Whether you are a diver, a geologist, or simply someone with an interest in natural history, you are likely to have a misconception about the structure of coral reefs. The error is ubiquitous in textbooks and is reinforced by media treatments of the topic. Everyone ‘knows’ that coral reefs have a central zone of organically bound material (the reef core), a leeward zone of flat lying sediments (the back-reef lagoonal area) and a seaward zone of steeply-dipping rubble (the reef talus). The misconception relates to the reef talus. The source of the erroneous view can be traced to Charles Darwin, who sought to follow his mentor (Charles Lyell) in explaining the past by reference to present-day processes.
“Darwin and his many followers regarded contemporary reefs as having shelf-like forms, with steep slopes facing deep water. This morphology differentiates the familiar zones of backreef, reef-crest and fore-reef. Most accounts emphasize the importance of the reef-crest, comprising the growth framework responsible for generating the reef structure. Material eroded from both the reef-crest and the upper reef-slope has been assumed to accumulate on the fore-reef, and it was argued that this provided the foundations that enabled construction to take place in waters that were otherwise too deep. This pervasive idea can be traced to Darwin (1842) and Dana (1853), although it typically only applies to windward, moderately high hydrodynamic energy, regimes. However, numerous conceptual models illustrate reefs in which the fore-reef is shown as a steep debris slope, on which depositional increments are correlated with contemporary intervals of reef growth.” (from the Introduction).
Why is this worthy of our attention? The principles in evidence here are relevant to a large number of topics that relate to the past. Unfortunately, these origins issues often are characterised by excessive appeals to consensus and cherished models, and not enough attention is given to the weight of evidence. Lyell’s and Darwin’s uniformitarianism still have an undue influence on our educational system and the media. Attempts to increase the level of critical scrutiny are met with emotive responses rather than reasoned arguments. To help us think through our methodology for dealing with these tensions, Braithwaite’s approach to the “reef talus” model may provide a useful case study.
For the full text of this blog, go here.