Effects of food particle concentration on feeding current velocity in sex species of marine Bryozoa

Experiments were carried out using established methods to measure feeding current velocity in six species of marine Bryozoa collected in 1982 and 1983 around low-tide mark at Port St. Mary, Isle of Man (Flustrellidra hispida, Alcyonidium gelatinosum, A. hirsutum, Electra pilosa, Membranipora membranacea and Bowerbankia gracilis feeding on Tetraselmis suecica). It was found that there was a positive correlation between feeding current velocity and the concentration of food (phytoplankton) in the environment. It was also found that, at a fixed particle concentration, feeding current velocity was strongly correlated with lophophore height and (less strongly) with tentacle number. The competitive and evolutionary implications of these relationships are considered. It is tentatively suggested that interspecific competition for food may be of some significance in marine Bryozoa and that the removal of food supplies to competing colonies may play a role in colony overgrowth and competition for space.     

Hydrodynamic study of the functional morphology of the benthic suspension feeder Phoronopsis viridis (Phoronida)

Ambient water currents were altered by the morphology of an active suspension feeder, Phoronopsis viridis Hilton (phylum Phoronida), to produce a flow around its ciliated crown of feeding tentacles (lophophore). To test the effects of specific morphological characteristics on patterns of water movement, the morphology of model phoronids was varied and the resultant paths of water movement were compared to those around living phoronids. Living individuals were collected from the intertidal sandflats at Bodega Bay, California/USA, in the springs of 1984 and 1985. Although P. viridis actively produce a feeding current, use of various models demonstrated that the gross pattern of flow around a living phoronid was created by the physical interaction of its morphology with ambient currents. The important aspects of that morphology were the presence of a wide, porous crown of tentacles atop a cylindrically-shaped body. A hydrodynamic consequence of this morphology was that dye eroded off the substratum from a circular area around the base of the body and entrained upwards into the lophophore. In addition, rates of water movement were slowed at the lophophore and near the substratum adjacent to a phoronid, particles were slowed and diverted from horizontal paths immediately downstream of the lophophore, and the number of visible suspended particles within the wake per unit time increased with ambient velocity. Paths of water movement around a phoronid were also influenced by its angle and height relative to the substratum, indicating that P. viridis could behaviorally modify their local flow environment.     

Influence of flow speed on the functional response of a passive suspension feeder,the spionid polychaete <Emphasis Type="Italic">Polydora cornuta</Emphasis>

Passive suspension feeders rely on surrounding flow to deliver food particles to them. Therefore, the classic conception of functional response (feeding rate vs. food concentration) may require modification to account for flow speed as a second independent variable. I compared the functional response of Polydora cornuta at different velocities and determined whether food capture was proportional to particle flux (concentration × velocity). To understand feeding responses at a mechanistic level, I measured the functional responses in terms of contact and capture rates and determined particle retention efficiency. Experiments were run separately with two sizes of food particles, and with juvenile or adult worms. For both worm sizes and both particle sizes, capture rate in weak flow was directly related to concentration, but in strong flow it was constant. Worms were therefore unable to benefit from abundant food when in strong flow. The critical velocity at which the capture rate became constant was lower for adult worms than for juvenile worms, and it was lower for small particles than for large particles. Retention efficiency was constant among all treatments, and the results for contact rate were essentially the same as for capture rate. Therefore, the mechanics of particle contact must explain the effects of velocity on the functional response. Contact rate was not a constant proportion of particle flux; treatments with similar fluxes yielded different contact rates depending on the strength of flow. The results appeared to be caused by a velocity-induced behavioral change in appendage posture that affects contact rates: in moderate flow, worms form their feeding palps into helical coils, which they tighten as the velocity increases. I suggest this behavior constrains suspension feeding rates and the mechanical selection between particle sizes when worms are in strong flow, and that the effect changes with ontogeny. Because the results are consistent with patterns in measured growth rates of P. cornuta, I hypothesize that this influence of velocity on the functional response can constrain growth and population dynamics in this species.     

