Jiang Houshuo

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Jiang

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Houshuo

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0000-0002-8175-3500

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Process modeling studies of physical mechanisms of the formation of an anticyclonic eddy in the central Red Sea

(John Wiley & Sons, 2014-02-25) Chen, Changsheng ; Li, Ruixiang ; Pratt, Lawrence J. ; Limeburner, Richard ; Beardsley, Robert C. ; Bower, Amy S. ; Jiang, Houshuo ; Abualnaja, Yasser ; Xu, Qichun ; Lin, Huichan ; Liu, Xuehai ; Lan, Jian ; Kim, Taewan

Surface drifters released in the central Red Sea during April 2010 detected a well-defined anticyclonic eddy around 23°N. This eddy was ∼45–60 km in radius, with a swirl speed up to ∼0.5 m/s. The eddy feature was also evident in monthly averaged sea surface height fields and in current profiles measured on a cross-isobath, shipboard CTD/ADCP survey around that region. The unstructured-grid, Finite-Volume Community Ocean Model (FVCOM) was configured for the Red Sea and process studies were conducted to establish the conditions necessary for the eddy to form and to establish its robustness. The model was capable of reproducing the observed anticyclonic eddy with the same location and size. Diagnosis of model results suggests that the eddy can be formed in a Red Sea that is subject to seasonally varying buoyancy forcing, with no wind, but that its location and structure are significantly altered by wind forcing, initial distribution of water stratification and southward coastal flow from the upstream area. Momentum analysis indicates that the flow field of the eddy was in geostrophic balance, with the baroclinic pressure gradient forcing about the same order of magnitude as the surface pressure gradient forcing.
Zonal surface wind jets across the Red Sea due to mountain gap forcing along both sides of the Red Sea

(American Geophysical Union, 2009-10-10) Jiang, Houshuo ; Farrar, J. Thomas ; Beardsley, Robert C. ; Chen, Ru ; Chen, Changsheng

Mesoscale atmospheric modeling over the Red Sea, validated by in-situ meteorological buoy data, identifies two types of coastal mountain gap wind jets that frequently blow across the longitudinal axis of the Red Sea: (1) an eastward-blowing summer daily wind jet originating from the Tokar Gap on the Sudanese Red Sea coast, and (2) wintertime westward-blowing wind-jet bands along the northwestern Saudi Arabian coast, which occur every 10–20 days and can last for several days when occurring. Both wind jets can attain wind speeds over 15 m s−1 and contribute significantly to monthly mean surface wind stress, especially in the cross-axis components, which could be of importance to ocean eddy formation in the Red Sea. The wintertime wind jets can cause significant evaporation and ocean heat loss along the northeastern Red Sea coast and may potentially drive deep convection in that region. An initial characterization of these wind jets is presented.
Danger of zooplankton feeding : the fluid signal generated by ambush-feeding copepods

( 2010-06) Kiørboe, Thomas ; Jiang, Houshuo ; Colin, Sean P.

Zooplankton feed in either of three ways: they generate a feeding current, cruise through the water, or they are ambush feeders. Each mode generates different hydrodynamic disturbances and hence exposes the grazers differently to mechanosensory predators. Ambush feeders sink slowly and therefore perform occasional upward repositioning jumps. We quantified the fluid disturbance generated by repositioning jumps in a mm-sized copepod (Re ~ 40). The kick of the swimming legs generates a viscous vortex ring in the wake; another ring of similar intensity but opposite rotation is formed around the decelerating copepod. A simple analytical model, that of an impulsive point force, properly describes the observed flow field as a function of the momentum of the copepod, including the translation of the vortex and its spatial extension and temporal decay. We show that the time-averaged fluid signal and the consequent predation risk is much less for an ambush feeding than a cruising or hovering copepod for small individuals, while the reverse is true for individuals larger than about 1 mm. This makes inefficient ambush feeding feasible in small copepods and is consistent with the observation that ambush feeding copepods in the ocean are all small, while larger species invariably use hovering or cruising feeding strategies.
Copepod manipulation of oil droplet size distribution

(Nature Research, 2019-01-24) Uttieri, Marco ; Nihongi, Ai ; Hinow, Peter ; Motschman, Jeffrey ; Jiang, Houshuo ; Alcaraz, Miquel ; Strickler, J. Rudi

