Effects of small-scale turbulence on growth and grazing of marine microzooplankton (original) (raw)
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Increased grazing rates of microplankton in response to small-scale turbulence
Marine Ecology-progress Series, 1994
Grazing rates of free-living microplanktonic organisms on bacteria-sized particles, as measured by the decrease of tracer particles over time, increased in response to small-scale turbulence. This was observed in the field, with the natural community, and in the laboratory, with a model protozoan. When ingestion rates were measured at the beginning of laboratory incubations, no statistical difference between treatments was found. Protozoan concentrations increased faster in the turbulence treatment but their cell sizes decreased compared to the non-turbulence treatment. Since direct ingestion rates were not affected by turbulence, the mechanism to explain the difference in tracer decrease remains unresolved. A complex picture of physiological and possibly behavioral changes in the protozoa owing to small-scale turbulence emerged from this study. Some of these changes have been observed before with copepods and might represent a common trend in free-living planktonic organisms. Turbulence could be an important factor in the control of bacterial populations in aquatic systems by means of increasing protozoan grazing rates.
Limnology and Oceanography, 2005
We investigated the effect of natural levels of turbulence on the vertical distribution and net population growth of the dinoflagellate Ceratium tripos and on the interaction with its predator, the mixotrophic dinoflagellate Fragilidium subglobosum. Unialgal cultures of each species were exposed to four kinetic energy dissipation rates, : 0.0001, 0.01, 0.05, and 1 cm 2 s Ϫ3 , generated by vertically oscillating grids in 2-liter cylindric containers. Autotrophic growth of F. subglobosum was not affected by any level of turbulence tested. In contrast, at Ն 0.05 cm 2 s Ϫ3 (this value is generated in the upper 10 m of the ocean by a moderate gale or at 0.5 m in depth by a gentle breeze), C. tripos decreased its net population growth, and the vertical distribution of the cells was affected. At the highest turbulence level, C. tripos stopped swimming, settled, and accumulated at the bottom. Mixotrophic growth of F. subglobosum, when fed C. tripos at high densities (i.e., k10 prey cells mL Ϫ1 ), was not affected by turbulence. However, at low prey cell densities (i.e., 5 to 8 C. tripos cells mL Ϫ1 ), growth and ingestion rates of F. subglobosum were significantly higher at the highest turbulence level compared to the rates at other turbulence levels and were close to the rates measured at high prey cell densities, presumably because sedimentation of C. tripos cells resulted in patches where the cell densities were not food-limiting for F. subglobosum.
Limnology and Oceanography, 1995
Laminar shear below the turbulence microscale can create relative motion between protozoan suspension feeders and their prey, potentially influencing encounter and retention. Theory suggests that ingestion rate may rise sigmoidally with increasing turbulence strength, although interference with feeding mechanisms might occur at some turbulence levels. We measured rates of feeding on fluorescently labeled prey at concentrations below feeding saturation in a survey of cultured bacterivorous and herbivorous flagellates, ciliates, and a helioflagellate over a wide range of shear rates produced in rotating Couette flows. Shears of 0.1-10 s-l (corresponding to moderate to extremely strong marine and estuarine turbulence) enhanced clearance rates by the aloricate choanoflagellate, Monosiga sp., up to 2.7 x the mean rate in still water. Shears of l-10 s-l enhanced clearance rates by the helioflagellate, Ciliophrys marina, up to 7.0 x the mean in still water. The data are consistent with a sigmoidal response to increasing shear rate. In contrast, clearance rates of the tintinnid, Helicostomella sp., were suppressed at 10 s-l to as low as 0.42 x the still-water rate. Several other flagellates and ciliates (Paraphysomonas sp., two unidentified chrysomonads, Diaphanoeca grandis, Favella sp., and an unidentified heterotrich) showed no significant effects. We hypothesize that the protozoa most susceptible to an influence of turbulence are nonmotile (e.g. Heliozoa, Foraminifera, Radiolaria) or are weak swimmers (e.g. some flagellates and ciliates). Current methods for measuring feeding rates in still-water incubations may underestimate grazing by these taxa under strong turbulence in the field. Through speciesspecific influences on feeding rates, spatial and temporal variations in turbulence may have very selective effects on microbial food-web dynamics. * Current address: Appl. Ocean Physics and Engineering Dept., WHOI, Woods Hole, Massachusetts 02543. Acknowledgments We thank W. Hicks, R. Johnson, and D. Thoreson for building the Couette tanks and D. Caron and T. Fenchel for providing cultures. The manuscript benefited from discussions and comments provided by P. Hill, L. Karp-Boss, M. Pace, and two anonymous reviewers. This work was supported by ONR contract NO00 14-90-J-1078 to P. A. Jumars and A. R. M. Nowell, NSF grant OCE 89-16 165 to E. J. Lessard, and an NSF Graduate Fellowship to J. Shimeta. Contribution 2 118 from the School of Oceanography, University of Washington. P Rt, & r1, r2 u Hamaker constant, J Particle concentration, m-3 Clearance rate, ml h-l Prey dilfusivity, m2 s-l Collision efficiency in Couette flow and in turbulence, dimensionless Encounter rate, s-l Mean shear rate in Couette flow, s-l Mean laminar shear rate below the turbulence microscale, s-l Peclet number as a ratio of either advection or shear to diffusion, nondimensional Radius ratio, r,/r, , dimensionless Inner and outer radius of gap in Couette tank, m Radius of protozoan cell and food particle, or radii of spheres, m Swimming speed, m s-* Mean turbulent kinetic energy dissipation rate per unit of mass, W kg-' Conservative estimate of E (Eq. 9), W kg-' Critical values of E and E,,,, for turbulence to influence encounter rate, W kg-' Kolmogorov length microscale of turbulence, m Bottom angle in Couette tank, rad Kinematic viscosity of seawater, 1 X 1O-6 m2 s-l Rotation rate of Couette tank, rad s-l
Marine Ecology-progress Series, 2000
From the literature we obtained experimental data on the effects of small-scale turbulence on plankton at the organism scale. Normalized rates in response to turbulence were calculated in the present study for parameters related to growth, ingestion and energy expenditure. Growth rates are, in general, negatively affected by turbulence. Nevertheless, the data are highly biased towards a specific group of organisms, dinoflagellates, which could have peculiar physiological impediments under turbulence. Ingestion rates seem to be increased by turbulence, especially at low and intermediate levels.
