Carbohydrate dynamics and growth rate of natural phytoplankton populations

Diurnal changes in carbohydrate content of natural phytoplankton populations differed from those found for cyanobacteria grown in continuous cultures. The carbohydrate accumulation rate was not constant during the light period. Also in contrast to results obtained using continuous cultures the photosynthetic characteristics changed during the light period. A close correlation was observed between changes in carbohydrate accumulation rate and the efficiency of photosynthesis over 24 hours. Seasonal changes in carbohydrate consumption rate over the dark period were proportional to changes in growth rate.     

The effects of the evolution of stoichiometry-related traits on population dynamics in plankton communities

Both ecological stoichiometry and the evolution of traits for energetic interactions such as prey protection and predatory efficiency are considered to be important aspects affecting population dynamics. However, no attempt has been made to examine the effect of the evolution of traits relating to stoichiometry. This study first examined the effects of the evolution of nutrient utilization traits (i.e., the minimum nutrient content of prey, the maximum nutrient uptake affinity of prey and the nutrient contents of predators) on population dynamics in a plankton community. When the evolution of these traits was assumed, the range of the nutrient loading conditions where the system became unstable was smaller than when the evolution was not assumed, but the range of the conditions for zooplankton extinction became larger. Furthermore, when the trade-offs (i.e. genetic correlation between the traits) were assumed, the system rarely became extinct and the range of the nutrient loading conditions where the system became stable became larger through evolution. Stable dynamics were caused by increasing uptake affinity through evolution, and zooplankton extinction was caused by decreasing the minimum content of limiting nutrients. Thus, our results suggest that the evolution of traits relating to stoichiometry can affect the dynamics of the systems, and the outcomes the dynamics change greatly depend on which traits can evolve.     

Decreased diversity caused by differential inhibition among artificial phytoplankton communities in an undisturbed environment

Cultures of freshwater algae were assembled into artificial communities consisting of 2, 3, 4 and 8 species. The same species were also grown simultaneously in unialgal cultures in separate containers. Different combinations of algae in the same-sized artificial communities were grown three times for 17 weeks. Data obtained from the algae grown separately were treated in the same manner as those from algae grown in the artificial communities. The algae grown as unicultures in separate containers were found to grow in a descending order of abundance: a hierarchical order. When they grew as part of a community, several things happened: (1) all species were inhibited in growth; (2) the inhibition among the species was not uniform; (3) the species often exchanged numerical position in the hierarchy; and (4) the hierarchical order always increased, the degree of hierarchy being determined from the formula ?Σp_i ln p_i . The greater hierarchy in the communities means there was less evenness of numerical distribution and, therefore, less diversity. This study corroborated Connell's intermediate disturbance hypothesis from the aspect of the increase in hierarchy. Normally, this hypothesis has referred to the reduction of the number of species in an undisturbed community.     

Parasitic chytrids: their effects on phytoplankton communities and food-web dynamics

Many phytoplankton species are susceptible to fungal parasitism. Parasitic fungi of phytoplankton mainly belong to the Chytridiomycetes (chytrids). Here, we discuss the progression made in the study of chytrids that parasitize phytoplankton species. Specific fluorescent stains aid in the identification of chytrids in the field. The established culturing methods and the advances in molecular science offer good potential to gain a better insight into the mechanisms of epidemic development of chytrids and coevolution between chytrids and their algal hosts. Chytrids are often considered to be highly host-specific parasites, but the extent of host specificity has not been fully investigated. Chytrids may prefer larger host cells, since they would gain more resources, but whether hosts are really selected on the basis of size is not clear. The dynamics of chytrids epidemics in a number of studies were partly explained by environmental factors such as light, temperature, nutrients, pH, turbulence and zooplankton grazing. No generalization was made about the epidemic conditions; some state unfavorable conditions for the host growth support epidemic development, while others report epidemics even under optimal growth conditions for the host. Phytoplankton is not defenseless, and several mechanisms have been suggested, such as a hypersensitivity response, chemical defense, maintaining a high genetic diversity and multitrophic indirect defenses. Chytrids may also play an important role in food webs, because zoospores of chytrids have been found to be a good food source for zooplankton.     