Oil spills are one of the most dangerous sources of pollution in aquatic ecosystems. Owing to their pivotal position in the food web, pelagic copepods can provide crucial intermediary transferring oil between trophic levels. In this study we show that the calanoid Paracartia grani can actively modify the size-spectrum of oil droplets. Direct manipulation through the movement of the feeding appendages and egestion work in concert, splitting larger droplets (Ø = 16 µm) into smaller ones (Ø = 4–8 µm). The copepod-driven change in droplet size distribution can increase the availability of oil droplets to organisms feeding on smaller particles, sustaining the transfer of petrochemical compounds among different compartments. These results raise the curtain on complex small-scale interactions which can promote the understanding of oil spills fate in aquatic ecosystems.
Waves in the Red Sea : response to monsoonal and mountain gap winds

( 2013-05-30) Ralston, David K. ; Jiang, Houshuo ; Farrar, J. Thomas

An unstructured grid, phase-averaged wave model forced with winds from a high resolution atmospheric model is used to evaluate wind wave conditions in the Red Sea over an approximately 2-year period. The Red Sea lies in a narrow rift valley, and the steep topography surrounding the basin steers the dominant wind patterns and consequently the wave climate. At large scales, the model results indicated that the primary seasonal variability in waves was due to the monsoonal wind reversal. During the winter, monsoon winds from the southeast generated waves with mean significant wave heights in excess of 2 m and mean periods of 8 s in the southern Red Sea, while in the northern part of the basin waves were smaller, shorter period, and from northwest. The zone of convergence of winds and waves typically occurred around 19-20˚N, but the location varied between 15 to 21.5˚N. During the summer, waves were generally smaller and from the northwest over most of the basin. While the seasonal winds oriented along the axis of the Red Sea drove much of the variability in the waves, the maximum wave heights in the simulations were not due to the monsoonal winds but instead were generated by localized mountain wind jets oriented across the basin (roughly east-west). During the summer, a mountain wind jet from the Tokar Gap enhanced the waves in the region of 18 and 20˚N, with monthly mean wave heights exceeding 2 m and maximum wave heights of 14 m during a period when the rest of the Red Sea was relatively calm. Smaller mountain gap wind jets along the northeast coast created large waves during the fall and winter, with a series of jets providing a dominant source of wave energy during these periods. Evaluation of the wave model results against observations from a buoy and satellites found that the spatial resolution of the wind model significantly affected the quality of the wave model results. Wind forcing from a 10-km grid produced higher skills for waves than winds from a 30-km grid, largely due to under-prediction of the mean wind speed and wave height with the coarser grid. The 30-km grid did not resolve the mountain gap wind jets, and thus predicted lower wave heights in the central Red Sea during the summer and along the northeast coast in the winter.
Copepod feeding strategy determines response to seawater viscosity: videography study of two calanoid copepod species

(Company of Biologists, 2020-06-11) Tyrell, Abigail S. ; Jiang, Houshuo ; Fisher, Nicholas S.

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.
Comment: On phytoplankton perception by calanoid copepods

(John Wiley & Sons, 2016-03-26) Paffenhöfer, Gustav-Adolf ; Jiang, Houshuo

Three publications recently reported that calanoid copepods, feeding on phytoplankton cells by using a feeding current, perceived such cells by mechanoperception. There was no evidence of remote chemically-mediated perception of those cells. These observations differ from earlier findings that feeding-current producing calanoids are able to detect phytoplankton cells by chemoperception at a distance from their particle-collecting setae of their cephalic appendages. The results on mechanoperception and the earlier published data on chemoperception will be presented and discussed. In addition, the concentration of chemicals within the phycosphere of food cells will be re-examined. We conclude that chemoperception of phytoplankton cells by calanoid copepods in a feeding current is feasible.
Flow disturbances generated by feeding and swimming zooplankton

( 2014-03) Kiørboe, Thomas ; Jiang, Houshuo ; Goncalves, Rodrigo Javier ; Nielsen, Lasse Tor ; Wadhwa, Navish

