Buddemeier,-R.W.; Hopley,-D. Turn-ons and turn-offs: Causes and mechanisms of the initiation and termination of coral reef growth. PROCEEDINGS-OF-THE-SIXTH- INTERNATIONAL-CORAL-REEF-SYMPOSIUM,-TOWNSVILLE,- AUSTRALIA,-8th-12th-AUGUST-1988.-VOLUME-1:-PLENARY- ADDRESSES-AND-STATUS-REVIEWS. Choat,-J.H.;Barnes,- D.;Borowitzka,-M.A.;Coll,-J.C.;Davies,-P.J.;Flood,- P.;Hatcher,-B.G.;et-al.-eds.. 1988. pp. 253-261. The importance of human impacts on reefs is repeatedly stressed. From the global scale of the Greenhouse Effect itself--which has been characterized as an "unprecedented (and uncontrolled) geophysical experiment"--to local development or fishing practices, few natural reef impacts have not been amplified, changed, or mimicked by man. The central question is "How may we best study reefs in a changing climate in order to understand (1) the natural forces and human impacts that have shaped reef development through the present and (2) the effects of natural and man- made environmental modifications that will change and define reefs in the future?" Answers to this question may be found only by studying coral reef systems over a wider and more thoughtfully defined range of time and space than has been common in the past.