Comment: On phytoplankton perception by calanoid copepods

Author Posting. © Association for the Sciences of Limnology and Oceanography, 2016. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 61 (2016): 1163–1168, doi:10.1002/lno.10294.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

Scaling for turbulent viscosity of buoyant plumes in stratified fluids : PIV measurement with implications for submarine hydrothermal plume turbulence

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 129 (2017): 89-98, doi:10.1016/j.dsr.2017.10.006.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.Part of this work was financially supported by the National Natural Science Foundation of China and Natural Science Foundation of Zhejiang Province under respective Project no. 11672267 and LR16E090001 to ZH. HJ was supported by a National Science Foundation Grant NSF OCE-1038055 through the RIDGE2000 program and an internal funding from WHOI

To eat and not be eaten : optimal foraging behaviour in suspension feeding copepods

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of The Royal Society for personal use, not for redistribution. The definitive version was published in Journal of The Royal Society Interface 6 (2013): 20120693, doi:10.1098/rsif.2012.0693.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.The work was supported by grants from the Danish Council for Independent Research, The Niels Bohr Foundation and The Carlsberg Foundation to T.K., and by grants from the US National Science Foundation to H.J. (NSF OCE-1129496 and IOS-0718506)

Waves in the Red Sea : response to monsoonal and mountain gap winds

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 65 (2013): 1-13, doi:10.1016/j.csr.2013.05.017.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.This research is based on work supported by Award No. USA00001, USA00002, KSA00011, made by the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia

Danger of zooplankton feeding : the fluid signal generated by ambush-feeding copepods

Author Posting. © The Authors, 2010. This is the author's version of the work. It is posted here by permission of The Royal Society for personal use, not for redistribution. The definitive version was published in Proceedings of the Royal Society B: Biological Sciences 277 (2010): 3229-3237, doi:10.1098/rspb.2010.0629.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.TK was supported by a grant from the Danish Research Council and by a Niels Bohr Fellowship to TK and HJ was supported by National Science Foundation grants NSF OCE-0352284 & IOS-0718506

The Tokar Gap jet : regional circulation, diurnal variability, and moisture transport based on numerical simulations

Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 5885–5907, doi:10.1175/JCLI-D-14-00635.1.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.This work was supported by a grant from the King Abdullah University of Science and Technology (KAUST) as well as National Science Foundation Grant OCE0927017 and from DOD (MURI) Grant N000141110087, administered by the Office of Naval Research.2016-02-0

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

Author Posting. © Company of Biologists, 2020. This article is posted here by permission of Company of Biologists for personal use, not for redistribution. The definitive version was published in Journal of Experimental Biology (2020): jeb.220830, doi: 10.1242/jeb.220830.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.This study was supported by the National Science Foundation [OCE1634024 to N.F.; OCE-1433979 and OCE-1559062 to H.J.]; and by Stony Brook University [Graduate Council Fellowship and Turner Fellowship to A.S.T].2021-06-1

Numerical simulation of two coalescing turbulent forced plumes in linearly stratified fluids.

Author Posting. © AIP Publishing, 2019. This article is posted here by permission of [publisher] for personal use, not for redistribution. The definitive version was published in Lou, Y., He, Z., Jiang, H., & Han, X. Numerical simulation of two coalescing turbulent forced plumes in linearly stratified fluids. Physics of Fluids, 31(3), (2019):037111, doi:10.1063/1.5087534.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.This work was financially supported by the National Natural Science Foundation of China (Grant No. 11672267) and Fundamental Research Funds for the Central Universities (Grant No. 2017XZZX001-02A). This work was supported by HPC Center of ZJU (Zhoushan campus). Yingzhong Lou would like to thank Liang Zhao at Zhejiang University for fruitful discussions. The authors gratefully acknowledge the constructive suggestions offered by the anonymous referees.2020-03-2

Editorial: small scale spatial and temporal patterns in particles, plankton, and other organisms

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nayak, A. R., Jiang, H., Byron, M. L., Sullivan, J. M., McFarland, M. N., & Murphy, D. W. Editorial: small scale spatial and temporal patterns in particles, plankton, and other organisms. Frontiers in Marine Science, 8, (2021): 669530, https://doi.org/10.3389./fmars.2021.669530Scientists 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).AN was supported through a National Academy of Sciences, Engineering, and Medicine (NASEM) Gulf Research Program (GRP) Early Career Research Fellowship and a faculty start-up grant at Florida Atlantic University. HJ was supported by US National Science Foundation awards (OCE-1559062 and IOS-1353937). MB was supported by a faculty start-up grant at Penn State University. AN, JS, and MM were supported by US National Science Foundation awards (OCE-1634053 and OCE-1657332). DM was supported by the US National Science Foundation (CBET-1846925)