Ecological Succession in Phanerozoic Reef Ecosystems: Is It Real?

Abstract

I define ecological succession as an orderly, directional, and predictable, pioneer-to-climax process of community and species development. It takes place in an environment where external physico-chemical constraints are not undergoing major change: ecological succession leads naturally to increasing biological control of the environment and a stabilized ecosystem. Ecological succession is an intrinsic feature of reef growth. I present criteria for the recognition of pioneering and climax stages in Phanerozoic reefs at both the species and community level. On the other hand, I use the term community replacement where changing external factors have forced the migration of organisms into an area thereby replacing existing species and communities. Development of reef ecosystems through the Phanerozoic generally follows the pattern of ecological succession but through a time frame of 30 to 10OMa, concluded by a phase of mass extinction. I call such long-term changes erathemic successions. Pioneering recovery of reef ecosystems following extinctions appears to take as much as 8 to 12Ma. Restricted marine environments or global periods of climatic change produce arrested successions-successions essentially halted in initial phases characterized by pioneering species and communities that fail to reach a full climax stage. I outline selective examples of arrested successions. Arrested succession may explain the lack of full reef development within most of the mid-Cambrian to midOrdovician and much of the Carboniferous and may provide a key to explaining global climatic change. Classification of reefs should take into account the role of community structure and ecological succession as these may play a stronger selective role on reef type than tectonic, sedimentological, or physico-chemical constraints.