Interactions between planktonic organisms, such as detection of prey, predators, and mates, are often mediated by fluid signals. Consequently, many plankton predators perceive their prey from the fluid disturbances that it generates when it feeds and swims. Zooplankton should therefore seek to minimize the fluid disturbance that they produce. By means of particle image velocimetry, we describe the fluid disturbances produced by feeding and swimming in zooplankton with diverse propulsion mechanisms, and ranging from 10-µm flagellates to > mm-sized copepods. We show that zooplankton, in which feeding and swimming are separate processes, produce flow disturbances during swimming with a much faster spatial attenuation (velocity u varies with distance r as u ∝ r-3 to r-4), than that produced by zooplankton for which feeding and propulsion are the same process (u ∝ r-1 to r-2). As a result, the spatial extension of the fluid disturbance produced by swimmers is an order of magnitude smaller than that produced by feeders at similar Reynolds numbers. The ‘quiet’ propulsion of swimmers is achieved either through swimming erratically by short-lasting power-strokes, generating viscous vortex rings, or by ‘breast stroke swimming’. Both produce rapidly attenuating flows. The more ‘noisy’ swimming of those that are constrained by a need to simultaneously feed is due to constantly beating flagella or appendages that are positioned either anteriorly or posteriorly on the (cell) body. These patterns transcend differences in size and taxonomy and have thus evolved multiple times, suggesting a strong selective pressure to minimize predation risk.
Why does the jumping ciliate Mesodinium rubrum possess an equatorially located propulsive ciliary belt?

( 2011-01-14) Jiang, Houshuo

It has long been thought that jumping by the ciliate Mesodinium rubrum can enhance its nutrient uptake. However, jumping can be energetically costly and also dangerous by inducing hydrodynamic disturbances detectable to rheotactic predators. Here, a computational fluid dynamics (CFD) model, driven by published empirical data, is developed to simulate the jump-induced unsteady flow as well as chemical field around a self-propelled jumping ciliate. The associated phosphorus uptake, hydrodynamic signal strength, mechanical energy cost and Froude propulsion efficiency are also calculated. An equatorial ciliary belt (ECB), i.e. the morphology used by M. rubrum for propulsion, is considered. For comparison purpose, three other strategies (pulled or pushed by cilia, or towed) are also considered. Comparison of the CFD results among the four strategies considered suggests: (1) jumping enhances phosphorus uptake with simulated values consistent with available field data; (2) the M. rubrum-like propulsion generates the weakest and spatially most limited hydrodynamic disturbance and therefore may effectively minimize the jump-induced predation risk; and (3) the M. rubrum-like propulsion achieves a high Froude propulsion efficiency (~0.78) and is least costly in mechanical energy expenditure among the three self-propelled strategies considered. Thus, using the ECB for propulsion can be essential in ensuring that M. rubrum is a successful ‘fast-jumping’ primary producer.
Hydrodynamic signal perception by the copepod Oithona plumifera

(Inter-Research, 2008-12-23) Jiang, Houshuo ; Paffenhöfer, Gustav-Adolf

Spatio-temporal hydrodynamic signal fields were quantified for ambush-feeding Oithona plumifera females sensing motile Strobilidium ciliates. First, videotaped Oithona–ciliate encounters were image-analyzed to retrieve ciliate trajectories, O. plumifera attack kinematics and reaction distances to the ciliates. Second, using computational fluid dynamics (CFD), flow disturbances created by swimming ciliates were examined for 5 common ciliary forcing schemes. Third, using the CFD results and measured ciliate trajectories as inputs, a hydrodynamic model was developed to calculate ciliate-generated hydrodynamic signal patterns for observed encounters. Wide variance was found in measured reaction distances. Good correlations existed between measured predator attack kinematics and measured pre-attack prey locations. Moreover, data analysis showed that O. plumifera preferred small attack angles, presumably to enhance capture success. From hydrodynamic modeling, several distinct spatio-temporal hydrodynamic signal patterns were identified, and estimated hydrodynamic signal strengths immediately prior to attack were all above a minimum required signal level but differed substantially in magnitude. These results support the notion that by monitoring and recognizing the spatio-temporal pattern of ciliate-created flow disturbances, O. plumifera can perceive and project the ciliate’s instantaneous location and velocity, and hence precisely time its attack when the ciliate reaches a location where it can most easily be captured. Instead of reacting to a constant signal strength, O. plumifera females adapt their capture behaviors to perceived signal patterns. CFD simulations also revealed species-specific flow patterns and spatial decays in hydrodynamic disturbances created by swimming protists. The predator may use this species-specific information to distinguish among prey species.
To eat and not be eaten : optimal foraging behaviour in suspension feeding copepods

