Kiørboe Thomas

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  • Preprint
    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.
  • Article
    Machine learning techniques to characterize functional traits of plankton from image data
    (Association for the Sciences of Limnology and Oceanography, 2022-06-30) Orenstein, Eric C. ; Ayata, Sakina Dorothée ; Maps, Frédéric ; Becker, Érica C. ; Benedetti, Fabio ; Biard, Tristan ; de Garidel-Thoron, Thibault ; Ellen, Jeffrey S. ; Ferrario, Filippo ; Giering, Sarah L. C. ; Guy-Haim, Tamar ; Hoebeke, Laura ; Iversen, Morten H. ; Kiørboe, Thomas ; Lalonde, Jean-François ; Lana, Arancha ; Laviale, Martin ; Lombard, Fabien ; Lorimer, Tom ; Martini, Séverine ; Meyer, Albin ; Möller, Klas O. ; Niehoff, Barbara ; Ohman, Mark D. ; Pradalier, Cédric ; Romagnan, Jean-Baptiste ; Schröder, Simon-Martin ; Sonnet, Virginie ; Sosik, Heidi M. ; Stemmann, Lars ; Stock, Michiel ; Terbiyik-Kurt, Tuba ; Valcárcel-Pérez, Nerea ; Vilgrain, Laure ; Wacquet, Guillaume ; Waite, Anya M. ; Irisson, Jean-Olivier
    Plankton imaging systems supported by automated classification and analysis have improved ecologists' ability to observe aquatic ecosystems. Today, we are on the cusp of reliably tracking plankton populations with a suite of lab-based and in situ tools, collecting imaging data at unprecedentedly fine spatial and temporal scales. But these data have potential well beyond examining the abundances of different taxa; the individual images themselves contain a wealth of information on functional traits. Here, we outline traits that could be measured from image data, suggest machine learning and computer vision approaches to extract functional trait information from the images, and discuss promising avenues for novel studies. The approaches we discuss are data agnostic and are broadly applicable to imagery of other aquatic or terrestrial organisms.
  • Preprint
    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.
  • Preprint
    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.
  • Preprint
    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.