Overwintering of Microcystis aeruginosa Kutz. in a shallow lake

The standing crop and photosynthetic activity of Microcystisaeruginosa Kütz. in both the plankton and sediment wereinvestigated from November 1979 to May 1982 in Lake Kasumigaura,Japan. The number of planktonic colonies of this species decreasedfrom early autumn to early spring, but increased in the sedimentduring late summer and autumn. The overwintering colonies inthe sediment were –100–1000 times greater per unitarea than those in lake water. No photoinhibition of photosynthesiscould be observed in overwintering Microcystis. The values ofthe initial slopes of photosynthesis-light (P-I) curves weresimilar to those of the summer population, although the maximumphotosynthetic rate (P_max) measured at 20°C was lower thanthat of the summer planktonic population. In winter the valuesof initial slope of the P-I curve, and the ratio of phycobilinto chlorophyll a sorted from sediment were higher than in coloniesfrom the plankton.     

Factors influencing the spatio-temporal distribution of benthic Microcystis aeruginosa colonies (Cyanobacteria) in the hypertrophic Grangent Reservoir (Loire, France)

The spatio-temporal distribution of benthic colonies of Microcystis aeruginosa in Grangent Reservoir (France) in 2000 was not homogeneous and appeared to be controlled by many external factors: lake depth, station morphometry, substratum and hydraulic regime (lacustrine or fluvial). A most important concentration of benthic colonies was found at deep sites with fine sediment or at sites where the sediment was rich in organic matter. In spite of a stable water level and a minimum flow during summer, the number of benthic colonies showed great variation in the lacustrine downstream part of the reservoir. These variations may be explained by the dynamics of planktonic cyanobacteria.     

Gloeotrichia echinulata, a colonial cyanobacterium with a unique phosphorus uptake and life strategy

Epilimnetic colonies of Gloeotrichia echinulata were harvestedfrom 200–300 I of water in Lake Erken with filtrationthrough appropriate plankton nets (200 or 70 µm). Phosphateuptake characteristics, phosphorus (P) status and photosynthesisof the colonies were determined twice a week during July andAugust 1991. Phosphate uptake was analysed according to thesimple force- flow relationship of Falkner et al. (Arch. Microbiol.,152, 353–361, 1989). The threshold concentration of Puptake below which uptake ceases for energetic reasons, wasconstantly much higher than the epilimnetic soluble reactivephosphorus (SRP) concentration, so that the planktonic colonieswere unable to acquire any Pin the epilimnion. Neither did organicP seem to be a source of P for planktonic colonies. Gloeotrichiaechinulata has a unique life strategy in comparison to othercommon genera of bloom-forming cynanobacteria. Its P assimilationand growth are completely separated both in time and space;growth is preceded by benthic P assimilation. Epilimnetic growthwas based solely on internally stored P and growth rates fittedthe Droop model well. Depletion of stored P restricts the lengthof the planktonic phase to 15–20 days under ‘optimal’growth conditions. Wind-induced surface drift seemed to be themost important loss factor from the epilimnion. Massive recruitmentof P-rich benthic colonies accounted for two-thirds of totalnet internal P loading observed between mid-July and mid-August(3.8 mg P m^–2 day^–1).     

The rates of sediment-water exchange of oxygen and sediment bioturbation in Lough Neagh,Northern Ireland

Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to be 6 × 10⁻⁸ cm² s⁻¹. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused by the irrigational activities of the benthic fauna.     

The Osmotic Pressure of Concentrated Solutions of Polyethylene Glycol 6000, and its Variation with Temperature

The vapour pressures of aqueous solutions of polyethylene glycol6000 have been measured (by equilibration with sucrose solutions)up to the saturation point at 25 °C (1.45 g g^–1 water).The reduced-osmotic-pressure (/c), when plotted versus concentration(c), rapidly and linearly increased up to a concentration ofabout 0.8 g g^–1 (crossing the similar plot for sucrose).Above this concentration, the reduced-osmotic-pressure rosemore slowly, but still more rapidly than sucrose. The maximumosmotic pressure achieved at saturation was nearly 18 MPa. Usingthe virial equation: /c= RT/M + RTA₂c, the calculated secondvirial coefficient (A₂) for the linear part is 4.5 x 10^–3mol g^–1, a value slightly greater than most literaturevalues at 25 °C. Data are cited showing that A₂ varies linearlyfrom 5–6 x 10^x3 at 0 °C, to zero at 80–90 °C     

Identification of a Water-soluble Fungal Inhibitor in the Leaves of Acer platanoides L.

