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gross photosynthesis and respiration. These values are used to
predict the nutritional status of A. granulosa at different depths
on the reef, and predicted nutritional status is compared with
observed abundance.
METHODS
Instantaneous i!!.. situ rates of photosynthesis by ~. granulosa
growing at different depths on Davies Reef during the summer
(December) and winter (June) were estimated using the model of
Chalker and Dunlap (l9B3b).
Light saturation curves for
photosynthesis were simulated by equation (l).
p~, Ik' and R were calculated for the light intensities
corresponding to each depth by the formulae :
P~l exp (c lnT),
Ikl exp (a InT),
and
(4 )
(5)
(6 )
The logarithmic forms of equations (4-6) are developed in Chalker
~~., (19B3). The values of the slopes and y-intercepts were
calculated from data presented by Chalker and Dunlap (l983a).
Daily changes in solar photosynthetic photon flux density 400700 nm (PPFD) were simulated by the equation
I = Im sin (n H/D) ,
(7 )
where Im is the maximum irradiance at local solar noon, H is the
hour of the day, and D is the length of the day from civil twilight
in the morning until civil twilight in the evening. Values for D