Phytoplankton in Sardinian reservoirs

Abstract

A picture of the studies carried out in the past 20 years on phytoplankton from the 36 reservoirs and one natural lake in Sardinia is presented. Processing of the 1994 seasonal data shows that the dominant or subdominant algal species in the 36 reservoirs in terms of density belong to only 8 genera, with species of the genus Microcystis in 17 reservoirs, Chlorella in 15, Cyclotella in 12, Ankistrodesmus and Anabaena in 9, Aphanizomenon in 8, Melosira in 7 and Oocystis in 6. Processing of the data from the 16 reservoirs in which annual or plurennial surveys were carried out, shows that on the basis of the biomass the most likely floristic pattern is Microcystis aeruginosa Kg., Microcystis flos-aquae (Wittr.) Kichn., Anabaena flos-aquae (Lyngb.) Bréb., Anabaena planctonica Brunnth., Aphanizomenon flos-aquae (L.) Ralfs., Melosira granulata (E.) Ralfs and Closterium aciculare T. West. In general terms this means that most of these reservoirs are eutrophic. In fact the species are capable of describing an increasing trophic gradient in agreement with the one described using other variables. Specific cases of reservoirs where plurennial surveys have been carried out are considered. From these surveys a great quali-quantitative variability of the phytoplankton is inferred.     

Phytoplankton stoichiometry

Because phytoplankton live at the interface between the abiotic and the biotic compartments of ecosystems, they play an important role in coupling multiple nutrient cycles. The quantitative details of how these multiple nutrient cycles intersect is determined by phytoplankton stoichiometry. Here we review some classic work and recent advances on the determinants of phytoplankton stoichiometry and their role in determining ecosystem stoichiometry. First, we use a model of growth with flexible stoichiometry to reexamine Rhee and Goldman’s classic chemostat data. We also discuss a recent data compilation by Hall and colleagues that illustrates some limits to phytoplankton flexibility, and a model of physiological adaptation that can account for these results. Second, we use a model of resource allocation to determine the how the optimal nitrogen-to-phosphorus stoichiometry depends on the ecological conditions under which species grow and compete. Third, we discuss Redfield’s mechanism for the homeostasis of the oceans’ nitrogen-to-phosphorus stoichiometry and show its robustness to additional factors such as iron-limitation and temporal fluctuations. Finally, we suggest areas for future research.     

Phytoplankton dynamics

We present a model of the phytoplankton dynamics. The distribution of the size of the phytoplankton aggregates is described by a non-linear transport equation that contains terms responsible for the growth of phytoplankton aggregates, their fragmentation and coagulation. We study asymptotic behaviour of moments of the solutions and we explain why phytoplankton tends to create large aggregates.     

Field and Laboratory Studies on Nile Phytoplankton in Egypt. II. Phytoplankton

Variations in chlorophyll a concentration and in qualitative and quantitative counts of Nile phytoplankton were followed at Assiut from September 1980 to September 1982. Chlorophyll a concentrations usually correlated well with phytoplankton density. The total phytoplankton exhibited higher counts in spring and summer than in autumn and winter. While diatoms exhibited the highest counts, green algae contributed more genera to the phytoplankton community.     

Phytoplankton productivity in findley lake

Findley Lake is a dimictic, oligotrophic, subalpine lake located in the western Cascade Mountains, Washington. The lake is snow covered for most of the year so that the growing season was 3.5 months in 1971 and 4.5 months in 1972. Rapid melt of the lake's snow cover in summer allowed the sudden development of a phytoplankton productivity maximum (as measured by the ¹⁴C tracer method) of 86 mg m⁻² hr⁻¹ and a peak of 48 mg chlorophyll a per m¹ within two weeks of surface clearing in 1972, followed by a rapid decline of productivity and biomass. Annual production (between 10 October, 1971 and 21 October, 1972) was 36 g/m² in the 27.5 m water column. Autotrophic carbon assimilation during the snow-covered period was insignificant. The total production for the lake in 1972 was 530 kg carbon. The concentration of available nitrogen (NO₂ + NO₃ + NH₃ as N) at 15 m ranged from 12 to 76 mg/m³ while PO₄-P ranged from 0.5 to 8.3 mg/m³. In vitro nutrient enrichment experiments with natural phytoplankton communities from the lake indicated that while N and P together were growth limiting, P alone produced a growth response while N alone did not. Contributions to production from net-, nanno-, and ultraplankton were determined by fractional filtration of ¹⁴C-labeled phytoplankton samples. The nannoplankton, dominated by diatoms, accounted for 58% to 94% of productivity.     

