Global Reconnaissance of Reef Spur and Groove Variability: A Systematic Geomorphic Classification.
Abstract
Spur and Groove (SaG) formations are found on the fore reef of many coral reef systems around the world. SaG features are constructed of coral buildups called “spurs”, and separated by erosive channelized features, or “grooves”. But, while almost ubiquitous to tropical reefs, their variability in form among reefs as well as within reef settings is far from constant. But before one can ascribe processes to the geomorphic responses, one must first describe the SaG geomorphology in terms that can be then related to hydrodynamic and biologic processes. Using Google Earth, Landsat and NAIP, this study examined twelve reef sites spanning the major reef bearing ocean basins from around the globe. A categorical classification scheme was developed to facilitate the statistical analysis of the variability of SaG features measurement methods. The data revealed several statistically significant associations which are related to physical process associations. These dominating factors are (a) wave exposure and energy, (b) wave and wind direction, (c) reef biology and associated latitude, and (d) tidal magnitude. Wave energy and exposure, and tidal magnitude control feature length, definition, density and more. Increasing incoming wave angle to shore can result in features that are up to twice the length of normal features. Higher abundance of hard coral is correlated to higher SaG density. While these correlations represent idealized affects from an individual attribute, the reality is that each of these factors is codependent and all have varying effects on SaG morphology from one site to the next. Viewing these morphological processes though the lens of a quantitative classification scheme contributes to the understanding of the complexity of geomorphologic responses and controlling processes of SaG formations.
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