified with the most dominant species being the polychaete Spirorbis corallinae and small individuals of the mussel Mytilus edulis. There are significant differences in the invertebrate assemblage at different depths in tide pools and higher diversity and richness at shallower depths nearer the edge of pools where the alga is shorter and more compact than at deeper depths. Pool size and tidal height were also clearly important in structuring the assemblage where there were significant differences in diversity, richness and assemblage pattern, although these differences were not consistent between shores. Some measures of habitat complexity, such as algal volume, correlate well with species richness, though occasionally diversity is negatively correlated with the number of holdfasts. Variations in physical conditions afforded by different depths and in tide pools of different size at different tidal heights at the scales measured clearly play an important role in structuring both the complexity of habitat and its associated assemblage

ULTRASTRUCTURE OF THE GLAND CELLS OF THE RED ALGA ASPARAGOPSIS ARMATA (BONNEMAISONIACEAE)1

Localization of natural products in the gland cells of the tetrasporophyte of Asparagopsis armata Harvey was examined using light microscopy, epifluorescence microscopy, and TEM. A. armata produces a range of halogenated metabolites that deter herbivores and inhibit bacterial fouling. The halogenated metabolites accumulate as a refractile inclusion inside specialized gland cells and this inclusion was no longer produced when the alga was cultured without bromine. Gland cells are formed soon after the apical division and can occupy a large portion of the algal volume, up to 10% of some parts of the filament. TEM was carried out on cryofixed and freeze‐substituted samples. Ultrastructure studies revealed that gland cells are positioned inside the pericentral cell, originating from the axial cell wall. The refractile inclusion of these gland cells is comprised of numerous electron‐translucent vacuoles enclosed by an electron‐opaque matrix. Some contents of the inclusion autofluoresced under UV excitation by epifluorescence microscopy. Light microscopy further revealed that stalk‐like structures connected the gland cell to the outer wall of the pericentral cell. These stalk‐like structures may provide the mechanism for metabolite transfer to the algal surface. Gland cell walls are relatively thin, which in turn would aid the transfer of metabolites to the stalk‐like structure. These features of the gland cells provide essential clues to the production and storage of the halogenated metabolites in A. armata and offer new insights into a possible mechanism for their release.

Settling characteristics of problem algae in the water treatment process

The settling velocity or removal rates of problem algae in the water treatment process and their flocculants were measured with settling column (SETCOL) and fluorometric method. Our research who were centred on the algal density and shape affecting the settling. The settling velocities of large algae ranged from 0.1 cm/h to 2.6 cm/h, whereas those of small algae were below 1.0 cm/h. The settlings of algae in the stationary growth phase significantly increased and dead algae corresponded with the declining algae. The extent of deformation, which was expressed as the coefficient of form resistance of the algae had the great influences upon the settling. The most extreme deformed algae were needle-shaped ones like Synedra acus, which was known to be a problem in water treatment processes in Korea. Changes in the settling velocity of algae were correlated with algal volume and morphology rather than cell density.

The Importance of Lake Morphometry for the Structureand Function of Lakes

AbstractThis work demonstrates quantitatively and in a comprehensive way that the size and form of lakes regulate many general transport processes, such as sedimentation, resuspension, diffusion, mixing, burial and outflow, which in turn regulate many abiotic state variables, such as concentrations of phosphorus, suspended particulate matter, many water chemical variables and water clarity, which in turn regulate primary production, which regulate secondary production, for example of zooplankton and fish. Such relationships are discussed not qualitatively but quantitatively using a new generation of validated dynamic ecosystem models (LakeWeb and LakeMab) based on mechanistic principles. It has been shown by critical model tests (including blind tests using data covering wide limnological ranges) that these models give predictions that agree well with empirical data. This should lend credibility to the results presented in this work, which would have been very difficult to obtain using traditional methods with extensive field studies in a few lakes. Simulations have been carried out where the inflow of phosphorus is held constant and the consequences simulated for small, large, shallow and deep lakes. There are striking differences in total phosphorus (TP) concentrations and trophic state (from 10 to 100 µg TP/l) and hence also in changes in many variables characterizing lake structure and function, such as Secchi depth, suspended particulate matter, pH, water temperature, chlorophyll, algal volume, macrophyte cover; as well as production and biomasses of benthic algae, bacterioplankton, macrophytes, herbivorous zooplankton, predatory zooplankton, zoobenthos, prey fish and predatory fish. These changes have been quantified in a comprehensive manner in this work and the approach to calculate such changes are basic for an understanding of how different lakes react to changes in nutrient loading (eutrophication). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Changes to lake ecosystem structure resulting from fish cage farm emissions

