INVERTEBRATES AND FLUID DYNAMICS:
HOLDING ON
BOUNDARY LAYER
Mainstream Velocity (U)
Boundary layer thickness (99%)
Boundary layer thickness (90%)
Dis
tanc
e fr
om su
bstra
te
Velocity
BOUNDARY LAYER
Using the boundary layer – water pennies (Psephenidae)
BOUNDARY LAYER
Mainstream Velocity (U)
Dis
tanc
e fr
om su
bstra
te
Velocity
BOUNDARY LAYER
Using the boundary layer – water pennies (Psephenidae)
Other stream insects
Plecoptera
Trichoptera
Ephemeroptera
Stream animals– Strategies for holding on
Baetis
Rhithrogena
Ancylus
Psephenus
Neothremma
Bibliocephala
Stream animals– Strategies for holding on
Extreme Gradients – Swash Zone
Donax
Swash Surfing
Donax
Density
Shape
Weight distribution
Density
2.0
1.0
0
Density(103 kg/m3)
DonaxChione
Mercenaria
Spisula
Macrocallis
ta
Divaric
ella
Tellina
Tagellus
Weight Distribution
Pivot point
AnteriorPosterior
Ventral
Dorsal
Behaviour in a Swash Zone
WAVE STRESS
a. Limitation of size
Water flow100%
90%
Boundary layer
WAVE STRESS
a. Limitation of size
Water flow
WAVE STRESS
b. Holding on – flow tolerance
Flow rate(m/s)
3
0
Time to dislodge
WAVE STRESS
c. Holding on - orientation
Keyhole limpet
WAVE STRESS
c. Holding on - orientation
Water flow
WAVE STRESS
c. Holding on - orientation
<.5 m/s
-90 0 90 -90 0 90
>.5 m/s
Freq
Orientation (º to flow)
WAVE STRESS
d. Holding on - tenacity
What is “tenacity”?
1. Testing holding power
WAVE STRESS
d. Holding on - tenacity
What is “tenacity”?1. Testing holding power
Kg required to dislodge
100
0
Foot area (cm2)15
WAVE STRESS
d. Holding on - tenacity
What is “tenacity”?
1. Suction?
Atmospheric pressure ≈ 1 kg/cm2
Patella ≈ 3 - 7 kg/cm2
-can’t generate a force > atmospheric pressure
- No negative pressure under foot
WAVE STRESS
d. Holding on - tenacity
What is “tenacity”?
Patella
Mucous layer
WAVE STRESS
d. Holding on - tenacity
What is “tenacity”?
2. Adhesion area
surface tension
Thickness of fluid
Theoretical adhesion = 600 kg/cm2
3. WAVE STRESS
d. Holding on - tenacity
What is “tenacity”?
2. Adhesion
Tenacity(kg/cm2 to detach)
Weight of mucous
3. WAVE STRESS
d. Holding on - tenacity
What is “tenacity”?
Foot rigidity
3. WAVE STRESS
d. Holding on - tenacity
What is “tenacity”? Foot rigidity
l
d
3. WAVE STRESS
d. Holding on - tenacity
What is “tenacity”? Foot rigidity
Tenacity
Flexibility
High
HighLow
Low
In field -
3. WAVE STRESS
d. Holding on - tenacity
What is “tenacity”? Drag
FLOW
Resistance to water movement depends on:
1) Size
2) Shape
3) Texture
3. WAVE STRESS
d. Holding on - tenacity
What is “tenacity”? Drag
Drag
Side Front Rear
Drag – not well correlated with density
Types of Limpets
Non-Migratory Migratory
-don’t move far
-often fixed and territorial
-low r
-low growth
-move up shore
-high r
-high growth
(need high food intake)
-react to predators by clamping -flee from predators
LESS FLEXIBLE MORE FLEXIBLE
A COMPROMISE OF SEVERAL FACTORS
Sea Urchins - Echinoidea
lunules
WHAT IS THE FUNCTION OF LUNULES?
1) Aid in burrowing
2) Removal of feces
3) Maintain a “communication” with the surface if buried
4) Maintain inclined posture
5) Feeding
Log lunule length
Log test diameter
p < .05
If lunules have a hydrodynamic function-they should grow with the animal
isometric
observed
Time to burrow
Burrowing speed
Plugged Not plugged
230 sec 231 sec
Flow through a sand dollar
Lift
Weight
Weight
Lift
Weight
Burrowing to add weight
Sand Dollar reorientation - Dendraster
Adding weight – incorporate magnetite
Reducing lift and drag
Skin drag – important?
Pressure drag – depends on shape
Reducing lift and drag
Skin drag – important?
Pressure drag – depends on shape
Very flat
Reducing lift and drag
Skin drag – important?
Pressure drag – depends on shape
Rounded
Area of lower pressure
How do you reduce lift
Reduce pressure differential between
upper and lower surfaces
Can sand dollars tell the direction of orientation?
Anterior
Posterior
Can sand dollars tell the direction of orientation?
-inverted sand dollars – can flip over more easily with posterior edge facing upstream(i.e critical velocity to re-orient is lower)
Hardy & Merz. 2013. Invert. Bio 132:52
Initial orientation
Final orientation(1 hr)