Microatoll

Abstract

Darwin (1842) first described coral microatolls, with further accounts by various other early reef scientists (e.g., Dana, 1872; Semper, 1880). Guppy’s (1889) description of "miniature atolls" from the Cocos (Keeling) Islands first compared the living coral annulus on microatolls to the circular reef rim of coral atolls, followed by Agassiz (1895) and Krempf (1927) who referred to microatolls as "diminutive atolls" and "dwarf atolls" respectively. The specific term microatoll was coined by Wood-Jones (1910) who argued that microatolls resemble coral atolls and form because sedimentation restricts coral growth to their peripheral rim, as he proposed in his largely discounted theory of atoll formation. Abe (1937) referred to microatolls as "table-forming corals", emphasizing their flat dead tops.

Patch reefs composed of multiple coral colonies with raised rims and sand-filled centres have been referred to as microatolls (e.g., Kornicker and Boyd, 1962; Larkum and Steven, 1994), but are better described as "mini-atolls" (Scheer, 1971). Thirty years ago, Scoffin and Stoddart reviewed "the nature and significance of microatolls" and recommended that only single coral colonies be described as microatolls (Scoffin and Stoddart, 1978; Stoddart and Scoffin, 1979). This has been applied with only rare exceptions. The focus of these earlier investigations was almost entirely on microatolls as high quality sea-level indicators (see Chapter Sea-Level Indicators), an application improved further by recent technological advances that have increased the resolution of elevation survey and radiometric dating. Further, exceptional palaeoenvironmental records preserved in the geochemistry and structure of microatoll skeletons are being discovered, and represent exciting new areas for research.