AbstractThis study demonstrates how a given lake (Lake S. Bullaren, Sweden) would respond to emissions from a fish cage farm. The main questions to be answered are: How would emissions of feed spill and faeces from a fish farm influence the production and biomass of key functional organisms and how long would such changes remain if the fish farm is closed down? The work is based on a comprehensive lake ecosystem model, LakeWeb, which accounts for production, biomass, predation, abiotic/biotic interactions of nine key functional groups of organisms, phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), two types of fish (prey and predatory), as well as zoobenthos, macrophytes and benthic algae. The LakeWeb model gives seasonal variations (the calculation time is one week). It has been calibrated and critically tested using empirical data and regressions based on data from many lakes. These tests have demonstrated that the model can capture typical functional and structural patterns in lakes very well, lending credibility to the results presented in this study. To the best of the author's knowledge, this is the first time that effects from fish cage farm emissions on lake ecosystem structure have been quantified at the ecosystem scale. To carry out studies such as these in the traditional manner, by extensive field work in one or a few lakes, would be very demanding, in terms of costs, personnel and time. This work has demonstrated that fish farm emissions would cause significant increases in the biomass of wild fish, without corresponding increases in algal volume. Thus, it is concluded that the fish farm emissions influence the lake's secondary production more markedly than primary production. Although this finding might seem to be a paradox, it is related to the fact that wild fish directly consume food spill and faeces from the fish farm, thereby creating a specific foodweb pathway, as described in this study.

The influence of biomanipulations (fish removal) on the structure of lake foodwebs, case studies using the LakeWeb-model

This paper presents results on how intensive fishing (fish removal) islikely to influence the structure of lake foodwebs. The work is based on acomprehensive dynamic lake ecosystem model, LakeWeb, which accounts forproduction, biomasses, predation and abiotic/biotic interactions of nine keyfunctional groups of organisms: phytoplankton, bacterioplankton, two types ofzooplankton (herbivorous and predatory), two types of fish (prey and predatory),zoobenthos, macrophytes and benthic algae. The model uses ordinary differentialequations, the ecosystem scale and gives seasonal variations (the calculationtime is 1 week). It is designed to account for all fundamental abiotic/bioticinteractions and feedbacks for lakes in general for the nine target groups. TheLakeWeb-model has been calibrated and critically tested using empirical data andregressions based on data from many lakes. It has been shown that the model canclosely capture typical functional and structural patterns in lakes, whichshould give credibility to the results presented in this work. Obtaining suchresults using traditional methods, i.e., extensive field studies in one or a fewlakes, would be very demanding (in terms of money, persons involved and time).In this paper, results are presented for two lakes, one Swedish and oneBelarussian. The intensive fishing operations carried out in LakeBlacksastjarn, Sweden, to reduce Hg-concentrations in fish did notsucceed. A typical cost of an intensive fishing is about 10,000–30,000 USDper lake of this size (≤ 0.25 km2). The costs toremove fish would be about 40–120 USD per kg ww fish removed! Intensivefishing simulated for Lake Batorino, Belarus, to reduce the fish biomass willlikely increase the prey fish biomass as long as the predation pressure on preyfish is lower than during the prefishing stage. The biomass of predatory fishwill recover only slowly. However, this operation is not likely to succeed inlowering the algal volume in lakes with a high biomass of predatory zooplankton.This is easy to state qualitatively and the LakeWeb-model offers a practicallyuseful tool to quantify such changes and identify lakes where biomanipulationsare likely to fail or succeed.

