Life in transition: balancing inertial and viscous forces by planktonic copepods

Nectophore coordination and kinematics by physonect siphonophores

Siphonophores are ubiquitous and often highly abundant members of pelagic ecosystems throughout the open ocean. They are unique among animal taxa in that many species use multiple jets for propulsion. Little is known about the kinematics of the individual jets produced by nectophores (the swimming bells of siphonophores) or whether the jets are coordinated during normal swimming behavior. Using remotely operated vehicles and SCUBA, we video recorded the swimming behavior of several physonect species in their natural environment. The pulsed kinematics of the individual nectophores that comprise the siphonophore nectosome were quantified and, based on these kinematics, we examined the coordination of adjacent nectophores. We found that, for the five species considered, nectophores located along the same side of the nectosomal axis (i.e. axially aligned) were coordinated and their timing was offset such that they pulsed metachronally. However, this level of coordination did not extend across the nectosome and no coordination was evident between nectophores on opposite sides of the nectosomal axis. For most species, the metachronal contraction waves of nectophores were initiated by the apical nectophores and traveled dorsally. However, the metachronal wave of Apolemia rubriversa traveled in the opposite direction. Although nectophore groups on opposite sides of the nectosome were not coordinated, they pulsed with similar frequencies. This enabled siphonophores to maintain relatively linear trajectories during swimming. The timing and characteristics of the metachronal coordination of pulsed jets affects how the jet wakes interact and may provide important insight into how interacting jets may be optimized for efficient propulsion.

Diet of Adult Sardine Sardina pilchardus in the Gulf of Trieste, Northern Adriatic Sea

Food availability is thought to exert a bottom-up control on the population dynamics of small pelagic fish; therefore, studies on trophic ecology are essential to improve their management. Sardina pilchardus is one of the most important commercial species in the Adriatic Sea, yet there is little information on its diet in this area. Adult sardines were caught in the Gulf of Trieste (northern Adriatic) from spring 2006 to winter 2007. Experimental catches conducted over 24-h cycles in May, June and July showed that the sardines foraged mainly in the late afternoon. A total of 96 adult sardines were analysed: the number of prey varied from a minimum of 305 to a maximum of 3318 prey/stomach, with an overall mean of 1259 ± 884 prey/stomach. Prey items were identified to the lowest possible taxonomical level, counted and measured at the stereo-microscope. Overall, sardines fed on a wide range of planktonic organisms (87 prey items from 17 μm to 18.4 mm were identified), with copepods being the most abundant prey (56%) and phytoplankton never exceeding 10% of the prey. Copepods of the Clauso-Paracalanidae group and of the genus Oncaea were by far the most important prey. The carbon content of prey items was indirectly estimated from prey dry mass or body volume. Almost all carbon uptake relied on a few groups of zooplankton. Ivlev’s selectivity index showed that sardines positively selected small preys (small copepods < 1 mm size), but also larger preys (such as teleost eggs, decapod larvae and chaetognaths), confirming their adaptive feeding capacity.

Dual Phase-Shifted Ipsilateral Metachrony in Americamysis bahia

Previously documented metachrony in euphausiids focused on one, 5-paddle metachronal stroke, where contralateral pleopod pairs on the same abdominal segment beat in tandem with each other, propelling the animal forward. In contrast, the mysid shrimp Americamysis bahia's pleopods on the same abdominal segment beat independently of each other, resulting in two, 5-paddle metachronal cycles running ipsilateral along the length of the body, 180° out of phase. The morphology, kinematics, and nondimensional measurements of efficiency are compared primarily to the one-cycle Euphausia superba to determine how the two-cycle approach alters the design and kinematics of metachrony. Pleopodal swimming in A. bahia results in only fast-forward swimming, with speeds greater than 2BL/s (body lengths per second), and can reach speeds up to 12BL/s, through a combination of increasing stroke amplitude, beat frequency, and changing their inter-limb phase lag. Trends with Strouhal number and advance ratio suggest that the kinematics of metachrony in A. bahia are favored to achieve large normalized swimming speeds.

