Swimming Species Research Articles

On the fluid drag reduction in scallop surface.

In the field of biomimetics, the tiny riblet structures inspired by shark skin have been extensively studied for their drag reduction properties in turbulent flows. Here, we show that the ridged surface texture of another swimming creature in the ocean, i.e., the scallops, also has some friction drag reduction effect. In this study, we investigated the potential drag reduction effects of scallop shell textures using computational fluid dynamics simulations. Specifically, we constructed a conceptual model featuring an undulating surface pattern on a conical shell geometry that mimics scallop. Simulations modeled turbulent fluid flows over the model inserted at different orientations relative to the flow direction. The results demonstrate appreciable friction drag reduction generated by the ribbed hierarchical structures encasing the scallop, while partial pressure drag reduction exhibits dependence on alignment of scallop to the predominant flow direction. Theoretical mechanisms based on classic drag reduction theory in turbulence was established to explain the drag reduction phenomena. Given the analogous working environments of scallops and seafaring vessels, these findings may shed light on the biomimetic design of surface textures to enhance maritime engineering applications. Besides, this work elucidates an additional evolutionary example of fluid drag reduction, expanding the biological repertoire of swimming species.

Traits mediate environmental responses of benthic ciliates in dynamic coastal habitats

AbstractAimUnderstanding how species' traits mediate environmental responses provides a mechanistic perspective on community assembly processes. Although traits that influence the response of multicellular organisms to environments have been studied, the identification of such traits in unicellular organisms, like ciliates, is underexplored. Since ciliates are dominant animals in coastal sandy sediments and contribute significantly to interstitial community respiration, identifying links between their occurrence and sandy‐coast characteristics is crucial for conserving biodiversity and protecting coastal habitats.LocationCoasts of China.MethodsWe used Hierarchical Modelling of Species Communities, a trait‐based joint species distribution model, to analyse ciliate community data collected from 344 sites belonging to 31 beaches across the Chinese coastline.ResultsWe found that physical variables play the most important role in determining ciliate occurrence. The beach index combines the tidal range, sediment grain size and beach slope of beach‐selected species based on body size as well as feeding type, while sediment grain size constrained different mobility types, with swimming species favouring fine sandy sediments. The significant contribution of phylogeny in explaining the residual variation among species responses indicates that there are phylogenetically conserved but unmeasured traits too that influence species' responses. Species richness of benthic ciliates was higher in dissipative beaches with high primary productivity.Main ConclusionsBased on our research, ciliate occurrence in coastal beaches is mediated by their traits which are filtered by local environmental variables. The beach index is essential in predicting distribution patterns and species richness of benthic ciliates. Nevertheless, further research is needed to identify additional traits that will enhance the accuracy of predicting ciliate niches. Our study provides insights into the mechanisms driving ciliate community assembly processes and has implications for the conservation of biodiversity in sandy coastal habitats.

No difference between critical and sprint swimming speeds for two galaxiid species.

Researchers have used laboratory experiments to examine how fish might be affected by anthropogenic alterations and conclude how best to adjust fish passage and culvert remediation designs in response. A common way to document swimming performance for this purpose is measuring fish critical swimming speed (Ucrit ). Nonetheless, the Ucrit protocol as defined by Brett [(1964) Journal of the Fisheries Research Board of Canada, 21, 1183-1226] may be inappropriate for studying swimming performance and determining how it relates to upstream migration in benthic fish, as they may not actively swim throughout the entire Ucrit test. An alternative method to estimate swimming performance is sprint swimming speed (Usprint ), which is suggested to be a measure of the burst speed of fish rather than maximum sustained swimming speed. The authors conducted comparative swimming performance experiments to evaluate whether Usprint can be used to compare swimming performance of benthic species to that of pelagic, actively swimming species. They measured individual swimming speeds of īnanga (Galaxias maculatus), an actively swimming pelagic species, and banded kōkopu (Galaxias fasciatus), a fish that exhibits benthic station-holding behaviour, using both the Usprint and Ucrit test. Experiments revealed that no significant statistical difference between swimming speeds was estimated using the Ucrit and Usprint test protocols for both G. maculatus and G. fasciatus. The result of this study suggests that fish swimming speeds obtained using these two methods are comparable for the species used in this study. By using Usprint for benthic-associated fish and Ucrit for pelagic fish, we may be able to compare a broader range of species' swimming abilities for use in a fish passage context.