Comparison of methods to assess water column primary production in wetlands

We compared a number of techniques to measure water column autotroph production in a shallow, hypereutrophic wetland: diurnal oxygen changes; light and dark bottle incubations; chlorophyll a concentrations; daily changes in pH; and algal volume. Productivity from diurnal oxygen changes calculated at 0.25, 0.5, 1, 2, 3, and 4 h intervals give similar estimates, but not ∼12 h intervals (dawn-dusk-dawn). Net productivity in bottles was slightly lower than that indicated by diurnal oxygen changes, and gross productivity in bottles was much lower than diurnal changes. Changes in pH correlated well with gross and net productivity measurements, as well as algal volume. Chlorophyll a is correlated with diurnal and bottle net productivity measurements and pH changes, but not algal volume. Since daily pH flux and oxygen changes provide a better overall assessment of ecosystem processes than standing crop or bottle incubations, they could be useful measurements for ecological engineers interested in assessing the ecosystem function.

Seasonal fluctuations in environmental factors and variations in symbiotic algae and chlorophyll pigments in four Indo-Pacific coral species

Marked seasonality is observed in sea-surface temperature (SST) and photosynthetically active radiation (PAR) received by shallow water corals at Phuket, Thailand (7° N latitude). This seasonality is reflected in both algal densities and algal chlorophylls (a and c 2 ) in 4 massive species of scleractinian corals, namely Coeloseris mayeri, Goniastrea retiformis, Porites lutea, and G. aspera. Algal numbers and algal chlorophylls are generally maximal at the end of the wet season (November) and minimal at the end of the dry season (March to May). Algal densities are reduced by up to 53 % in May compared to November in some species, while algal chlorophylls may be up to 4-fold greater in November. Concomitant with these changes are differences in algal cell volume in 3 out of the 4 species studied and alterations in host tissue depth, with smaller algal volume and greater tissue depth at the end of the wet compared with the dry season. Over the period 1993 to 1996 algal numbers showed a significant negative correlation with monthly (30 d) and short-term (1 to 2 d) values of both SST and PAR dose, while algal chlorophylls displayed a significant negative correlation with PAR dose in the 5 d preceding collection. Rising SST and increasing PAR in the dry season are paralleled by decreasing algal numbers and algal chlorophylls on an annual basis. Recovery of algal densities and a build-up in algal chlorophylls follow reductions in SST and PAR at the end of the wet season. In one of the years, when coral 'bleaching' was widespread at the study site (May 1995), the interaction between SST and PAR resulted in an 86 % reduction in algal densities in bleached corals compared to their annual maximum density. This study highlights the importance of seasonal fluctuations in physical environmental parameters and concomitant changes in the coral/algal symbiosis. Furthermore, it emphasises the need for greater understanding of the potential effects of seasonal and inter-annual variability on the status of algal symbionts, as well as identification of critical times of the year when visible bleaching may not be obvious but when algal numbers and algal chlorophylls are low and effects on coral physiology may be far-reaching.

Fish farming in lakes and acceptable total phosphorus loads: Calibrations, simulations and predictions using the LEEDS model in Lake Southern Bullaren, Sweden