It was confirmed that the leaves of Acer platanoides containan antifungal inhibitory substance. Low concentrations of sterilecold water extracts inhibited the germination of the sporesof Cladosporium herbarum (three isolates), Cladosporium sphaerospermumand Cylindrocarbon radiclcola. In the concentration range 0·06–0·125per cent (w/v) of leaf material the inhibitory response wasdemonstrated to increase linearly as the concentration of leafmaterial increased logarithmically. Inhibitory activity wasfound in leaf samples collected during a period from July toOctober but activity had disappeared from leaves collected inthe following January. The inhibitory activity was located intwo components of the water extract by bioassay tests followingether extraction and separation by chromatography. One of theactive components has been identified as gallic acid by gaschromatography. Gallic acid has also been detected in dew collectedfrom leaf surfaces where it is suggested that it may play animportant part in the colonization of the leaves by fungi.     

Colony growth and evidence for colony multiplication in Phaeocystis pouchetii (Prymnesiophyceae) isolated from mesocosm blooms

Using well plates of Phaeocystis pouchetii colonies isolatedfrom experimental mesocosms in western Norway, increases incolony size and division were documented. Median longest lineardimensions increased 0–7 µm h^–1; literaturePhaeocystis globosa values are 0.9–4.7 µm h^–1.Ten to twelve percent of colonies divided at rates of 0.21–0.28divisions day^–1. Daughter colonies were 100 µm smallerthan mother colonies. Colonies delayed 3.5–4.9 days tofirst division, compared with literature values of 4–5days for P. globosa. This study provides the first experimentalevidence for colony division of wild P. pouchetii.     

Phytoplankton seasonal dynamics in a Mediterranean coastal lagoon: emphasis on the picoeukaryote community

The dynamics of the phytoplankton community were investigatedin a marine coastal lagoon (Thau, NW Mediterranean) from February1999 to January 2000. Dilution experiments, chlorophyll a (Chla) size-fractionation and primary production measurements wereconducted monthly. Maximum growth and microzooplankton grazingrates were estimated from Chl a biomass fractions to separatepico- from nano- and microphytoplankton and by flow cytometryto distinguish between picoeukaryotes and picocyanobacteria.In spring, the phytoplankton community was dominated by Chaetocerossp. and Skeletonema costatum, which represented most of biomass(B) and primary production (P). Nano- and microphytoplanktongrowth was controlled by nutrient availability and exceededlosses due to microzooplankton grazing (g). Picoeukaryote andcyanobacteria growth was positively correlated with water temperatureand/or irradiance, reaching maximum values in the summer (2.38and 1.44 day^–1 for picoeukaryotes and cyanobacteria, respectively).Picophytoplankton accounted for 57% of the biomass-specificprimary productivity (P/B). Picophytoplankton was strongly controlledby protist grazers (g = 0.09–1.66 day^–1 for picoeukaryotes,g = 0.25–1.17 day^–1 for cyanobacteria), and microzooplanktonconsumption removed 71% of the daily picoplanktonic growth.Picoeukaryotes, which numerically dominate the picoplanktoncommunity, are an important source of organic carbon for theprotistan community and contribute to the carbon flow to highertrophic levels.     

Studies in Sieve-tube Exudation through Aphid Mouth-parts: The Effects of Light and Girdling