Surfing on Turbulence: A Strategy for Planktonic Navigation.

In marine plankton, many swimming species can perceive their environment with flow sensors. Can they use this flow information to travel faster in turbulence? To address this question, we consider plankters swimming at constant speed, whose goal is to move upward. We propose a robust analytical behavior that allows plankters to choose a swimming direction according to the local flow gradients. We show numerically that such plankters can "surf" on turbulence and reach net vertical speeds up to twice their swimming speed. This new physics-based model suggests that planktonic organisms can exploit turbulence features for navigation.

Hybrid Metachronal Rowing Augments Swimming Speed and Acceleration via Increased Stroke Amplitude.

Numerous aquatic invertebrates use drag-based metachronal rowing for swimming, in which closely spaced appendages are oscillated starting from the posterior, with each appendage phase-shifted in time relative to its neighbor. Continuously swimming species such as Antarctic krill generally use "pure metachronal rowing" consisting of a metachronal power stroke and a metachronal recovery stroke, while burst swimming species such as many copepods and mantis shrimp typically use "hybrid metachronal rowing" consisting of a metachronal power stroke followed by a synchronous or nearly synchronous recovery stroke. Burst swimming organisms need to rapidly accelerate in order to capture prey and/or escape predation, and it is unknown whether hybrid metachronal rowing can augment acceleration and swimming speed compared to pure metachronal rowing. Simulations of rigid paddles undergoing simple harmonic motion showed that collisions between adjacent paddles restrict the maximum stroke amplitude for pure metachronal rowing. Hybrid metachronal rowing similar to that observed in mantis shrimp (Neogonodactylus bredini) permits oscillation at larger stroke amplitude while avoiding these collisions. We comparatively examined swimming speed, acceleration, and wake structure of pure and hybrid metachronal rowing strategies by using a self-propelling robot. Both swimming speed and peak acceleration of the robot increased with increasing stroke amplitude. Hybrid metachronal rowing permitted operation at larger stroke amplitude without collision of adjacent paddles on the robot, augmenting swimming speed and peak acceleration. Hybrid metachronal rowing generated a dispersed wake unlike narrower, downward-angled jets generated by pure metachronal rowing. Our findings suggest that burst swimming animals with small appendage spacing, such as copepods and mantis shrimp, can use hybrid metachronal rowing to generate large accelerations via increasing stroke amplitude without concern of appendage collision.

Comparing five methods for quantifying abundance and diversity of fish assemblages in seagrass habitat

Seagrass fishes perform key ecological roles and are a critical component of many of the world’s fisheries. A sound understanding of seagrass fish communities, based on robust methods, is therefore integral for their successful environmental management and conservation. Here we quantitatively compare taxa and size class of seagrass fish assemblages collected using; baited and unbaited remote underwater video (BRUV, URUV), diver operated video (DOV), underwater visual census (UVC) and trawling. We assess comparisons of these methods in terms of biodiversity indicators and power to detect change. All five methods were deployed in coastal embayments dominated by Posidonia spp. and within three marine parks along the south-western coast of Western Australia. Fish assemblages recorded using the different methods separated into two distinct groups; those dominated by smaller and less motile species, that are typically present beneath the canopy among seagrass leaves; and those dominated by larger, faster swimming species present above the seagrass canopy. Trawling provided the most effective method for assessing species within the canopy, including those of conservation concern. Conversely, BRUV followed by URUV recorded the greatest number of individuals, successfully detecting the larger supra-canopy and highly motile species typically omitted by trawling. Both trawl and BRUV methods had a higher power to detect change in species richness of seagrass fishes compared to other methods, even though each method recorded different components of the fish assemblage. Fish assemblages recorded using UVC detected both inter and supra-canopy species, but fish abundances recorded by this method were low compared to trawl and BRUV surveys, resulting in reduced power to detect change in richness. DOV was a comparatively less effective method, recording few fish, as well as low richness and diversity values. The combination of trawling and stationary video techniques, particularly BRUV, provided a two-method combination able to holistically measure commonly used indicators of fish assemblage composition in seagrass habitat. These results demonstrate that careful consideration of the methodology is essential when assessing ichthyofauna in seagrass habitat, particularly when only a single method can be employed. As the extent of methodological influence on recording fish assemblages also varied among the three survey areas, geographical differences in the structure of fish and seagrass communities should be considered when selecting an appropriate sampling method.