Separating Thermal and Viscous Effects of Temperature on Copepod Respiration and Energy Budget

AbstractChanges in temperature alter the viscosity of fluids, which impacts the force needed to move and the diffusion rates of gases. This is particularly salient for organisms that operate at mid to low Reynolds numbers. In this study, we investigated the independent effects of changes in temperature and viscosity on oxygen consumption rates of two coastal copepods (Acartia tonsa and Parvocalanus crassirostris) and used bioenergetic models to predict how these patterns could influence copepods in the natural environment. We found that only temperature influenced copepod oxygen consumption rates, indicating that copepods were not impacted by reduced oxygen diffusivity or increased energetics of movement resulting from higher seawater viscosity. We developed energy budgets based on novel respiration experiments in conjunction with data from the literature and found that cold temperatures do not result in higher scope for growth, because decreased metabolic costs are offset by reduced feeding capability. Our energy budgets imply that observed copepod temperature ranges in natural waters match theoretical ranges of optimal net carbon assimilation. At cold temperatures, feeding on motile prey yielded higher net carbon assimilation compared to feeding on non-motile prey, implying that motile prey are more favorable and may be actively selected for at cold temperatures. Finally, our models predicted that A. tonsa had a higher maximum net carbon assimilation as a percentage of body mass, indicating that copepods that use a similar sink-and-wait feeding strategy may be better able to exploit ephemeral food sources compared to continuous-swimming copepods such as P. crassirostris.

Copepod feeding strategy determines response to seawater viscosity: videography study of two calanoid copepod species

Calanoid copepods, depending on feeding strategy, have different behavioral and biological controls on their movements, thereby responding differently to environmental conditions such as changes in seawater viscosity. To understand how copepod responses to environmental conditions are mediated through physical, physiological and/or behavioral pathways, we used high-speed microvideography to compare two copepod species, Acartia hudsonica and Parvocalanus crassirostris, under different temperature, viscosity and dietary conditions. Acartia hudsonica exhibited 'sink and wait' feeding behavior and typically responded to changes in seawater viscosity; increased seawater viscosity reduced particle-capture behavior and decreased the size of the feeding current. In contrast, P. crassirostris continuously swam and did not show any behavioral or physical responses to changes in viscosity. Both species showed a physiological response to temperature, with reduced appendage beating frequency at cold temperatures, but this did not generally translate into effects on swimming speed, feeding flux or active time. Both copepod species swam slower when feeding on diatom rather than dinoflagellate prey, showing that prey type mediates copepod behavior. These results differentiate species-specific behaviors and responses to environmental conditions, which may lead to better understanding of niche separation and latitudinal patterns in copepod feeding and movement strategies.

Direct-forcing fictitious domain method for simulating non-Brownian active particles

We present a direct-forcing fictitious domain method for simulating non-Brownian squirmer particles with both the hydrodynamic interactions and collisions being fully resolved. In this method, we solve the particle motion by distributing collocation points inside the particle interior domain that overlay upon a fixed Eulerian mesh. The fluid motions, including those of the "fictitious fluids" being extended into the particle, are solved on the entire computation domain. Pseudo-body forces are used to enforce the fictitious fluids to follow the particle movement. A direct-forcing approach is employed to map physical variables between the overlaid meshes, which does not require additional iterations to achieve convergence. We perform a series of numerical studies at both small and finite Reynolds numbers. First, accuracy of the algorithm is examined in studying benchmark problems of a free-swimming squirmer and two side-by-side squirmers. Then we investigate statistic properties of the quasi-two-dimensional collective dynamics for a monolayer of squirmer particles that are confined on a surface immersed in a bulk flow. Finally, we explore the physical mechanisms of how a freely moving short cylinder interacts with a monolayer of active particles, and find out that the cylinder movement is dominated by collision. We demonstrate that a more directional migration of cylinder can be resultant from an inhomogeneous distribution of active particles around the cylinder that has an anisotropic shape.

Not Just Going with the Flow: The Effects of Fluid Flow on Bacteria and Plankton

Microorganisms often live in habitats characterized by fluid flow, from lakes and oceans to soil and the human body. Bacteria and plankton experience a broad range of flows, from the chaotic motion characteristic of turbulence to smooth flows at boundaries and in confined environments. Flow creates forces and torques that affect the movement, behavior, and spatial distribution of microorganisms and shapes the chemical landscape on which they rely for nutrient acquisition and communication. Methodological advances and closer interactions between physicists and biologists have begun to reveal the importance of flow-microorganism interactions and the adaptations of microorganisms to flow. Here we review selected examples of such interactions from bacteria, phytoplankton, larvae, and zooplankton. We hope that this article will serve as a blueprint for a more in-depth consideration of the effects of flow in the biology of microorganisms and that this discussion will stimulate further multidisciplinary effort in understanding this important component of microorganism habitats.