Exudation from the mouth-parts of the willow aphid Tuberolachnussalignus (Gmelin) inserted in the phloem of Salix sp. was studied.Leafy rooted cuttings 80–100 cm. in length were grownin artificial light. Exuding mouth-parts were located on thestem below the crown of leaves and the rates of exudation andconcentration of sucrose in the exudate measured whilst theleaves were alternately illuminated (600–800 f.c.) anddarkened. In darkness the rate of sap and sucrose exudationincreased and the concentration fell, relative to the valuesin the light. Similar effects were produced by girdling thestem just beneath the crown of leaves. These were shown to besecondary effects due to a lessening of transpirational tensionsduring darkness or after girdling. They were eliminated if changesin water tension were avoided. Direct effects of light and girdling on exudation were demonstratedby allowing the leaves to assimilate ¹⁴CO₂ and measuring thespecific activity of the exudate. These changes in radioactivityseen against the constancy in total sugar exudation demonstratea switch in source from leaf to stem. An attempt is made toexplain the pattern of changes in specific activity of the exudateduring light and dark periods in terms of shifts in the locationof contributing sources. The rate of translocation between two aphid colonies situateda measured distance apart was estimated by noting the timeswhen the honeydew from each reached a certain level of radioactivity.A mean figure of 28 cm./hr. was obtained.     

Food and suspended sediment influences on the naupliar and copepodid durations of freshwater copepods: comparative studies on Tropodiaptomus and Metadiaptomus

Post-embryonic durations of Tropodiaptomus spectabilis (Kiefer)and Metadiaptomus colonialis(van Douwe) were determined at 20°Cin laboratory factorial experiments involving four algal foodenrichment levels (0, 100, 500 and 2500 µg l^–1 Cof Selenastrum added to 20 µm filtered water from respectivesource-lakes) and three suspended sediment levels (filtered,natural, and 2- to 3-fold sediment-enriched lake water). Foodeffects (30, 75, 225 and 600 (µg ^–1 C of Scenedesmus)were tested alone at 20°C for Metadiaptomus meridianus (vanDouwe). Total naupliar (D_n) and total copepodid (D_c) developmenttimes [summed to give total post-embryonic duration (D_t)] andmetasome lengths at maturity were measured In all taxa, foodsupply maximally affected D_c values 2- to 3-fold, whereas itsmaximal influence on D_n values was relatively slight (generally25%). The measured effect of food supply on D_t, was as strongas the predicted influence of temperature over an appropriateannual range. Food supply influenced size at maturity, and probablythereby fecundity, thus exerting additional demographic influences.Sediment effects were inconsistent, and quantitatively weakerthan food effects Total development of T.spectabilis was 20%raster, and that of M.colonialis 15% slower in sediment-enrichedthan in natural sediment level treatments; contrasting baselinesediment levels (2–3 times higher for the latter species)and different enrichment procedures confound interpretation.Unexpectedly, and inexplicably, development almost invariablyfailed in sediment-free water, implying an apparent dependencyon inorganic particles in these taxa This contrasts with thegenerally adverse influences of high sediment concentrationsupon zooplankton. Minimal male and female D_t values at 20°Cwere comparable and significantly longer in M.colonialis (15.5and 17 7 days) and M meridianus (16.5 and 21.5 days) than inT.spectabilis (11.7 and 12 2 days). These differences in durationare ecologically incongruous in relation to expected r –K life history strategies of genera characteristic of temporaryor semipermanent waters and permanent waters respectively.     

The influence of micro-algae on the oxygen dynamics in a brackish ditch

Summary Seasonal changes in the activity of phytoplankton and benthic algae in relation to diurnal oxygen pulses were investigated in a 120 cm deep, brackish hypertrophic ditch. A vertical chloride gradient was built up by saline seepage and drain-water effluent. The stable chloride gradient could lead to oxygen stratification near the sediment, and to oxygen gradients towards the water surface. The oxygen gradients were rather unstable, depending on the chloride gradient and the wind velocity.Light was limiting photosynthesis both in summer and in winter. Surface oxygen maxima increased with solar radiation during summer.In summer the diatomCyclotella caused surface oxygen maxima at light saturation in the late afternoon. Simultaneously, the dominant flagellatesPeridinium andChlamydomonas produced oxygen in dim light, probably choosing their favourite light energy level by vertical migration. Oxygen fluctuations ranged from 0 to 34 mg O₂.l^–1 in a 100 cm vertical profile above a 20 cm anoxic layer. The amplitude of the diurnal oxygen maxima varied from 10 to 34 mg O₂.l^–1.In winter the water became very clear. The oxygen gradient was inverted during the day showing a characteristic oxygen maximum above the bottom, produced by benthicAchnanthes colonies.Communication no. 193.     