Pre-Messinian ecological diversity of Mediterranean sharks revealed by the study of their dermal denticles

The Messinian salinity crisis (~5.59 Ma) is regarded as one of the most determining events for the recent evolutionary and palaeobiogeographic history of the Mediterranean biota. The impact of such episode has usually been assessed by evaluating the associated taxonomic turnover, however its consequences have rarely been interpreted from an ecological perspective. Here we assess the functional diversity of shark dermal denticles in a Serravallian locality from southeast Spain, providing a primary view into the pre-Messinian ecological diversity of shark communities from the Western Mediterranean. Our results reveal a high diversity of functional types of dermal denticles including dermal denticles that prevent the settlement of ectoparasites and epibiontes, abrasion resistant dermal denticles, drag reduction dermal denticles and dermal denticles with less specific, or more generalized, functions. This variety of dermal denticles supports the presence of several ecological groups of sharks such as schooling and strong swimming species and, possibly, demersal species, slow sharks of the open water bioluminescent taxa. Therefore, the application of this methodology to Pliocene and Pleistocene fossiliferous sites will be crucial for unravelling the impact of Messinian salinity crisis and other recent geological events from an ecological perspective, allowing us to understand the shark communitycompositionand diversityof the current Mediterranean Sea.

A cis-regulatory change underlying the motor neuron-specific loss of Ebf expression in immotile tunicate larvae.

Many species in the tunicate family Molgulidae have independently lost their swimming larval form and instead develop as tailless, immotile larvae. These larvae do not develop structures that are essential for swimming such as the notochord, otolith, and tail muscles. However, little is known about neural development in these nonswimming larvae. Here, we studied the patterning of the Motor Ganglion (MG) of Molgula occulta, a nonswimming species. We found that spatial patterns of MG neuron regulators in this species are conserved, compared with species with swimming larvae, suggesting that the gene networks regulating their expression are intact despite the loss of swimming. However, expression of the key motor neuron regulatory gene Ebf (Collier/Olf/EBF) was reduced in the developing MG of M. occulta when compared with molgulid species with swimming larvae. This was corroborated by measuring allele-specific expression of Ebf in hybrid embryos from crosses of M. occulta with the swimming species M. oculata. Heterologous reporter construct assays in the model tunicate species Ciona robusta revealed a specific cis-regulatory sequence change that reduces expression of Ebf in the MG, but not in other cells. Taken together, these data suggest that MG neurons are still specified in M. occulta larvae, but their differentiation might be impaired due to reduction of Ebf expression levels.

Multispecies Fish Passage Evaluation at a Rock‐Ramp Fishway in a Colorado Transition Zone Stream

AbstractStream habitat fragmentation caused by manmade structures is ubiquitous in Colorado, creating a need for passage solutions that accommodate multiple fish species. This study tested the effectiveness of a rock‐ramp fishway for passing nine fish species with a range of swimming abilities. The target species for the fishway design included Brassy MinnowHybognathus hankinsoni(weakest swimming), Longnose DaceRhinichthys cataractae, Longnose SuckerCatostomus catostomus, and Brown TroutSalmo trutta(strongest swimming). Testing included a 46‐h enclosure study and 3‐month extended study, during which fish passage was evaluated using PIT tags. All of the species exhibited successful passage through the fishway during the enclosure study, but movement probabilities varied by species. Five species were not detected at the fishway during the extended study, possibly due to issues with attraction flows, entrance conditions, or motivation. Hydraulic conditions within the fishway were also evaluated. Roughness elements maintained a benthic, low‐velocity zone across a range of flows, even when surface and depth‐averaged velocities surpassed the design criteria for the weakest swimming species. The methods from this study could be replicated at other locations to evaluate design criteria (e.g., slope, capacity, roughness, and configuration) and performance for a variety of fish species and fishway types.

