EXPLORING AND QUANTIFYING THE EFFECTS OF EARLY METAZOAN REEF-BUILDING ON HABITAT HETEROGENEITY

The Ordovician transition from microbe-dominated to metazoan-dominated reef construction has been casually equated by researchers to an increase in physical complexity of the reef environment. This complexity is inferred to lead to increased habitat heterogeneity—realized through the development of novel niche space and faunal interactions. However, little attention has been given to elucidating and quantifying the effects of novel metazoan construction on habitat heterogeneity. Discrete and serial structural components, as well as the dense packing of diverse frame-building morphologies, may bring increased opportunity for novel local structures and cavities. In addition, they may also promote greater facies diversity through autogenic processes.

Through examination of Ordovician reefs, bioherms and buildups, we can explore the scales at which heterogeneity is affected by novel metazoan framework builders, and make strides towards quantification through measurements in outcrop. I present five ways to describe heterogeneity at multiple scales, from the qualitative and semi-quantitative (e.g. facies diversity, frame-builder morphological diversity), to the fully quantitative (e.g. transect-intercept methods), and apply these methods to North American reefs and bioherms from the Floian to the Katian Stage of the Ordovician.

Examining the impact of metazoan reef building on heterogeneity is not only important for understanding the evolution of reefs as complex physical structures, but as complex and dynamic ecological structures as well. A more quantitative, ecology-centered approach to describing reef structure will allow meaningful comparison across time and space, and provide greater insight into the development of the reef system.