Predation-driven dynamics of zooplankton and phytoplankton communities in a whole-lake experiment

Summary 1. Species compositions of zooplankton and phytoplankton were followed in Tuesday Lake before and after experimental manipulation of its fish populations (addition of piscivorous largemouth bass, removal of planktivorous minnows). Plankton dynamics were compared to those of adjacent, unmanipulated Paul Lake, where piscivorous fish have been dominant historically. 2. Indices of similarity for the zooplankton communities in the two lakes in 1984 prior to the manipulation were low; however, following the manipulation in spring, 1985, similarity of the zooplankton in the two lakes rose considerably and remained high throughout 1986. This was the result of an increase in Tuesday Lake of previously rare large-bodied cladocerans (Daphnia pulex, Holopedium gibberum) which were the dominants in Paul Lake, and the disappearance in Tuesday Lake of the dominant small-bodied copepod Tropocyclops prasinus, a minor component of the Paul Lake zooplankton. These observations are consistent with prior observations of the effects of size-selective predation on zooplankton communities. 3. Phytoplankton communities also responded strongly to the manipulation, with similarity indices for the two lakes rising from low levels in 1984 to high levels of similarity in 1985 and 1986, reflecting the decrease of formerly dominant Tuesday Lake taxa which were unimportant in Paul Lake and the appearance or increase in Tuesday Lake of several taxa characteristic of the Paul Lake phytoplankton assemblage. these results clearly show that food web structure can have pronounced effects on community composition at all levels of the food web, and that, just as zooplankton communities are structured by sizeselective predation, phytoplankton communities are structured by herbivory. These observations may provide some insight into factors governing the complex distributions of phytoplankton species among various lakes.A contribution from the University of Notre Dame Environmental Research Center, funded by NSF grants BSR-83-08918 and BSR-86-06271     

Effect of temperature on rate of photosynthesis in Antarctic phytoplankton

Summary The rate of photosynthesis of marine antarctic phytoplankton (western Scotia Sea and Bransfield Strait) was determined as a function of temperature, from ambient (-0.8°C to 1.0°C) to 28°C. Photosynthetic rates, based on radiocarbon incorporation during half-day incubations, were increased by as much as 2x with temperatures up to 7°C; at higher temperatures the rates decreased rapidly, so that at 28°C the rates were only 3% of that at ambient temperatures. In antarctic surface waters during the austral summer the rate of photosynthesis by phytoplankton thus is limited by thermodynamic effects on metabolic reactions, in spite of high nutrient concentrations and saturating light levels. The observed rates were in agreement with thermodynamic models of the dependence of phytoplankton growth rate on temperature.     

Temporal plankton dynamics in an oligotrophic maritime Antarctic lake

• 1 The population density, diversity and productivity of the microbial plankton in an oligotrophic maritime Antarctic lake were studied for a 15‐month period between December 1994 and February 1996.
• 2 In the lake, concentrations of nutrients and dissolved organic carbon were uniformly low, temperature varied over a small annual range of 0.1–3 °C, and the surface was ice‐covered except during a period of approximately 6 weeks in summer.
• 3 The total of 57 morphotypes of protozoa observed during the study is a higher taxonomic diversity than previously reported from continental Antarctic lakes, but lower than that found in more eutrophic maritime Antarctic lakes. Likewise, planktonic abundance and productivity were lower than has been reported in other lakes on Signy Island, but generally higher than those of lakes on the Antarctic continent.
• 4 There were marked seasonal and interannual variations in planktonic population density.
• 5 Chlorophyll a concentrations ranged from undetectable to 4.2 µg L^‐1 and the greatest rate of primary productivity measured was 4.5 mg C m^‐3 h^‐1. The phytoplankton was dominated by small chlorophytes and chrysophytes, with phototrophic nanoflagellate abundance ranging from 1.1 × 10³ to 1.2 × 10⁷ L^‐1.
• 6 Bacterial densities of 3.6 × 10⁸ to 1.9 × 10¹⁰ L^‐1 were recorded and bacterial productivity reached a peak of 0.36 µg C L^‐1 h^‐1. Numbers of heterotrophic nanoflagellates between 5.0 × 10⁴ and 1.8 × 10⁷ L^‐1, and of ciliates from undetectable to 1.1 × 10⁴ L^‐1 were observed. Naked amoebae were usually rare, but occasionally reached peaks of up to 1.5 × 10³ L^‐1.