The Pattern of Glycogen Recovery in Muscles and Liver of Fish with Different Swimming Capabilities after being Caught in a Bottom Trawl

The dynamics of glycogen recovery in the muscles and liver of the European flounder Plathichthys flesus (Linnaeus, 1758) and the European sprat Sprattus sprattus (Linnaeus, 1758) after exposure to trawl fishing has been studied. As the results show, the stress-inducing effect of fishing does not alter the glycogen content of the organs in the flounder, which leads a sedentary life, whereas a sharp decrease in glycogen is observed in the white and red muscles and the liver of the sprat, which is an actively swimming species. After capture, the dynamics of glycogen recovery in the organs of flounder has an undulatory pattern. The glycogen is completely restored within 12 h and is accompanied by a 100% survival rate of the flounder. The assumption is made that the resynthesis of glycogen in the organs of flounder occurs through the activation of carbohydrate metabolism in the liver. In sprat that had 3 h of “rest” after being caught and then placed in a 100‑liter tank to restore glycogen in tissues, a pronounced (4.5-fold) increase in the level of the polysaccharide was recorded from the white muscles, with a simultaneously low glycogen level in the liver. The glycogen compensation in the sprat possibly occurred through the reverse involvement of lactate in the polysaccharide resynthesis in the white muscles. The following additional 3-h period of rest was characterized by a significant (1.7-fold) decrease in the glycogen level in the white muscles compared to that in the previous rest period. No glycogen recovery in the sprat liver was observed throughout the entire rest period. Apparently, this organ is not involved in the polysaccharide recovery processes. The low survival rate of sprat (30%) is explained by the long exposure to stress caused by both capture and captivity in the tank, to which this “excitable” species is particularly sensitive.

A potential engineering solution to facilitate upstream movement of fish in mountain rivers with weirs: Southern Carpathians, the Azuga River

An important aspect in the restoration of longitudinal connectivity in rivers and streams is the implementation of fish migration systems at the upstream of the functional hydraulic structures (weirs, drop structures or river sills). The diversity of these existing structures as well as the different locations of these weirs within the river, watershed and riparian zone challenge the design engineers to find new holistic solutions for fish migration systems. The Azuga River study area requires a new synergistic fish migration design system. Being a mountain area, rapid increase in water level is quite frequent, especially after heavy or prolonged rainfalls and during spring snow melt. Therefore, it is necessary to design a specific system for fish migration to meet this locations requirements. Due to the characteristics in this location of the Azuga river, the classic fish migration systems would not be functional. The indigenous/mountain trout is considered as the target species in this paper. Although this is a good swimming species, the use of classical systems could, due to exhaustion, prevent and/or reduce the movement of fish upstream of the two weirs (also known as river sills). This new, comprehensive solution, presented in this paper includes: (i) the restoration and stabilization works of the right bank in the weir study area by using biotechnical measures and (ii) the upstream migration system itself - for supporting the migration of fish on the Azuga River.

Swimming strategies and energetics of endothermic white sharks during foraging.

Some fishes and sea turtles are distinct from ectotherms by having elevated core body temperatures and metabolic rates. Quantifying the energetics and activity of the regionally endothermic species will help us understand how a fundamental biophysical process (i.e. temperature-dependent metabolism) shapes animal ecology; however, such information is limited owing to difficulties in studying these large, highly active animals. White sharks, Carcharodon carcharias, are the largest fish with regional endothermy, and potentially among the most energy-demanding fishes. Here, we deployed multi-sensor loggers on eight white sharks aggregating near colonies of long-nosed fur seals, Arctocephalus forsteri, off the Neptune Islands, Australia. Simultaneous measurements of depth, swim speed (a proxy for swimming metabolic rate) and body acceleration (indicating when sharks exhibited energy-efficient gliding behaviour) revealed their fine-scale swimming behaviour and allowed us to estimate their energy expenditure. Sharks repeatedly dived (mean swimming depth, 29 m) and swam at the surface between deep dives (maximum depth, 108 m). Modal swim speeds (0.80-1.35 m s-1) were slower than the estimated speeds that minimize cost of transport (1.3-1.9 m s-1), a pattern analogous to a 'sit-and-wait' strategy for a perpetually swimming species. All but one shark employed unpowered gliding during descents, rendering deep (>50 m) dives 29% less costly than surface swimming, which may incur additional wave drag. We suggest that these behavioural strategies may help sharks to maximize net energy gains by reducing swimming cost while increasing encounter rates with fast-swimming seals.

Life in Changing Fluids: A Critical Appraisal of Swimming Animals Before the Cambrian.

