Effects of small-scale turbulence on lower trophic levels under different nutrient conditions (original) (raw)
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Marine Ecology Progress Series, 2002
The control exerted by different intensities and temporal inputs of small-scale turbulence on the balance between C production and respiration in planktonic communities has been studied by means of laboratory microcosms. The different turbulence conditions modified the temporal pattern of phytoplankton (chlorophyll a) and total biomass development. However, the differences between average values of total (after re-suspension) biomass were not statistically significant. Net primary production (NP) was significantly higher at intermittent turbulence (alternating turbulence and calm periods), with maxima coinciding with the turbulence periods. Respiration (R) was less sensitive to turbulence conditions, but on average was significantly higher under continuous turbulence. The relationships between analysed total particulate organic carbon (TPOC) and theoretical estimates of total organic carbon (according to the daily balance between NP and R) indicated that between 30 and 50% of NP could be released as dissolved organic carbon. The quotient between daily C production and R (indicative of auto- or heterotrophic conditions) was higher under turbulence conditions. Autotrophy lasted for longer periods of time under intermittent turbulence. These results confirm the importance of turbulence in the modulation of the trophic status of the system, opening new perspectives for the study of the mechanisms controlling the selection of planktonic food webs.
Effects of turbulence on the composition of phytoplankton assemblages in marine microcosms
Mar. Ecol. Prog. Ser, 1987
Changes in composition of natural phytoplankton assemblages enclosed in 30 dm3 cylindrical culture vessels were followed under different conditions of water stirring. Experiments were started at different times of the year with seawater taken off Masnou (20 km north of Barcelona, Spain) and each treatment was assayed in 2 replicates. Enclosure of phytoplankton assemblages was followed in general by a pronounced increase in chlorophyll concentration and phytoplankton abundance due to proideration of centric diatoms. As nutrients were consumed, phytoplankton abundance decreased and the diatoms were substituted by coccolithophorids, dinoflagellates and flagellates. Different stirring treatments affected the timing and intensity of the initial population peak and induced repeatable (within each experiment) changes in the composition of the phytoplankton assemblages of the later phases of the experiments.
Marine Ecology Progress Series, 2012
We carried out 2 experimental simulations in which natural planktonic communities were subjected to a combination of turbulence and variable nutrient forcing. Nutrient addition was varied both in terms of total nutrient load and in the balance of elements. Unbalanced nutrient inputs (with regard to Redfield values) and varying nitrogen sources are frequent in coastal areas heavily exposed to human perturbations. The relative abundance of nitrate and ammonium has been related to shifts in the size distribution of the planktonic community, so we explored whether uneven inputs of ammonium and nitrate could be major factors driving plankton dynamics in coastal environments. The occasional uncoupling between turbulence and nutrient pulses is also a distinctive feature of nearshore waters compared with open ocean environments. Thus, we further tested the match–mismatch between nutrient enrichments and turbulent mixing. Both turbulence and nutrient inputs had a significant positive effect on the growth of planktonic organisms, with some synergistic effects. Shifts in community composition appeared to be mostly related to the interplay between turbulence and N partitioning. Under still conditions, ammonium-rich waters favoured small organisms and reinforced the microbial loop, whereas nitrate mostly favoured diatom growth. Turbulence added complexity to the final outcome, because mixing tended to favour large over small osmotrophs. Accordingly, the rapid growth of small autotrophs and heterotrophic bacteria in ammonium-rich waters may be partly counteracted by diatom increases if nutrient pulses are coupled with turbulent mixing; diatom bursts after nitrate enrichments may also be enhanced by concomitant turbulence.
Aquatic Microbial Ecology, 2002
The response of phytoplankton and bacteria dynamics to turbulence and nutrient availability interactions was studied in natural coastal waters enclosed in 15 l microcosms. The effect of turbulence was examined under 3 different nutrient-induced conditions: nitrogen surplus (N, with initial addition of an excess of nitrogen, N:P ratio = 160), nitrogen:phosphorus ratio balanced (NP, with initial addition of nitrogen and phosphorus as Redfield ratio, N:P ratio = 16) and control (C, no nutrient addition). Turbulence (ε = 0.055 cm 2 s -3 ) was generated by vertically oscillating grids. The experiment lasted for 8 d and samples were generally taken daily for nutrient and plankton measurements. Turbulence increased the relative importance of phytoplankton to bacteria when nutrients were added, while in the control the effect of turbulence was negligible. Turbulence also influenced the species' composition and the size distribution of the phytoplankton community. The relative contribution of diatoms to total phytoplankton biomass and the average cell size were higher under turbulence, particularly in N and NP treatments. The results of these experiments indicate the importance of considering the hydrodynamic conditions in studies addressing competition for nutrients among different osmotrophic organisms in plankton communities.
Journal of Plankton Research, 2009
A year-long series of monthly experiments with laboratory enclosures were conducted with water from Blanes Bay (NW Mediterranean) to analyse the change in the short-time response of the osmotrophic planktonic community to simulated turbulence and nutrient input events. Both experimental factors triggered a relative increase of biomass in the enclosures, in terms of chlorophyll a, bacteria and particulate organic matter. Ratios of particulate organic nitrogen to phosphorus became lower in the water than in the sediment, although turbulence partially smoothed out this difference. Initial physico-chemical conditions significantly influenced the short-time responses to experimental forcing. The response to turbulence, in terms of chlorophyll a, was maximum in spring. The response to nutrient enrichment was found to be seasonal, and was correlated with photoperiod and temperature, and also in situ nitrate and silicate concentrations and Secchi depth, which are proxies of recent inputs of nutrients resulting from episodes of resuspension and river discharge. This study shows robust qualitative regularities in the response of the osmotrophic planktonic community to episodes of turbulence and nutrient enrichment, with quantitative variability throughout the year, depending mostly on the recent record of hydrodynamic forcing.