This work presents a dynamic model, Lake Eutrophication, Effect-Dose-Sensitivity (LEEDS), designed to predict how large a fish farm a lake could sustain without incurring eutrophication problems. Since the model included various time-dependent phosphorus cycling processes, the second goal was to estimate the relative importance of those processes. We studied the dimictic and mesotrophic Lake Southern Bullaren, Sweden for several reasons. The lake had a fish farm which produced between 70 and 500 tons of rainbow trout per year from 1980 to 1992 (the permit was for a maximum of 70 tons y −1). Rather severe blooms of Cyanophyceae occurred twice during the last six years of production. Based on comprehensive water chemistry and biology data sets, the LEEDS model was calibrated at 14 specific points in order to yield reliable predictions for this lake. The dominating phosphorus loads were the fluxes from tributaries and the fish farm (assuming a production of 500 tons y −1), which accounted for about 70% and 25% of the total phosphorus load, respectively. The simulations suggested that about 50% of the annual deposition of phosphorus was resuspended, of which about 60% reached the productive surface waters. Further, the lake should have been able to sustain a fish farm producing about 500 tons of rainbow trout per year without sustaining marked ecosystem effects such as increased algal volume. LEEDS includes all major fluxes for evaluations of fish farm emissions in temperate lakes. The relative importance of the various processes vary from lake to lake. Among internal fluxes, the largest uncertainty lies in the rate of total phosphorus sedimentation. All other internal fluxes (resuspension, diffusion, etc.) depend on this rate. By identifying the major fluxes in a given lake, one could also identify the major uncertainties of model predictions of target variables, e.g., lake total phosphorus concentration and maximum algal volume. A future improvement of this model would be the development of a general, validated sub-model for the rate of total phosphorus sedimentation as well as the development of a generic sub-model for the distribution coefficient ( K d), which regulates the amount of phosphorus in dissolved and suspended phases and hence the rate of phosphorus sedimentation.

Fish farming in lakes and acceptable total phosphorus loads: Calibrations, simulations and predictions using the LEEDS model in Lake Southern Bullaren, Sweden

AbstractThis work presents a dynamic model, Lake Eutrophication, Effect-Dose-Sensitivity (LEEDS), designed to predict how large a fish farm a lake could sustain without incurring eutrophication problems. Since the model included various time-dependent phosphorus cycling processes, the second goal was to estimate the relative importance of those processes. We studied the dimictic and mesotrophic Lake Southern Bullaren, Sweden for several reasons. The lake had a fish farm which produced between 70 and 500 tons of rainbow trout per year from 1980 to 1992 (the permit was for a maximum of 70 tons y−1). Rather severe blooms of Cyanophyceae occurred twice during the last six years of production.Based on comprehensive water chemistry and biology data sets, the LEEDS model was calibrated at 14 specific points in order to yield reliable predictions for this lake. The dominating phosphorus loads were the fluxes from tributaries and the fish farm (assuming a production of 500 tons y−1), which accounted for about 70% and 25% of the total phosphorus load, respectively. The simulations suggested that about 50% of the annual deposition of phosphorus was resuspended, of which about 60% reached the productive surface waters. Further, the lake should have been able to sustain a fish farm producing about 500 tons of rainbow trout per year without sustaining marked ecosystem effects such as increased algal volume.LEEDS includes all major fluxes for evaluations of fish farm emissions in temperate lakes. The relative importance of the various processes vary from lake to lake. Among internal fluxes, the largest uncertainty lies in the rate of total phosphorus sedimentation. All other internal fluxes (resuspension, diffusion, etc.) depend on this rate. By identifying the major fluxes in a given lake, one could also identify the major uncertainties of model predictions of target variables, e.g., lake total phosphorus concentration and maximum algal volume. A future improvement of this model would be the development of a general, validated sub-model for the rate of total phosphorus sedimentation as well as the development of a generic sub-model for the distribution coefficient (Kd), which regulates the amount of phosphorus in dissolved and suspended phases and hence the rate of phosphorus sedimentation.

Seasonal patterns of food limitation in Daphnia galeata: separating food quantity and food quality effects

Food limitation for the cladoceran Daphnia galeta was measured growing them with natural lake seston for one growing season under standardized conditions in the laboratory. Growth rates were related to several measures of food quantity. Particulate organic carbon (POC) <30 μm was the best predictor of total food availability measured. It was better than chlorophyll-a (Chl-a) of the same size fraction, algal volume calculated from cell counts or total particle volume from Coulter Counter measurements. Daphnids were also grown with Scenedesmus acutus under the same conditions and their growth rates were compared. Sestonic carbon concentrations were related to Scenedesmus carbon concentrations, that provided equal growth rates. The ratio of the carbon concentrations of both food types (seston, Scenedesmus) represented the food quality of seston. Thus, the nutritional quality of natural lake seston relative to a standard alga was determined over one growing season. Growth rates of seston fed animals revealed that they were food limited during long periods of the year. This was also ascertained by standard clutch sizes of field animals. However, the causes of food limitation varied within the duration of the studied period. Whereas during the clear-water phase the food quantity was limiting (while the quality was high: 100% Scenedesmus), shortly after on 10 June and 17 June food conditions were close to threshold concentrations due to low food quality. For the remainder of the summer, a POC of 0.3–0.6 mg C I−1 with a quality of ∼50% Scenedesmus. resulted in moderate food limitation of Daphnia.

