79
Thus, it can be expected that Acropora granulosa will do well
metabolically from the surface to a depth transmitting
approximately 5% of the irradiance at the surface of the summer;
will do poorly from that depth down to a depth transmitting 1% of
summer surface light; and is unlikely to survive below the 1% light
level. These metabolic expectations coincide with subjectively
observed abundances from A. granulosa from depths of 6-51 m on
Davies Reef.
It is universally recognized that most reef-building corals
possess considerable heterotrophic potential (Yonge, 1973); but the
relative importance of heterotrophy to total coral metabolism, has
never been quantified in the field. Our calculations and field
observations of Acropora granulosa suggest that any heterotrophy
which might occu'r does not result in an extension of the range of
Acropora granulosa below the depths that are predicted based upon
known rates of respiration and photosynthesis. These studies
emphasise the predictive value of quantitative metabolic studies
and the importance of light as an ecological parameter affecting
reef-building corals and their symbionts.