The physical environment The physical environment -- summarysummary

20052005

Solar insolationSolar insolation(kWh/m(kWh/m22/day)/day)

Amount of electromagnetic energy (solar Amount of electromagnetic energy (solar radiation) incident on the surface of the radiation) incident on the surface of the

earth. earth.

Jan- March June-Aug

North South

Solar insolation

2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 above

Northern hemisphere (Longitude 132 East)Solar insolation (kWh/m^2/day)

Latitude

JANFEBMARAPRMAYJUNJUL

AUGSEPOCTNOVDEC

0 5 10 15 20 25 30 35 40

Beer’s lawBeer’s law

K = 0.25

K = 0.75

Beers Law of light extinction

Iz =Io exp(-k*d)

Iz is the intensity of light at z, z is the depth of interestIo is the intensity at the surfacek is the extinction coefficient of water

Water temperatureWater temperature

Birkeland C (1996) Life and death of coral reefs.

Castro PC and Huber ME (1997) Marine Biology.

19831983--8484

19981998

The The Southern Oscillation Index (SOI)Southern Oscillation Index (SOI) is calculated from the monthly or seasonal is calculated from the monthly or seasonal

fluctuations in the air pressure difference between Tahiti and Dfluctuations in the air pressure difference between Tahiti and Darwin.arwin.

Pacific Decadal Oscillation Pacific Decadal Oscillation (PDO) (PDO)

Pacific Decadal Oscillation (PDO)

Warm periods have seen enhanced coastal ocean biological productivity in Alaska and inhibited productivity off the west coast of the contiguous United States, while cold PDO eras have seen the opposite north-south pattern of marine ecosystem productivity.

Storms and hydrodynamicsStorms and hydrodynamics

TyphoonsTyphoons-- CyclonesCyclones-- HurricanesHurricanes

Australia: 1 typhoon Australia: 1 typhoon (cyclone) every 12 years (cyclone) every 12 years in 100 kmin 100 km22

Ryukyus: at least 1 Ryukyus: at least 1 typhoon every year in typhoon every year in 100 km100 km22

Florida: I hurricane every Florida: I hurricane every 10 years in 100 km10 years in 100 km22

Typhoon 11Typhoon 11

August-2001July – 2001

Tropical storms Tropical storms

Before After

HydrodynamicsHydrodynamics

Reef induced circulationReef induced circulation

Wolanski. 1994. Physical Oceanographic Processes of the Great Barrier Reef

Wolanski. 1994. Physical Oceanographic Processes of the Great Barrier Reef

Eddies Eddies –– high retention areas high retention areas

Wolanski. 1994. Physical Oceanographic Processes of the Great Barrier Reef

SlicksSlicks

Wolanski. 1994. Physical Oceanographic Processes of the Great Barrier Reef

Black K. 1993. Coral Reefs 12: 43-53

k

Wolanski E & Sarenski J. 1997. Am Sci 85(3): 6

Often the conditions at the boundary layer are the rate-determining step in nutrient exchange and

mass transfer.

Frictional drag

“Boundary layer thickness is a potentially important component of the diffusive pathway for gas exchange in aquatic organisms”

(Patterson & Sebens 1989, Proc Nat Acad Sci 86, 8833-8836)

Hydrogen bubbles are released periodically and are carried by the fluid. The fluid speed near the aerofoil...in the boundary layer...is slower than

in the free stream.

Low flow High flowAs the flow rate increases, the boundary layer thins and resistance to

passive diffusion progressively decreasesImages courtesy of Iowa Institute of Hydraulic Research, University of Iowa

Newton’s Law of Newton’s Law of ViscosityViscosity

☺ is the shear stress (or force per unit area exerted by the water, kg m-2 s-1), is the density of water (998.4 kg m-3),

U is water’s velocity (m s-1), and CD is the drag coefficient of the object or organism.

Forced convection can greatly enhance mass transfer.

Partial differential equation model - van Woesik (in prep.)

Atkinson’s work on Stanton numbers showed that:

At low-flow velocities, rough morphologies are an advantage because frictional drag increases the mass-transfer across the diffusion-limiting boundary layers.