Particle-size selection by Pseudopolydora paucibranchiata (Polychaeta: Spionidae) in suspension feeding and in deposit feeding: influences of ontogeny and flow speed

Pseudopolydora paucibranchiata Okuda suspension feeds and deposit feeds at the sediment-water interface, where it is exposed to a variety of particles differing in physical characteristics and nutritional value. In flume experiments (conducted in August 1994 and May 1995) with two sizes of either suspended or deposited beads, I measured particle-size selection separately in each feeding mode. The same influences of palp width and of ambient flow speed were observed in each mode. At velocities 0.74 cm s^-1 there were no relationships between palp width and the proportion of gut contents composed of large beads. At velocities 1.8 cm s^-1 worms with narrower palps ingested relatively fewer large beads (and more small beads) than did worms with wider palps. Palp width and body length were linearly related, and results were similar when analyzed with body length as the independent variable. As flow speed increased, selectivity changed in a worm-size-specific manner: worms with a palp width -1. Assuming that in the field (1) particle size is the principle criterion for selection, and (2) the amount of digestible food component in deposited and suspended particles, respectively, is related to particle surface area and volume, I hypothesize that changes in selectivity as velocity rises can cause juveniles to experience a decreasing profitability of suspension feeding and a simultaneously increasing profitability of deposit feeding. Juveniles could maintain a diet of high food value despite flow variations by adjusting the proportion of time they spend suspension feeding relative to deposit feeding.     

Methods of ciliary filter feeding in adult Phoronis muelleri (phylum Phoronida) and in its free-swimming actinotroch larva

Microscope-video recordings were used to describe basic characteristics of particle capture in adult Phoronis muelleri and in its actinotroch larva. The larva captures food particles by means of close interplay between the tentacles and the oral hood. Suspended particles in the incoming water flow set up by the lateral "pump" cilia on the tentacles approach the tentacles with a velocity of about 1.5 mm s^-1. Near the tentacles, the particles are stopped by the stiff sensory laterofrontal cilia acting as a mechanical sieve. Simultaneous with stoppage of a particle, the oral hood is rapidly lifted so that water from the surrounding area flows in to occupy the volume created under the hood. Due to the proximity of the tentacle with the arrested particle, this suction will draw the particle away from the laterofrontal cilia into the increased space under the oral hood with a velocity of about 0.6 mm s^-1 before it is subsequently carried to the mouth. If a particle is stopped near the tip of a tentacle this may trigger a tentacle flick, with a tip velocity of about 5-7 mm s^-1, which brings the particle down toward the lifting edge of the hood. A stopped particle may cause a local disruption of the metachronism of the lateral cilia for about 0.14 s. Likewise in the adult, when an incoming particle with a velocity of about 1.6 mm s^-1 is stopped near the tip of a tentacle this triggers a flick, which brings the particle down towards the mouth. The duration of the active flick phase is about one-tenth of the flick cycle. Only when a particle is stopped on the outer part of a tentacle is a flick triggered. Otherwise the particle is either transported down along the frontal surface of the tentacle by means of the frontal cilia, or transferred into the downward current created by the lophophore. The metachronal wave velocity is about 0.25 mm s^-1, the wavelength about 12 µm, and hence the ciliary beat frequency about 21 Hz (at ~16°C). Essential features of the filter-feeding process in both actinotroch larvae and adult P. muelleri reported here resemble the ciliary-sieving process described for bryozoans in recent years. It should be pointed out that the stiff, mechanosensory laterofrontal cilia may be a decisive factor for understanding ciliary upstream collecting, also in pterobranchs and brachiopods in which sensory laterofrontal cilia are present.     

Grazing rates of the Atlantic menhaden Brevoortia tyrannus as a function of particle size and concentration

The feeding behavior of adult Atlantic menhaden (Brevoortia tyrannus) upon 5 species of phytoplankton and 2 species of zooplankton has been studied. Four recognizable feeding stages which were a function of the concentration and size of the food particles were observed. During rapid feeding the fish swam at a constant speed for a prolonged period over a wide range of particle concentrations. Particle and food carbon-concentrations at the threshold for initiation and termination of feeding were inversely related to particle size. Carteria chuii (13.2 μ) was not grazed at a significant rate, while two-cell chains of Skeletonema costatum (16. 5 μ) were filtered from the water, indicating a minimum-size threshold for filtration of between 13 and 16 μ. The most rapid filtering rates were observed for the copepod Acartia tonsa ( \(\bar x\) volume swept clear = 24.8 l/fish/min). The maximum food-particle size acceptable to a menhaden appears to be between Acartia tonsa (1200 μ) and adult Artemia salina (10 mm). These results suggest that the large schools of menhaden found in Atlantic coastal waters could have a significant effect on the plankton, selectively grazing zooplankton, larger phytoplankton, and the longer chains of chain-forming diatoms.     