Effects of small-scale turbulence on lower trophic levels under different nutrient conditions
2010
Small-scale turbulence affects the pelagic food web and energy flow in marine systems and the impact is related to nutrient conditions and the assemblage of organisms present. We generated five levels of turbulence (2*10 29 to 1*10 24 W kg 21) in landbased mesocosms (volume 2.6 m 3) with and without additional nutrients (31:16:1 Si:N:P mM) to asses the effect of small-scale turbulence on the lower part of the pelagic food web under different nutrient conditions. The ecological influence of nutrients and small-scale turbulence on lower trophic levels was quantified using multivariate statistics (RDA), where nutrients accounted for 31.8% of the observed biological variation, while 7.2% of the variation was explained by small-scale turbulence and its interaction with nutrients. Chlorophyll a, primary production rates, bacterial production rates and diatom and dinoflagellate abundance were positively correlated to turbulence, regardless of nutrient conditions. Abundance of autotrophic flagellates, total phytoplankton and bacteria were positively correlated to turbulence only when nutrients were added. Impact of small-scale turbulence was related to nutrient conditions, with implications for oligotrophic and eutrophic situations. The effect on community level was also different compared to single species level. Microbial processes drive biogeochemical cycles, and nutrient-controlled effects of small-scale turbulence on such processes are relevant to foresee altered carbon flow in marine systems.
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.
Species-specific physiological response of dinoflagellates to quantified small-scale turbulence 1
Journal of Phycology, 2007
Turbulence has been shown to alter different aspects of the physiology of some dinoflagellates. The response appears to be species-specific and dependent on the experimental design and setup used to generate small-scale turbulence. We examined the variability of the response of three dinoflagellate species to the turbulence, following the same experimental design used by Berdalet (1992) on Akashiwo sanguinea (Hirasaka) Ge. Hansen et Moestrup (=Gymnodinium nelsonii G. W. Martin). In all experiments, turbulence was generated by an orbital shaker at 100 rpm, which corresponded on bulk average, to dissipation rates (e, quantified using an acoustic Doppler velocimeter) of %2 cm 2 AE s )3 . Turbulence did not appreciably affect Gymnodinium sp., a small dinoflagellate. However, Alexandrium minutum Halim and Prorocentrum triestinum J. Schiller exhibited a reduced net growth rate (33% and 28%, respectively) when shaken during the exponential growth phase. Compared to the still cultures, the shaken treatments of A. minutum and P. triestinum increased the mean cell volume (up to 1.4-and 2.5-fold, respectively) and the mean DNA content (up to 1.8-and 5.3-fold, respectively). Cultures affected by turbulence recovered their normal cell properties when returned to still conditions. The swimming speed of the cells exposed to agitation was half that of the unshaken ones. Overall, the response of A. minutum and P. triestinum was similar, but with lower intensity, to that observed previously on A. sanguinea. We found no clear trends related to taxonomy or morphology.
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.
Effects of turbulence on the feeding rate of a pelagic predator : the planktonic hydroid 1
2006
23 Relatively little is known about the role of turbulence in a predator prey system where the 24 predator is a passive, pelagic forager. The Campanulariid hydroid Clytia gracilis (Cnidaria, 25 Hydrozoa) is unusual because it occurs as planktonic colonies and is reported to forage passively 26 in the water column on Georges Bank, Massachusetts, USA. In this study we investigated the role 27 of various turbulence conditions on the feeding rate of C. gracilis colonies in laboratory 28 experiments. We found a positive relationship between turbulence velocities and feeding rates up 29 to a turbulent energy dissipation rate of ca 1 cm s. Beyond this threshold feeding rate decreased 30 slightly, indicating a dome-shaped relationship. Additionally, a negative relationship was found 31 between feeding efficiency and hydroid colony size under lower turbulent velocities, but this 32 trend was not significant under higher turbulence regimes. 33 34