How do larvae carried in turbulent water flow settle onto coral reefs ?

It has been suggested that Odors… …from organisms on the substratum… (conspecifics, prey) …can induce larval settlement into right habitat It has been suggested that Odors… …from organisms on the substratum… (conspecifics, prey) …can induce larval settlement into right habitat (dissolved chemical cues) (dissolved chemical cues)

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? Can odors help larvae land in the right habitat in nature … … in turbulent flowing water: *dilute odors? *overwhelm larval swimming?

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 Interdisciplinary, multi-institutional

Porites compressa (prey coral) Porites compressa (prey coral) Phestilla sibogae (predator)

Larva of Phestilla ciliated velum 200  m

Steps to recruit onto coral reef with abundant Porites ?

Larva transported to suitable habitat “Settlement” (attachment) “Recruitment” (metamorphosis & survival) Porites reef

Can dissolved chemical cue affect: Larval transport to suitable habitat? Settlement? (attachment) Metamorphosis?

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? Do responses to cue affect where larvae land in ambient water flow?

1. Water flow in the field?

Kaneohe Bay, Oahu, Hawaii Patch reefs

Measured (ADV) water velocity profiles above the reef Measured (ADV) water velocity profiles above the reef 2 cm above reef

Time (s) Velocity (cm/s) Flow shoreward Flow seaward Waves

Time (s) Velocity (cm/s) turbulence

waves turbulence spectral analysis spectral analysis

VERY slow flow through the reef VERY slow flow through the reef Slow NET transport shoreward  Slow NET transport shoreward  Fast, wave-driven turbulent flow above reef Fast, wave-driven turbulent flow above reef

Slow net flow up out of reef (flat & convex reef surfaces) Slow net flow up out of reef (flat & convex reef surfaces) Slow net flow down into reef (depressions in reef surface) 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… Water collected in reef… … induces metamorphosis … induces metamorphosis ( contains CUE ) VERY slow flow through the reef VERY slow flow through the reef

Dye dispersal studies of smelly (i.e. cue-bearing) water from reef To us, substances dispersing from reef look like a diffuse cloud To us, substances dispersing from reef look like a diffuse cloud Cue distribution on scale of the larva?

.. Take a closer look in wave-flume in the lab (mimic field flow: turbulence, waves )

“Reef” of P. compressa skeletons in wave-flume Fluorescent dye dissolves from coating on coral Fluorescent dye dissolves from coating on coral Sheet of laser light “PLIF”

coral water ”coral odor cue” (dye) dissolving off coral ”coral odor cue” (dye) dissolving off coral 1 cm Microscopic larva encounters filaments of cue as it swims Microscopic larva encounters filaments of cue as it swims.

coral water 1 cm follow trajectory of larva On-off encounters with cue: Gradient in frequency of encounters with cue NOT diffuse concentration gradient ! follow trajectory of larva On-off encounters with cue: Gradient in frequency of encounters with cue NOT diffuse concentration gradient !.

1. Water flow in the field 2. Dispersal of dissolved cues 3. Behavioral responses of competent larvae to dissolved cue ?

Behavior of competent larva in: cue-free water cue above threshold concentration  SWIMS (0.17cm/s)  SINKS (0.13cm/s) Animation by G. Rangan

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? Do responses to cue affect where larvae land in ambient water flow? Flow on scale of mm’s

Benthic organisms on floor of wave tank water flows back and forth in wave tank neutrally-buoyant marker particles illuminated by sheet of laser light 1 cm

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) (Red – fast) (Blue – slow) & instantaneous “cue” concentrations (PLIF) (lighter pixels – higher concentrations) Velocity vectors & “cue” concentrations CHANGE with time (scale of seconds)

Velocity & “cue” concentrations VARY on fine spatial scale (microns to mm’s) filaments of high ‘cue’ concentration filaments of high ‘cue’ concentration intermediate velocity high velocity low velocity 1 cm

Put “larvae” Put “larvae” with with this behavior this behavior into into PLIF/PIV video data Odor-free water Cue above threshold concentration swims

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) Larval velocity at each time step = CALCULATE TRAJECTORY OF 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 ? Once you land, can you stay put ? How does flow through a reef affect where larvae can hang on to the reef to settle ?

Flume LDA: measure velocities 200  m from coral surfaces (velocities encountered by larvae on surfaces) within reef top of reef

cm below top of reef time (s) top of reef Velocity (m/s) time (s) SLOWER flow within reef SLOWER flow within reef Flow 200  m from surfaces

cm below top of reef time (s) top of reef Velocity (m/s) time (s) Flow 200  m from surfaces Will larvae wash away in this flow? Will larvae wash away in this flow?

Measure adhesive strength of larvae (shear stress to wash them off surface) Dissolved cue from Porites induces Phestilla to stick to substratum.

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

Time to stick Force fluctuates rapidly

Time to stick Chance of larva attaching much greater within reef Larva unlikely to attach on top of reef

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 !

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 field? * waves, turbulence * slow flow through & up from reef

Drag on larva >> juvenile * larvae can only settle within reef * juveniles can crawl up to reef top & forage without blowing away Water flow in the reef on the scale of larva (200  m) * varies on time scale of seconds * slower flow within reef than on top

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 & temporal scales relevant to the larvae

Challenge: Quantify hydrodynamic & chemical environment on spatial (  m’s-mm’s) & temporal (ms’s-hr’s) scales relevant to the larvae Challenge: Quantify hydrodynamic & chemical environment on spatial (  m’s-mm’s) & temporal (ms’s-hr’s) scales relevant to the larvae

now…

Can use model to test effects of other larval behaviors…

neutrally buoyant sinker swimmer example: What does shear do to a larva?

% landing on substratum: sinkers > swimmers > neutrally-buoyant

% landing on substratum: sinkers > swimmers > neutrally-buoyant

% landing on substratum: sinkers > swimmers > neutrally-buoyant