The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay

Ammonia excreted by mixed zooplankton populations over an annual(1972–1973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH₃-N dry wt^–1 day^–1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH³-N mg dry wt^–1 day^–1. Grossphytoplankton production integrated over the year (1972–1973)averaged 151 mg C m^–3 day^–1 for an 8 m water column;peaks of 332 and 905 mg C m^–3 day^–1 occurred duringthe winter-spring and summer blooms, respectively. Excretedammonia, integrated seasonally and annually, contributed only0.2% and 4.9% of the nitrogen required for observed gross productionduring the winter-spring and summer blooms, respectively, and4.4% annually. However, excreted ammonia may be an importantsource of the nitrogen required by Skeletonema costatum, thedominant diatom in Narragansett Bay, during the post-bloom periodwhen 186% of the nitrogen required for its net production wasmet by ammonia excretion. A combination of zooplankton ammoniaexcretion and benthic ammonia flux contributed 22% of the nitrogenrequired for the annual gross production (440 g C m^–2)while 51% of the nitrogen required for the net production ofSkeletonema was accounted for by regenerated nitrogen. ¹This research was supported by NSF grant GA 31319X awardedto Dr.T.J.Smayda.     

Utilization of Sediment CO2 by Selected North American Isoetids

The photosynthetic uptake of root-zone CO₂ was determined forEriocaulon septangulare, Gratiola aurea, Isoetes macrospora,Littorella uniflora var. americana and Lobelia dortmanna aspart of a study of the photosynthetic carbon economy of submergedaquatic isoetids. The pH and dissolved inorganic carbon (DIC)of the sediment interstitial water in four Wisconsin lakes reflectedthe water column character, where the DIC increased with depthin the sediment to concentrations five to ten times those ofthe water column. Sediment free CO₂ concentrations were 5–50times those in the water column and were similar at all sites(about 05–1.0mM CO₂ in the root-zone). In ‘pH-drift’studies these plants were unable to take up HCO₂^–. Laboratory determinations of the carbon uptake from the rootand shoot-zones were made for all five species. These experimentsshowed that CO₂ in the root-zone accounted for 65–95 percent of external carbon uptake for the five species. For G.aurea and E. septangulare, root-zone CO₂ was > 85 per centof carbon uptake. Carbon, CO₂, photosynthesis, sediment, isoetid, Eriocaulon septangulare, Gratiola aurea, Isoetes macrospora, Littorella uniflora, Lobelia dortmanna     

Comparison of east and west chlorophyll a standing stock and oceanic habitat along the Transition Domain of the North Pacific

Chlorophyll (Chl) a was measured every 10 m from 0 to 150 min the Transition Domain (TD), located between 37 and 45°N,and from 160°E to 160°W, in May and June (Leg 1) andin June and July (Leg 2), 1993–96. Total Chl a standingstocks integrated from 0 to 150 m were mostly within the rangeof 20 and 50 mg m^–2. High standing stocks (>50 mg m^–2)were generally observed westof 180°, with the exceptionof the sporadic high values at the easternmost station. Thetotal Chl a standing stock tended to be higher in the westernTD (160°E–172°30'E) than in the central (175°E–175°W)and eastern (170°W–160°W) TD on Leg 1, but thesame result was not observed on Leg 2. It was likely that largephytoplankton (2–10 and >10 µm fractions) contributedto the high total Chl a standing stock. We suggest that thehigh total Chl a standing stock on Leg 1, in late spring andearly summer, reflects the contribution of the spring bloomin the subarctic region of the northwestern Pacific Ocean. Thedistribution of total Chl a standing stock on Leg 2 was scarcelyaffected by the spring phytoplankton bloom, suggesting thattotal Chl a standing stock is basically nearly uniform in theTD in spring and summer. Moreover, year-to-year variation inthe total Chl a standing stock was observed in the western TDon Leg 1, suggesting that phytoplankton productivity and/orthe timing of the main period of the bloom exhibits interannualvariations.     