Molecular and fossil data place the initial diversification of animals in the Neoproterozoic, though there remains too much enough uncertainty to produce an exact chronology. This is unfortunate, as the Neoproterozoic represents a period of intense climate change, including multiple global glaciation events as well changes to ocean chemistry and oxygen content. Several authors have suggested that the coevolution of animals and their environment was tightly coupled, but such hypotheses rest on the presence of swimming (pelagic) species. In this paper, I review the evidence for pelagic animals during the Neoproterozoic. I conclude that there are very few groups of planktotrophic swimming animals that were likely to have existed at this time, with the possible exception of medusozoan cnidarians (jellyfish). Ultimately, hypotheses connecting Earth and animal evolution in the Neoproterozoic need to be tested with more geochemical work, fossil discoveries, and refinement of molecular clocks targeted on the relevant groups.

Hydraulics driven upstream migration of taiwanese indigenous fishes in a fish-bone-type fishway

Discharges of 0.016, 0.032, 0.048, 0.075, 0.1, and 0.15m3/s in a fish-bone-type fishway were employed to analyse its complex hydraulics for fish migration. Four swimming and three leaping and climbing species endemic to Taiwan migrated upstream along the fishway, and their swimming speeds, migration ratios, and pathways were observed. The swimming species all had migration ratios above 50 %; a hemp rope helped the other fishes and algae shrimps migrate at low discharge. The fishway proved suitable for all the considered species, except for the leaping and climbing species which needed a hemp rope to successfully migrate. Computational fluid dynamics modelling explained the observed complex flow fields, and supported the observed velocities and flow depths. Additional numerical results such as turbulence in the fishway are also discussed.

3-D spatial memory and navigation: functions and disorders.

The aim of this review is to report on the specialized neuronal systems mediating spatial orientation and navigation discovered in animal experiments. These findings have important implications for the clinical management of patients with vestibular disorders or dementia and for translational research in these fields. The following anatomically and functionally separate, but nevertheless cooperative cell types have been characterized: angular head velocity cells and head direction cells, which depend on vestibular input and interact with place cells and grid cells, which represent position and distance. The entire system is thought to encode internal cognitive maps whose spatial data can be utilized for navigation and orientation. Flying and swimming species use spatial orientation and navigation isotropically, i.e., in the earth-horizontal and vertical directions, whereas ground-based species, including humans, perform better in the earth-horizontal plane (anisotropically). Examples of clinical disorders with deficits of spatial orientation and navigation are bilateral peripheral vestibulopathy, mild cognitive impairment, and dementia. Testing spatial orientation and navigation should become an integral part of routine neurological examinations, especially in the elderly. Also desirable are the further development and standardization of simple and reliable smart phone-based bedside tests to measure these functions in patients.

Community structure of deep-water decapod crustaceans below the oxygen minimum zone in the south-east Gulf of California and analysis of environmental drivers

Despite the ecological importance of decapod crustaceans in energy transfer in marine ecosystems, little is known on their distribution below oxygen minimum zones (OMZs). To understand the spatio-temporal dynamics of benthic and benthopelagic decapod crustaceans living below the OMZ cores, four seasonal oceanographic and sledge surveys were performed in the south-east Gulf of California at depths between 730 and 2250m. Multivariate analyses indicate the existence of three major depth-related assemblages at: 800–1000, 1000–1200 and >1200m (mean trawl depth). Benthic detritivores dominated between 800 and 1000m and benthopelagic (i.e. swimming) predators dominated deeper, where dissolved oxygen (DO) values were higher. Assemblages comprised the same species throughout the year, but aggregations of smaller organisms were observed in June. DO significantly controlled the distribution of decapod crustaceans, likely through physiological exclusion of swimming species from hypoxic waters. Besides, the combined effects of DO and temperature contributed to defining the depth ranges occupied by each species. Food derived from surface-water production modulated changes in community parameters with different time lags in the different depth-related assemblages. These findings demonstrate the vulnerability of bathyal communities to the global pattern of OMZ expansion.