( 2012-08) Kiørboe, Thomas ; Jiang, Houshuo

Zooplankton feed on microscopic prey that they either entrain in a feeding current or encounter as they cruise through the water. They generate fluid disturbances as they feed and move, thus elevating their risk of being detected and encountered by predators. Different feeding modes generate different hydrodynamic signals to predators and different predator encounter speeds but may also differ in their efficiency; the optimal behaviour is that which maximizes the net energy gain over the predation risk. Here, we show by means of flow visualization and simple hydrodynamic and optimization models that copepods with a diversity of feeding behaviours converge on optimal, size-independent specific clearance rates that are consistent with observed clearance rates of zooplankton, irrespective of feeding mode, species and size. We also predict magnitudes and size-scaling of swimming speeds that are consistent with observations. The rationalization of the magnitude and scaling of the clearance rates of zooplankton makes it more suitable for development of models of marine ecosystems, and is particularly relevant in predicting the size structure and biomass of pelagic communities.
Scaling for turbulent viscosity of buoyant plumes in stratified fluids : PIV measurement with implications for submarine hydrothermal plume turbulence

( 2017-10-07) Zhang, Wei ; He, Zhiguo ; Jiang, Houshuo

Time-resolved particle image velocimetry (PIV) has been used to measure instantaneous twodimensional velocity vector fields of laboratory-generated turbulent buoyant plumes in linearly stratified saltwater over extended periods of time. From PIV-measured time-series flow data, characteristics of plume mean flow and turbulence have been quantified. To be specific, maximum plume penetration scaling and entrainment coefficient determined from the mean flow agree well with the theory based on the entrainment hypothesis for buoyant plumes in stratified fluids. Besides the well-known persistent entrainment along the plume stem (i.e., the ‘plumestem’ entrainment), the mean plume velocity field shows persistent entrainment along the outer edge of the plume cap (i.e., the ‘plume-cap’ entrainment), thereby confirming predictions from previous numerical simulation studies. To our knowledge, the present PIV investigation provides the first measured flow field data in the plume cap region. As to measured plume turbulence, both the turbulent kinetic energy field and the turbulence dissipation rate field attain their maximum close to the source, while the turbulent viscosity field reaches its maximum within the plume cap region; the results also show that maximum turbulent viscosity scales as νt,max = 0.030 (B/N)1/2, where B is source buoyancy flux and N is ambient buoyancy frequency. These PIV data combined with previously published numerical simulation results have implications for understanding the roles of hydrothermal plume turbulence, i.e. plume turbulence within the cap region causes the ‘plume-cap’ entrainment that plays an equally important role as the ‘plume-stem’ entrainment in supplying the final volume flux at the plume spreading level.
The Tokar Gap jet : regional circulation, diurnal variability, and moisture transport based on numerical simulations

(American Meteorological Society, 2015-08-01) Davis, Shannon R. ; Pratt, Lawrence J. ; Jiang, Houshuo

The structure, variability, and regional connectivity of the Tokar Gap jet (TGJ) are described using WRF Model analyses and supporting atmospheric datasets from the East African–Red Sea–Arabian Peninsula (EARSAP) region during summer 2008. Sources of the TGJ’s unique quasi-diurnal nature and association with atypically high atmospheric moisture transport are traced back to larger-scale atmospheric dynamics influencing its forcing. These include seasonal shifts in the intertropical convergence zone (ITCZ), variability of the monsoon and North African wind regimes, and ties to other orographic flow patterns. Strong modulation of the TGJ by regional processes such as the desert heating cycle, wind convergence at the ITCZ surface front, and the local land–sea breeze cycle are described. Two case studies present the interplay of these influences in detail. The first of these was an “extreme” gap wind event on 12 July, in which horizontal velocities in the Tokar Gap exceeded 26 m s−1 and the flow from the jet extended the full width of the Red Sea basin. This event coincided with development of a large mesoscale convective complex (MCC) and precipitation at the entrance of the Tokar Gap as well as smaller gaps downstream along the Arabian Peninsula. More typical behavior of the TGJ during the 2008 summer is discussed using a second case study on 19 July. Downwind impact of the TGJ is evaluated using Lagrangian model trajectories and analysis of the lateral moisture fluxes (LMFs) during jet events. These results suggest means by which TGJ contributes to large LMFs and has potential bearing upon Sahelian rainfall and MCC development.
The land-sea breeze of the Red Sea: observations, simulations, and relationships to regional moisture transport

(American Geophysical Union, 2019-11-16) Davis, Shannon R. ; Farrar, J. Thomas ; Weller, Robert A. ; Jiang, Houshuo ; Pratt, Lawrence J.