Going with the flow: hydrodynamic cues trigger directed escapes from a stalking predator

In the coevolution of predator and prey, different and less well-understood rules for threat assessment apply to freely suspended organisms than to substrate-dwelling ones. Particularly vulnerable are small prey carried with the bulk movement of a surrounding fluid and thus deprived of sensory information within the bow waves of approaching predators. Some planktonic prey have solved this apparent problem, however. We quantified cues generated by the slow approach of larval clownfish ( Amphiprion ocellaris) that triggered a calanoid copepod ( Bestiolina similis) to escape before the fish could strike. To estimate water deformation around the copepod immediately preceding its jump, we represented the body of the fish as a rigid sphere in a hydrodynamic model that we parametrized with measurements of fish size, approach speed and distance to the copepod. Copepods of various developmental stages (CII-CVI) were sensitive to the water flow caused by the live predator, at deformation rates as low as 0.04 s-1. This rate is far lower than that predicted from experiments that used artificial predator-mimics. Additionally, copepods localized the source, with 87% of escapes directed away (greater than or equal to 90°) from the predator. Thus, copepods' survival in life-threatening situations relied on their detection of small nonlinear signals within an environment of locally linear deformation.

Distinctive diffusive properties of swimming planktonic copepods in different environmental conditions

Suspensions of small planktonic copepods represent a special category in the realm of active matter, as their size falls within the range of colloids, while their motion is so complex that it cannot be rationalized according to basic models of self-propelled particles. Indeed, the wide range of individual variability and swimming patterns resemble the behaviour of much larger animals. By analysing hundreds of three-dimensional trajectories of the planktonic copepod Clausocalanus furcatus, we investigate the possibility of detecting how the motion of this species is affected by different external conditions, such as the presence of food and the effect of gravity. While this goal is hardly achievable by direct inspection of single organism trajectories, we show that this is possible by focussing on simple average metrics commonly used to characterize colloidal suspensions, such as the mean square displacement and the dynamic correlation functions. We find that the presence of food leads to the onset of a clear localization that separates a short-time ballistic from a long-time diffusive regime. Such a benchmark reflects the tendency of C. furcatus to remain temporally feeding in a limited space and disappears when food is absent. Localization is clearly evident in the horizontal plane, but is negligible in the vertical direction, due to the effect of gravity. Our results suggest that simple average descriptors may provide concise and useful information on the swimming properties of planktonic copepods, even though single organism behaviour is strongly heterogeneous.

Locomotion of arthropods in aquatic environment and their applications in robotics

Many bio-inspired robots have been developed so far after careful investigation of animals' locomotion. To successfully apply the locomotion of natural counterparts to robots for efficient and improved mobility, it is essential to understand their principles. Although a lot of research has studied either animals' locomotion or bio-inspired robots, there have only been a few attempts to broadly review both of them in a single article. Among the millions of animal species, this article reviewed various forms of aquatic locomotion in arthropods including relevant bio-inspired robots. Despite some previous robotics research inspired by aquatic arthropods, we found that many less-investigated or even unexplored areas are still present. Therefore, this article has been prepared to identify what types of new robotics research can be carried out after drawing inspiration from the aquatic locomotion of arthropods and to provide fruitful insights that may lead us to develop an agile and efficient aquatic robot.

Underwater flight by the planktonic sea butterfly

In a remarkable example of convergent evolution, we show that the zooplanktonic sea butterfly Limacina helicina 'flies' underwater in the same way that very small insects fly in the air. Both sea butterflies and flying insects stroke their wings in a characteristic figure-of-eight pattern to produce lift, and both generate extra lift by peeling their wings apart at the beginning of the power stroke (the well-known Weis-Fogh 'clap-and-fling' mechanism). It is highly surprising to find a zooplankter 'mimicking' insect flight as almost all zooplankton swim in this intermediate Reynolds number range (Re=10-100) by using their appendages as paddles rather than wings. The sea butterfly is also unique in that it accomplishes its insect-like figure-of-eight wing stroke by extreme rotation of its body (what we call 'hyper-pitching'), a paradigm that has implications for micro aerial vehicle (MAV) design. No other animal, to our knowledge, pitches to this extent under normal locomotion.