     

The effect of elevated CO2 on growth and competition in experimental phytoplankton communities

We report an experiment designed to identify the effect of elevated CO₂ on species of phytoplankton in a simple laboratory system. Major taxa of phytoplankton differ in their ability to take up CO₂, which might lead to predictable changes in the growth rate of species and thereby shifts in the composition of phytoplankton communities in response to rising CO₂. Six species of phytoplankton belonging to three major taxa (cyanobacteria, diatoms and chlorophytes) were cultured in atmospheres whose CO₂ concentration was gradually increased from ambient levels to 1000 parts per million over about 100 generations and then maintained for a further 200 generations at elevated CO₂. The experimental design allowed us to trace a predictive sequence, from physiological features to the growth response of species to elevated CO₂ in pure culture, from the growth response in pure culture to competitive ability in pairwise mixtures and from pairwise competitive ability to shifts in the relative abundance of species in the full community of all six species. CO₂ altered the dynamics of growth in a fashion consistent with known differences among major taxa in their ability to take up and use CO₂. This pure‐culture response was partly successful in predicting the outcome of competition in pairwise mixtures, especially the enhanced competitive ability of chlorophytes relative to cyanobacteria, although generally statistical support was weak. The competitive response in pairwise mixtures was a good predictor of changes in competitive ability in the full community. Hence, there is a potential for forging a logical chain of inferences for predicting how phytoplankton communities will respond to elevated CO₂. Clearly further extensive experiments will be required to validate this approach in the greater complexity found in diverse communities and environments of natural systems.     

Characteristics of plankton communities in Chinese integrated fish ponds: effects of excessive grazing by planktivorous carps on plankton communities

Biomass and production of plankton communities were investigated in two Chinese integrated fish culture ponds in August, Dianshanhu Pond (with high density of planktivorous carp) and Pingwang Pond (with low density of planktivorous carp). The plankton communities were composed of rotifers, protozoans, phytoplankton (<40 µm) and bacteria. The large phytoplankton (>40 µm), cladocerans and copepods were rare because of grazing pressure by the carp. The density or biomass of bacteria (1.93 × 10⁷ and 2.20 × 10⁷ cells ml^–1 on average in Dianshanhu and Pingwang Ponds, respectively), picophytoplankton (24.6 and 18.5 mg m^–3 Chla on average) and rotifers (5372 and 20733 ind. 1^–1 on average) exceeded the maximum values reported for natural waters.The average [³H]thymidine uptake rates were 694 and 904 pmoles 1^–1 h^–1 (13.4 and 20.6 µgC 1^–1) and the bacterial production by the >2 µm fraction amounted 21–28% of total [³H] thymidine uptake rate in both ponds. The mean chlorophylla concentrations were 59.1 and 183 mg m^–3 in Dianshanhu and Pingwang Ponds, respectively. 82.4% and 65.3% of the total Chla was contributed by the <10 µm nano- and picophytoplankton in each pond, respectively. In particular, the picophytoplankton contribution amounted 41.2% of thtal Chla in Dianshanhu Pond. Primary production was 2.5 and 3.4 gC m^–2 d^–1 in each pond, respectively, and >50% of production was contributed by picophytoplankton. The mean biomasses of protozoa were 168 µg 1^–1 and 445 µg 1^–1 and those of rotifers were 763 µg 1^–1 and 1186 µg 1^–1 in Dianshanhu and Pingwang Ponds, respectively. The ecological efficiencies expressed in terms of the ratios of primary production to zooplankton production were 0.22 and 0.31, for the two ponds.     

