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Woods Hole Oceanographic Institution

Karl R. Helfrich

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Publications
»Isolating the hydrodynamic triggers of the diver response in the larval eastern oyster (Crassostrea virginica)
»Whales and waves: humpback whale foraging response and the shoaling of internal waves at Stellwagen Bank
»The formation and fate of internal waves in the South China Sea
»Laboratory experiments and simulations for solitary internal waves with trapped cores
»Internal bores in continuous stratifications
»Combined effect of rotation and topography on shoaling oceanic internal solitary waves
»Large-scale, realistic laboratory modeling of the M2 internal tide generation at the Luzon Strait
»Upward swimming of competent oyster larvae
»Experimental study of the effect of rotation on nonlinear internal waves
»Rapid gravitational collapse of a horizontal shear layer
»Swimming behavior and velocities of barnacle cyprides in a downwelling flume
»The effect of rotation on internal solitary waves
»A general description of a gravity current front propagating in a two-layer stratified fluid
»The reduced Ostrovsky equation: integrability and breaking
»Strongly nonlinear, simple internal waves in continuously-stratified, shallow fluids
»A model of internal solitary waves with trapped cores
»Synthetic aperature radar observations of resonantly generated internal solitary waves at Race Point Channel (Cape Cod)
»The skirted island: the effect of topography on the flow around planetary scale islands
»Continuously stratified nonlinear low-mode internal tides.
»Gravity currents and internal waves in a continuously stratified fluid
»Long-time solutions of the Ostrovsky equation
»Nonlinear disintegration of the internal tide
»On the stability of ocean overflows
»A transverse hydraulic jump in a model of the Faroe Bank Channel outflow
»Decay and return of rotating internal solitary waves
»Mixing at the head of a canyon: A laboratory laboratory investigation of fluid exchanges in a rotating, stratified basin
»Nonlinear adjustment of a localized layer of buoyant fluid against a vertical wall
»Long Nonlinear Internal Waves
»Generalized conditions for hydraulic criticality of oceanic overflows
»Gravity currents from a dam-break in a rotating channel
»A laboratory study of localized boundary mixing in a rotating stratified fluid
»Mixing and entrainment in hydraulically-driven, stratified sill flows


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J. D. Wheeler, K. R. Helfrich, E. J. Anderson and L. S. Mullineau
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Isolating the hydrodynamic triggers of the diver response in the larval eastern oyster (Crassostrea virginica)
, Limnology and Oceanography, accepted

Understanding the behavior of larval invertebrates during planktonic and settlement phases remains an open and intriguing problem in larval ecology.  Larvae modify their vertical swimming behavior in response to water column cues in order to feed, avoid predators, and search for settlement sites.  The larval eastern oyster (Crassostrea virginica) can descend in the water column via active downward swimming, sinking, or “diving”, which is a flick and retraction of the ciliated velum to propel a transient downward acceleration.  Diving may play an important role in active settlement, since diving larvae move rapidly downward in the water column and may regulate their proximity to suitable settlement sites.  Alternatively, it may function as a predator-avoidance escape mechanism.  We examined potential hydrodynamic triggers to this behavior by observing larval oysters in a grid-stirred turbulence tank.  Larval swimming was recorded for two turbulence intensities and flow properties around each larva were measured using particle image velocimetry.   The statistics of flow properties likely to be sensed by larvae (fluid acceleration, deformation, vorticity, and angular acceleration) were compared between diving and non-diving larvae.  Our analyses showed that diving larvae experienced high average flow accelerations in short time intervals (approximately 1-2 seconds) prior to dive onset, while accelerations experienced by non-diving larvae were significantly lower.  Further, the probability that larvae dove increased with the fluid acceleration they experienced.  These results indicate that oyster larvae actively respond to hydrodynamic signals in the local flow field, which has ecological implications for settlement and predator avoidance.



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