Phytoplankton productivity in turbid waters

Many of the freshwater areas in the world are turbid, due tosuspended inorganic particles. The euphotic depth of the shallowturbid impoundment, Wuras Dam, varies between 0.3–1.3m. This results in a compressed production profile where accuratemeasurements become difficult. Tubes of various lengths havebeen used and usually render higher rates, when compared todiscrete bottle incubations. A tube the depth of the euphoticzone confines the phytoplankton in the light and the rates measuredrepresent the maximal possible under the prevailing conditions.Longer tubes include an aphotic portion and give an idea ofthe magnitude of respiration losses. The depth of the mixinglayer appears to be especially important in turbid systems asthe time spent in the dark, relative to the light is of greatimportance and may be the most important regulating factor insuch waters. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP), Second International Workshop heldat the National Oceanographic Institute, Haifa, Israel in April–May1984.     

Phytoplankton Succession in Recurrently Fluctuating Environments

Coastal marine systems are affected by seasonal variations in biogeochemical and physical processes, sometimes leading to alternating periods of reproductive growth limitation within an annual cycle. Transitions between these periods can be sudden or gradual. Human activities, such as reservoir construction and interbasin water transfers, influence these processes and can affect the type of transition between resource loading conditions. How such human activities might influence phytoplankton succession is largely unknown. Here, we employ a multispecies, multi-nutrient model to explore how nutrient loading switching mode might affect phytoplankton succession. The model is based on the Monod-relationship, predicting an instantaneous reproductive growth rate from ambient inorganic nutrient concentrations whereas the limiting nutrient at any given time was determined by Liebig’s Law of the Minimum. When these relationships are combined with population loss factors, such as hydraulic displacement of cells associated with inflows, a characterization of a species’ niche can be achieved through application of the R* conceptual model, thus enabling an ecological interpretation of modeling results. We found that the mode of reversal in resource supply concentrations had a profound effect. When resource supply reversals were sudden, as expected in systems influenced by pulsed inflows or wind-driven mixing events, phytoplankton were characterized by alternating succession dynamics, a phenomenon documented in inland water bodies of temperate latitudes. When resource supply reversals were gradual, as expected in systems influenced by seasonally developing wet and dry seasons, or annually occurring periods of upwelling, phytoplankton dynamics were characterized by mirror-image succession patterns. This phenomenon has not been reported previously in plankton systems but has been observed in some terrestrial plant systems. These findings suggest that a transition from alternating to “mirror-image” succession patterns might arise with continued coastal zone development, with crucial implications for ecosystems dependent on time-sensitive processes, e.g., spawning events and migration patterns.     

Phytoplankton phenology in the global ocean

In recent years, phytoplankton phenology has been proposed as an indicator to monitor systematically the state of the pelagic ecosystem and to detect changes triggered by perturbation of the environmental conditions. Here we describe the phenology of phytoplankton growth for the world ocean using remote-sensing ocean colour data, and analyse its variability between 1998 and 2007. Generally, the tropics and subtropics present long growing period (≈15-20 weeks) of low amplitude (<0.5 mg Chl m⁻³), whereas the high-latitudes show short growing period (<10 weeks) of high amplitude (up to 7 mg Chl m⁻³). Statistical analyses suggest a close coupling between the development of the growing period and the seasonal increase in insolation in the North Atlantic and Southern Ocean. In the tropics and subtropics, variability in light is low, and the growing period is controlled by nutrient supply occurring when mixing increases. Large interannual variability in the duration of the growing period is observed over the decade 1998-2007, with positive anomalies following the major 1997-1998 El Niño-La Niña events, and generally negative anomalies from 2003 to 2007. Warmer Sea-Surface Temperature (SST) over the duration of the growing period is associated with longer duration at high-latitudes indicating an extension of the growing period over summer months. The opposite is observed in the tropics and subtropics, where the duration is shorter when the SST is warmer, indicating increased stratification. Positive phases of North Atlantic Oscillation and Southern Annular Mode and negative phases of Multivariate El Niño-Southern Oscillation index (El Niño conditions), associated with enhanced water mixing and nutrients supply, generally sustain longer growth. On the basis of the results, perspectives are drawn on the utility of phenology as an organising principle for the analysis of pelagic ecosystem.     