Structure of plankton communities in Ilchir, an alpine lake in eastern Siberia

 Lake Ilchir is an alpine lake located 1963 m above sea level in the mountain ranges of eastern Sayan, eastern Siberia. Observations are presented from October 1998 to September 1999 in order to provide the phytoplankton and zooplankton community structures. Sixty-six taxa of phytoplankton and 66 taxa of zooplankton were recorded. Of much interest was the finding of rare species, such as the dinoflagellate Gymnodinium coeruleum, the diatoms Pliocaenicus costatus and Cyclotella tripartita, and the calanoids Acanthodiaptomus tibetanus and Arcthodiaptomus (S.) paulseni. Received: August 24, 2001 / Accepted: April 13, 2002     

Persistence and growth of the fecal indicator bacteria enterococci in detritus and natural estuarine plankton communities

Enterococci are used to evaluate recreational-water quality and health risks in marine environments. In addition to their occurrence in feces of warm blooded animals, they are also common epiphytes. We investigated the contribution of plankton- or particle-associated enterococci in estuarine and coastal water. Seven water and size-fractionated plankton samples were collected monthly between April 2008 and January 2009 in the tidal reaches of the Skidaway River (Georgia, USA). Each size fraction, along with filtered (<30 μm) and bulk estuarine water, was processed according to U.S. Environmental Protection Agency method 1600. Presumptive enterococci were selected and species were identified using carbon substrate utilization patterns. The highest average densities occurred within the 30-, 63-, 105-, and 150-μm size fractions, which also represented the majority (>99%) of the particles within the sampled water. Particle-associated enterococci accounted for as little as 1% of enterococci in bulk water in April to as much as 95% in July. Enterococcus faecalis was the most commonly isolated species from both water and plankton and represented 31% (16/51) and 35% (6/17) of the identified Enterococcus species from water and plankton, respectively. Enterococcus casseliflavus represented 29% of the selected isolates from plankton and 16% from water. Both E. faecalis and E. casseliflavus were able to survive and grow in plankton suspensions significantly longer than in artificial seawater. Enterococcus spp. may be highly concentrated in plankton and associated particles, especially during summer and fall months. These findings could have implications for the effectiveness of enterococci as an indicator of coastal water quality, especially in particle-rich environments.     

Phytoplankton biomass from continuous plankton recorder data: an assessment of the phytoplankton colour index

A 15 month time-series of simultaneous fluorometric measurementsof chlorophyll a, and phytoplankton cell abundance and a phytoplanktoncolour index (PCI) from continuous plankton recorder (CPR) samplesare compared for the Iberian margin, western Europe. The relationshipsbetween fluorometrically determined chlorophyll, cell abundanceand PCI are all significant, with PCI showing a better relationshipto chlorophyll than cell abundance. This supports previous researchwhich suggests that the PCI is a useful index of phytoplanktonstanding stock and, furthermore, may be a measure of cells thatare not preserved or counted in the routine microscopic processingof CPR samples. The relationship between PCI and chlorophyllappears to vary seasonally, although more extensive data areneeded to quantify this variability. The study also comparesthe PCI and fluorometer data with chlorophyll values obtainedfrom satellite imagery (SeaWiFS) for the Iberian margin. Significantcorrelations exist during the 15 month time-series between thesethree estimates of phytoplankton concentration. This resultdemonstrates that the ~50 year time-series of PCI for the NorthAtlantic can provide valuable information on changes in phytoplanktonstanding stock.     

