Physiological measurements
Productivity and respiration rates were measured using dissolved oxygen
probes in customized transparent glass chambers (approx. 4L) to detect
oxygen evolution (production), and oxygen uptake (respiration rate).
Each chamber had an oxygen sensor spot (PyroScience) glued to the inner
chamber wall and a small in-line aquarium pump for water mixing during
incubation. Oxygen concentration was monitored using a fiber optic
sensor (PyroScience). Colonies were set individually inside the chamber
that was bathed in and filled with the filtered, temperature-controlled
seawater from the experimental tray table. Dissolved oxygen
concentration was measured in the chamber during a 1h-dark period to
calculate dark respiration rates (R) and subsequently during a light
exposure period of 1h to calculate net productivity (NP). The difference
of dissolved oxygen concentration at incubation the start and end of the
experiment was normalized over time and colony surface area as described
by Schneider & Erez (2006). Surface area was determined by the aluminum
foil technique (Marsh, 1970) and image analysis (Image J, US National
Institutes of Health) of planar digital images. The dark respiration and
photosynthesis rates were analyzed according to their linearity over
time for quality control. Gross productivity (GP) was calculated (gross
productivity = net productivity + dark respiration). Photosynthesis to
respiration (GP:R ratios) were calculated as a ratio of gross
productivity (GP) to respiration (R) to estimate if production by theSymbiodiniaceae cells is exceeding maintenance requirements of
both the symbiont and the coral host (Coles and Jokiel 1977). Maximum
photochemical efficiency of photosystem II (i.e., effective quantum
yield) was quantified via pulse-amplitude modulate (PAM) fluorometry
(Warner et al. 1996; Jones et al. 1998). After an overnight dark
acclimation period, fluorescence (Fm and F0) was measured by saturation
pulses at three random spots on each colony to calculate the colony’s
average Fv/Fm. Maximum photochemical efficiency of the PSII (Fv/Fm, Fv =
Fm – F0) was calculated based on fluorescence measurements using a
pulse amplitude modulated fluorometer (DIVING-PAM Walz Inc.).