A hydromechanical principle for particle retention in Mytilus edulis and other ciliary suspension feeders

It is generally thought that the laterofrontal cirri of the bivalve gill act as filters that retain suspended particles in the through current and transfer the particles onto the frontal surface of the gill filaments. In Mytilus edulis calculations indicated that if water passed between the branching cilia of the cirri that are assumed to constitute the filter the pressure drop needed would amount to about 10 times the actual pressure drop across the whole gill. Thus, instead of acting as filters the laterofrontal cirri seem to move water. Presumably, the cirri together with the frontal cilia produce the water currents along the frontal surface of the gill filaments. Particle retention in the bivalve gill implies the transfer of suspended particles from the current of water about to enter an interfilamentar space into a neighbouring frontal surface current. The complex three-dimensional pattern of flow that arises where the 2 systems of current meet is characterized by steep velocity gradients. Particles that enter such steep, steady velocity gradients become exposed to transverse forces that cause the particles to migrate perpendicularly to the direction of flow. Whether particles enter the surface current, i.e. are retained, or they stay within the through current andescape, depends primarily upon particle size, and upon the steepness and height of the gradients within the boundary zone between the surface current and through current. Further studies are needed to evaluate the capacities and relative importance of this hydromechanical particle-trapping mechanism in suspension feeding bivalves. It is suggested that in downstream particle-retaining systems, e.g. on the tentacles of polychaetes and entoprocts, velocity gradients between through currents and surface currents also act as the particle-collecting mechanism.     

Suspension feeding in the brittle-star Ophiothrix fragilis : efficiency of particle retention and implications for the use of encounter-rate models

Dense beds of the suspension-feeding brittle-star Ophiothrix fragilis are common in European waters. Their potential importance in benthic–pelagic coupling has been highlighted, but little is known about the feeding dynamics of this species. Encounter-rate models provide a potential mechanism for the estimation of feeding rates on suspended material of varying sizes. This work investigates factors essential to the application of such models. Particle-retention efficiency (RE) converts encounter rate into capture, or clearance rate. Laboratory studies demonstrated that RE varied with the interactive effects of flow velocity and particle size. RE was lowest for large particles, particularly at high flow velocity where RE as low as 59% was observed. This indicates that if RE is not accounted for in encounter-rate models, significant overestimates of feeding rates on large particles may occur. Flow around feeding arms and tube feet was characterised by intermediate Reynolds numbers, precluding application of the most simple encounter-rate models. Complex secondary-flow patterns were observed, which carried particles along the downstream side of the feeding arms, but these did not appear to increase the area available for particle capture. Previously reported particle capture by arm spines was not observed. Evidence of active rejection of large particles by tube feet was recorded. Difficulties in the application of encounter-rate models for prediction of seston-removal rates are highlighted by these results. Predicted encounter rate may deviate from actual clearance rate due to the effects of retention dynamics, localised flow patterns and differential particle handling. Other methods of estimation of seston-removal rates are equally problematic however, so that encounter-rate models are likely to remain a useful tool for such estimates. Received: 23 January 1998 / Accepted: 24 June 1998     

The role of marine aggregates in the ingestion of picoplankton-size particles by suspension-feeding molluscs

Suspension-feeding molluscs are important members of coastal communities and a large body of literature focuses on their feeding processes, including the efficiency of particle capture. Some molluscs, such as bivalves, capture individual picoplankton cells (0.2–2.0 μm) with a retention efficiency of less than 50%, leading to the assumption that such particles are not an important food resource. Picoplankton, however, are often concentrated in particle aggregates of much larger size. This study investigates the ability of suspension feeders to ingest picoplankton-size particles (0.2–2.0 μm) bound in marine aggregates. We fed clams (Mercenaria mercenaria), mussels (Mytilus edulis), oysters (Crassostrea virginica), scallops (Argopecten irradians) and slipper snails (Crepidula fornicata) 1.0- and 0.5-μm fluorescent particles (either polystyrene beads or bacteria) that were (1) dispersed in seawater, or (2) embedded within laboratory-made aggregates. Dispersed 10-μm beads were also delivered so that feeding activity could be determined. Ingested fluorescent particles were recovered in feces or isolated digestive glands and quantified. Results indicate that aggregates significantly enhance the ingestion of 1.0- and 0.5-μm beads by all species of bivalves, and enhance the ingestion of bacteria (greatest cell dimension ca. 0.6 μm) by all suspension feeders examined. Differences among species in their ability to ingest aggregates and picoplankton-size particles, however, were evident. Compared to mussels and clams, scallops and oysters ingested fewer aggregates with 1.0-μm beads or bacteria, and slipper snails ingested the most dispersed beads and bacteria. These differences may be a consequence of variations in gill structure and mechanisms of particle processing. Our data demonstrate that suspension feeders can ingest picoplankton-size particles that are embedded within aggregates, and suggest that such constituent particles may be an important food resource.     