Hydrodynamic interaction of swimming organisms in an inertial regime

We numerically investigate the hydrodynamic interaction of swimming organisms at small to intermediate Reynolds number regimes, i.e., Re∼O(0.1-100), where inertial effects are important. The hydrodynamic interaction of swimming organisms in this regime is significantly different from the Stokes regime for microorganisms, as well as the high Reynolds number flows for fish and birds, which involves strong flow separation and detached vortex structures. Using an archetypal swimmer model, called a "squirmer," we find that the inertial effects change the contact time and dispersion dynamics of a pair of pusher swimmers, and trigger hydrodynamic attraction for two pullers. These results are potentially important in investigating predator-prey interactions, sexual reproduction, and the encounter rate of marine organisms such as copepods, ctenophora, and larvae.

Lagrangian model of copepod dynamics: Clustering by escape jumps in turbulence

Planktonic copepods are small crustaceans that have the ability to swim by quick powerful jumps. Such an aptness is used to escape from high shear regions, which may be caused either by flow perturbations, produced by a large predator (i.e., fish larvae), or by the inherent highly turbulent dynamics of the ocean. Through a combined experimental and numerical study, we investigate the impact of jumping behavior on the small-scale patchiness of copepods in a turbulent environment. Recorded velocity tracks of copepods displaying escape response jumps in still water are here used to define and tune a Lagrangian copepod (LC) model. The model is further employed to simulate the behavior of thousands of copepods in a fully developed hydrodynamic turbulent flow obtained by direct numerical simulation of the Navier-Stokes equations. First, we show that the LC velocity statistics is in qualitative agreement with available experimental observations of copepods in turbulence. Second, we quantify the clustering of LC, via the fractal dimension D_{2}. We show that D_{2} can be as low as ∼2.3 and that it critically depends on the shear-rate sensitivity of the proposed LC model, in particular it exhibits a minimum in a narrow range of shear-rate values. We further investigate the effect of jump intensity, jump orientation, and geometrical aspect ratio of the copepods on the small-scale spatial distribution. At last, possible ecological implications of the observed clustering on encounter rates and mating success are discussed.

Simultaneous measurement of 3D zooplankton trajectories and surrounding fluid velocity field in complex flows

We describe an automated, volumetric particle image velocimetry (PIV) and tracking method that measures time-resolved, 3D zooplankton trajectories and surrounding volumetric fluid velocity fields simultaneously and non-intrusively. The method is demonstrated for groups of copepods flowing past a wall-mounted cylinder. We show that copepods execute escape responses when subjected to a strain rate threshold upstream of a cylinder, but the same threshold range elicits no escape responses in the turbulent wake downstream. The method was also used to document the instantaneous slip velocity of zooplankton and the resulting differences in trajectory between zooplankton and non-inertial fluid particles in the unsteady wake flow, showing the method's capability to quantify drift for both passive and motile organisms in turbulent environments. Applications of the method extend to any group of organisms interacting with the surrounding fluid environment, where organism location, larger-scale eddies and smaller-scale fluid deformation rates can all be tracked and analyzed.

Hydrodynamic trails produced by Daphnia: size and energetics

This study focuses on quantifying hydrodynamic trails produced by freely swimming zooplankton. We combined volumetric tracking of swimming trajectories with planar observations of the flow field induced by Daphnia of different size and swimming in different patterns. Spatial extension of the planar flow field along the trajectories was used to interrogate the dimensions (length and volume) and energetics (dissipation rate of kinetic energy and total dissipated power) of the trails. Our findings demonstrate that neither swimming pattern nor size of the organisms affect the trail width or the dissipation rate. However, we found that the trail volume increases with increasing organism size and swimming velocity, more precisely the trail volume is proportional to the third power of Reynolds number. This increase furthermore results in significantly enhanced total dissipated power at higher Reynolds number. The biggest trail volume observed corresponds to about 500 times the body volume of the largest daphnids. Trail-averaged viscous dissipation rate of the swimming daphnids vary in the range of to and the observed magnitudes of total dissipated power between and , respectively. Among other zooplankton species, daphnids display the highest total dissipated power in their trails. These findings are discussed in the context of fluid mixing and transport by organisms swimming at intermediate Reynolds numbers.