Elevational distribution and species diversity of freshwater Ostracoda (Crustacea) in Çankırı region (Turkey)

We investigated how the richness and ecological characteristics of non-marine ostracod species varied across nine 100-m elevation bands (from 549 to 1457 m) in the Çankırı region. We collected a total of 37 taxa (25 living and 12 sub-recent) from 114 of 130 aquatic sites sampled during September of 2011; 34 of the taxa were new records for the region. Eight widely distributed ‘cosmopolitan’ species (Candona neglecta, Cypridopsis vidua, Heterocypris incongruens, Ilyocypris bradyi, Limnocythere inopinata, Potamocypris villosa, Prionocypris zenkeri, and Psychrodromus olivaceus) were found more frequently than other species. The first two axes of canonical correspondence analyses (CCA) explained 73.2% of the correlation between 11 species and 5 environmental variables. Of which, electrical conductivity (F = 3.99, p = 0.028) and altitude (F = 2.69, p = 0.004) were the most explanatory (p < 0.05) variables for species. Optimum altitude and water temperature values of the cosmopolitan species were relatively higher than the other species. Significant regression models (p < 0.01, r2 = 0.81) indicate that the frequency of occurrence was affected by changes in numbers of samplings sites from 549 to 1457 m. When highest numbers of species (15 spp.) were found at the range of 1231–1332 m, numbers of asexual species (10 spp.) were twice of the sexual species (5 spp.) with no statistical difference between numbers of swimming (7 spp.) and non-swimming (8 spp.) species. Results were discussed based on the ecological conditions that individual species prefer.

Studying the movement behavior of benthic macroinvertebrates with automated video tracking.

Quantifying and understanding movement is critical for a wide range of questions in basic and applied ecology. Movement ecology is also fostered by technological advances that allow automated tracking for a wide range of animal species. However, for aquatic macroinvertebrates, such detailed methods do not yet exist. We developed a video tracking method for two different species of benthic macroinvertebrates, the crawling isopod Asellus aquaticus and the swimming fresh water amphipod Gammarus pulex. We tested the effects of different light sources and marking techniques on their movement behavior to establish the possibilities and limitations of the experimental protocol and to ensure that the basic handling of test specimens would not bias conclusions drawn from movement path analyses. To demonstrate the versatility of our method, we studied the influence of varying population densities on different movement parameters related to resting behavior, directionality, and step lengths. We found that our method allows studying species with different modes of dispersal and under different conditions. For example, we found that gammarids spend more time moving at higher population densities, while asellids rest more under similar conditions. At the same time, in response to higher densities, gammarids mostly decreased average step lengths, whereas asellids did not. Gammarids, however, were also more sensitive to general handling and marking than asellids. Our protocol for marking and video tracking can be easily adopted for other species of aquatic macroinvertebrates or testing conditions, for example, presence or absence of food sources, shelter, or predator cues. Nevertheless, limitations with regard to the marking protocol, material, and a species’ physical build need to be considered and tested before a wider application, particularly for swimming species. Data obtained with this approach can deepen the understanding of population dynamics on larger spatial scales and of the effects of different management strategies on a species’ dispersal potential.

Motility of the diplomonad fish parasite Spironucleus vortens through thixotropic solid media.

Investigation of a series of nutrient-supplemented thixotropic gels at successive dilutions that impede the trajectories of a highly vigorous motile flagellated protist, Spironucleus vortens, provides insights into both its swimming characteristics and a means for its immobilization. The progress of movement of this organism through the solidified growth medium was monitored by the in situ reductive production of a formazan chromophore from a dissolved tetrazolium salt. The physical properties of the gels were measured using an Anton Paar rheometer. The test parameters and measurements included: angular frequency, complex viscosity, complex shear modulus, shear rate and rotational recovery. These rheological characteristics affected the forward velocity of the organism through the gels, during and after multiple resetting, information potentially useful for determination of the dynamic characteristics of flagellar movement and propulsion rates of the organism. Application to separation of single cells, individuals of distinct sizes or the differing species from mixed cultures of motile and non-motile organisms or less actively swimming species was evident. These applications can be used when isolating the parasite from the intestinal contents of its host or from faecal pellets.

The influence of mixing frequency and depth on phytoplankton mobility

The influence of mixing frequency and depth on phytoplankton functional group composition (mobile versus immobile species) was studied by enclosure experiments in a shallow, stratified lake. Mixing events were artificially induced at intervals from 2–12 d. The mixing depth was increased from the natural level (4 m) to 6 and 9 m. The mobile phytoplankton in the experiments consisted of cyanobacteria and flagellates. Among the latter, large and rapid swimming species were represented by dinoflagellates. An increase of the relative abundance of gas vacuolated cyanobacteria occurred with increasing frequency of mixing. Additionally Reynolds' hypothesis predicting the occurrence of certain mobile phytoplankton genera in response to the mixing regime could be confirmed for the condition when mixing depth exceeds the euphoric depth.