Seasonal and interannual variability of size-fractionated phytoplankton biomass and community structure at station Kerfix, off the Kerguelen Islands, Antarctica

Time series of phytoplankton biomass and taxonomic compositionhave been obtained for the 3 years 1992, 1993 and 1994 in thenorthern part of the Southern Ocean (station Kerfix, 5040'S,6825;E) Autotrophic biomass was low throughout the year (<0.2mg m^–3 except during a short period in summer when a maximumof 1.2 mg chlorophyll (Chl) a m– was reached. During winter,the integrated biomass was low (<10 mg m^–2) and associatedwith deeply mixed water, whereas the high summer biomass (>20mg m^–2) was associated with increased water column stability.During summer blooms, the >10 µ;m size fraction contributed60% to total integrated biomass. Large autotrophic dinoflagellates,mainly Prorocentrum spp., were associated with the summer phytoplankton maxima and accounted for >80% of the total autotrophcarbon biomass. In November and December, the presence of thelarge heterotrophic dinoflagellates Protoperidinium spp. andGyro dinium spp. contributed a high proportion of total carbonbiomass. During winter, the <10 µm size fraction contributed80% of total Chi a biomass with domination of the picoplanktonsize fraction. The natural assemblage included mainly nakedflagellates such as species of the Prasinophyceae, Cryptophyceaeand Prymnesiophyceae. During spring, picocyanobacteria occurredin sub-surface water with a maximum abundance in September of106 cells 1^–1     

Influence of Cadmium on Growth and Nitrogen Metabolism of Anabaena cylindrica Lemm

A study was made of the effects of cadmium on the Cyanobacterium(blue-green alga) Anabaena cylindrica Lemm. as part of the paddy-fieldecosystem. A simple culture vessel has been designed, which allows periodicalmeasurement of growth (optical density) and nitrogenase activity(C₂H₂-C₂H₄ method). The influence of medium renewal was checked:the renewal of the medium maintained a higher growth rate andhigher nitrogen fixation ability. The cadmium effects were studied using six concentration levelsranging from 0 (control) to 2 parts 10^–6 with renewedmedia (10% every day). No significant differences could be seen up to 1 part 10^–6for nitrogenase activity and relative percentage of heterocysts(decreasing as a function of time from ±4% to ±1.5%). Inhibition of growth (OD and dry weight) was weak at 1 part10^–6 but important at 2 parts 10^–6; at this concentrationcadmium induced morphological and physiological effects: chlorosis,cellular malformations and destruction, and increase in heterocystfrequency (up to 7.72% ±0.19). The cadmium concentration factors were much lower than thosereported for other plants like Chlorella and water pests     

Pyrosoma atlanticum (Tunicata, Thaliacea): grazing impact on phytoplankton standing stock and role in organic carbon flux

Pyrosomas are the large group of pelagic tunicates whose trophicrole in pelagic communities has not yet been sufficiently studied.We ran across a local area of high concentration of the mostwidespread and commonest species of pyrosomas, Pyrosoma atlanticum,450 miles off the Congo river mouth. The following was estimated:gut pigment content, defecation rate, organic carbon and pigmentcontent of fecal pellets, and sinking rate. Based on these dataand the measured number of pyrosomas colonies the grazing impacton phytoplankton and the fecal pellet flux were calculated.During the night swarms of 50–65 mm P.atlanticum removed53% of phytoplankton standing stock in the 0–10 m layer;sparsely distributed pyrosomas consumed only 4%. The grazingimpact in the 0–50 m layer was only 12.5 and <1% respectively.The fecal pellet flux resulting from nocturnal feeding of P.atlanticumwhile swarming made up 1.4–1.6 x 10⁶ pellets m^–210 h^–1 or 305–1035 mg C m^–2 10 h^–1 and1.4 x 10⁵ pellets m^–2 10 h^–1 or 87.4 mg C m^–210 h^–1 while non-swarming. Incubation experiments showedthe rapid degradation of fecal pellets at 23°C: the lossof pigment and carbon content was {small tilde}60–70%after 45 h. We believe that given the sinking rate of 70 m day^–1the main part of fecal material does not leave the upper watercolumn and is retained in the trophic web of the epipelagiclayer.     