St = a dimensionless number giving the ratio of uptake rate per unit area to the rate of

advection of the substance past the uptake surface

Baird & Atkinson 1997 Limnol Oceanogr 42(8): 1685-1693

If we increase water flow rate we may also increase If we increase water flow rate we may also increase the rate of removal of photosynthetic the rate of removal of photosynthetic

byproductsbyproducts that accumulate under stress (i.e., that accumulate under stress (i.e., during high SSTs and high irradiance)...during high SSTs and high irradiance)...

The hypothesisThe hypothesis

‘coral colonies growing in high‘coral colonies growing in high--flow habitats are flow habitats are more resistant to high SSTs than colonies in more resistant to high SSTs than colonies in

lowlow--flow habitats’.flow habitats’.

Acropora digitifera experimental set up

Minimal flow Flow

Acropora digitifera (SST 26.2 - 33.6ºC)

0

20

40

60

80

100

0 2 4 6 8 10 12 14

Time (days)

Sur

viva

l % (S

E, n

=15)

Flow (50-70 cm/sec)

Minimum flow (<3 cm/sec)

SST ( 26.2 - 33.8 º C )

24.525.526.527.528.529.530.531.532.533.534.5

Time (days)

Tem

pera

ture

(ºC

)

1 2 3 4 5 6 7 8 9 10 11 12

Acropora digitifera (SST 26.6 - 29.7 ºC)

0

20

40

60

80

100

0 2 4 6 8 10 12 14

Time (days)

Sur

viva

l % (S

E, n

=11)

Flow (50-70 cm/sec)

Minimum flow (< 3cm/sec)

SST (26.6 - 29.7 ºC )

24.525.526.527.528.529.530.531.532.533.534.5

Time (days)

Tem

pera

ture

(ºC

)

1 2 3 4 5 6 7 8 9 10 11

Nakamura T & Van Woesik R (2001) Marine Ecology Progress Series 212: 301-304

Weeks

Zoox

anth

ella

e nu

mbe

r per

are

a (#

/cm

2 )

Still (<3cm/s)

0

50000

100000

150000

200000

250000

300000

0 3 5 7 control Flow (20cm/s)

0 3 5 7 control

Nakamura, Yamasaki & Van Woesik. Mar Ecol Prog Ser (In Press)

0 5 10 15 20 25 30 35 40 4510

-6

10-5

10-4

10-3

Size, W (cm)

Rat

e of

pas

sive

diff

usio

n (m

2s-1

)

U = 0.8 m s -1

U = 0.4 m s -1

U = 0.2 m s -1Turbulent flow, d = 0.8

Laminar flow, d = 0.5

U = 0.8 m s -1

U = 0.4 m s -1U = 0.2 m s -1

Nakamura T & Van Woesik R (2001), Marine Ecology Progress Series

0 5 10 15 20 25 30 35 40 4510-6

10-5

10-4

10-3

Size, W (cm)

Rat

e of

pas

sive

diff

usio

n (m

2 s-1

)

U = 0.8 m s -1 U = 0.4 m s -1

U = 0.2 m s -1 Turbulent flow, d = 0.8

Laminar flow, d = 0.5

U = 0.8 m s -1

U = 0.4 m s -1 U = 0.2 m s -1

Theory suggests that small coral colonies should have higher mass transfer than large coral colonies, and if high-mass transfer is critical in times of stress, for example when SSTs are high, small colonies are expected to survive in preference to large colonies under similar flow regimes.

Nakamura T & Van Woesik R (submitted), Marine Ecology Progress Series

0

5

10

15

20

25

30

5 10 15 20 25 30 35 40 45 50 55 60 65

Size class (cm2)

Freq

uenc

y (%

)

Loya Y, Sakai K, Yamazato K, Nakano Y, Sambali H, Van Woesik R (2001) Ecology Letters 4: 122-131

Theory and empirical evidence concur

µρ..Re UW

=

High-water flow allows high-mass transfer rates; thereby potentially sequestering the build-up of toxins within corals subjected to high SSTs.