Growth forms of hermatypic corals: stable states and noise-induced transitions

Field observations show that some coral species may assume different growth forms, or morphotypes, within apparently uniform habitats. The present pap er examines the causes of this morphological diversity in hermatypic cnidar ians and more particularly the following questions: Are there stable morpho types among all the possible growth forms of a coral; if so, can a colony b elonging to a certain stable morphotype change its growth form, and what ca n induce transition from type to type when the environment is relatively st eady and only limited random (and short-term) variations of the external co nditions occur? The approach adopted was to construct a mathematical model of the form dynamics of a coral colony and validate it by field data on the Red Sea hydrocoral Millepora dichotoma. The ratio between the volume and t he surface area of a coral served as an index of its form and enabled treat ment of the coral morphology in terms of dynamical systems. Such a dynamica l system must have certain stable states corresponding to specific growth f orms of a coral colony. Computer simulations showed that limited stochastic disturbances in the processes of biomass and skeletal growth caused by ran dom fluctuations in environmental conditions may induce transitions of a co ral from one stable growth form to another. (C) 2001 Elsevier Science BN. A ll rights reserved.