Modeling the temperature effect on the specific growth rate of phytoplankton: a review

Phytoplankton are key components of ecosystems. Their growth is deeply influenced by temperature. In a context of global change, it is important to precisely estimate the impact of temperature on these organisms at different spatial and temporal scales. Here, we review the existing deterministic models used to represent the effect of temperature on microbial growth that can be applied to phytoplankton. We first describe and provide a brief mathematical analysis of the models used in constant conditions to reproduce the thermal growth curve. We present the mechanistic assumptions concerning the effect of temperature on the cell growth and mortality, and discuss their limits. The coupling effect of temperature and other environmental factors such as light are then shown. Finally, we introduce the models taking into account the acclimation needed to thrive with temperature variations. The need for new thermal models, coupled with experimental validation, is argued.     

Evolved physiological responses of phytoplankton to their integrated growth environment

Phytoplankton growth and productivity relies on light, multiple nutrients and temperature. These combined factors constitute the 'integrated growth environment'. Since their emergence in the Archaean ocean, phytoplankton have experienced dramatic shifts in their integrated growth environment and, in response, evolved diverse mechanisms to maximize growth by optimizing the allocation of photosynthetic resources (ATP and NADPH) among all cellular processes. Consequently, co-limitation has become an omnipresent condition in the global ocean. Here we focus on evolved phytoplankton populations of the contemporary ocean and the varied energetic pathways they employ to solve the optimization problem of resource supply and demand. Central to this discussion is the allocation of reductant formed through photosynthesis, which we propose has the following three primary fates: carbon fixation, direct use and ATP generation. Investment of reductant among these three sinks is tied to cell cycle events, differentially influenced by specific forms of nutrient stress, and a strong determinant of relationships between light-harvesting (pigment), photosynthetic electron transport and carbon fixation. Global implications of optimization are illustrated by deconvolving trends in the 10-year global satellite chlorophyll record into contributions from biomass and physiology, thereby providing a unique perspective on the dynamic nature of surface phytoplankton populations and their link to climate.     

Dominance of phosphorus over nitrogen as the limiter to phytoplankton growth rate

Laboratory experiments with natural phytoplankton assemblages from three lakes (two mesotrophic and one oligotrophic) showed that added PO₄ predictably affected growth rate (μ, determined as P : B) while NO₃ had little effect even when the N P ratio approached one. The response to PO₄ followed the typical Monod-type function. The lack of effect of NO₃ on μ at such low N : P ratios is in striking contrast to the added effect of NO₃ Plus PO₄ on maximum biomass produced versus only PO₄ alone. Contribution No. 193 to the IBP-Coniferous Forest Biome. The work was supported in part by National Science Foundation Grant No. GB-20963 (IBP-Coniferous Forest Biome), and in part by Environmental Protection Agency Training Grant T900313-W P293-03,04. Contribution No. 193 to the IBP-Coniferous Forest Biome. The work was supported in part by National Science Foundation Grant No. GB-20963 (IBP-Coniferous Forest Biome), and in part by Environmental Protection Agency Training Grant T900313-W P293-03,04.     

Effects of UVB radiation on marine phytoplankton communities

The impact of enhanced and reduced UVB radiation (UVBR) on pelagicecosystems was studied during two mesocosm experiments in May and June/July1994. The ambient UVBR exposure was either reduced with mylar foil orartificially enhanced with UVB fluorescent tubes. Developments in thephytoplankton communities were followed during 11 and 8 day periods usingseveral structural and functional parameters. In the May experiment,enhanced UVBR significantly stimulated carbon dioxide fixation, activity ofalkaline phosphatase and content of fatty acids. In the June-Julyexperiment, the effects induced by changed UVBR were smaller with someindications of decreased algal biomass with enhanced UVBR. Several of themeasured parameters indicated that the two experiments representeddifferent stages in the plankton community development. In the Mayexperiment, the community was in a development stage, moving fromnutrient-replete to nutrient-depleted conditions, while the community inJune/July was depleted of nutrients from the start. The stimulating effectsof UVBR in May are suggested to be the secondary effects of aphotochemically induced breakdown of dissolved organic matter, resulting inan increase in available nutrients.