Particle size,flow velocity,and suspension-feeding by the erect bryozoansBugula neritina andB. stolonifera

Patterns of feeding by the erect bryozoansBugula neritina andB. stolonifera were studied by assessing ingestion rates of mixtures of polystyrene particles of three sizes present in equal densities at two ambient water-flow velocities. Particle size was found to influence feeding byB. neritina, while feeding byB. stolonifera was influenced by an interaction between particle size and flow velocity. Large and mediumsized particles were ingested at rates disproportionate to their numerical abundance, and small particles were always ingested in low numbers. Disproportionate feeding did not appear to be due to the greater likelihood of directly intercepting or of detecting particles of larger sizes, but may be explained by other size-dependent particle behaviors, active selection or rejection by the bryozoans, and/or the utilization of different feeding techniques. Comparison with a parallel study indicated that patterns of feeding on single-sized suspensions cannot be used to predict patterns of feeding on mixed suspensions. This is one of the few studies to test the combined influence of variation in both suspended particulate matter and in properties of the fluid medium. Such investigations will provide more realistic views of suspensionfeeding performance.     

Function of lateral cilia in suspension feeding of lophophorates (Brachiopoda,Phoronida, Ectoprocta)

Suspension feeding by the brachiopod Laqueus californianus (Koch), the phoronid Phoronis vancouverensis Pixell, the ectoprocts Bugula sp., Membranipora villosa Hincks, and Schizoporella unicornis (Johnston), and actinotrocha and cyphonautes larvae was observed. Lophophorates retain particles on the upstream side of the band of lateral cilia, even after particles have moved lateral to the frontal surface. This suggests that these animals utilize an induced local reversal of beat of the lateral cilia for concentration and capture of suspended food particles. Retention of particles can cease while the current past the tentacles continues. Movement of particles down the frontal surface of the tentacles of L. californianus and the ectoproct species confirms previous observations that mucus strands are not used in particle capture. Possible functions of latero-frontal cilia or bristles are considered. Distribution of the feeding mechanism among phyla, clearance rates, and the lack of fusion of tentacles in brachiopods are discussed. The impingement mechanism previously suggested for lophophorates cannot account for the movements of particles observed here.     

Particle size-selection of two deposit feeders: the amphipod Corophium volutator and the prosobranch Hydrobia ulvae

The feeding biology of the deposit-feeding amphipod Corophium volutator is compared to that of the coexisting, deposit-feeding prosobranch Hydrobia ulvae. Regarding ingestion of particles, both forms show size selection which alone can explain their coexistence. Particle size-selection also explains some qualitative differences in the composition of the food of the two forms; thus, diatoms play a relatively larger role in the diet of H. ulvae than in the diet of c. volutator, whereas bacteria are probably relatively more important for the latter. Results of experiments with feeding of C-14 labelled microorganisms are in accordance with the findings on particle size-distribution of the gut contents, and show that (1) C. volutator can only utilize bacteria adsorbed to particles within the size range 4 to 63 (this is why the presence of clay and silt particles in the sediment are necessary for efficient feeding of this amphipod); (2) C. volutator can utilize bacteria suspended in the water pumped through its burrow for respiration if silt and clay particles are present in the sediment. (3) H. ulvae can utilize large particles, and also browses on surfaces, and some evidence is brought forward that it also utilizes mucus for trapping microorganisms. The coexistence of deposit-feeding animals is discussed. It is concluded that the number of coexisting, closely related species is usually small, and that their resource partitioning is probably mainly based on particle-size selectivity. In the case of unrelated forms (e.g. H. ulvae and C. volutator, a number of behavioural, physiological and morphological differences, and also the widespread ability of deposit feeders to utilize alternative feeding mechanisms may also lead to resource partitioning. Thus, there are often several niche dimensions related to feeding allowing a certain diversity of coexisting deposit feeders.     