Plankton and seston structure in a shallow, eutrophic subtropic Chinese lake

The seasonal dynamics in the nutrient concentrations, chlorophyll-a amount (Chl-a), total algal volume (CV), Chl-a/CV ratio, seston structure were studied at two sampling stations in a shallow, highly eutrophicated subtropic lake (the Guozheng Hu area of the East Lake) on the plain of the middle basin of the Chang Jiang (the Yangtze River) of China. The lake ecosystem of the Guozheng Hu area is dominated by two planktivorous fishes (silver carp and bighead carp), phytoplankton and zooplankton. Macrophytes are extremely scarce in this area. Concentrations of the total dissolved nitrogen and phosphorus in the Guozheng Hu area in 1990 were very high. Fish yield, of which, more than 90 % was composed of silver carp and bighead carp in the Guozheng Hu area was very high (ca. 1140 kg/ha or 45.6 g/m3 in 1990). Grazing pressure by the fishes on the plankton community is considered to be rather strong. The annual average biomass of zooplankton was ca. 1/3 - 1/2 that of phytoplankton. On the average, dry matter in the living plankton only constituted ca. 3-7 % of the total dry seston, and plankton carbon only constituted ca. 5 - 10 % of the seston carbon. The present results indicate that, in the Guozheng Hu area of the East Lake, of the organic part of the seston, detritus is quantitatively an important constituent, while living plankton is only a very small component.

Filtering rates of Daphnia carinata King (Crustacea: Cladocera) on the blue‐green algae Microcystis aeruginosa Kütz. and Anabaena cylindrica (Lemm.)

Abstract Non‐toxic strains (by mouse toxin assay test) of unicellular Microcystis aeruginosa and short filamentous Anabaena cylindrica were fed to Daphnia carinata in the laboratory at an algal volume concentration of 4.0 mm3 L−1 at 24 ± 1°C. The filtering rates (FR, mL animal−1 hr−1) of D. carinata on M. aeruginosa and A. cylindrica increased with increasing body length (L, mm), and were expressed as a power curve: FR = 0.061L209. and FR = 0.232L2.09, respectively. The potential for control of natural blue‐green algal populations by D. carinata grazing is discussed briefly.

A comparison of chlorophyll a and carotenoid concentrations as indicators of algal volume

SUMMARY. 1. Carotenoid concentration, as measured hy absorbance at 480 nm. was a better indicator of algal volume than chlorophyll a when the results from two lakes and laboratory studies on Osciltaloria agardhii var. isothrix Skuja were compared. The correlation between algal volume and carotenoid in White Lough (r=0.91) was significantly higher (0.001 P&lt;0.01) than ihat between algal volume and chlorophyll a(r=0.77). The Lotigh Neagh correlation coefficient lor algal volume with carotenoid (r=0.89) was only marginally stronger than that with chlorophyll a(r=0.87).2. The relatively weak correlation between algal volume and chlorophyll a in White Lough was a result of a summer decline in the chlorophyll a content of O. agardhii var. isothrix, which dominated the phytoplankton. The chlorophyll a content of the phytoplankton was depressed by high summer daily totals ol light hours received by the phytoplankton in White Lough of up to 14 h in comparison to a maximum value of 3.8 h in Lough Neagh. where no seasonal cycle of chlorophyll a content was evident.3. Laboratory studies demonstrated that while chlorophyll a per unit algal volume of O. agardhii var. isothri.x declined with increasing light dose, carotenoid content did not. Nitrogen and phosphorus limitation depressed the carotenoid content but to a lesser degree than was observed for chlorophyll a.

