LIGHT DEPENDENT ACTIVITY PATTERNS AMONG REEF CORALS: MONTASTREA CAVERNOSA

¹ Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois 60637

1. Colonies of M. cavernosa exhibit two separate types of activity cycle, one of nighttime expansion and one of night and daytime expansion. These activity cycles correspond to the nocturnal and diurnal morphs of this species.

2. At the operational level, light per se controls expansion behavior. Colonies are sensitive to light and react quickly to it. This sensivitiy is not, on the short term, dependent on photosynthesis. The reaction to light of both morphs is one of contraction, but in the diurnal morph the contraction response is inhibited.

3. The inhibition of daytime contraction only occurs in the diurnal morph, which has a high rate of photosynthesis, and only occurs above 20 m (in Panama). Loss of zooxanthellae, or removal to deep water, both of which reduce photosynthesis, results in the loss of daytime expansion.

4. Although photosynthetically based light sensing is not involved in short term control of expansion behavior, colonies may measure their photosynthetic production, and if photosynthesis falls below some level, daytime expansion is halted. The sensing of conditions conducive to daytime expansion can occur within small areas of a single colony.

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