Trace metal ingestion and assimilation by the green mussel <Emphasis Type="Italic">Perna viridis </Emphasis>in a phytoplankton and sediment mixture

We examined trace metal ingestion and assimilation (Cd, Se, Zn) by the green mussel Perna viridis in a mixture of diatoms and sediment at concentrations below and above the pseudofeces production levels. Dual gamma radiotracers (¹⁰⁹Cd, ⁶⁵Zn) were used to investigate particle selection on marine diatoms and sediments. The diatom (Thalassiosira weissflogii) was radiolabeled with ¹⁰⁹Cd, and the natural sediment was radiolabeled with ⁶⁵Zn. By comparing the ratios of ¹⁰⁹Cd:⁶⁵Zn in the particle mixture, mussel tissues and pseudofeces within a short-term exposure period (35 min), the results demonstrated that the green mussels were able to selectively ingest the diatom particles at a high particle load. Efficiency of selection for nutritious particles (e.g. diatoms) increased with increasing ratio of sediments in the particle mixture. Pseudofeces contained a higher ratio of sediments relative to that in the feeding suspension. No major particle selection was observed at concentrations below the level for pseudofeces production. The assimilation of Cd, Se and Zn by the green mussels was quantified using a pulse-chase feeding technique. The assimilation of Se and Zn by the green mussels from ingested diatoms was reduced with the presence of sediment within the mussel gut, presumably due to the resorption of metals onto the sediment, leading to a quicker passage of metals through the digestive tract and a lower proportion of metals subjected to intensive digestion. In contrast, the presence of diatoms did not significantly affect metal assimilation from ingested sediment. A significant correlation between metal assimilation efficiency and metal gut passage time was also observed. Metal assimilation by the green mussels appeared to be little dependent on the particle concentration in seawater. Our study suggests that particle selection may potentially alter metal influx from ingested food sources, particularly at high particle concentrations. Selective feeding of nutritious particles, coupled with a high assimilation efficiency from these ingested particles, may increase metal influx into mussels from the dietary phase.     

Factors influencing particle selection and feeding rate in the polychaete Cistenides (Pectinaria) gouldii

Feeding behavior of the deposit feeding polychaete Cistenides (Pectinaria) gouldii was examined to determine factors affecting particle selection and feeding rate. Worms were found to select large particles preferentially and particle size selection increased with worm size. Particle selection behavior was unaffected by changes in sediment bacterial abundance. Feeding rates were affected by sediment size, bacterial density and worm size. Generally feeding rates increased in sediment containing more food, although the response was worm size specific. When viewed in a theoretical construct these results were inconsistent with predictions of deposit feeder optimal foraging models. Alternative explanations, such as morphological constraints placed upon the polychaete, may explain C. gouldii feeding behavior.     

Food quality and season affect gene expression of the mucosal lectin MeML and particle sorting in the blue mussel Mytilus edulis

The blue mussel, Mytilus edulis, is able to use biochemical cues to sort food particles. Recently, a mucosal lectin (MeML) identified in pallial organs of M. edulis was suggested to play a role in the capture and sorting of food particles. The current study presents data obtained in 2010 showing that sorting efficiencies and MeML gene expression in M. edulis increased when mussels were either fed poor quality food or starved. In addition, results suggest that particle capture and degree of selection increased during the spawning period, although the quality of food delivered to mussels before the experiments seemed to have a stronger impact on particle-sorting efficiency. Overall, the impact of both endogenous (physiological status) and exogenous (food quality) factors were shown to affect the expression of MeML in mussel feeding organs, and the food sorting abilities.     

Selection of unicellular algae by the littoral amphipods Gammarus oceanicus and Calliopius laeviusculus (Crustacea)

The effect of microalgal strength of adhesion to surfaces was examined with regard to their susceptibility to grazing by Gammarus oceanicus Segerstråle and Calliopius laeviusculus (Krøyer). Observations of the feeding behaviour and two feeding experiments were carried out under laboratory conditions. Naturally attached periphyton (strongly attached cells), homogenized periphyton (loosely attached cells), filtered phytoplankton (unattached cells) and bare surfaces (controls) were randomly located in a grid and offered for grazing to a fixed number of amphipods of each species separately. The number of individuals visiting each type of food presented in the grid was recorded for 24-h periods. The feeding habit of each species, their effect on food distribution and their efficiency at collecting small particles were also recorded. G. oceanicus has a low efficiency at collecting particles and does not select a particular type of food, owing to its feeding habit of indiscriminately resuspending loosely attached particles. C. laeviusculus is a highly efficient and selective grazer, preferring homogenized periphyton and phytoplankton to naturally attached periphyton. For epibenthic diatoms, strong adhesion to surfaces is advantageous to avoid grazers.     