Effect of grazing-mediated dimethyl sulfide (DMS) production on the swimming behavior of the copepod Calanus helgolandicus

Chemical interactions play a fundamental role in the ecology of marine foodwebs. Dimethyl sulfide (DMS) is a ubiquitous marine trace gas that acts as a bioactive compound by eliciting foraging behavior in a range of marine taxa including the copepod Temora longicornis. Production of DMS can rapidly increase following microzooplankton grazing on phytoplankton. Here, we investigated whether grazing-induced DMS elicits an increase in foraging behavior in the copepod Calanus helgolandicus. We developed a semi-automated method to quantify the effect of grazing-mediated DMS on the proportion of the time budget tethered females allocate towards slow swimming, typically associated with feeding. The pooled data showed no differences in the proportion of the 25 min time budget allocated towards slow swimming between high (23.6 ± 9.74%) and low (29.1 ± 18.33%) DMS treatments. However, there was a high degree of variability between behavioral responses of individual copepods. We discuss the need for more detailed species-specific studies of individual level responses of copepods to chemical signals at different spatial scales to improve our understanding of chemical interactions between copepods and their prey.

The fluid dynamics of swimming by jumping in copepods

Copepods swim either continuously by vibrating their feeding appendages or erratically by repeatedly beating their swimming legs, resulting in a series of small jumps. The two swimming modes generate different hydrodynamic disturbances and therefore expose the swimmers differently to rheotactic predators. We developed an impulsive stresslet model to quantify the jump-imposed flow disturbance. The predicted flow consists of two counter-rotating viscous vortex rings of similar intensity, one in the wake and one around the body of the copepod. We showed that the entire jumping flow is spatially limited and temporally ephemeral owing to jump-impulsiveness and viscous decay. In contrast, continuous steady swimming generates two well-extended long-lasting momentum jets both in front of and behind the swimmer, as suggested by the well-known steady stresslet model. Based on the observed jump-swimming kinematics of a small copepod Oithona davisae, we further showed that jump-swimming produces a hydrodynamic disturbance with much smaller spatial extension and shorter temporal duration than that produced by a same-size copepod cruising steadily at the same average translating velocity. Hence, small copepods in jump-swimming are in general much less detectable by rheotactic predators. The present impulsive stresslet model improves a previously published impulsive Stokeslet model that applies only to the wake vortex.

On the role of copepod antennae in the production of hydrodynamic force during hopping

We integrate high-resolution experimental observations of a freely hopping copepod with three-dimensional numerical simulations to investigate the role of the copepod antennae in production of hydrodynamic force during hopping. The experimental observations revealed a distinctive asymmetrical deformation of the antennae during the power and return strokes, which lead us to the hypothesis that the antennae are active contributors to the production of propulsive force with kinematics selected in nature in order to maximize net thrust. To examine the validity of this hypothesis we carried out numerical experiments using an anatomically realistic, tethered, virtual copepod, by prescribing two sets of antenna kinematics. In the first set, each antenna moves as a rigid, oar-like structure in a reversible manner, whereas in the second set, the antenna is made to move asymmetrically as a deformable structure as revealed by the experiments. The computed results show that for both cases the antennae are major contributors to the net thrust force during hopping, and the results also clearly demonstrate the significant hydrodynamic benefit in terms of thrust enhancement and drag reduction derived from the biologically realistic, asymmetric antenna motion. This finding is not surprising given the low local Reynolds number environment within which the antenna operates, and points to striking similarities between the copepod antenna motion and ciliary propulsion. Finally, the simulations provide the first glimpse into the complex, highly 3-D structure of copepod wakes.

Phenotypic plasticity in juvenile jellyfish medusae facilitates effective animal-fluid interaction

Locomotion and feeding in marine animals are intimately linked to the flow dynamics created by specialized body parts. This interaction is of particular importance during ontogeny, when changes in behaviour and scale challenge the organism with shifts in fluid regimes and altered functionality. Previous studies have indicated that Scyphozoan jellyfish ontogeny accommodates the changes in fluid dynamics associated with increasing body dimensions and velocities during development. However, in addition to scale and behaviour that-to a certain degree-underlie the control of the animal, flow dynamics are also dependent on external factors such as temperature. Here, we show phenotypic plasticity in juvenile Aurelia aurita medusae, where morphogenesis is adapted to altered fluid regimes imposed by changes in ambient temperature. In particular, differential proportional growth was found to compensate for temperature-dependent changes in viscous effects, enabling the animal to use adhering water boundary layers as 'paddles'-and thus economize tissue-at low temperatures, while switching to tissue-dominated propulsion at higher temperatures where the boundary layer thickness is insufficient to serve for paddling. This effect was predicted by a model of animal-fluid interaction and confirmed empirically by flow-field visualization and assays of propulsion efficiency.

