To quantify induction time, the time to steady state photosynthesis was measured by evaluating the performance of photosystem II (PSII) using chlorophyll fluorescence (Bradbury and Baker, 1984, 1981). Calculation of the rate of production of high energy electrons by PSII (relative electron transfer rate, rETR) at a fixed Photon Flux Density is a measure of induction time (Suggett et al., 2010). rETR was calculated by the Diving PAM using the manufacturers software:

rETR = ΔF/Fm X PAR X 0.5 X 0.0001

where ΔF is the change in fluorescence (F) resulting from the saturation pulse, Fm is the maximum fluorescence, PAR is the PFD to which the sample is exposed, 0.5 is an estimate of the quanta absorbed by PSII, and 0.001 is an absorptance constant for light at the coral surface. As neither the absorptance of light by the coral surface, nor quanta by PSII, are known for P. astreoides, this equation estimates relative ETR.

To generate an induction time from Diving PAM rETR measurements the time to steady state photosynthesis (induction time) was taken as the intersection on the abscissa of two straight lines, one calculated using least squares linear regression of the first three points on the rETR curve, and the second representing the mean rETR of the last three points of the curve. This calculation was performed in Microsoft® Excel® for Microsoft 365 MSO (Version 2212 Build 16.0.15928.20196) by using the =Linest() function to generate a linear equation (y = mx + b) from the first three induction data points such that x is time (min) and y is rETR. Then solving for x (time) by using the mean of the last three rETR points as the rETR value (y).

BCO-DMO Data Manager Processing Notes:

* Source file "St.John_Porites Astreoides Induction Time and Octocorals.csv" imported into the BCO-DMO data system
* Column names adjusted to conform to BCO-DMO naming conventions designed to support broad re-use by a variety of research tools and scripting languages. [Only numbers, letters, and underscores. Can not start with a number]
* lat and lon added to the data from a site list.
* Columns Mean_Octocoral_Height, Canopy_Closure_above_P_astreoides,Mean_rETR_3pts rounded to three decimal places.
* Date format converted to ISO 8601 format

photosynth_induction.csv