Ecological Archives E090-053-A3

Mia O. Hoogenboom and Sean R. Connolly. 2009. Defining fundamental niche dimensions of corals: synergistic effects of colony size, light, and flow. Ecology 90:767–780.

Appendix C. Sensitivity of niche boundaries to light acclimation.

Photoacclimation to high light typically increases maximum rates of photosynthesis (Pmax) and dark respiration (Rd) per unit surface area, and also increases the light level at which Pmax is reached (summarized by the sub-saturation irradiance parameter, EK). Depending on the relative rates of increase of Pmax and Rd, this can lead to a hump-shaped relationship between daily energy acquisition and growth irradiance. To test the sensitivity of niche boundaries to variation in photoacclimatory state, we re-calculated energy acquisition allowing for variation in the relationship between tissue surface oxygen concentration and Reynolds number (Eq. 9 and Fig. 2 of main text). These calculations were made for three photoacclimatory states in addition to the low-light acclimated colonies for which our model is parameterized. Variation in photophysiology for these additional photoacclimatory states was designed to capture changes in oxygen production and consumption with acclimation to high light, as follows:

1) Rates of oxygen production at maximum photosynthesis increase with acclimation to intermediate irradiance but decline at the highest light levels (e.g., Green et al 1998). At low to intermediate light levels, we modelled these dynamics by allowing an increase in tissue oxygen concentrations in stagnant water (parameter βP) and a decrease in the rate at which tissue oxygen concentrations decline with increasing flow (parameter αP). The effect of these parameter changes is to increase oxygen flux during photosynthesis at all flow speeds by increasing the concentration gradient across the DBL. To capture processes occurring during photoacclimation to high light, we allowed a decrease in βP and an increase in αP (i.e., a decline in oxygen production).

2) Rates of respiration typically increase with acclimation to high light. To simulate high-light acclimation of respiration we decreased tissue oxygen concentrations in stagnant water (parameter βR) and decreased the rate at which tissue oxygen concentrations increase with flow (parameter aR). Again, these changes increase oxygen flux during respiration by increasing the concentration gradient across the DBL.

3) The subsaturation irradiance parameter (EK) generally shows a saturating increase with acclimation to high light (Anthony and Hoegh-Guldberg 2003). We modified the values of this parameter accordingly.

Hypothetical parameter values for four different photoacclimatory states are given in Table C1 and results of the simulations are presented in Fig. C1 (below).

TABLE C1. Parameter values of equations describing the relationship between Reynolds number and tissue oxygen concentrations for hypothetical photoacclimatory states.

Species

Parameter

Photoacclimatory state

Low (as measured)

Low intermediate

High intermediate

High

A. nasuta

aP

0.41

0.35

0.35

0.41

bP

28

36

36

28

aR

0.36

0.32

0.28

0.24

bR

-18

-20

-22

-24

EK

100

160

190

200

M. foliosa

aP

0.39

0.32

0.32

0.39

bP

23

31

31

23

aR

0.81

0.78

0.75

0.72

bR

-52

-56

-60

-64

EK

100

160

190

200

L. phrygia

aP

0.25

0.19

0.19

0.25

bP

35

44

44

35

aR

0.35

0.32

0.29

0.26

bR

-44

-46

-48

-50

EK

100

160

190

200

 

FigC1
 
   FIG. C1. Niche dimensions for colonies of three species acclimated to different light levels (see Table C1 for photoacclimation parameters). Figure panels show positive energy acquisition contours along gradients of light intensity (daily maximum irradiance, x-axis of panels) and flow (y-axis of panels), for corals acclimated to low, intermediate low, intermediate high, and high light levels respectively.

 

LITERATURE CITED

Anthony, K. R. N., and O. Hoegh-Guldberg. 2003. Kinetics of photoacclimation in corals. Oecologia 134:23–31.

Green, T. G. A., B. Schroeter, L. Kappen, R. D. Seppelt and K. Maseyk. 1998. An assessment of the relationship between chlorophyll a fluorescence and CO2 gas exchange from field measurements on a moss and lichen. Planta. 206:611–618.


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