RECRUITMENT OF BENTHIC MICROCYSTIS (CYANOPHYCEAE) TO THE WATER COLUMN: INTERNAL BUOYANCY CHANGES OR RESUSPENSION?1

In some lakes, large amounts of the potentially toxic cyanobacterium Microcystis overwinter in the sediment. This overwintering population might inoculate the water column in spring and promote the development of dense surface blooms of Microcystis during summer. In the Dutch Lake Volkerak, we found photochemically active Microcystis colonies in the sediment throughout the year. The most vital colonies originated from shallow sediments within the euphotic zone. We investigated whether recruitment of Microcystis colonies from the sediment to the water column was an active process, through production of gas vesicles or respiration of carbohydrate ballast. We calculated net buoyancy, as an indication of relative density, using the amounts and densities of the major cell constituents (carbohydrates, proteins, and gas vesicles). Carbohydrate content of benthic Microcystis cells was very low throughout the year. Buoyancy changes of benthic Microcystis were mostly a result of changes in gas vesicle volume. Before the summer bloom, net buoyancy and the amount of buoyant colonies in the sediment did not change. Therefore, recruitment of Microcystis from the sediment does not seem to be an active process regulated by internal buoyancy changes. Instead, our observations indicate that attachment of sediment particles to colonies plays an important part in the buoyancy state of benthic colonies. Therefore, we suggest that recruitment of Microcystis is more likely a passive process resulting from resuspension by wind‐induced mixing or bioturbation. Consequently, shallow areas of the lake probably play a more important role in recruitment of benthic Microcystis than deep areas.     

Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy

• Background and Aims Summer dormancy in perennial grasseshas been studied inadequately, despite its potential to enhanceplant survival and persistence in Mediterranean areas. The aimof the present work was to characterize summer dormancy anddehydration tolerance in two cultivars of Dactylis glomerata(dormant ‘Kasbah’, non-dormant ‘Oasis’)and their hybrid using physiological indicators associated withthese traits. • Methods Dehydration tolerance was assessed in a glasshouseexperiment, while seasonal metabolic changes which produce putativeprotectants for drought, such as carbohydrates and dehydrinsthat might be associated with summer dormancy, were analysedin the field. • Key Results The genotypes differed in their ability tosurvive increasing soil water deficit: lethal soil water potential(_s) was –3·4 MPa for ‘Kasbah’ (althoughnon-dormant), –1·3 MPa for ‘Oasis’,and –1·6 MPa for their hybrid. In contrast, lethalwater content of apices was similar for all genotypes (approx.0·45 g H₂O g d. wt^–1), and hence the greater survivalof ‘Kasbah’ can be ascribed to better drought avoidancerather than dehydration tolerance. In autumn-sown plants, ‘Kasbah’had greatest dormancy, the hybrid was intermediate and ‘Oasis’had none. The more dormant the genotype, the lower the metabolicactivity during summer, and the earlier the activity declinedin spring. Decreased monosaccharide content was an early indicatorof dormancy induction. Accumulation of dehydrins did not correlatewith stress tolerance, but dehydrin content was a function ofthe water status of the tissues, irrespective of the soil moisture.A protein of approx. 55 kDa occurred in leaf bases of the mostdormant cultivar even in winter. • Conclusions Drought avoidance and summer dormancy arecorrelated but can be independently expressed. These traitsare heritable, allowing selection in breeding programmes.     

Size, composition and distribution of particles related to wind induced resuspension in a shallow tropical lagoon

The size, composition and distribution of particles in the watercolumn were surveyed in a shallow area (1 m depth) of a tropicallagoon (Cte d'Ivoire) during a sequence of wind-induced resuspension.Water samples were collected hourly near the surface duringone tidal cycle. Three characteristic periods were distinguished:a calm period with low wind speed (average 1.2 m s^–1 awindy period with wind speed >3 m^–1 s (range between4 and 6 m s^–1) inducing sediment resuspension and a relaxationperiod during the decrease of wind velocity. From the analysisof several parameters (particle size and volume, bacteria. pico-and nanophytoplankton, ciliates and detritus), sediment resuspensioncaused a regular injection of particles from the bed. The finestparticles (1.5–6 µm: chlorophytes such as Chiorellaspp., picocyanobacteria such as Synechococcus) were the firstto be affected by wind-induced turbulence, whereas large particles(6–12 µm: diatoms. cyanobacteria such as Lyngbiaspp.) were dispersed into the water column at the highest windspeed. The fate of the different seston components differedaccording to their size. Therefore, wind-induced resuspensioncould greatly influence the food web organization through thequantity, quality and size of edible particles available ata given time.