Experimental tests of suspension feeding in Atlantic reef corals

The ability of 15 species of Atlantic reef corals to act as suspension feeders was demonstrated by their removal of suspended particles from sea water in culture vessels. Mean clearance rates varied from 16.6 to 145.5 ml water cleared/h/cm² of live coral tissue. The lowest rates was found in Porites porites which is primarily a tentacle feeder, and the highest in Diploria clivosa which acts as both a tentacle feeder and suspension feeder. Rates of particle clearance in Agaricia agaricites, which is primarily a suspension feeder, were influenced by current velocity and type of food.     

Role of particle wettability in capture by a suspension-feeding crab (Emerita talpoida)

Suspension feeders sometimes depend on adhesion between particle and collector to capture food. If food particles have different adhesive properties than other particles, food could be passively selected by adhesive mechanisms. In this regard, the effect of particle wettability on adhesion to artificial and natural collectors was studied. First, the adhesion of glass particles to artificial collectors, both varying in wettability, was assessed to determine if wettability influenced adhesion in seawater. The adhesive force between glass particles and artificial collectors was measured by increasing the force pulling particles away from the collector until 50% of the particles fell off the collector. Adhesion increased as particle wettability decreased. Next, glass particles were used to determine if the antennal collector of the suspension-feeding mole crab Emerita talpoida captured particles based on particle wettability. 0.5 to 10 and 15 to 25 μm particles were suspended in a recirculating flow tank filled with seawater, and ablated antennae were exposed to this flow, after which the captured particles were counted. Results for the 0.5 to 10 μm particles confirmed predictions based on results from artificial collectors; particle capture increased as particle wettability decreased. The 15 to 25 μm particles may have been captured by sieving, and consequently did not follow predictions based on adhesion. Passive selection of particles based upon wettability differences can occur. Received: 17 April 1998 / Accepted: 14 September 1998     

Ammonium and free amino acid uptake by a deep-sea mussel (Bathymodiolus sp., undescribed) containing methanotrophic bacterial symbionts

The morphology of the lophophore and mouth was measured for freshly collected colonies of seven common bryozoan reef species at three sites along the central Caribbean coast of Panamá during the dry season, from the end of December 1988 through May 1989. Characters measured or scored include the number of tentacles, circumference of the lophophore, abanal and anal tentacle length, abanal and anal tentacle spacing, and perimeter of the mouth. Taxa studied include three species each of Stylophoma Levinsen, and Steginoporella (Smitt), and one species of Trematooecia Osburn. Individuals were collected from both continental and offshore fringing reefs from depths of 1 to>30 m. Terrestrial runoff from heavy tropical rains, sedimentation, and sea exposure vary greatly between sites. Congeneric species showed small but consistent differences in lophophore size, but little or no difference in spacing of tentacles or perimeter of the mouth. This suggests that closely related species feed on similarly sized particles despite their overall differences in zooidal size. Lopophore morphology also varied intraspecifically between reefs, particularly in the length of the tentacles and spacing between tentacles. Patterns of variation were similar for all species, which implies that species shift their diets in similar directions between the different reefs. The combination of these patterns suggests that niche diversification in feeding does not occur among congeneric species in the cheilostomes examined.     

Turbulence structure and fluid–particle interaction in sediment-laden flows over developing sand dunes

In this study, we conducted the fluid–particle simultaneous measurements in order to reveal the fluid–particle interaction mechanism in the developing stages of sand dunes. We measured the instantaneous velocities over the growing sand dunes by the use of both the discriminator particle-image velocimetory (D-PIV) and the discriminator particle-tracking velocimetory (D-PTV). In this D-PIV&PTV system, fluid tracers and sediment particles are discriminated accurately by their occupied particle sizes, and thus, the particle velocity U _p and fluid velocity U _f can be measured simultaneously. It was found from the present measurements that turbulence intensities in the trough area became larger after the generation of the reverse flow, i.e., U _f < 0. There are two kinds of coherent eddies behind dunes, i.e., one is convected along the shear layer behind dune and the other is lifted up from the reattachment point due to the kolk-boil vortex.