Unique in situ observations of atmospheric conditions over the Red Sea and the coastal Arabian Peninsula are examined to study the dynamics and regional impacts of the local land‐sea breeze cycle (LSBC). During a 26‐month data record spanning 2008–2011, observed LSBC events occurred year‐round, frequently exhibiting cross‐shore wind velocities in excess of 8 m/s. Observed onshore and offshore features of both the land‐ and sea‐breeze phases of the cycle are presented, and their seasonal modulation is considered. Weather Research and Forecasting climate downscaling simulations and satellite measurements are used to extend the analysis. In the model, the amplitude of the LSBC is significantly larger in the vicinity of the steeper terrain elements encircling the basin, suggesting an enhancement by the associated slope winds. Observed and simulated conditions also reflected distinct gravity‐current characteristics of the intrinsic moist marine air mass during both phases of the LSBC. Specifically, the advance and retreat of marine air mass was directly tied to the development of internal boundary layers onshore and offshore throughout the period of study. Convergence in the lateral moisture flux resulting from this air mass ascending the coastal topography (sea‐breeze phase) as well as colliding with air masses from the opposing coastline (land‐breeze phase) further resulted in cumulous cloud formation and precipitation.
Editorial: small scale spatial and temporal patterns in particles, plankton, and other organisms

(Frontiers Media, 2021-03-22) Nayak, Aditya R. ; Jiang, Houshuo ; Byron, Margaret L. ; Sullivan, James M. ; McFarland, Malcolm N. ; Murphy, David W.

Scientists have long known that small-scale interactions of aquatic particles, plankton, and other organisms with their immediate environment play an important role in diverse research areas, including marine ecology, ocean optics, and climate change (Guasto et al., 2012; Prairie et al., 2012). Typically, the distribution of particles and other organisms in the water column tends to be quite “patchy,” i.e., non-homogeneous, both spatially and temporally (Durham and Stocker, 2012). Patchiness can manifest itself through well-known phenomena such as harmful algal blooms (HABs), phytoplankton and zooplankton “thin layers,” deep scattering layers, and schooling of marine organisms such as krill and fish. This non-homogeneous distribution can significantly influence predator-prey encounters and outcomes, export fluxes, marine ecosystem health, and biological productivity (Sullivan et al., 2010; Durham et al., 2013). Thus, there is a continuing need to study and characterize the small-scale biological-physical interactions between particles/organisms and their local environment, as well as the scaled-up effects of these small-scale interactions on larger-scale dynamics. These studies are also directly linked to broader research topics listed as part of the future “grand challenges” in marine ecosystem ecology, as outlined in Borja et al. (2020).
Numerical simulation of two coalescing turbulent forced plumes in linearly stratified fluids.

(AIP Publishing, 2019-03-28) Lou, Yingzhong ; He, Zhiguo ; Jiang, Houshuo ; Han, Xiqiu

A computational fluid dynamic model that can solve the Reynolds-averaged Navier-Stokes equations and the species transport equation is developed to simulate two coalescing turbulent forced plumes, which are released with initial momentum and buoyancy flux into a linearly stable stratified environment. The velocity fields, turbulence structures, and entrainment of two plumes with different source separations and source buoyancy fluxes are analyzed quantitatively, in comparison with a series of physical experiments. An empirical parameterization is proposed to predict the amplification of the maximum rise height of two coalescing forced plumes caused by superposition and mutual entrainment. The maximum values of both turbulent kinetic energy and turbulence dissipation rate decrease monotonically with the increase in source separation of the two turbulent plumes. However, the trajectory of the maximum turbulent viscosity attained in the plume cap region presents two notable enhancements. This variation may be attributed to the turbulence transported from the touching region and the strong mixing around the neutrally buoyant layer between two plumes, while the mixing is caused by the lateral convection and the rebound after overshooting. The plume entrainment coefficient in near vent stems has a positive relationship with the source Richardson number. A transition of flow regimes to plume-like flows would occur when the contribution of initial momentum is important. The entrainment coefficient will decrease in the touching region of two plumes due to mutual entrainment, while the superposition of plumes can lead to distortion of the boundary of plume sectors.
Swimming speed of larval snail does not correlate with size and ciliary beat frequency

