Reefal Microbial Crusts
Fine-grained, non-skeletal crusts, variously described as laminar micrite crusts, cements, stromatolite s, and microbialite s, are locally common in late Quaternary coral reefs. They occur on wave-swept margins in dark or low-light habitats, such as cavities and deep fore-reef slope surfaces. They have often been regarded as cements, but are now widely interpreted as microbial carbonates produced by heterotrophic bacterial communities. The crusts typically form at the end of active reef development, as late stage veneers on framework skeletons. They can be up to 20 cm thick, and locally constititute 80% of the reef structure. Crusts are particularly important in strengthening cavernous reef frameworks. Their development in poorly illuminated cavity and deepwater habitats suggests eukaryote competition for substrates. Their preferential development at wave-swept reef margins probably indicates the effect of increased carbonate saturation state by intense seawater flushing....
I am grateful to Juan Carlos Braga and Jody Webster for advice on the manuscript.
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