Phosphorus inactivation in a eutrophic lake by the direct addition of ferric aluminium sulphate changes in phytoplankton populations

SUMMARY. 1. Reduced total phosphorus concentrations in the summer which followed the addition of iron aluminium sulphate to White Lough failed to reduce significantly the phytoplankton. which continued to be dominated by Oscitlatoria agardhii var. isothrix Skuja.This species was present throughout the 4 years studied, forming over 50% of the algal volume in 80% of samples. In contrast, species which occurred principally in the summer months were found to be severely curtailed when sediment release of phosphorus was suppressed.2. The phosphorus: carotenoid ratio was used to assess the extent of phosphorus limitation because laboratory studies on O. agardhii var. isothrix showed that this ratio was a much beter indicator of cell phosphorus content than the phosphorus: chlorophyll a ratio. Reduced summer phosphorus concentrations in White Lough caused a transition from intermittent to continuous phosphorus limitation rather than a proportional reduction in the summer phytoplankton.3. Reduced autumn grazing pressure by Daphnia hyatina Leydig allowed large algal populations to develop in the winters following phosphorus reduction despite a 50% decline in total phosphorus. The combination of increased winter phytoplankton and lower total phosphorus reduced soluble reactive phosphorus concentrations to less than 5,μg P l−1 which in turn curtailed the spring diatom pulse.

Adaptation of biochemical composition and cell size to irradiance in two microalgae: possible ecological implications

Two marine microalgae (Haptophyceae), Hymenornonas elongata and Isochrysis galbana, were grown in turbidostats in order to investigate the influence of light intensity on cell volume and biochemical composition. At irradiance levels that saturated growth (400pE m-2 S-'), the algae contained a high level of carbon compounds, especially soluble sugars. At the irradiance that limited growth (25 pE m-2 S-') sugar pools were lower for the 2 algae and H. elongata decreased its volume by 25 %. In the transitional phase that followed a shift from 400 pE m-2 S-' to 25 pE m-2 S-' rates at which biochemical ratios reached stability differed for the 2 algae. Re-establishing high light intensity after a period under low light intensity influenced algal volume in H. elongata; t h s event followed a particular lunetic pattern that we attempt to explain on theoretical grounds. Results are discussed with regard to durations of irradiance perturbations that can occur in the sea.

Bacterioplankton, Phytoplankton, and Zooplankton Communities in a British Columbia Coastal Lake Before and After Nutrient Reduction

Inorganic nitrogen and phosphorus were applied weekly during the growing season from 1980 to 1982 and twice weekly in 1983 to Hobiton Lake, a warm monomictic coastal lake in British Columbia. The lake was not fertilized in 1984. Average numbers of bacteria during the growing season decreased from a high of 1.53 × 106∙mL−1 in the fertilized condition to 0.84 × 106∙mL−1 in the unfertilized condition. Chlorophyll a concentrations decreased from a maximum seasonal average of 2.69 μg∙L−1 (1981) to 1.30 μg∙L−1 (1984), and algal numbers decreased from 5.83 × 104∙mL−1 (1983) to 2.29 × 104∙mL−1 (1984). Although the numbers of phytoplankton in each size fraction (picoplankton, nanoplankton, or microplankton) decreased in the unfertilized condition, the greatest change was an almost fourfold decrease in picoplankton, which consisted of 90% cyanobacteria (primarily Synechococcus spp.). Abundance of the large diatoms Rhizosolenia spp. and Melosira spp. increased in 1984, resulting in an increase in average seasonal algal volume. Average densities of medium (0.15–0.84 mm) and large (0.85–1.5 mm) zooplankton were greatest in 1982, while rotifers and small zooplankton (0.10–0.14 mm) were most dense in 1984 following nutrient reduction. The lake had relatively high concentrations of planktivorous juvenile sockeye salmon (Oncorhynchus nerka) that appeared to minimize any direct effect of nutrient additions on zooplankton densities.