How do larvae carried in turbulent water flow
How do larvae carried in turbulent water flow settle onto coral reefs ?
It has been suggested that Odors… (dissolved chemical cues) …from organisms on the substratum… (conspecifics, prey) …can induce larval settlement into right habitat
Evidence for role of odors: Experiments done in dishes in the lab…
Can odors help larvae land in the right habitat in nature … … in turbulent flowing water: *dilute odors? *overwhelm larval swimming?
Interdisciplinary, multi-institutional M. Koehl (ecological biomechanics) J. Strother (math) M. Hadfield (developmental biology) J. Koseff & M. Reidenbach (engineering) J. Jaffe (biophysics) Univ. of California, Berkeley Kewalo Marine Lab, Univ. of Hawaii Environmental Fluid Mechanics Lab, Stanford Univ. Scripps Inst. of Oceanography, UCSD
Phestilla sibogae (predator) Porites compressa (prey coral)
ciliated velum 200 mm Larva of Phestilla
Steps to recruit onto coral reef with abundant Porites ?
Larva transported to suitable habitat “Recruitment” (metamorphosis & survival) “Settlement” (attachment) Porites reef
Can dissolved chemical cue affect: Larval transport Metamorphosis? to suitable habitat? Settlement? (attachment)
Hadfield: Dissolved chemical cue from Porites… …induces metamorphosis
Can dissolved chemical cue affect: Larval transport to suitable habitat?
Can larvae use ODOR (dissolved cue) to help them land on the right reef in NATURE ? ! 1. Water flow in the field? 2. Dispersal of dissolved cue? 3. Larval behavioral responses to dissolved cue? Do responses to cue affect where larvae land in ambient water flow?
1. Water flow in the field?
Patch reefs Kaneohe Bay, Oahu, Hawaii
Measured (ADV) water velocity profiles above the reef 2 cm above reef
Waves Velocity (cm/s) 60 Flow shoreward 40 20 0 -20 -40 -60 Flow seaward 10 20 Time (s) 30 40
turbulence Velocity (cm/s) 60 40 20 0 -20 -40 -60 10 20 Time (s) 30 40
spectral analysis waves turbulence
Fast, wave-driven turbulent flow above reef Slow NET transport shoreward VERY slow flow through the reef
Slow net flow up out of reef (flat & convex reef surfaces) Slow net flow down into reef (depressions in reef surface)
1. Water flow in the field 2. Dispersal of dissolved cues?
Water collected in reef… … induces metamorphosis VERY slow flow (through contains CUE the )reef
Dye dispersal studies of smelly (i. e. cue-bearing) water from reef ef e r om r f Cue distribution g n i s r e d p u s i o l d c on s e e s c u n f a f t i s d ub ofkethe a larva? s scale , s i l u k o o T lo
Take a closer look in wave-flume in the lab (mimic field flow: . turbulence, waves)
“Reef” of P. compressa skeletons in wave-flume Sheet of laser light Fluorescent dye dissolves from coating on coral “PLIF”
water Microscopic larva encounters filaments of cue as it swims. ”coral odor cue” (dye) dissolving off coral 1 cm
follow trajectory of larva water On-off encounters with cue: Gradient in frequency of encounters with cue NOT diffuse. concentration gradient ! coral 1 cm
1. Water flow in the field 2. Dispersal of dissolved cues 3. Behavioral responses of competent larvae to dissolved cue ?
Animation by G. Rangan Behavior of competent larva in: cue-free water SWIMS (0. 17 cm/s) cue above threshold concentration SINKS (0. 13 cm/s)
1. Water flow in the field? 2. Dispersal of dissolved cue? 3. Larval behavioral responses to dissolved cue? Do responses to cue affect where larvae land in ambient water flow? Flow on scale of mm’s
water flows back and forth in wave tank neutrally-buoyant marker particles illuminated by sheet of laser light 1 cm Benthic organisms on floor of wave tank
Video motion of marker particles (PIV) 1 cm
Simultaneous video records: Camera 1(filter): particles (PIV- calculate velocities) Camera 2(filter): fluorescent dye from benthos (PLIF- measure “odor” concentrations)
instantaneous velocity&vectors (PIV) Velocity vectors “cue” concentrations (Red – fast)with (Bluetime – slow) CHANGE & instantaneous concentrations (PLIF) (scale“cue” of seconds) (lighter pixels – higher concentrations)
intermediate velocity filaments of high ‘cue’ concentration high velocity low velocity 1 cm Velocity & “cue” concentrations VARY on fine spatial scale (microns to mm’s)
Odor-free water Cue above threshold concentration swims sinks Put “larvae” with this behavior into PLIF/PIV video data
CALCULATE TRAJECTORY OF LARVA Larval velocity at each time step = Larva’s swimming or sinking velocity (depends on local instantaneous cue concentration at its position in frame of PLIF video) + Local instantaneous ambient water velocity (carrying larva)
INDIVIDUAL-BASED MODEL: Calculate trajectories of 1000’s of larvae (randomly-chosen starting positions in water) Calculate rate of transport of larvae into the reef
In turbulent, wavy flow … …model predicts: Sinking in cue enhances transport rates into the reef by ~ 20%
Once you land, can you stay put ? How does flow through a reef affect where larvae can hang on to the reef to settle ?
top of reef Flume LDA: measure velocities 200 mm from coral surfaces (velocities encountered by larvae on surfaces) within reef
Flow 200 mm from surfaces Velocity (m/s) top of reef 10 SLOWER flow 20 30 40 within reef time (s) 8 cm below top of reef 10 20 30 time (s) 40
Flow 200 mm from surfaces Velocity (m/s) top of reef 10 Will larvae 20 30 40 wash time (s) away in this flow? 8 cm below top of reef 10 20 30 time (s) 40
Dissolved cue from Porites induces Phestilla to stick to substratum. Measure adhesive strength of larvae (shear stress to wash them off surface)
Dynamically-scaled physical models Hydrodynamic forces on a larva (higher in faster flow)
If hydrodynamic force > adhesion, larval blows away
Time to stick top of reef down within reef
Force fluctuates rapidly Time to stick
Chance of larva attaching much Larva unlikely attach greater withintoreef on top of reef Time to stick
But drag on sleek juvenile is much LOWER than on larva: they can stick anywhere on reef Juveniles can crawl up to reef top & forage without blowing away !
Water flow in the field? * waves, turbulence * slow flow through & up from reef Dispersal of dissolved cues? * filaments above reef * larvae have on-off encounters with cue Responses of competent larvae to dissolved cue * sink: enhances transport into reef * stick to surfaces
Water flow in the reef on the scale of larva (200 mm) * varies on time scale of seconds * slower flow within reef than on top Drag on larva >> juvenile * larvae can only settle within reef * juveniles can crawl up to reef top & forage without blowing away
How do larvae carried in turbulent water flow settle onto coral reefs ? Behavior of larva… (swim, sink, stick, crawl) …biases how ambient water flow moves it
Challenge: Quantify hydrodynamic & chemical environment on spatial & temporal scales relevant to the larvae
Challenge: Quantify hydrodynamic & chemical environment on spatial (mm’s-mm’s) & temporal (ms’s-hr’s) scales relevant to the larvae
now…
Can use model to test effects of other larval behaviors…
example: What does shear do to a larva? neutrally buoyant sinker swimmer
Start neutral, neutral swimming, swimming and sinking “larvae” at same positions in water. Calculate trajectories in PIV video
% landing on substratum: sinkers > swimmers > neutrally-buoyant
% landing on substratum: sinkers > swimmers > neutrally-buoyant
% landing on substratum: sinkers > swimmers > neutrally-buoyant
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