Phytoplankton dynamics in the Congo River

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Phytoplankton ecology in an Antarctic lake

SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.
The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and ¹⁴C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll- a concentration (maximum value 170 mg m⁻²) but carbon fixation remained low, with values <500 mg C m⁻² day⁻¹. The algae contributing to this peak were mainly small chlorophytes and chrysophytes. The summer open-water period (December-March) was characterized by a different phytoplankton population dominated by cryptophytes. Chlorophyll levels were lower ( c . 40 mg m⁻²) but ¹⁴C fixation rates >3 g C m⁻² day⁻¹ were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h⁻¹ mg⁻¹ (chlorophyll- a ) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.     

Phytoplankton Population Efficiency Studies

Experiments designed to determine the photosynthetic capacity and efficiency of the phytoplankton of a small body of water were performed for a twelve month period. The experimental design was able to distinguish between actively growing large populations and those which were senescent.     

Phytoplankton of Estonian rivers in midsummer

Fifty-nine species of Odonata were collected in a recent study in the freshwater swamp lake of Tasek Bera, Peninsular Malaysia, in contrast to 33 species that were recorded previously from the Ramsar site. This study added 35 species to the odonate records and together with the museum records, the number of species for the site now stands at 78 from 12 families. The causal factors for the absence of 19 species and other biological aspects such as habitat clustering and temporal activity profile were discussed.     

Phytoplankton competition in deep biomass maximum

Resource competition in heterogeneous environments is still an unresolved problem of theoretical ecology. In this article, I analyze competition between two phytoplankton species in a deep water column, where the distributions of main resources (light and a limiting nutrient) have opposing gradients and co-limitation by both resources causes a deep biomass maximum. Assuming that the species have a trade-off in resource requirements and the water column is weakly mixed, I apply the invasion threshold analysis (Ryabov and Blasius, Ecol Lett 14:220–228, 2011) to determine relations between environmental conditions and phytoplankton composition. Although species deplete resources in the interior of the water column, the resource levels at the bottom and surface remain high. As a result, the slope of resources gradients becomes a new crucial factor which, rather than the local resource values, determines the outcome of competition. The value of resource gradients nonlinearly depend on the density of consumers. This leads to complex relationships between environmental parameters and species composition. In particular, it is shown that an increase of both the incident light intensity or bottom nutrient concentrations favors the best light competitors, while an increase of the turbulent mixing or background turbidity favors the best nutrient competitors. These results might be important for prediction of species composition in deep ocean.     

Phytoplankton communities in channel catfish ponds

Seasonal changes in the quantity and quality of phytoplankton were studied in six channel catfish culture ponds. Chlorophyll a concentrations were generally highest in the summer (averaging >200 g 1^–1) but the highest individual chlorophyll a value recorded (910 g 1^–1) occurred in the winter during a bloom of Dictyosphaerium pulchellum. On the average, green algae (Chlorophyta) and euglenoids (Euglenophyta) represented relatively constant proportions of the phytoplankton community seasonally (about 35 and 10%, respectively). In the summer and fall, blue-green algae (Cyanophyta) became abundant. Diatoms were relatively abundant at all times and constituted the majority of the community in the winter and spring.     

Phytoplankton Respiration in the Peru Upwelling

Respiratory electron transport system (ETS) measurements weremade on the microplankton in the Peru upwelling system near15°S during March, April, and May of 1977. The close associationbetween chlorophyll- biomass and ETS activity indicate thatthe microplankton were predominantly phytoplankton. Phytoplanktonrespiration average 14% of gross fixed carbon. When zooplanktonrespiration in the euphotic zone is considered, the total planktonrespiration represented an average of 19% of gross primary production. ^*Contribution Number 79002 from the Bigelow Laboratory for OceanSciences.     

Phytoplankton Assemblage Characteristics in Recurrently Fluctuating Environments

Annual variations in biogeochemical and physical processes can lead to nutrient variability and seasonal patterns in phytoplankton productivity and assemblage structure. In many coastal systems river inflow and water exchange with the ocean varies seasonally, and alternating periods can arise where the nutrient most limiting to phytoplankton growth switches. Transitions between these alternating periods can be sudden or gradual and this depends on human activities, such as reservoir construction and interbasin water transfers. How such activities might influence phytoplankton assemblages is largely unknown. Here, we employed a multispecies, multi-nutrient model to explore how nutrient loading switching mode might affect characteristics of phytoplankton assemblages. The model is based on the Monod-relationship, predicting an instantaneous growth rate from ambient inorganic nutrient concentrations whereas the limiting nutrient at any given time was determined by Liebig’s Law of the Minimum. Our simulated phytoplankton assemblages self-organized from species rich pools over a 15-year period, and only the surviving species were considered as assemblage members. Using the model, we explored the interactive effects of complementarity level in trait trade-offs within phytoplankton assemblages and the amount of noise in the resource supply concentrations. We found that the effect of shift from a sudden resource supply transition to a gradual one, as observed in systems impacted by watershed development, was dependent on the level of complementarity. In the extremes, phytoplankton species richness and relative overyielding increased when complementarity was lowest, and phytoplankton biomass increased greatly when complementarity was highest. For low-complementarity simulations, the persistence of poorer-performing phytoplankton species of intermediate R*s led to higher richness and relative overyielding. For high-complementarity simulations, the formation of phytoplankton species clusters and niche compression enabled higher biomass accumulation. Our findings suggest that an understanding of factors influencing the emergence of life history traits important to complementarity is necessary to predict the impact of watershed development on phytoplankton productivity and assemblage structure.     