(Public Library of Science, 2013-12-18) Chan, Kit Yu Karen ; Jiang, Houshuo ; Padilla, Dianna K.

Many marine invertebrates have planktonic larvae with cilia used for both propulsion and capturing of food particles. Hence, changes in ciliary activity have implications for larval nutrition and ability to navigate the water column, which in turn affect survival and dispersal. Using high-speed high-resolution microvideography, we examined the relationship between swimming speed, velar arrangements, and ciliary beat frequency of freely swimming veliger larvae of the gastropod Crepidula fornicata over the course of larval development. Average swimming speed was greatest 6 days post hatching, suggesting a reduction in swimming speed towards settlement. At a given age, veliger larvae have highly variable speeds (0.8–4 body lengths s−1) that are independent of shell size. Contrary to the hypothesis that an increase in ciliary beat frequency increases work done, and therefore speed, there was no significant correlation between swimming speed and ciliary beat frequency. Instead, there are significant correlations between swimming speed and visible area of the velar lobe, and distance between centroids of velum and larval shell. These observations suggest an alternative hypothesis that, instead of modifying ciliary beat frequency, larval C. fornicata modify swimming through adjustment of velum extension or orientation. The ability to adjust velum position could influence particle capture efficiency and fluid disturbance and help promote survival in the plankton.
Oscillations in the near-field feeding current of a calanoid copepod are useful for particle sensing

(Nature Research, 2019-11-28) Giuffre, Carl ; Hinow, Peter ; Jiang, Houshuo ; Strickler, J. Rudi

Calanoid copepods are small crustaceans that constitute a major element of aquatic ecosystems. Key to their success is their feeding apparatus consisting of sensor-studded mouth appendages that are in constant motion. These appendages generate a feeding current to enhance the encounter probability with food items. Additionally, sensing enables the organism to determine the position and quality of food particles, and to alter the near-field flow to capture and manipulate the particles for ingestion or rejection. Here we observe a freely swimming copepod Leptodiaptomus sicilis in multiple perspectives together with suspended particles that allow us to analyse the flow field created by the animal. We observe a highly periodic motion of the mouth appendages that is mirrored in oscillations of nearby tracer particles. We propose that the phase shift between the fluid and the particle velocities is sufficient for mechanical detection of the particles entrained in the feeding current. Moreover, we propose that an immersed algal cell may benefit from the excitation by increased uptake of dissolved inorganic compounds.
The fluid dynamics of swimming by jumping in copepods

( 2010-11-04) Jiang, Houshuo ; Kiørboe, Thomas

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 counterrotating 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 jumpswimming are 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.
Plankton reach new heights in effort to avoid predators

( 2012-01) Gemmell, Brad J. ; Jiang, Houshuo ; Strickler, J. Rudi ; Buskey, Edward J.

The marine environment associated with the air-water interface (neuston) provides an important food source to pelagic organisms where subsurface prey is limited. However, studies on predator-prey interactions within this environment are lacking. Copepods are known to produce strong escape jumps in response to predators but must contend with a low Reynolds number environment where viscous forces limit escape distance. All previous work on copepods interaction with predators has focused on a liquid environment. Here, we describe a novel anti-predator behavior in two neustonic copepod species where individuals frequently exit the water surface and travel many times their own body length through air to avoid predators. Using both field recordings with natural predators and high speed laboratory recordings we obtain detailed kinematics of this behavior, and estimate energetic cost associated with this behavior. We demonstrate that despite losing up to 88% of their initial kinetic energy, copepods which break the water surface travel significantly further than escapes underwater and successfully exit the perceptive field of the predator. This behavior provides an effective defense mechanism against subsurface feeding visual predators and the results provide insight into trophic interactions within the neustonic environment.

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