Marine Ecology Progress Series, 1988
Effects of turbulence on the dynamics of copepods as well as on the development of phytoplankton biomass were studied in 30 dm3 laboratory microcosms. Two experiments were carried out, with different successional stages of the plankton populations, using seawater from the Masnou nautical harbour, 20 km north of Barcelona. Two experimental conditions were established (stirred microcosms with copepods, and unstirred microcosms with copepods). Enclosure of plankton populations was followed by a phytoplankton bloom, which differed in intensity in stirred and unstirred microcosms. Time changes in the abundance of the dfferent developmental stages of copepods (from eggs to adults), sex ratios (d / P + d) , fecundty (no. eggs/no. females), total copepod biornass, and the ratio consumers/producers, also differed in stirred and unstirred microcosms. Turbulence seems to reduce consumer biomass through changes in the demographic composition (lower proportion of males and higher development rates) and probably by increasing the metabolic activity of copepods (feeding pressure and excretion rates). The ultimate effect of turbulence would be a reduction of the trophic efficiency of the system, and accelerated turnover rates.
Coastal plankton responses to turbulent mixing in experimental ecosystems
Marine Ecology Progress Series, 1998
Turbulent mixing is increasingly implicated as a key factor regulating ecological dynamics in coastal planktonic systems. Although photosynthesis is directly fueled by light energy, it has been hypothesized that the 'auxiliary' energy provided by mixing can subsidize or control ecosystem function. Unrealistic mixing has also been cited as one explanation for difficulties in reproducing natural plankton dynamics in enclosed experimental ecosystems (mesocosms). To explore the importance of mixing in shallow planktonic ecosystems, we traced changes over a 4 wk period in population, community, and ecosystem level properties in replicate 1 m3 experimental ecosystems subjected to different mixing regimes. Mixing energy was delivered by slolvly rotating impellers on a cycle of 4 h on and 2 h off to match the sernidiurnal pattern of tidal mixing that characterizes many temperate estuaries. Three mixing levels were generated by altering impeller rotation rates. The intermediate level was scaled to match typical mixing intensities of waters in Chesapeake Bay, the low mixing level approximated calm oceanic surface waters, and the high mixing level approximated the environment withln a tidal front. High and low mixing levels encompassed a 6x range in turbulence intensity, a 9x range in the surface-bottom mixing time and eddy diffusivitv coefficients, and a 230x range in turbulent energy dissipation rates. Mixing had a significant negative effect on copepod and gelatinous zooplankton abundance and also altered the timing of peak copepod densit~es. Chlorophyll a dynamlcs and phytoplankton group composition, as assessed with accessory pigment concentrations, also exhibited modest differences among mixing treatments. Mixing had negligible effects on nutnent concentrations and on community and whole-system productivity and respiration. lmportant caveats in Interpreting the results of this experiment are that system size excluded observation of the effects of large-scale mixing processes, trophic complexity was limited (e.g. no fish), and in thls whole-ecosystem context it was difficult to distinguish direct from indirect effects of mixing. Nevertheless, our results imply that ecosystem-level processes in planktonic systenls may often be less sensitive to differences in small-scale turbulence than population and community dynamics, and also that mixing effects may be strongly dependent on the specific structure of particular ecosystems. KEY WORDS: Mixing. Turbulence. Plankton. Copepod Mesocosm. Production. Respiration. Auxiliary energy 'Even the relatively small flows of physical energy from the wind and the tide set in motion a cascade of eddies and ecological effects that can alter dramatically the much larger flows of solar and chemical energy.' (Nixon 1988
Effects of small-scale turbulence on growth and grazing of marine microzooplankton
Aquatic Sciences
We report the effects of small-scale turbulence at realistic intensity (=1.110-2 cm 2 s-3) on the growth and grazing rates of three marine heterotrophic dinoflagellates (Peridiniella danica, Gyrodinium dominans and Oxyrrhis marina) and one ciliate (Mesodinium pulex). All the dinoflagellates showed a reduction of volume-based growth rates, whereas M. pulex did not. P. danica was the most affected by small-scale turbulence, followed by G. dominans, and O. marina. Turbulence slightly increased O. marina ingestion rates, but this increase was not statistically significant. G. dominans and M. pulex ingestion rates were modestly lower under turbulence, and P. danica Manuscript Click here to download Manuscript Microzoo turbulence_revised v4.docx completely ceased feeding in turbulent treatments. Gross growth efficiencies of G. dominans and O. marina were negatively affected by turbulence, whereas they remained unaltered for M. pulex. P. danica feeding and growth rates in the presence of turbulence were close to zero. Overall, there was a negative relationship between the effects of turbulence on ingestion rates and the time needed to process a prey item. Neglecting the effects of turbulence in microzooplankton grazing estimates in the field could produce biased approximations of their impacts on primary producers.
Analysis of the effect of small scale turbulence on the phytoplancton dynamics in the upper ocean
This work quantifies the effect of turbulence on plankton behaviour and its vertical distribution in the ocean, the two basic forcing physical and chemical ingredients are light coming from above and nutrients, (P, N, etc,,) coming from below. The Turbulent Schmidt number is not considered to be fundamental in this work. But the parameter conditions where turbulence is important are shown using real inputs from data from the NW Mediterranean Sea.