Phytoplankton observations in the Eastern Caribbean Sea

A total of 88 taxa were noted in these samples, of which there were 44 diatoms, 41 pyrrhophyceans, 2 cyanophyceans and 1 silicoflagellate. Totals of 37 and 38 different phytoplankters were observed during cruises E46K-67-68 and E1-C-70, respectively, with 58 species noted in the extensive samplings of E 5013-68-69. A diatomaceaous flora predominated in each series of collections. The phytoflagellates were well represented, but in low numbers. The overall phytoplankton concentrations were low for each of the areas studied during these three January cruises. Even the preliminary data on the coccolithophore concentration does not indicate a major development at this time of the year. Generally, phytoplankton counts were lowest at stations most distant from the island complex and especially in the shallow waters that passed between the islands, directly from the north Atlantic into the Caribbean Sea. Results from the 1969 and 1970 collections west of the Lesser Antilles correspond closely to the findings reported by Hargraves et al. (1970). There was considerable diversity of phytoplankton species, but they were present in low numbers. They have related this condition to the low nutrient concentrations in the oceanic waters of the Lesser Antilles region.The writer thanks Duke University Marine Laboratory for the use of the facilities of the R/V EASTWARD on cruises E46K-67-68, E50D-68-69, and E1C-70, in the Cooperative Oceanographic Program supported through National Science Foundation grant G17669.     

Seasonal Development of Phytoplankton in Fish Ponds

At the fish ponds under study the authors defined several types of plankton which have been frequently found during the season (April – October). These types are: Early-spring maximum of phytoplankton, Depression of phytoplankton, Bloom of Aphanizomenon, Maximum of Chlorococcales. The periods of “depression” seem to be typical for the managed carp ponds in the spring. They are characterized by the low density of rapidly reproducing algal populations (e. g. Cryptomonas) and by the dense populations of large cladocerans of the genus Daphnia. Chlorophyll in phytoplankton is less than 5μg/l, transparency is higher than 2 meters. Periods of the spring depression may be followed by the maxima of either Aphanizomenon or Chlorococcales, with concentrations of chlorophyll increasing to 100 μg/l and more. The change from the phase of “depression” to the “maximum of Chlorococcales” is accompanied by decrease in numbers of Daphnia and increase in numbers of the small cladoceran species, but all the mechanisms responsible for the transition are not yet fully understood.     

Phytoplankton succession in Lake Valencia,Venezuela

Phytoplankton counts and supporting physical and chemical data were taken on Lake Valencia, Venezuela, over a five-year interval. The data are used to test the validity of a successional paradigm for class-level taxa. According to the paradigm, formulated from previous studies of Lake Lanao, Philippines, and from data on temperate lakes, the order of taxa from early to late succession is: diatoms, chlorophytes, blue-green algae, dinoflagellates. A successional episode is considered to begin when stability of a water column is restored after deep mixing. As the episode progresses, there is a steady decrease in concentration of the limiting macronutrient (in this case, N). In a test of the validity of the paradigm for Lake Valencia, dates of exceptional population increase or decrease were obtained for each taxon. Since nitrate concentration declines steadily as succession progresses, the entry of a given taxon into the successional sequence is indicated quantitatively by the mean nitrate concentration on dates of exceptional increase in population density, and exit from the successional sequence is indicated by mean nitrate concentration on dates of exceptional population declines. The successional position of each major taxon, bounded by its entry and exit in the sequence, can be mapped on the complete spectrum of nitrate concentrations observed in the lake. For Lake Valencia, the nitrate mapping procedure agrees exactly with the predictions based on the successional paradigm. Conformance of Lake Valencia phytoplankton with predictions made a priori suggests that there is a generalized pattern in the phytoplankton succession of the mixed layers of temperate and tropical lakes.