Advances in comparative physiology from high-speed imaging of animal and fluid motion

Since the time of Muybridge and Marey in the last half of the nineteenth century, studies of animal movement have relied on some form of high-speed or stop-action imaging to permit analysis of appendage and body motion. In the past ten years, the advent of megapixel-resolution high-speed digital imaging with maximal framing rates of 250 to 100,000 images per second has allowed new views of musculoskeletal function in comparative physiology that now extend to imaging flow around moving animals and the calculation of fluid forces produced by animals moving in fluids. In particular, the technique of digital particle image velocimetry (DPIV) has revolutionized our ability to understand how moving animals generate fluid forces and propel themselves through air and water. DPIV algorithms generate a matrix of velocity vectors through the use of image cross-correlation, which can then be used to calculate the force exerted on the fluid as well as locomotor work and power. DPIV algorithms can also be applied to images of moving animals to calculate the velocity of different regions of the moving animal, providing a much more detailed picture of animal motion than can traditional digitizing methods. Although three-dimensional measurement of animal motion is now routine, in the near future model-based kinematic reconstructions and volumetric analyses of animal-generated fluid flow patterns will provide the next step in imaging animal biomechanics and physiology.

Eat and run? The hunger/satiation hypothesis in vertical migration: history, evidence and consequences

The study of vertical migrations in aquatic organisms has a long and colourful history, much of it to do with the effects of changing sampling technology on our understanding of the phenomenon. However, the overwhelming majority of such studies carried out today still depend on detecting differences in vertical distribution profiles during some course of time, or acoustic echoes of migrating bands of organisms. These can not distinguish migratory activity of individual organisms, but can only assess net results of mass transfers of populations, which may integrate many individual migrations. This is an important distinction, for without knowing the actual movements of individuals it seems unlikely that we will be able to understand their causes, nor the effects of vertical migrations on the environment or on the migrators themselves. This review examines evidence for individual vertical movements gathered from 'tracers', mainly gut contents, and reviews the evidence for the hypothesis that such movements are in fact driven by hunger and satiation. The more recently appreciated vertical migrations of phytoplankters and their similarities in form and driving forces to those of zooplankton and nekton are also discussed. Finally, the role of vertical migrators in vertical fluxes of materials is discussed, along with the consequences of satiation-driven descent for such estimates.

Invertebrate-Inspired sensory-motor systems and autonomous, olfactory-guided exploration

The localization of resources in a natural environment is a multifaceted problem faced by both invertebrate animals and autonomous robots. At a first approximation, locomotion through natural environments must be guided by reliable sensory information. But natural environments can be unpredictable, so from time to time, information from any one sensory modality is likely to become temporarily unreliable. Fortunately, compensating mechanisms ensure that such signals are replaced or disambiguated by information from more reliable modalities. For invertebrates and robots to rely primarily on chemical senses has advantages and pitfalls, and these are discussed. The role of turbulence, which makes tracking a single odor to its source a complex problem, is contrasted with the high-fidelity identification of stimulus quality by the invertebrate chemoreceptor and by artificial sensors.

Fan organs of crayfish enhance chemical information flow

Animals as well as autonomous robots need to acquire environmental signals in order to adjust their activity in time and space. Some information is accessible to the sensors only as a result of specific behaviors for stimulus acquisition. Due to the slow rate of molecular diffusion, dispersal of chemical stimuli depends on fluid flow. Aquatic crustaceans can generate directed water currents by specialized appendages. Here I describe the crayfish fan organs, which are feathered flagella of the mouthparts, and their activity in sending and receiving chemical signals in environments with stagnant flow conditions. During the power-stroke, the fan opens and displaces water; during the return stroke, it collapses and thereby minimizes drag. These organs can create a variety of flow fields including water jets, and in many different directions. Bilateral upward fanning draws water horizontally from all directions toward the anterior chemoreceptors. Unilateral upward fanning draws water from only one side towards the body. The versatility of the crayfish fan organ makes it a candidate for biomimetic reconstruction and use in autonomous robots that can search chemical sources.